45

C H A P T E R

Human
Immunodeficiency Virus
cells ie
of RNA
(Diploide)
↳ Enveloped virus/contains reverse transcriptase
integrase/RNA vinus

Call MissisE
, and has 2

=manote
copies
dendritic cell microglia cells
, follicular dendres
CDU*
,
>
- infected cell : call Chelper I cells) Es , masophage ,

&2-oad
structure
virus

CHAPTER CONTENTS * *
-

Disease Laboratory Diagnosis

Important Properties Treatment
Summary of Replicative Cycle Prevention
Transmission & Epidemiology Self-Assessment Questions
Pathogenesis & Immunity Summaries of Organisms
Clinical Findings Practice Questions: USMLE & Course Examinations

Disease required for replication, and the other four, nef, vif, vpr, and
vpu, are not required for replication and are termed “acces-
Human immunodeficiency virus (HIV) is the cause of
sory” genes.
acquired immunodeficiency syndrome (AIDS).
The gag gene encodes the internal “core” proteins, the
Both HIV-1 and HIV-2 cause AIDS, but HIV-1 is found
most important of which is the p24 protein. It is important
worldwide, whereas HIV-2 is found primarily in West
Africa. This chapter refers to HIV-1 unless otherwise noted.

Important Properties
HIV is one of the two important human T-cell lympho-
tropic retroviruses (human T-cell leukemia virus is the
other). HIV preferentially infects and kills helper (CD4)
T lymphocytes, resulting in the loss of cell-mediated
immunity and a high probability that the host will develop
opportunistic infections. Other cells (e.g., macrophages
and monocytes) that have CD4 proteins on their surfaces
can be infected also.
HIV belongs to the lentivirus subgroup of retroviruses,
which cause “slow” infections with long incubation periods
(see Chapter 44). HIV has a cylinder-shaped (type D) core
surrounded by an envelope containing virus-specific glyco-
proteins (gp120 and gp41) (Figures 45–1 and 45–2). The
genome of HIV consists of two identical molecules of
FIGURE 45–1 Human immunodeficiency virus (HIV)—electron
single-stranded, positive-polarity RNA and is said to be
micrograph. Large arrow points to a mature virion of HIV that has just
diploid. The HIV genome is the most complex of the known been released from the infected lymphocyte at the bottom of the
retroviruses (Figure 45–3). In addition to the three typical figure. Small arrow (in bottom left of image) points to several nascent
retroviral genes gag, pol, and env, which encode the struc- virions in the cytoplasm just prior to budding from the cell membrane.
tural proteins, the genome RNA has six regulatory genes (Source: Dr. A. Harrison, Dr. P. Feirino, and Dr. E. Palmer, Public Health Image Library,
(Table 45–1). Two of these regulatory genes, tat and rev, are Centers for Disease Control and Prevention.)

378
 -* Dute .
- Hi
--
e6
120 with CDU + Of macrophage -
> CCR5

CXCR4
receptor HelperTg &
2-23 attachment >
-
gp1 with chemokine
↳

-gp4is e
i
CHAPTER 45 Human Immunodeficiency Virus 379
ident s blockinger is is direentication &
C Entry inhibitors) .

maravirozd s
1
- -

protein .. *1, glycopro surface & <I

# sfusion! block " - ,

in Enfavirtide-Is's

cleaved to form the two envelope (surface) glycoproteins,

rest peace &
O
gp41env
I

REI %
*

-5 HIV I
reco integeProteste gp120 and gp41. isu

-Jadei
-

Reverse OT - subtypes -

transcriptase
transcriptase Differences in the base sequence of the gp120 gene are
Free it used to subdivide HIV into subtypes called clades. Differ-
- gene /1. 3 -
-

-most
outer thing-gpus
O
ent clades are found in different areas of the world. For
-

gp120env
example, the B clade is the most common subtype in North
-

-
RNA America. Subtype B preferentially infects mononuclear
! - - e - -1 -

satingcells and appears to be passed readily during anal sex,

.
-
-

diesgrat go
·

& anco

-
..

O
Protein
p17 matrix ise whereas subtype E preferentially infects female genital tract
3
⑪

Browntem
cells and appears to be passed readily during vaginal sex.
-

protein onmaine
domise i n

Three enzymes are located within the nucleocapsid of

·

-Damenesse the virion: reverse transcriptase, integrase, and protease

S

DNAsiglstDrARun and
I
↳ -

④ p24gag Lipid bilayer I

families
(NR sa
Nucleosiderew traninhibitors
senme's od
2 copies
Tenofovir
-
, Zidovudine ,
(see Figure 45–2).
Lamivudine

tran· (NNRTS
Didanosine ,
Abacan

2 = non-nucleoside new. hi

NevirapineSuenzyme -
Reverse transcriptase is the RNA-dependent DNA poly-
Sil... -

Rilpivirine Delavirdive > Efavirent Stravirine !

FIGURE 45–2 Cross-section of human immunodeficiency virus ;'

gravir-& Ralteg ravir

merase that is the source of the family name retroviruses.

s
-

978
(HIV). In the interior, two molecules of viral RNA are shown associ- 19( -
·

ated with reverse transcriptase. Surrounding those structures is a This enzyme transcribes the RNA genome into the proviral
rectangular nucleocapsid composed of p24 proteins. Note that the DNA. Reverse transcriptase is a bifunctional enzyme; it
viral protease and integrase are also located within the nucleocapsid also has ribonuclease H activity. Ribonuclease H degrades
(in addition to the reverse transcriptase), but, for lack of space, are RNA when it is in the form of an RNA–DNA hybrid mol-
not shown in the figure. On the exterior are the two envelope pro- ecule. The degradation of the viral RNA genome is an
teins, gp120 and gp41, which are embedded in the lipid bilayer essential step in the synthesis of the double-stranded provi-
derived from the cell membrane. (Reproduced with permission from Green ral DNA. Integrase, another important enzyme within the
WC. Mechanisms of disease: the molecular biology of human immunodeficiency
virion, mediates the integration of the proviral DNA into
virus type I infection. NEJM. 1991;324[5]:309.)
O the host cell DNA. The viral protease cleaves the precursor
3gelos gpugp enrD gag Hirgenne Gigood-is integratin
9
- & -

*
.

d ↳
,

i -

polyproteins into functional viral polypeptides.

-

enty mes
-- -/

d * - 6 61825
Accessory .
.

