Download CHAPTER 40 Rickettsia, Ehrlichia, Coxiella

CHAPTER 40
Rickettsia, Ehrlichia, Coxiella, Bartonella
Rickettsia are Gram negative, intracellular bacteria that have been recently classified into
3 phyla: Rickettsia, Ehrlichia and Coxiella. They are the causes of spotted fevers, typhus
and similar illnesses. Ehrlichia are distinct from true rickettsiae and have four genera of
which Ehrlichia and Anaplasma are the most important in humans. Coxiella burnetii is
the cause of Q fever. Bartonella are similar bacteria but are not members of the same
taxonomic family. All are Gram-negative bacilli and all but Bartonella are strict
intracellular pathogens. The reservoir is animals, and, with the exception of R. prowazekii
the cause of epidemic typhus, they are animal pathogens which infect humans only
incidentally. Almost all are transmitted by arthropod vectors. The diseases are typically
fevers, often with vasculitis. The most common infections are the various spotted fevers
found throughout the world.
RICKETTSIA
I. BACTERIOLOGY
1. Small, Gram-negative coccobacilli stained best by immunofluorescence
2. Abundant outer membrane proteins at surface
3. Grow in cytoplasm following induced endocytosis
4. Growth slow compared to most bacteria
5. Obligate intracellular growth related to exogenous cofactors and ATP required
from the host cell
6. Rapidly lose infectivity outside of host cell
II. RICKETTSIAL DISEASE
A. EPIDEMIOLOGY AND PATHOGENESIS
1. Infect vascular endothelium with resultant vasculitis and thrombosis
2. Multiple vascular lesions, including adrenal glands
B. DIAGNOSIS
1. In vitro cultivation is hazardous
2. Indirect fluorescent antibody (IFA) IFA method usually employed for serologic
diagnosis
III. RICKETTSIAL DISEASE: CLINICAL ASPECTS
A. SPOTTED FEVER GROUP
1. Many tick-borne rickettsioses occur throughout the world
a. Rocky Mountain Spotted Fever (RMSF)
i. Epidemiology
1. R. rickettsii is primarily a parasite of ticks
2. Ticks naturally infected
3. Transovarial spread perpetuates tick infection
4. Most cases in children
ii. Manifestations
1. Incubation period 2–14 days after tick bite
2. Acute febrile illness that occurs in association with wooded
areas where infected ticks exist
3. Second or third day of illness as small erythematous macules
that rapidly become petechial
4. Rash spreads from extremities to trunk and often involves palms
and soles
iii. Diagnosis
1. Rising antibody titers or DFA of skin biopsy confirm diagnosis
2. Prompt initiation of therapy based on clinical and epidemiologic
considerations
iv. Treatment
1. Treatment during first week most effective
2. Doxycycline is the treatment of choice
v. Prevention
1. Frequent deticking, avoidance, and protective clothing important
in prevention
b. Rickettsialpox
1. Benign disease transmitted by rodent mites
2. Local eschar followed by fever and vesicular rash
3. Doxycycline therapy
B. TYPHUS GROUP
a. Epidemic Louse-Borne Typhus Fever
1. Severe louse-borne disease due to R. prowazekii
2. Endemic foci in the homeless population.
3. