Long: Principles and Practice of Pediatric Infectious

Diseases, 3rd ed.
Copyright © 2008 Churchill Livingstone, An Imprint of Elsevier
Section B – Viruses: DNA VIRUSES: Papovaviridae

CHAPTER 211 – Human Papillomaviruses

Kevin A. Ault,
Joseph A. Bocchini Jr

Papillomaviruses (or “wart” viruses) are species-specific viruses, widely distributed among
mammals. They are found in humans, cattle, dogs, rabbits, horses, deer, elk, and other
species. Some papillomaviruses (e.g., of cattle, deer, and elk) affect both epithelial and
fibroblastic tissues and produce fibropapillomas. Human papillomaviruses (HPVs) are strictly
epitheliotropic and produce infections of the skin or the mucous membranes. HPV infections
are very common and these viruses produce a variety of human diseases. The lifetime risk for
genital HPV infection in women from developed countries may approach 80%. [1] HPV
infections are associated with 90% of cases of anogenital dysplasias and carcinomas, in both
women and men. Because HPVs cannot readily be propagated in culture, the rapid growth in
knowledge about HPVs dates from the 1970s, when molecular cloning allowed comparisons of
HPV genomes from different sites and provided reagents for examining affected tissues for
HPV genomic sequences.

THE VIRUS AND PATHOGENESIS

HPVs are nonenveloped, double-stranded DNA viruses with a small circular genome of
approximately 8000 basepairs, which provides only a limited number of genes or open reading
frames, the function of which is listed inTable 211-1 . The HPV genome is divided into genes
that are expressed early and late in the virus replication cycle. Three are of special importance
in pathogenesis. Two early genes, E6 and E7, are oncogenes. Their gene products inhibit host
cell defenses such as apoptosis and DNA repair. The L1 gene encodes the surface protein of
HPV that is the basis of prophylactic vaccines. Papillomaviruses are classified on the basis of
the species of origin and the genetic relatedness between viruses of the same species.

TABLE 211-1   -- Functions associated with Key Genes/Open Reading Frames (ORF) of

Human Papillomaviruses (HPVs)
ORF Function
E2 Regulation of transcription; secondary role in viral DNA replication
E5 Cellular proliferation; main transforming protein for bovine papillomaviruses but not
for HPVs; membrane protein interacting with growth factor receptors
E6 Transforming protein of HPVs; targets destruction of cellular tumor suppressor p53
protein
E7 Transforming protein of HPVs; binds and degrades the tumor suppressor family of
retinoblastoma proteins
L1 Major capsid protein; can be recognized by host immune responses to HPVs and is
ORF Function
the key antigen in HPV vaccines
L2 Minor capsid protein

More than 100 HPVs infect humans. HPVs can be divided into two groups by their natural
tropism for mucosal and cutaneous sites. The genital tract is the main reservoir for mucosal
HPVs, but two mucosal HPVs infect the oral cavity exclusively.

Infection with HPV occurs when the basal cells of the mucosal or cutaneous epithelium are
exposed to infectious virus particles after minor trauma (e.g., during sexual intercourse or after
minor skin abrasions). In the basal and parabasal cells, only the early viral genes are
expressed, and the viral DNA is replicated in low copy numbers. The scant expression of viral
antigens in the basal layer is likely one of the reasons that this virus evades the host immune
system. In the upper, more differentiated layers of the epithelium, all viral genes are
expressed, leading to production of fully infectious virus particles. The presence of infectious
virus in the most superficial layers of the epithelium, which are shed constantly, facilitates
transmission.

Measurement of antibody responses to HPV infections requires antigens in which the

conformational epitopes of the native virus particle are maintained. Infectious particles
prepared in mouse xenografts, or virus-like particles assembled by expression of HPV L1
protein in recombinant vaccinia or baculovirus systems, satisfy this criterion. Studies with
these antigens in enzyme immunoassays show that the antibody response to HPV infections
is low in titer and is not demonstrable in all infected individuals.  [2] [3] Women who have HPV-
associated invasive cervical cancer develop antibodies to the transforming E6 and E7 proteins
of the virus.[4] It is known that HPV infections are more common and have more severe
consequences in individuals with depressed cell-mediated immunity, but assays to measure
HPV-specific cell-mediated immune response are not commercially available or clinically
useful.