One essential regulatory gene is the tat (transactivation

medically as it is the antigen in the initial serological test of transcription)1 gene, which encodes a protein that
that determines whether the patient has antibody to HIV enhances viral (and perhaps cellular) gene transcription.
(i.e., has been infected with HIV). (See “Laboratory Diag- The Tat protein and another HIV-encoded regulatory
nosis” section in this chapter.) protein called Nef repress the synthesis of class I major his-
The pol gene encodes several proteins, including the tocompatibility complex (MHC) proteins, thereby reducing
virion “reverse transcriptase,” which synthesizes DNA by the ability of cytotoxic T cells to kill HIV-infected cells. The
using the genome RNA as a template, an integrase that other essential regulatory gene, rev, controls the passage of
integrates the viral DNA into the cellular DNA, and a pro- late mRNA from the nucleus into the cytoplasm. The func-
tease that cleaves the various viral precursor proteins. The tion of the four accessory genes is described in Table 45–1.
env gene encodes gp160, a precursor glycoprotein that is The accessory protein Vif (viral infectivity) enhances
HIV infectivity by inhibiting the action of APOBEC3G, an
enzyme that causes hypermutation in retroviral DNA.
gag pol env APOBEC3G is “apolipoprotein B RNA-editing enzyme”
LTR p24* PROT POL H INT gp120 gp41 LTR that deaminates cytosines in both mRNA and retroviral
5' 3'
VIF TAT VPU REV NEF DNA, thereby inactivating these molecules and reducing
infectivity. APOBEC3G is considered to be an important
FIGURE 45–3 The genome of human immunodeficiency virus member of the innate host defenses against retroviral infec-
(HIV). Above the line are the three genes for the main structural pro- tion. HIV defends itself against this innate host defense by
teins: (1) gag encodes the internal group-specific antigens (e.g., p24); producing Vif, which counteracts APOBEC3G, thereby
(2) pol encodes proteins that have four enzymatic activities: protease preventing hypermutation from occurring.
(PROT), polymerase that functions as a reverse transcriptase (POL),
There are several important antigens of HIV:
RNase H (H), and integrase (INT); (3) env encodes the two envelope
glycoproteins, gp120 and gp41. Below the line are five regulatory (1) gp120 and gp41 are the type-specific envelope gly-
proteins: viral infectivity factor (VIF), transactivating protein (TAT), coproteins. gp120 protrudes from the surface and interacts
viral protein U (VPU), regulator of expression of virion protein (REV), with the CD4 receptor (and a second protein, a chemokine
and negative regulatory factor (NEF). At both ends are long terminal
repeats (LTR), which are transcription initiation sites. Within the 5′ LTR
is the binding site for the TAT protein, called the transactivation 1
Transactivation refers to activation of transcription of genes distant from
response element (TAR). TAT enhances the initiation and elongation the gene (i.e., other genes on the same proviral DNA or on cellular
of viral mRNA transcription. (*p24 and other smaller proteins such as DNA). One site of action of the Tat protein is the long terminal repeat at
p17 and p7 are encoded by the gag gene.) the 5′ end of the viral genome.
380 PART IV Clinical Virology

TABLE 45–1 Genes and Proteins of Human Immunodeficiency Virus

Gene Proteins Encoded by Gene Function of Proteins

I. Structural genes found in all retroviruses

gag p24, p7 Nucleocapsid
p17 Matrix
1
pol Reverse transcriptase Transcribes RNA genome into DNA
Protease Cleaves precursor polypeptides
Integrase Integrates viral DNA into host cell DNA
env gp120 Attachment to CD4 protein
gp41 Fusion with host cell
II. Regulatory genes found in human immunodeficiency virus that are required for replication
pin active
simgeremm Activation of transcription of viral genes
trans

tat =>
Tat
&565

rev Rev - Transport of late mRNAs from nucleus to cytoplasm

.

III. Regulatory genes found in human immunodeficiency virus that are not required for replication (accessory genes)
Nef > is M
Steen
&

&

nef Decreases CD4 proteins and class I MHC proteins on surface of infected cells; induces death of
-

uninfected cytotoxic T cells; important for pathogenesis by SIV2

#PO[ C36& 2.

vif Vif
-Enhances infectivity by inhibiting the action of APOBEC3G (an enzyme that causes hypermutation
>
-

↳ innate
·

defense
in retroviral DNA) host .

vpr Vpr - Transports viral core from cytoplasm into nucleus in nondividing cells
vpu Vpu
j, Enhances virion release from cell
MHC = major histocompatibility complex.
gpkg-killing st85 is Antibodies enee
,
I

1
Reverse transcriptase also contains ribonuclease H activity, which degrades the genome RNA to allow the second strand of DNA to be made. ...

dismisse i
I

di
-

Serology
-
- 4 d
↳
2
Mutants of the nef gene of simian immunodeficiency virus (SIV) do not cause acquired immunodeficiency syndrome in monkeys.

receptor) on the cell surface. gp41 is embedded in the enve- (1) Human immunodeficiency virus type 2 (HIV-2) was
lope and mediates the fusion of the viral envelope with the isolated from AIDS patients in West Africa in 1986. The
cell membrane at the time of infection. The gene that proteins of HIV-2 are only about 40% identical to those of
encodes gp120 mutates rapidly, resulting in many anti- the original HIV isolates. HIV-2 remains localized primar-
genic variants. The most immunogenic region of gp120 is ily to West Africa and is much less transmissible than
called the V3 loop; it is one of the sites that varies antigeni- HIV-1.
cally to a significant degree. Antibody against gp120 neu- (2) Simian immunodeficiency virus (SIV) was isolated
tralizes the infectivity of HIV, but the rapid appearance of from monkeys with an AIDS-like illness. Antibodies in
gp120 variants has made production of an effective vaccine some African women cross-react with SIV. The proteins of
difficult. The high mutation rate may be due to lack of an SIV resemble those of HIV-2 more closely than they resem-
editing function in the reverse transcriptase. ble those of the original HIV isolates.
(2) The group-specific antigen, p24, is located in the
nucleocapsid core and is not known to vary. Antibodies Summary of Replicative Cycle
against p24 do not neutralize HIV infectivity but serve as
In general, the replication of HIV follows the typical retro-
important serologic markers of infection.
viral cycle (Figure 45–4). The initial step in the entry of
The natural host range of HIV is limited to humans, HIV into the cell is the binding of the virion gp120 enve-
although certain primates can be infected in the laboratory. lope protein to the CD4 protein on the cell surface. The
HIV is not an endogenous virus of humans (i.e., no HIV virion gp120 protein then interacts with a second protein
sequences are found in normal human cell DNA). The ori- on the cell surface, one of the chemokine receptors. Next,
gin of HIV and how it entered the human population the virion gp41 protein mediates fusion of the viral enve-
remains uncertain. There is evidence that chimpanzees lope with the cell membrane, and the virion core contain-
living in West Africa were the source of HIV-1. If chimpan- ing the nucleocapsid, RNA genome, and reverse
zees are the source of HIV in humans, it would be a good transcriptase enters the cytoplasm.
example of a virus “jumping the species barrier.” Chemokine receptors, such as CXCR4 and CCR5 pro-
In addition to HIV-1, two other similar retroviruses are teins, are required for the entry of HIV into CD4-positive
worthy of comment: cells. The T cell–tropic strains of HIV bind to CXCR4,
 CHAPTER 45 Human Immunodeficiency Virus 381

Inhibited by entry inhibitors

(enfuvirtide, maraviroc)

<JUMRNA -
A 1 structural proje I
Virion
.

Polyproteins
~'Bes
-

· = -) proteases
②
-

I
CD4
CCR5
Nucleus
d Ritonavir AtaZanavir s indinavirssPl7 Pz4 idee
,
I'

is
J
/I d
or CXCR4
solid
wine
Polyprotein
~

197 non-functional i t 's

22,
·

38
-

Q
18 -

>
-
RNA
5
MRNA trans
ston
.

cril
RNA
3
si

1656
-

S 4; 9
Provirus↳ 1

-3
--
RNA
· d-
release
DNA ackayirg
-

Es arim
P S&
RASB.
en
Protein &
,
17
-I /

& -

E
MRNA -

Integration Transcription

RNA genomes
Reverse
transcription

mRNAs Precursor Cleavage

id to
polyproteins by

p s in
Inhibited by

Tr
ns protease

ly
DNA copy b

a
reverse transcriptase la t em a
inhibitors (zidovudine of genome io n A s s leoc
and others) nuc
Inhibited
by protease
Inhibited by integrase inhibitors
inhibitors (raltegravir) (indinavir
and others)

FIGURE 45–4 Replicative cycle of human immunodeficiency virus (HIV). Showing the sites of action of the important drugs
used to treat HIV infection. The mode of action of the reverse transcriptase inhibitors, the entry inhibitors, the integrase inhibitor, and
the protease inhibitors is described in Chapter 35. On the right side of the figure, “cleavage by protease” describes the process by
which the virus-encoded protease cleaves the Gag-Pol polyprotein into functional viral proteins as the virion buds from the cell mem-
brane. These newly formed functional proteins are transported by the mature virion to the next cell and function within that newly
infected cell. The viral reverse transcriptase and integrase are two such proteins. (Reproduced with permission from Ryan K et al.
Sherris Medical Microbiology. 3rd ed. Originally published by Appleton & Lange. Copyright 1994 McGraw-Hill.)

