Rickettsia
Special Features
>Grow at low nutrients level; some with stalks (page 305, MAI 7th edition)
>Not resistant enough to survive airborne transmission
>Characteristics of being obligated Intracellular parasites-that is, they reproduce only within a
mammal cell
>One distinguishing feature of most rickettsias is that they are transmitted to humans by bites of
insects and ticks, not as same to coxiella. (page 307, MAI 7th edition)
Rickettsia enter their host cell by inducing phagocytosis. They quickly enter the cytoplasm of the
cell and begin reproducing by binary Fission. (page 307, MAI 7th edition)
Additional Info: Ehrlichia Ehrlichia are gram negative, rickettsia like bacteria that live
obligately within blood cells. Erlichia species are transmitted by ticks to humans and cause
ehrlichiosis (page 307, MAI 7th edition)
The rickettsia are responsible for a number of disease knows at the Spotted Fever Group.
Disease Causative agent Reservoir Method of
Transmission
Rocky Mountain Rickettsia rickettsii Rodents (rats and Tick Bites
Spotted Fever mice)
Endemic Typhus Rickettsia Typhi Rodents (rats and Flea Bites
mice)
Epidemic Typhus Rickettsia prowazekii Lice Bites
(page 307, MAI 7th edition)
Additional info: Except for the species that causes Lyme disease (discussed below), all
members of the spirochete genus Borrelia cause relapsing fever. In the United States, the disease
is trans-mitted by soft ticks that feed on rodents. The incidence of relapsing fever increases
during the summer months, when the activity of rodents and arthropods increases.
The disease is characterized by fever, sometimes in excess of 40.5°C (105°F), jaundice, and
rose-colored skin d spots. After 3-5 days, the fever subsides. Three or four re-hlapses may occur,
each shorter and less severe than the initial fever. Each recurrence is caused by a different anti-y
genic type of the spirochete, which evades existing im-emunity.
Lyme Disease (Lyme Borreliosis)
The seasonal occurrence (summer months), lack of contagiousness among family – members,
and descriptions of an unusual skin rash that ap-peared several weeks before the first symptoms
suggested a tickborne disease. The fact that penicillin alleviated the progression of symptoms
suggested a bacterial pathogen. E In 1983, a spirochete that was later named Borrelia burgdorferi
was identified as the cause. Lyme disease may now be the most common tickborne disease in the
United States.
Rickettsia have:
Intracellular Parasite - they absolutely require living host cell in order to multiply
Plasma Membrane
Binary Fission
Pass through bacterioliogical filters
Passes both DNA and RNA
Ribosomes
Sensitive to antibiotics
Sensitive to interferon
Rickettsia very small bacteria
PAGE 372 ( MICROBIOLOGY AN INTRODUCTION 7th edition)(tortora-funke-case)
The various typhus diseases are caused by rickettsias, bac-teria that are obligate intracellular
parasites of eukaryotes. Rickettsias, which are spread by arthropod vectors, infect mostly the
endothelial cells of the vascular system and multiply within them. The resulting inflammation
causes local blockage and rupture of the small blood vessels. (page 307, MAI 7th edition) .
Rickettsia ricketssi
Rocky Mountain spotted fever (tickborne Typhus)
>Transmitted by ticks
Probably the best-known Rickettsial Disease in United States. Despite its name (it was first
recognized in the rocky mountain area). This rickettsia is a parasite of ticks and is usually passes
from one generation of ticks to another trough their eggs, a mechanism called transovarian
passage.
Antibiotics – tetracycline and chloramphenicol are very effective if administered early enough.
The rash caused by Rocky
Mountain spotted fever
This rash is often mistaken for
measles. People with dark skin
have a higher mortality rate
because the rash is often not
recognized enough for effective
treatment.
The life cycle of the tick vector of Rocky Mountain spotted fever
>Mammals are not essential to survival of pathogen, Rickettsia ricketssi, in
the thick population ; the bacteria may be passed by transovarian passage,
so new ticks are infected upon hatching. A blood meal is required for ticks to
advance to the next stage in life cycle. (page 637, MAI 7 th edition)
Disease Pathogen Comments
Rocky Mountain spotted Rickettsia ricketssii A tickborne rickettsial
fever Disease, characterized
by rash, fever,
headache, high
mortality rate.
Endemic murine Typhus Rickettsia typhii A fleaborne rickettsial
disease; rodents are
the reservoir.
Resembles epidemic
typhus but mortality
rate is low.
Epidemic typhus Rickettsia prowazekii A louse Borne
rickettsial disease,
characterized by high
fever, high mortality
rate
(page 650, MAI 7th edition)
Table. Representative Anthropod Vectors and the Diseases They
Transmit
Disease Causative Agent Anthropod Vector
Rocky Mountain spotted Rickettsia rickettsii Dermacentor Anderson
fever and other species (tick)
Endemic Murine Typhus Rickettsia typhi Xenopsylla cheopis (rat
flea)
Epidemic typhus Rickettsia prowazekii Pediculus humanus
(louse)
(page 419, MAI 7th edition
Rickettsia Typhi
Endemic Murine Typhus
>Transmitted by the rat flea
The term murine (derived from Latin for mouse) refers to the facts that
rodents, such as rats and squirrels, are the common host.
The pathogen responsible for the disease is Rickettsia Typhi, a common
inhabitant of rats.
Antibiotics-tetracycline and chloramphenicol are effective treatment,
and rat control is the best preventive measure
(page 637, MAI 7th edition)
Rickettsia Prowazekii
Epidemic Typhus (louseborne typhus)
The pathogen grows in the gastrointestinal tract of the louse and is
excreted by it.
It is not transmitted directly by the bite of an infected louse; rather, it
is transmitted when the feces of the louse are rubbed into the wound
when the bitten host scratches the bite
The disease can flourish only in crowded and unsanitary surroundings,
when lice can transfer readily from an infected host to a new host.
Epidemic Typhus disease produces a high and prolonged for at least 2
weeks
Stupor and a rash of small red spots caused by subcutaneous
hemorrhaging are characteristics as the rickettssi as invade blood
vessels linings.
Mortality rates are very high when untreated.
Antibiotics – Tetracycline an Chloramphenicol are usually effective
against epidemic typhus
(page 635, MAI 7th edition )