EPIDEMIOLOGY AND CLINICAL FEATURES

The major clinical conditions associated with HPV infections, and the HPV types involved, are
listed in Table 211-2 . Some genital HPV types (especially types 16, 18, 31, 33, 35, and 45)
are the causative agents of cervical cancer, whereas other HPV types (6 and 11) cause
anogenital warts (condylomas). An association of HPV-16 with squamous cell carcinoma of
the head and neck also has been demonstrated. [5] [6] HPV-6 and HPV-11 can be transmitted at
the time of birth from an infected mother to the newborn infant, producing juvenile recurrent
respiratory papillomatosis or anogenital warts in infants. Cutaneous HPVs are transmitted by
nonsexual contact and are responsible for skin warts. A large number of HPV types are
recovered from the lesions of a rare dermatologic disorder, epidermodysplasia verruciformis.
Likewise, HPV-5 and -8 have been associated with nonmelanoma skin cancers. [7]

TABLE 211-2   -- Human Papillomavirus (HPV) Infections: Major Clinical Associations

Disease HPV Types Transmission
Cervical cancer 16, 18, 45, 31, 33, Sexual contact
35, and others
Disease HPV Types Transmission
Anogenital warts 6, 11 Sexual contact; vertical
transmission at birth
“Juvenile-onset” recurrent respiratory 6, 11 Vertical transmission at
papillomatosis birth
Cutaneous warts 1, 2, 3, 4, 10, and Nonsexual skin-to-skin
others contact
Epidermodysplasia verruciformis and 5, 8, and others Nonsexual skin-to-skin
nonmelanoma skin cancers contact

Genital Tract Human Papillomavirus Infections

HPV is the most common sexually transmitted pathogen, with over 6 million new infections
occuring annually in the United States. More than 30 HPV types infect the genital tract. Initial
HPV infection occurs shortly after sexual debut. HPV prevalence, as measured by detection of
viral sequences by polymerase chain reaction (PCR)-based assays, is > 40% in young,
sexually active adolescent and college-aged women. HPV prevalence is highest in 15- to 25-
year-olds and declines in older age groups. Infection risk is directly related to sexual history
(e.g., number of lifetime sexual partners and recent change in sexual partners) [8] and the
sexual history of the partner. Most women with HPV infections have normal cervical cytology,
have infections of several months' duration, and clear their infections completely. It is not
known whether infection with an HPV type confers immunity to reinfection with the same type.
In women who are infected with the human immunodeficiency virus (HIV) or who have other
conditions of immunodeficiency, the prevalence of HPV infections and cervical cytologic
abnormalities is markedly increased.

Cervical Cancer

Squamous cell carcinoma of the cervix (cervical cancer) is the second most frequent female
malignancy worldwide and the most common female malignancy in the developing world.
About 500,000 new cases of cervical cancer are diagnosed annually worldwide. It has long
been recognized that cervical cancer has the characteristics of a sexually transmitted disease.
Studies over the past 20 years have clearly established that certain HPV types are the
causative agents of cervical cancer, initiating the multistep process that leads to invasive
cervical cancer.[9]

Invasive cervical cancer originates from precursor squamous intraepithelial lesions in the
cervical epithelial squamous cell–columnar cell transition zone. The time between the initial
infection with intraepithelial lesions and the development of invasive cancer is several years to
decades. HPVs are found in > 90% of invasive cancers and in most precursor lesions.
[10]
 Approximately 70% of cervical cancers contain either HPV-16 or -18. Other types, such as
HPV-45, -31, and -33, contribute a smaller percentage of cervical cancer cases. HPV-18 is
associated preferentially with adenocarcinoma of the cervix. The viral genome is integrated
into cellular DNA in most invasive cancers but is present as free copies in women with normal
cervical histology or low-grade intraepithelial lesions.

Laboratory studies strongly reinforce the epidemiologic evidence in favor of an HPV etiology of
cervical cancer. [7] [9]Phylogenetic trees based on nucleotide sequence data show that cancer-
associated HPVs and low-risk HPVs cluster in different branches. The E6 gene of the cancer-
associated HPV-16 and HPV-18 can transfect and immortalize human keratinocytes, but the
 same gene of the low-risk HPV-6 and HPV-11 cannot. The E6 and E7 genes are always
expressed in invasive cancers. Furthermore, the break in the circular viral genome required for
integration occurs in such a way that the E6 and E7 genetic sequences not only remain intact
but upon transcription are released from the inhibitory activity of the viral E2 protein. The HPV
E6 and E7 proteins contribute to viral transformation through their interactions with cellular
tumor suppressor proteins, which, in the normal cell cycle, inhibit cellular proliferation and
allow the cells time to repair DNA damage. The functional inactivation of the cellular tumor
suppressor protein p53 by E6, and of the tumor suppressor retinoblastoma proteins (pRb) by
E7, results in the accumulation of additional cellular mutations, which then leads to invasive
cancer.