whereas the macrophage-tropic strains bind to CCR5. proteins. The Pol polyprotein is cleaved to form the reverse
Mutations in the gene encoding CCR5 endow the individ- transcriptase, integrase, and protease. The immature virion
ual with protection from infection with HIV. People who containing the precursor polyproteins forms in the cyto-
are homozygotes are completely resistant to infection, and plasm, and cleavage by the viral protease occurs as the
heterozygotes progress to disease more slowly. Approxi- immature virion buds from the cell membrane. It is this
mately 1% of people of Western European ancestry have cleavage process that results in the mature, infectious
homozygous mutations in this gene, and about 10% to 15% virion.
are heterozygotes. One of the best-characterized mutations Note that HIV replication is dependent on cell proteins
is the delta-32 mutation, in which 32 base pairs are deleted as well as viral proteins. First there are the cell proteins
from the CCR5 gene. required during the early events, namely CD4, and the che-
In the cytoplasm, reverse transcriptase transcribes the mokine receptors, CCR5 and CXCR4. Cell proteins, such as
genome RNA into double-stranded DNA, which migrates actin and tubulin, are involved with the movement of viral
to the nucleus, where it integrates into the host cell DNA. DNA into the nucleus. The cell protein cyclin T1 and the
The viral DNA can integrate at different sites in the host viral protein Tat are part of the complex that transcribes
cell DNA, and multiple copies of viral DNA can integrate. viral mRNA. Cell proteins are also involved in the budding
Integration is mediated by a virus-encoded endonuclease process by which the virus exits the cell.
(integrase). Viral mRNA is transcribed from the integrated
(proviral) DNA by host cell RNA polymerase (augmented
by virus-encoded Tat protein) and translated into several Transmission & Epidemiology D
large polyproteins. The Gag and Pol polyproteins are Transmission of HIV occurs primarily by sexual contact 81s
ostdis
② ③ &
cleaved by the viral protease, whereas the Env polyprotein
-

and by transfer of infected blood. Perinatal transmission ↳

- &
drdis
-

is cleaved by a cellular protease. from infected mother to neonate also occurs, either across
The Gag polyprotein is cleaved to form the main core the placenta, at birth, or via breast milk. It is estimated that
protein (p24), the matrix protein (p17), and several smaller more than 50% of neonatal infections occur at the time of
 382 PART IV Clinical Virology
3 %
Boy -is riskoy
Haw transm [0 , ge
on
.

,
-

delivery and that the remainder is split roughly equally HIV-infected blood is estimated to be about 0.3%. The -

between transplacental transmission and transmission via transmission of HIV from health care personnel to patients
-

breast feeding. There is no evidence for airborne, water- is exceedingly rare.

borne, or insect transmission of HIV.
Infection occurs by the transfer of either HIV-infected
cells or free HIV (i.e., HIV that is not cell-associated).
Pathogenesis -
& Immunity
Although small amounts of virus have been found in other HIV infects helper
--
T cells (CD4-positive cells) and kills
them, resulting in suppression of cell-mediated immu-
=>

fluids (e.g., saliva and tears), there is no evidence that they

play a role in infection. In general, transmission of HIV nity. This predisposes the host to various opportunistic
follows the pattern of hepatitis B virus (HBV), except that infections and certain cancers such as Kaposi’s sarcoma and
HIV infection is much less efficiently transferred (i.e., the lymphoma. HIV does not directly cause these tumors
dose of HIV required to cause infection is much higher because HIV genes are not found in these cancer cells. The
than that of HBV). People with sexually transmitted dis- initial infection of the genital tract occurs in dendritic cells
that line the mucosa (Langerhans’ cells), after which the
eases, especially those with ulcerative lesions such as syphi-
local CD4-positive helper T cells become infected. HIV is
lis, chancroid, and herpes genitalis, have a significantly
first found in the blood 4 to 11 days after infection.
higher risk of acquiring HIV. Uncircumcised males have a
HIV infection also targets a subset of CD4-positive cells
higher risk of acquiring HIV than do circumcised males. ⑭Ginfect ji) (i) 6I 28 ee

called Th17 cells. These cells are an important mediator of

.
,

Transmission of HIV via blood transfusion has been -

mucosal immunity, especially in the gastrointestinal tract.

greatly reduced by screening donated blood for the pres-
-2 /(Window period
Screen JABs (3-4Ws)) > a c te phase- Many mucosal Th17 cells are killed early in HIV infection.
" 221-3-4 weeks
vims & < Js AB 55 8
&

ence of antibody to HIV. However, there is a “window”

,

JERNA
virus 11 E

Th17 cells produce interleukin-17 (IL-17), which attracts

I

period early in infection when the blood of an infected

neutrophils to the site of bacterial infection. The loss of
person can contain HIV but antibodies are not detectable.
Th17 cells predisposes HIV-infected individuals to blood-
Blood banks now test for the presence of p24 antigen in an
stream infections by bacteria in the normal flora of the
effort to detect blood that contains HIV. colon, such as Escherichia coli.
The Centers for Disease Control and Prevention (CDC) HIV also infects brain monocytes and macrophages, AIDS & HIV 2
estimates that at the end of 2011, there were approximately producing multinucleated giant cells and significant central &disc8
&
I
·

+
=

1.1 million people infected with HIV living in the United

"signsise
nervous system symptoms. The fusion of HIV-infected
States. The transmission rate has declined markedly, pri- cells in the brain and elsewhere mediated by gp41 is one of
marily due to increased prevention efforts and improved the main pathologic findings. The cells recruited into the
·

treatments for HIV; the latter reduces the number of people syncytia ultimately die. The death of HIV-infected cells is
with high titers of HIV. CDC estimates that approximately also the result of immunologic attack by cytotoxic CD8
50,000 people new infections occur each year. CDC also lymphocytes. Effectiveness of the cytotoxic T cells may be
estimates that 15% of those who are infected with HIV do limited by the ability of the viral Tat and Nef proteins to
not know it because they have not been tested. reduce class I MHC protein synthesis (see later).
Approximately 630,000 people have died of AIDS in the Another mechanism hypothesized to explain the death
United States since 1981, when AIDS wasCHI first recognized.
&'s of helper T cells is that HIV acts as a “superantigen,” which
E
As of 2011, it is estimated that approximately 34 million
·
.

indiscriminately activates many helper T cells and leads to

Lfemale
people worldwide
**
are infected,
emale) heterosexal transm
.
two-thirds
-6
&
of whom live in their demise. The finding that one member of the retrovi-
. sub-Saharan Africa. Three regions, Africa, Asia, and Latin
.

rus family, mouse mammary tumor virus, can act as a

&

homosex-america
I
-

America, have the highest rates of new infections. AIDS is superantigen lends support to this theory. Superantigens
the fourth leading cause of death worldwide. (Ischemic are described in Chapter 58.
heart disease, cerebrovascular disease, and acute lower Persistent noncytopathic infection of T lymphocytes
respiratory disease are ranked first, second, and third, also occurs. Persistently infected cells continue to produce
respectively.) [* *). -125 HIV, which may help sustain the infection in vivo. Lym-
-
How

In the United States and Europe during the 1980s, HIV phoid tissue (e.g., lymph nodes) is the main site of ongoing
. HIV/
infection and AIDS occurred primarily in men who have HIV infection. · 3d
2 /

&
sex with men (especially those with multiple partners), In addition, a true latent infection can occur in which
intravenous drug users, and hemophiliacs. Heterosexual no HIV is produced. This occurs in resting CD4-positive
transmission was rare in these regions in the 1980s but is memory T cells within which an integrated HIV genome is
now rising significantly. Heterosexual transmission is the found. The latent period can last for months to years but if
predominant mode of infection in African countries. the resting cell is activated, HIV can be produced. HIV
Very few health care personnel have been infected replication depends on host cell transcription factors made
despite continuing exposure and needle-stick injuries, sup- in activated, but not resting, CD4-positive cells.
porting the view that the infectious dose of HIV is high. A person infected with HIV is considered to be
iBs discare
infected for life. This seems likely to be the result of
genome

The risk of being infected after percutaneous exposure to

e

lymphadenopathy ,
sure throat rash -1
& : acuse HEV syndrome I
&i
mononucleosis sid
· 843 -syn .
) <B ,
-

(generalized lymphadenop .
.
W s WI latentge
&52-JOglaale HIV6Ims's =

candida)N ) opport infections *-sigad

1

thrush
-(500"
is · -
[ 3 -&
-

o
Cut 5
-

,
malignancies -F 7 9
-

s .
.
 CHAPTER 45 Human Immunodeficiency Virus 383

integration of viral DNA into the DNA of infected cells. Antibodies against various HIV proteins, such as p24,
Although the use of powerful antiviral drugs (see “Treat- gp120, and gp41, are produced, but they neutralize the
ment” section later) can significantly reduce the amount virus poorly in vivo and appear to have little effect on the
of HIV being produced, the silent, latent infection in course of the disease.
CD4-positive memory T cells can be activated and serve HIV has three main mechanisms by which it evades the
-530s 5 -
as a continuing
out,-[die 2 -
source of virus. -
immune system: (1) integration of viral DNA into host cell
Elite controllers
-
are a rare group of HIV-infected peo- DNA, resulting in a persistent infection; (2) a high rate of s :
Her
.

...
. - ⑫

rigSan
i
↳
Je ·
-

4 - non-eff
gphoAB gpI0
= ~ RNA

ple (less than 1% of those infected) who have no detectable mutation of the env gene; and (3) the production of the Tat
~ . ;

&
32
-

MHC 2
-

HIV in their blood. Their CD4 counts are normal without and Nef proteins that downregulate class I MHC proteins
-

-
molecules
.

-
homog Hetero
erous .

using antiretroviral drugs. The ability to be an elite control- required for cytotoxic T cells to recognize and kill HIV-
musation musacion
a E
- N --

normet , ler does not depend on gender, race, or mode of acquisition

s s

infected cells. The ability of HIV to infect and kill CD4-

.

j of the virus. Although the mechanism is unclear, there is

=
positive helper T cells further enhances its capacity to avoid
evidence that certain HLA alleles are protective and that an destruction by the immune system.
inhibitor of the cyclin-dependent kinase known as p21 synd ! 96
- acute retrovirus . HIV a

plays an important role.

- 188- HIV

Clinical Findings
or acute syn

In addition, there is a group of HIV-infected individuals

The clinical picture of HIV infection can be divided into
who have lived for many years without opportunistic infec-
three stages: an early, acute stage; a middle, latent stage; and
tions and without a reduction in the number of their helper
a late, immunodeficiency stage (Figure 45–5). In the acute
T (CD4) cells. The strain of HIV isolated from these indi-
stage, which usually begins 2 to 4 weeks after infection, a
viduals has mutations in the nef gene, indicating the impor-
mononucleosis-like picture of fever, lethargy, sore throat, iBWIsl HIV

tance of this gene in pathogenesis. The Nef protein

and generalized lymphadenopathy occurs. A maculopapu- regularHS .
>
-

decreases class I major histocompatibility complex (MHC)

lar rash on the trunk, arms, and legs (but sparing the palms HEVPCR
·

protein synthesis, and the inability of the mutant virus to

and soles) is also seen. Leukopenia occurs, but the number ve -
-
-

produce functional Nef protein allows the cytotoxic T cells

of CD4 cells is usually normal. A high-level viremia typi-
to retain their activity.
cally occurs, and the infection is readily transmissible dur-
Another explanation why some HIV-infected individu-
als are long-term “nonprogressors” may lie in their ability ing this acute stage. This acute stage typically resolves
to produce large amounts of α-defensins. α-Defensins are a spontaneously in about 2 weeks. Resolution of the acute
family of positively charged peptides with antibacterial
activity that also have antiviral activity. They interfere with
·
HIV binding to the CXCR4 receptor and block entry of the <200 -
> -

= spozd
Pneumoniaa (Pap)Pneumocystis
ACUTE LATENT IMMUNODEFICIENCY Lung al infect

virus into the cell.

Post see
dry cough-low

In addition to the detrimental effects on T cells, abnor- ⑦

creti > lasmosisa
med
-
toxop
protozoa
-

E
S

multiple
brain 9--

malities of B cells occur. Polyclonal activation of B cells is

-

lesis
1

I 20
3O -
>

Acute symptoms Opportunistic infections -"

P

seen, with resultant high immunoglobulin levels. Autoim-

.
Relative levels

My
cobac

d
Primus
-CD4 and malignancies atypical ↓
count - load
myCobal .

mune diseases, such as thrombocytopenia, occur. O CD4 lymphocytes

!
⑮ ↳ 4
/150 -

plasmosisa
Histo

The main immune response to HIV infection consists

800

= si
normal Q ↳ count -P
E

window gerod" AB s isen Anti-p24 antibodies

i
e
[1 5) Stationary <lents . <DU" ,o

of cytotoxic CD8-positive lymphocytes. These cells

21 e
d
diag
e
acute HEV HIV 2
-
.

respond to the initial infection and control it for many Anti-gp120 antibodies
years. Mutants of HIV, especially in the env gene encoding -ABI / d & Desper & Is s
CBU
⑥ &*
Count

gp120, arise, but new clones of cytotoxic T cells proliferateser

-

Virus, viral RNA, p24 antigen >

-

-5' -
>
- -9 200

↳ AB
-
M

supp
- -

> Bw;
and control the mutant strain. It is the ultimate failure of
.

Samay vis in co2" is T

Cell-med
.
Immuni
·
S

0 1 2 3 4 5 6 3 – ≥ 10
these cytotoxic T cells that results in the clinical picture of Time after infection (mo) Time after infection (y)
AIDS. Cytotoxic T cells lose their effectiveness because so
many CD4 helper T cells have died; thus the supply of lym- FIGURE 45–5 Time course of human immunodeficiency
phokines, such as interleukin-2 (IL-2), required to activate virus (HIV) infection. The three main stages of HIV infection—
the cytotoxic T cells is no longer sufficient. acute, latent, and immunodeficiency—are shown in conjunction
There is evidence that “escape” mutants of HIV are able with several important laboratory findings. Note that the levels of
to proliferate unchecked because the patient has no clone of virus and viral RNA (viral load) are high early in the infection,
become low for several years, and then rise during the immuno-
cytotoxic T cells capable of responding to the mutant
deficiency stage. The level of CD4 lymphocytes remains more or
strain. Furthermore, mutations in any of the genes encod- less normal for many years but then falls. This results in the immu-
ing class I MHC proteins result in a more rapid progression nodeficiency stage, which is characterized by opportunistic infec-
to clinical AIDS. The mutant class I MHC proteins cannot tions and malignancies. Not shown in the figure is the marked
present HIV epitopes, which results in cytotoxic T cells loss of the Th-17 subset of CD4-positive T cells early in the infec-
being incapable of recognizing and destroying HIV- tion. (Adapted from Weiss RA. How does HIV cause AIDS? Science.
infected cells. 1993;260:1273.) ·
②
therapy -valgiss-200-i CD4 (200 HIV !