In the United States, cervical cancer rates have decreased significantly due to routine cervical
screening and management of precancerous lesions; however, approximately 13,000 cases of
invasive cervical cancers continue to occur annually due in part to limitations of screening
methodology and failure to undergo testing. Most HPV infections probably resolve
spontaneously. Cervical lesions detected by Papanicolaou smear screening can be treated
very effectively. Therefore, despite the common finding of DNA of cancer-associated HPVs in
the genital tract of young women, infection by itself is not a cause for concern. HPV infections
in older women, however, and persistent HPV infections with progressive cytologic
abnormalities in women of any age are significant risk factors for cervical cancer. Women with
HIV infection or acquired immunodeficiency syndrome (AIDS) are at high risk of persistent
HPV infection with progression to cervical cancer. Indeed, invasive cervical cancer is
considered an AIDS-defining condition. Thus, women with HIV or AIDS should be monitored
regularly and treated aggressively for HPV-related neoplasia.

Anogenital Warts

Anogenital warts (condylomas) are the most common clinical manifestations of genital HPV
infections. It is estimated that each year more than 1 million individuals in the United States
consult private physicians for genital warts and that the incidence of external genital warts
among sexually active persons aged 18 to 49 is 1%[11] (Figure 211-1 ). Approximately 90% of
condylomas are caused by infections with HPV-6 and HPV-11, types that are almost never
associated with invasive cancers.

Figure 211-1  Prevalence of genital warts by age and gender (Females are shown in green bars,
and males in purple bars). Rates are based on health claims data of more than 3 million patients.
Rates are cases per 100,000. (Adapted from Insinga RP. Dasbach EJ. Myers ER. The health and
economic burden of genital warts in a set of private health plans in the United States. CID
2003;36:1397.)

Anogenital warts are found on the external genital area, upper thighs, and inguinal folds as
well as within the vagina, on the uterine cervix, and within the urethra (see Figure 54-1 ). In
men, the penile shaft is frequently involved. Condylomas occur predominantly in sexually
active young men and women. Infants can have anogenital HPV-associated warts acquired
perinatally from an infected mother. Rare cases of congenital infection have been reported.
The presence of anogenital warts in children can result from sexual abuse (see Chapter 58 ,
Infectious Diseases of Child Abuse).

Recurrent Respiratory Papillomatosis

 HPV types 6 and 11 are the causative agents of recurrent respiratory papillomatosis (RRP).
Juvenile-onset RRP (a term used to distinguish this condition from adult-onset RRP) usually is
acquired by transmission of HPV-6 or HPV-11 at the time of birth, during passage through an
infected birth canal. The incubation period for the development of perinatally acquired, clinical
disease can be as short as a few months; there is controversy regarding the longest period
before clinical manifestations. Most cases of perinatally acquired juvenile-onset RRP occur in
the first 5 years of life. Adult-onset RRP appears to have a different epidemiology.

RRP is a rare but serious disease. The annual number of new RRP cases in the United States
is estimated to be between 80 and 1500 (approximately 3.6 to 4.3 cases per 100,000 births).
[12]
 Although most individuals with RRP have isolated involvement of the larynx, papillomas can
affect the mucosal surfaces of the entire airway and upper digestive tract, including the
nasopharynx, oropharynx, trachea, and esophagus. Additionally, there are case reports of
bronchopulmonary involvement with malignant degeneration.

Risk factors for acquisition of juvenile-onset RRP are first-order birth and young maternal
age[13] and the presence of maternal condylomas at delivery.[14] Signs and symptoms of RRP in
the infant include hoarse or weak cry, stridor, and failure to thrive due to feeding difficulties.
The older child can manifest hoarseness, dysphonia, and stridor. Airway obstruction can result
from the papillomas. Diagnosis is made through direct laryngoscopic visualization and
histopathologic analysis. Treatment for RRP often involves extensive surgical excision and
may include chemotherapeutic adjuncts. Many patients experience frequent recurrences
necessitating multiple surgical procedures.