/
antiretroviral I
opp inf &,
- * S. HIV
.
-

Lymphoma& cancers d
-
~

inf ****
sulfamethoxazole-PP : -1200s & sopp
-

Trimethoprin .
.
·
1
-
-

eid- 12389 - d d
d
·

toxoplastAntibioticbutittreadsSangali
-
Papasi sarcoma
-

50 . Prophylaxis
05-6primary
Ed
. .
-
i

trimento o-Cut
n e
for un citomy
C E
 CD4
+
%.
1 16 if Eraconazole Du* 150
- 18, 1 ***25 11 -

384 PART IV Clinical Virology

stage is usually accompanied by a lower level of viremia and clinical latency, the virus itself does not enter a latent
a rise in the number of CD8-positive (cytotoxic) T cells state.
-
Serum s AB Seroconversion

directed against HIV. A syndrome called AIDS-related complex (ARC) can

the
& &

&
2-3 weeks
Antibodies to HIV typically appear 10 to 14 days after occur during the latent period. The most frequent manifes-
infection, and most patients will have seroconverted by 3 to tations are persistent fevers, fatigue, weight loss, and
4 weeks after infection. Note that the inability to detect lymphadenopathy. ARC often progresses to AIDS.
AB : 2
antibodies prior to that time can result in “false-negative” The late stage of HIV infection is AIDS, manifested by a
-
- 8

serologic tests (i.e., the person is infected, but antibodies decline in the number of CD4 cells to below 200/μL and an
are not detectable at the time of the test). This has impor- increase in the frequency and severity of opportunistic
tant implications because HIV can be transmitted to others infections. Table 45–2 describes some of the common
during this period. If the antibody test is negative but HIV opportunistic infections and their causative organisms seen
infection is still suspected, then a polymerase chain reac- in HIV-infected patients during the late, immunocompro-
tion (PCR)–based assay for viral RNA in the plasma should mised stage of the infection.
be done. The two most characteristic manifestations of AIDS are
Of those who become seropositive during the acute Pneumocystis pneumonia and Kaposi’s sarcoma. However,
infection, approximately 87% are symptomatic (i.e., about many other opportunistic infections occur with some fre-
13% experience an asymptomatic initial infection). quency. These include viral infections such as dissemi-
After the initial viremia, a viral set point occurs, which nated herpes simplex, herpes zoster, and cytomegalovirus
can differ from one person to another. The set point repre- infections and progressive multifocal leukoencephalopa-

Bang
s dont i , 0 9
- E Contol so
Tim T But is e

sents the amount of virus produced (i.e., the viral load) and thy; fungal infections such as thrush (caused by Candida
. -

tends to remain “set,” or constant, for years. The higher the albicans), cryptococcal meningitis, and disseminated his-
set point at the end of the initial infection, the more likely toplasmosis; protozoal infections such as toxoplasmosis
"Pimutations **d
the individual is to progress to symptomatic AIDS. It is and cryptosporidiosis; and disseminated bacterial infec-
-
estimated that an infected person can produce up to 10 bil- tions such as those caused by Mycobacterium avium-
-

- resistant -
·
antiviral
drugs
lion new virions each day. This viral load can be estimated intracellulare and Mycobacterium tuberculosis. Many AIDS
·

by using an assay for viral RNA in the patient’s plasma. patients have severe neurologic problems (e.g., dementia
(The assay detects the RNA in free virions in the plasma, and neuropathy), which can be caused by either HIV
not cell-associated virions.) infection of the brain or by many of these opportunistic
The amount of viral RNA serves to guide treatment organisms. Hive -
annPay ABI
99. for
85/ELISA
the

for

decisions and the prognosis. For example, if a drug regimen Classic s DELISAG
-

the

I e Westren blot
② Westren blot
fails to reduce the viral load, the drugs should be changed. >
-
me
1

Laboratory Diagnosis
·
- -

As far as the prognosis is concerned, a patient with more (2 the bands&

·

than 10,000 copies of viral RNA/mL of plasma is signifi- The presumptive diagnosis of HIV infection is often made
·

cantly more likely to progress to AIDS than a patient with by the detection of antibodies in the patient’s serum to the
fewer than 10,000 copies. p24 protein of HIV using the enzyme-linked immunosor-
The number of CD4-positive T cells is another impor- bent assay (ELISA) test. Because there are some false-
tant measure that guides the management of infected positive results with this test, the definitive diagnosis is
patients. It is used to determine whether a patient needs made by Western blot (also known as Immunoblot)
chemoprophylaxis against opportunistic organisms, to analysis, in which the viral proteins are displayed by acryl-
determine whether a patient needs anti-HIV therapy, and amide gel electrophoresis, transferred to nitrocellulose
to determine the response to this therapy. The lower limit paper (the blot), and reacted with the patient’s serum. If
of CD4 count considered as normal is 500 cells/μL. People antibodies are present in the patient’s serum, they will bind
with this level or higher are usually asymptomatic. The to the viral proteins (predominantly to the gp41 or p24
frequency and severity of opportunistic infections signifi- protein). Enzymatically labeled antibody to human IgG is
cantly increase when the CD4 counts fall below 200/μL. A then added. A color reaction reveals the presence of the
CD4 count of 200/μL or below is an AIDS-defining HIV antibody in the infected patient’s serum. Figure 64–9
condition. depicts a Western blot (Immunoblot) test used to diagnose
In the middle stage of HIV infection, a long latent HIV
"
infection. is

period, measured in years, usually ensues. In untreated OraQuick is a rapid, screening immunoassay for HIV
-

patients, the latent period typically lasts for 7 to 11 years. antibody that uses an oral swab sample in an ELISA-type
The patient is asymptomatic during this period. test that can be done at home. Results are available in
Although the patient is asymptomatic and viremia is low 20 minutes. Positive results for HIV antibody require con-
or absent, a large amount of HIV is being produced by firmation by a Western blot test. Slid '

lymph node cells but remains sequestered within the synd The PCR test is a very sensitive and specific technique
U e
aute syn
.

Jens
-

lymph nodes. This indicates that during this period of that can be used
d to detect HIV DNA within infected cells.
HIV. Wo'eds & dbi &s

Abso & by 51 si
-

plas '30s I'vls -

· is - ABS (false the) -as

 CHAPTER 45 Human Immunodeficiency Virus 385

4 = 25
we
· =

TABLE 45–2 Common Opportunistic Infections in AIDS Patients

Site of Infection Disease or Symptom Causative Organism

Lung 1. Pneumonia Pneumocystis jiroveci, cytomegalovirus

2. Tuberculosis Mycobacterium tuberculosis
Mouth 1. Thrush-Y Candida albicans
=>

2. Hairy leukoplakia Epstein–Barr virus

3. Ulcers Herpes simplex virus-1, Histoplasma capsulatum
> Oderophagia
Esophagus 1. Thrush C. albicans
2. Esophagitis Cytomegalovirus, herpes simplex virus-1
Intestinal tract Diarrhea - Salmonella species, Shigella species, cytomegalovirus,
Cryptosporidium parvum, Giardia lamblia
-

Central nervous system 1. Meningitis Cryptococcus neoformans

2. Brain abscess Toxoplasma gondii
3. Progressive multifocal leukoencephalopathy JC virus
Eye Retinitis R Cytomegalovirus
Skin 1. Kaposi’s sarcoma Human herpesvirus 8
2. Zoster Varicella-zoster virus
3. Subcutaneous nodules C. neoformans
Reticuloendothelial system Lymphadenopathy or splenomegaly Mycobacterium avium complex, Epstein–Barr virus

issee
Oboe
s
lifecycle *
-

&

-
>
- of HEU >
-
of NRIs
&

Treatment
.

Some individuals who do not have detectable antibodies

2
↳
+

have been shown by this test to be infected. As already UNRTIS-

"Protease , integrase inhi sd -
Slad
The treatment of HIV infection has resulted in a remark-
>8

nevirapine

mentioned, the amount of viral RNA in the plasma (i.e., D

Efavirens
able reduction in mortality and improvement in the quality
or
NNRTIs

the viral load) can also be determined using PCR-based of life of infected individuals. The two specific goals of Zid&
# 9384 20 - ,

s
-
sen

assays. treatment are (1) to restore immunologic function by - a 946 -

2 -

During the first month after infection, antibody tests

.

15
↳
1: 1-

increasing the CD4 count, which reduces opportunistic se

may be negative. These false-negative tests are due to insuf-

count

infections and certain malignancies, and (2) to reduce viral i

annes
·
ficient antibody being made early in infection to be detected load, which reduces the chance of transmission to others. 2
-

-10s5 * * &

i
-

There is evidence that starting drug therapy as soon as pos- jer

S

in the ELISA test. The average time for seroconversion is -

-

10 to 14 days, and most of those infected, but not all, will sible after making the diagnosis of HIV infection is the best
have seroconverted by 4 weeks. way to achieve these goals.
In view of this, the diagnosis of acute HIV infection may Unfortunately, no drug regimen results in a “cure” (i.e.,
not be able to be made using only tests for antibody in the eradicates the virus from the body), but long-term suppres-
serum. The presence of HIV can be detected during acute sion can be achieved. However, if drugs are stopped, the
infection by the plasma HIV RNA assay (viral load), as virus resumes active replication, and large amounts of
viremia is typically high at this early stage. Also useful for infectious virus reappear.
the diagnosis of early infections is the HIV antigen/ Treatment of HIV infection typically involves multiple
antibody “Combo” test that detects the presence of p24 antiretroviral drugs. The use of a single drug (monother-
antigen as well as antibodies to both HIV-1 and HIV-2. apy) for treatment is not done because of the high rate of
This combination test is useful for the diagnosis of early mutation to drug resistance.
infections because p24 antigen is typically detectable earlier The choice of drugs is complex and depends on several
in infection than antibody. factors (e.g., whether it is an initial infection or an estab-
Other laboratory tests that are important in the manage- lished infection, the number of CD4 cells, the viral load, the
ment of an HIV-infected person include CD4 cell counts, resistance pattern of the virus, and whether the patient is
viral load assays, and tests for drug resistance of the strain pregnant or is coinfected with HBV or hepatitis C virus
of HIV infecting the patient. Drug resistance tests are [HCV]). Table 45–3 describes the mechanism of action of
described at the end of the “Treatment” section in this the drugs and their main adverse effects. The number of
chapter. HIV can be grown in culture from clinical speci- drugs and the various determining factors mentioned pre-
mens, but this procedure is available only at a few medical viously make describing all the treatments beyond the
centers. scope of this book. The reader is advised to consult the
, - He ?-Mid-ijh
th yelid
HBV- HIE

&. Other inf SI2 i ~

HAV OSHAURHB,V&
. - & So &
I

HEU Z
. ed
&

Immune reconstitution inflammatory syndrome (IRIS) 04

 386 PART IV Clinical Virology

TABLE 45–3 Drugs Used for the Treatment of HIV Infection

Class of Drug Name of Drug Main Adverse Effect (AE) or Comment

Reverse transcriptase inhibitors

s
Nucleosides (NRTI) Abacavir (ABC) (Ziagen) AE: severe multiorgan hypersensitivity reaction, especially in patients
El
with HLA-B5701 abacanir
the
>
-
d
I

-
&
Didanosine (ddI) (Videx) -
- > AE: pancreatitis and peripheral neuropathy
-

Emtricitabine (FTC) (Emtriva) A derivative of lamivudine; well-tolerated

= >

Lamivudine (3TC) (Epivir) Well tolerated. Also used to treat hepatitis B virus infection
Stavudine (d4T) (Zerit) AE: peripheral neuropathy, lipoatrophy, lactic acidosis with hepatic
steatosis, pancreatitis
Zidovudine (AZT, ZDV) (Retrovir) AE: bone marrow suppression (anemia, neutropenia)
Nucleotides Tenofovir (Viread) AE: well-tolerated but renal toxicity occurs
Nonnucleosides (NNRTI) Delavirdine (Rescriptor) AE: rash; avoid in pregnancy; rarely used
phsycosis
Efavirenz (Sustiva)-
> AE: CNS changes and rash; possibly teratogenic so avoid in pregnancy
- - - -

Rilpivirine (Endurant) AE: rash

Etravirine (Intelence) AE: Stevens-Johnson syndrome; hepatotoxicity
Nevirapine (Viramune) AE: depression, insomnia
Protease inhibitors1 Amprenavir (Agenerase) AE: rash, hemolytic anemia
d
lipadystrophy -

Atazanavir (Reyataz) AE: hyperbilirubinemia, prolonged PR interval

j d Darunavir (Prezista) AE: hepatotoxicity
-

S961 -

I W1
=

Fosamprenavir (Lexiva) A prodrug of amprenavir; metabolized by phosphatases in gut

·

epithelium to amprenavir. AE: rash

Indinavir (Crixivan) AE: crystalluria and nephrolithiasis due to poor solubility. Infrequently
used
Lopinavir/ritonavir (Kaletra) Ritonavir inhibits CYP3A metabolism of lopinavir, thereby increasing
the effective concentration of lopinavir
Nelfinavir (Viracept) May contain levels of ethyl methanesulfonate (ethyl mesylate) that
may be carcinogenic, mutagenic, or teratogenic. AE; diarrhea. No
longer recommended
Ritonavir (Norvir) See lopinavir/ritonavir, saquinavir, and tipranavir
Saquinavir (Invirase and Fortovase) Invirase must be taken with ritonavir; Fortovase can be taken without
ritonavir. Infrequently used
Tipranavir (Aptivus) AE: if taken with ritonavir (Norvir), severe liver disease may occur
Entry inhibitors
Fusion inhibitor Enfuvirtide (Fuzeon) Binds to viral gp41 and blocks fusion of virus with cell membrane
AE: injection site reactions
Coreceptor antagonist Maraviroc (Selzentry) Blocks binding of viral gp120 to CCR5 coreceptor on cell membrane;
effective against CCR5-tropic viruses but not against CXCR4-tropic
viruses
AE: hepatotoxicity, especially in those infected with HBV and HCV
Integrase inhibitor Raltegravir (Isentress) Inhibits integration of proviral DNA into cellular DNA
AE: nausea, diarrhea, rash
Elvitegravir (Stribild) Available in combination with cobicistat, tenofovir, and emtricitabine
AE: diarrhea
Dolutegravir (Tivicay) AE: insomnia, headache

CNS = central nervous system.

1
All protease inhibitors cause lipodystrophy (“buffalo hump”) and central obesity as an adverse effect. Nausea and diarrhea are also
quite common. Hepatotoxicity occurs, especially in those infected with hepatitis B or C virus.