Cutaneous Warts

Skin warts are transmitted from one person to another by direct contact with infected tissue or
by contact with virus-contaminated objects. There is a correlation between the site and
morphology of warts and the infecting HPV type. HPV-1 is strongly associated with plantar
warts, HPV-2 with common warts, and types 3 and 10 with flat warts.

Skin warts are most prevalent in school-aged children and young adults. The prevalence
diminishes with further increase in age, probably because older individuals have some
acquired immunity as well as less exposure. Skin warts almost never undergo malignant
changes in immunocompetent individuals. In patients who are immunosuppressed as a result
of HIV infection or organ transplantation, extensive cutaneous warts, with the potential for
malignant transformation, are common.

Epidermodysplasia Verruciformis

Epidermodysplasia verruciformis is a rare, lifelong disease in which extensive cutaneous warts

due to HPV infections never resolve. In about one-third of cases, the warty lesions progress to
malignancy. Affected patients probably have a genetic immunologic defect, but the nature of
the defect is not known. The disease generally begins in infancy or childhood with multiple,
wartlike lesions on the face, trunk, and extremities that tend to become confluent.

The warts are flat or in the form of reddish brown macular plaques that resemble pityriasis
versicolor, or are excoriated plaques resembling chronic eczema. The flat warts often have the
same HPV types (e.g., HPV-3, HPV-10) found in flat warts of healthy individuals. However,
these patients also harbor about 20 additional HPV types, which are present in the macular
plaques or in flat warts. These types are seldom recovered from warts in healthy individuals
but may be found in patients with significant primary or secondary immunosuppression.
 Malignant transformation occurs in the reddish brown plaques located in areas exposed to
sunlight. A large proportion of the cancers are associated with HPV-5 and HPV-8. Malignant
transformation is probably multifactorial, related to specific virus types, host factors, and
environmental factors. Recent laboratory studies have also implicated HPV-5 and HPV-8 in
other skin cancers.

LABORATORY DIAGNOSIS

Most cutaneous and anogenital warts are diagnosed on the basis of history and clinical
inspection. Physical examination accompanied by cervical Papanicolaou testing is the primary
mode of diagnosis for HPV-associated cervical disease. Cytologic testing of the uterine cervix
should include a brush specimen obtained from the region of the squamocolumnar junction
within the cervical os as well as scrapings from the cervical surface. Detection of HPV-related
precancerous disease is enhanced by the use of colposcopy with application of 3% to 5%
acetic acid, which causes dysplastic lesions to turn white. Histologic examination of a biopsy
specimen is diagnostic. All sexually active women should undergo regular cytologic screening
for cervical dysplasia and cancer. Guidelines from the American Cancer Society [15] and the
United States Preventive Services Task Force[16] can be found at their respective websites.

HPV molecular diagnosis is made through the use of nucleic acid hybridization assays or PCR
methods. In PCR-based assays, consensus primers amplify a portion of the HPV genome,
and the HPV sequences in the PCR products are identified by type-specific probes. PCR
assays are mainly available as research tools, and are not available in routine clinical practice.
In a commercially available signal-amplified hybridization assay (Hybrid Capture, Digene
Laboratories, Gaithersburg, MD), the specimen DNA is tested with two pools of HPV RNA
probes, one pool representing 13 cancer-associated HPVs and the other pool representing 5
low-risk HPVs. This assay is being evaluated widely for its usefulness in clinical management
and in primary cervical cancer screening. This test is indicated for triage of patients with mildly
abnormal Papanicolaou test results (atypical squamous cells) and for primary cancer
screening of women > 30 years of age. Routine screening for HPV infection using this test is
otherwise discouraged. Many men and women will test positive for HPV infection and never
develop a clinical disease. Likewise, routine testing of all patients with any abnormal
Papaniculaou test results is not useful. This is expensive and no prognostic information can be
gained by this approach.

TREATMENT

Currently, therapies for HPV are directed toward destruction or excision of HPV-infected
tissues. HPV treatments are costly at both patient and societal levels and are associated with
significant discomfort and high rates of therapeutic failure. Development of specific HPV
antiviral agents is an area of important basic science and clinical research.