Department of Health and Human Services Antiretroviral two protease inhibitors (either ritonavir plus atazanavir or
Therapy Guidelines or other reliable sources, such as the ritonavir plus darunavir) or a combination of elvitegravir
Medical Letter. plus the enhancer cobicistat is added. A single pill given in
As of 2015, the preferred approach to initial antiretrovi- once-a-day dosing improves compliance so a variety of
ral therapy consists of one of four regimens, all of which these three or four drug combinations are now available in
consist of three or four drugs. Each regimen includes a single pill formulation.
emtricitabine and tenofovir (“the backbone”), to which These combinations are known as highly active antiret-
either efavirenz, raltegravir, rilpivirine, or a combination of roviral therapy (HAART). HAART is very effective in
 CHAPTER 45 Human Immunodeficiency Virus 387

prolonging life, improving quality of life, and reducing viral indinavir, nelfinavir, ritonavir, saquinavir, tipranavir, and a
load but does not cure the chronic HIV infection (i.e., rep- combination of lopinavir and ritonavir). Protease inhibitors
lication of HIV within CD4-positive cells continues indefi- when combined with nucleoside analogues are very effec-
nitely). Discontinuation of HAART almost always results in tive in inhibiting viral replication and increasing CD4 cell
viremia (a return of the viral load to its pretreatment set counts and are commonly used in HAART regimens. Lopi-
point) and a fall in the CD4 count. navir and ritonavir are given in combination because rito-
navir inhibits the degradation of lopinavir thereby
Nucleoside/Nucleotide Reverse Transcriptase increasing the concentration of lopinavir. A briefer way of
Inhibitors (NRTIs) saying that is ritonavir “boosts” lopinavir.
Table 45–3 describes six nucleoside reverse transcriptase Mutants of HIV resistant to protease inhibitors can be a
inhibitors (abacavir, didanosine, emtricitabine, lamivudine, significant clinical problem. Resistance to one protease
stavudine, and zidovudine) and a single nucleotide reverse inhibitor often conveys resistance to all; however, the com-
transcriptase inhibitor (tenofovir). These drugs are charac- bination of two protease inhibitors, namely, ritonavir and
terized by not having a 3′ hydroxyl group on the ribose ring lopinavir (Kaletra), is effective against both mutant and
and therefore are chain-terminating drugs. They inhibit nonmutant strains of HIV. Also, darunavir is effective
HIV replication by interfering with proviral DNA synthesis against many strains of HIV that are resistant to other pro-
by reverse transcriptase. They cannot cure an infected cell tease inhibitors. Mutants of HIV resistant to both protease
of an already integrated copy of proviral DNA. Additional inhibitors and reverse transcriptase inhibitors have been
information on these “nucleoside analogue” drugs and the recovered from patients.
other antiretroviral drugs can be found in Chapter 35. Note A major side effect of protease inhibitors is abnormal
that zalcitabine (Hivid), an NRTI analogue of cytosine, is fat deposition in specific areas of the body, such as the
no longer available. back of the neck (Figure 45–6). The fat deposits in the
Two main problems limit the use of NTRIs: the emer- back of the neck are said to give the person a “buffalo >
- Lipo kystrophy
gence of resistance and adverse effects. The main adverse hump” appearance. These abnormal fat deposits are a
effects are described in Table 45–3. For example, the long- type of lipodystrophy; the metabolic process by which
term use of zidovudine (ZDV) is limited by suppression of this occurs is unknown. Saquinavir and indinavir are
the bone marrow leading to anemia and neutropenia. This infrequently used because of toxicity and nelfinavir is no
hematotoxicity is due to the inhibition of the mitochondrial longer recommended.
DNA polymerase. Nevertheless, ZDV is used in postexpo- Treatment for acute HIV infection with two reverse
sure prophylaxis and to prevent vertical transmission from transcriptase inhibitors and a protease inhibitor is often
mother to fetus. Lamivudine and its analogue emtricitabine used. With this regimen, the viral load drops below the
have the same mechanism of action as ZDV but are better level of detection, CD4 cell counts rise, and CD8 activity
tolerated, and one or another is a common component of
HAART. Abacavir is also commonly used. Patients who
have an HLA-B1701 allele are more likely to have a severe
hypersensitivity reaction to abacavir. Patients should be
tested for this gene before being prescribed abacavir.

Nonnucleoside Reverse Transcriptase Inhibitors

Table 45–3 describes five nonnucleoside reverse transcrip-
tase inhibitors (delavirdine, efavirenz, etravirine, nevirap-
ine, and rilpivirine) that are effective against HIV. Unlike
the NRTIs, these drugs are not base analogues. Efavirenz
(Sustiva) and nevirapine (Viramune) are the most com-
monly used drugs in this class. Efavirenz is a common
component of HAART regimens, especially a single pill
containing efavirenz, tenofovir, and emtricitabine (Atri-
pla). Nevirapine is often used to prevent vertical transmis-
sion of HIV from mother to fetus. Both nevirapine and
efavirenz can cause skin rashes and Stevens-Johnson
syndrome. FIGURE 45–6 Lipodystrophy—note enlarged fat pad on back
of neck. This is known as a “buffalo hump” and is an adverse effect of
the protease inhibitor class of antiretroviral drugs. (Reproduced with
Protease Inhibitors permission from Wolff K, Johnson R. Fitzpatrick’s Color Atlas & Synopsis
Table 45–3 describes the currently available protease inhib- of Clinical Dermatology. 6th ed. New York: McGraw-Hill, 2009. Copy-
itors (amprenavir atazanavir, darunavir, fosamprenavir, right © 2009 by The McGraw-Hill Companies, Inc.)
388 PART IV Clinical Virology

increases. The long-term effect of this approach on rate of the RT and PR genes from the patient’s virus and splices
progression to AIDS has yet to be determined. them into a test strain of HIV, which is then used to infect
Pregnant women infected with HIV should be treated cells in culture. Another laboratory test can determine the
with two nucleosides and a protease inhibitor. A typical tropism of the patient’s isolate (i.e., whether it uses CCR5 as
regimen would include lamivudine, ZDV, and lopinavir/ its coreceptor). If so, then maraviroc can be used for
ritonavir. In addition, ZDV should be given to the neonate. treatment.
These drugs appear not to damage the fetus, although rare
instances of mitochondrial dysfunction and death attrib- Immune Reconstitution Inflammatory Syndrome
uted to ZDV have been reported. The reader is urged to Immune reconstitution inflammatory syndrome (IRIS)
consult the current information regarding the use of these may occur in HIV-infected patients who are treated with
drugs in pregnancy. A full discussion is beyond the scope a HAART regimen and who are coinfected with other
of this book. microbes such as HBV, HCV, M. tuberculosis, M. avium
complex, Cryptococcus neoformans, and Toxoplasma
Entry Inhibitors gondii. In this syndrome, an exacerbation of clinical
Table 45–3 describes two entry inhibitors, enfuvirtide and symptoms occurs because the antiretroviral drugs
maraviroc. Enfuvirtide (Fuzeon) is the first of a new class enhance the ability to mount an inflammatory response.
of anti-HIV drugs known as fusion inhibitors (i.e., they HIV-infected patients with a low CD4 count have a
prevent the fusion of the viral envelope with the cell mem- reduced capacity to produce inflammation, but HAART
brane). Enfuvirtide is a synthetic peptide that binds to gp41 restores the inflammatory response, and as a result,
on the viral envelope, thereby blocking the entry of HIV symptoms become more pronounced. To avoid IRIS, the
into the cell. It must be administered by injection and is coinfection should be treated prior to instituting HAART
quite expensive. whenever possible.
Maraviroc (Selzentry) also prevents the entry of HIV
into cells. It blocks the binding of the gp120 envelope Prevention > no
- Vaccine

protein of HIV to CCR-5, which is an important corecep-

No vaccine is available. Multiple trials of a variety of
tor on the cell surface. Before prescribing maraviroc, a
experimental vaccines have failed to induce protective
laboratory test (Trofile assay) should be performed to
antibodies, protective cytotoxic T cells, or mucosal immu-
ensure that the tropism of the patient’s strain of HIV is
nity. Prevention consists of taking measures to avoid
CCR5. Maraviroc should be used in combination with
exposure to the virus (e.g., using condoms, not sharing
other antiretroviral drugs in patients infected with CCR5-
needles, and discarding donated blood that is contami-
tropic strains of HIV and in treatment-experienced adults
nated with HIV).
infected with an HIV strain that is resistant to other anti-
Postexposure prophylaxis (PEP), such as that given
retroviral drugs.
after a needle-stick injury or a high-risk nonoccupational
-3352j2
exposure, employs three drugs: the preferred regimen con-
Integrase Inhibitors D e
sists of the combination of tenofovir and emtricitabine
Raltegravir (Isentress) is the first drug to inhibit the y
(given as Truvada) plus raltegravir. Three alternative drug 3

HIV-encoded integrase (see Table 45–3). It is recom- regimens are available. PEP should be given as soon as pos-
mended for use in patients who have been treated with sible after exposure and continued for 28 days. Truvada can
other antiretroviral drugs but continue to produce sig- also be used for preexposure prophylaxis (PrEP) in indi-
- - - 8. &

nificant levels of HIV. Two additional integrase inhibi- viduals at high risk of infection, such as men who have sex
tors are available: dolutegravir (Tivicay) and elvitegravir with men. ·*
14
5 CDU Count
-

? 2 os ili!

bisnis Two stepslowcan

↓ viral
load a d

(Stribild).
/
·

· undetectable
amiro acid be taken to reduce the number of cases of
mutations
HIV infection in children: antiretroviral therapy should be
>
-
test
> genotype resistance
- resistant
-

Resistance to Antiretroviral Drugs

+ more

By lig ! given to HIV-infected mothers and neonates, and HIV-

si

Drug-resistant mutants of HIV have emerged that signifi- infected mothers should not breast feed. The choice of
cantly affect the ability of both reverse transcriptase inhibi- antiretroviral drugs is dependent on several factors, so cur-
tors and protease inhibitors to sustain their clinical efficacy. rent guidelines should be consulted. In addition, the risk of
Approximately 10% of newly infected patients are infected neonatal HIV infection is lower if delivery is accomplished
with a strain of HIV resistant to at least one antiretroviral by cesarean section rather than by vaginal delivery. Cir-
drug. Laboratory tests to detect mutant strains include both cumcision reduces HIV infection.
genotypic and phenotypic analysis. Genotyping reveals the Several drugs are commonly taken by patients in the
presence of specific mutations in either the reverse tran- advanced stages of AIDS to prevent certain opportunistic
scriptase (RT) or protease (PR) genes. Phenotyping deter- infections (Table 45–4). Some examples are trimethoprim-
mines the ability of the virus to grow in cell culture in the sulfamethoxazole to prevent Pneumocystis pneumonia, flu-
presence of the drug. One method of phenotyping recovers conazole to prevent recurrences of cryptococcal meningitis,
 CHAPTER 45 Human Immunodeficiency Virus 389

TABLE 45–4 Drugs Used for the Prevention of (C) After infection with HIV, antibodies to the virus can be
Opportunistic Infections in AIDS Patients detected before the polymerase chain reaction (PCR) test can
detect nucleic acids specific to HIV.
Name of Drug Infection Prevented (D) Because false-positive results occur in the screening test for
Trimethoprim- 1. Pneumocystis pneumonia HIV, a confirmatory test called the Western blot assay should
sulfamethoxazole 2. Toxoplasmosis be performed for those with a positive result on the screen-
ing test.
Fluconazole Cryptococcal meningitis
4. Regarding the mode of action of drugs used in the treatment of
Clotrimazole Thrush caused by C. albicans human immunodeficiency virus (HIV) infection, which one of
Ganciclovir Retinitis caused by cytomegalovirus the following is most accurate?
(A) Maraviroc acts by inhibiting the reverse transcriptase in the
Azithromycin Mycobacterium avian complex
(MAC) infection
virion.
(B) Raltegravir inhibits the integration of HIV DNA into host cell
DNA.
(C) Zidovudine is a nucleoside analog that inhibits messenger RNA
(mRNA) synthesis of HIV.
ganciclovir to prevent recurrences of retinitis caused by
(D) Ritonavir acts by binding to the Tat protein, which prevents
cytomegalovirus, and oral preparations of antifungal budding and release of the HIV virion.
drugs, such as clotrimazole, to prevent thrush caused by (E) Lamivudine is a “chain-terminating” drug because it inhibits
C. albicans. the growing polypeptide chain by causing misreading of the
viral mRNA.
5. Regarding the adverse effects of drugs used in the treatment of
human immunodeficiency virus (HIV) infection, which one of
SELF-ASSESSMENT QUESTIONS the following is most likely to cause bone marrow suppression?
(A) Lamivudine
1. Regarding the structure and replication of human immuno- (B) Lopinavir
deficiency virus (HIV), which one of the following is most (C) Nevirapine
accurate? (D) Maraviroc
(A) Viral mRNA is the template for the synthesis of the genome (E) Zidovudine
RNA. 6. Regarding the adverse effects of drugs used in the treatment of
(B) During entry of HIV into the cell, the viral p24 protein inter- human immunodeficiency virus (HIV) infection, which one of
acts with the CD4 protein on the cell surface. the following is most likely to cause lipodystrophy (i.e., abnormal
(C) HIV contains an integrase within the virion that integrates cop- fat deposits)?
ies of the viral genome into the progeny virions. (A) Lamivudine
(D) HIV has an enzyme in the virion that synthesizes double- (B) Lopinavir
stranded DNA using the single-stranded genome RNA as the (C) Nevirapine
template. (D) Maraviroc
(E) The HIV genome encodes a protease that cleaves cellular ribo- (E) Zidovudine
somal proteins, resulting in the inhibition of cell-specific pro- 7. Regarding the adverse effects of drugs used in the treatment
tein synthesis. of human immunodeficiency virus (HIV) infection, which
2. Regarding clinical aspects of human immunodeficiency virus one of the following is most likely to cause Stevens-Johnson
(HIV), which one of the following is most accurate? syndrome?
(A) During the primary infection with HIV, Pneumocystis pneu- (A) Lamivudine
monia commonly occurs. (B) Lopinavir
(B) During the long asymptomatic period that can last for years, no (C) Nevirapine
HIV is synthesized. (D) Maraviroc
(C) During the period when many opportunistic infections occur, (E) Zidovudine
HIV usually cannot be detected in the blood. 8. Which of the following modes of transmission of human immu-
(D) The antibody response to a primary HIV infection usually is nodeficiency virus (HIV) occurs significantly MORE often than
detected within 7 to 10 days after infection. the others?
(E) People with a high level of viral RNA in their plasma are more (A) Direct skin contact
likely to have symptomatic AIDS (i.e., opportunistic infections) (B) During childbirth
than those with low levels. (C) Fecal–oral route
3. Regarding the laboratory diagnosis of human immunodeficiency (D) Respiratory aerosols
virus (HIV), which one of the following is most accurate? 9. Your patient is a 25-year-old man who was just found to be
(A) The initial screening of blood for antibodies to HIV is done by infected with HIV based on a positive enzyme-linked immuno-
the complement fixation test. sorbent assay (ELISA) and a positive Western blot test. His CD4
(B) Viral load is the term used to describe the amount of infectious count is 125, and his viral load is 7000. He has not received any
virus produced by the patient’s CD4-positive T lymphocytes in antiretroviral medications. Which one of the following is the best
cell culture. regimen to treat his infection?
390 PART IV Clinical Virology

(A) Acyclovir, foscarnet, and ribavirin SUMMARIES OF ORGANISMS

(B) Enfuvirtide, raltegravir, and maraviroc
(C) Lamivudine, ribavirin, and ritonavir/lopinavir Brief summaries of the organisms described in this chapter
(D) Zidovudine, lamivudine, and efavirenz begin on page 678. Please consult these summaries for a rapid
review of the essential material.

ANSWERS
1. (D)
2. (E) PRACTICE QUESTIONS: USMLE &
3. (D) COURSE EXAMINATIONS
4. (B)
5. (E) Questions on the topics discussed in this chapter can be found
6. (B) in the Clinical Virology section of Part XIII: USMLE (National
7. (C) Board) Practice Questions starting on page 723. Also see Part
8. (B) XIV: USMLE (National Board) Practice Examination starting
9. (D) on page 751.