Most patients with cutaneous HPV infection experience immune-mediated regression of

disease over a period of months to a few years. Because the risk of malignant transformation
of cutaneous warts is exceedingly low, the rationale for treatment of cutaneous warts is solely
cosmetic (Noteworthy exceptions are plantar and subungual warts, which may be painful.).
Cutaneous warts are treated with cryotherapy, electrocautery, or excision. A variety of acetic
acid–salicylic acid combinations are available without prescription and are suitable for
treatment of common cutaneous warts. Tretinoin has been used for the treatment of flat warts.
Deeply seated plantar and palmar warts may require a combination of treatment modalities.

The treatment goals for clinically significant anogenital HPV disease are: (1) to remove
exophytic lesions; and (2) to remove or destroy dysplastic anogenital epithelial cells before
 malignant transformation occurs. Anogenital warts are treated in a variety of ways, including
application of caustic agents (e.g., podophyllin), cryotherapy, application of an inhibitor of DNA
synthesis (e.g., fluorouracil), and surgical removal. Recurrences are common after
treatment. Box 211-1 includes current recommendations for treatment of genital warts from the
2006 Centers for Disease Control and Prevention Sexually Transmitted Diseases Treatment
Guidelines.[17]Premalignant cervical disease due to HPV is treated by a variety of methods
aimed at destroying or removing dysplastic tissue.

BOX 211-1 
Recommended Therapy for Genital Warts
PATIENT-APPLIED

Podofilox 0.5% solution or gel

or

Imiquimod 5% cream

PROVIDER-ADMINISTERED

Cryotherapy with liquid nitrogen or cryoprobe

or

Podophyllin resin 10-25% in a compound tincture of benzoin

or

Trichloroacetic acid (TCA) or bichloroacetic acid (BCA) 80-90%

or

Surgical removal

ALTERNATIVE

Intralesional interferon

or

Laser surgery

From Centers for Disease Control and Prevention. Sexually transmitted diseases
treatment guidelines, 2006. MMWR 2006;55(RR-11):62-67.
PREVENTION

Genital HPV infection can be avoided by sexual abstinence, and can be decreased by
monogamous relationships, delayed sexual debut, and minimizing the number of sex partners.
Consistent use of latex condoms can reduce but not eliminate, the risk of infection in women.
 [18]
 Cesarean delivery in women with anogenital warts to prevent transmission to the infant is
not currently recommended.[17]

The licensed quadrivalent HPV vaccine (Gardasi™) is composed of the HPV L1 protein of
types 6, 11, 16, and 18. Expression of L1 protein in yeast using recombinant DNA technology
produces noninfectious virus-like particles. Clinical trials indicate that the vaccine has high
efficacy (> 90%) in preventing persistent HPV infection, cervical cancer precursor lesions,
vaginal and vulvar cancer precursor lesions, and genital warts caused by HPV vaccine types
among females who have not already been infected with the respective HPV type. No
evidence exists of protection against disease caused by HPV types with which females are
infected at the time of vaccination. [19] [20] [21]. HPV vaccination is indicated for the prevention of
genital warts, cervical, vaginal, and vulvar dysplasias and cervical cancer in HPV-naive
persons. [22] [23] The vaccine is given in three injections over a 6-month period. The Centers for
Disease Control and Prevention, and the American Academy of Pediatrics, recommend HPV
vaccination of 11- to 12-year-old girls and “catch-up” vaccination of girls and women aged 13
to 26 ( Box 211-2 ). The series can be started in girls as young as 9 years of age.  [22] [23]

BOX 211-2 
Provisional Recommendations for Quadrivalent HPV Vaccine[a]; Advisory
Committee on Immunization Practices, Centers for Disease Control
   •    Routine vaccination of girls 11–12 years of age
•    Vaccination series can be started in girls as young as 9 years of age at
  
discretion of provider
•    Catch-up vaccination for adolescent and young women 13–26 years of age who
  
have not been vaccinated previously
a  Vaccination is a series of 3 doses of quadrivalent HPV vaccine.

Considering the burden of disease due to HPV, the potential of HPV vaccines to prevent
human disease is tremendous. An adjuvanted HPV vaccine containing L1 protein of HPV
types 16 & 18 is under regulatory review and may be availabale in the United States and other
countries in 2008. Interim results, from prophylactic clinical trials of this bivalent vaccine shows
> 90% efficacy.[24] Clinicans should be alert for upcoming recommendations for use of vaccine,
duration of immunity, and recommendations for vaccination of boys and men.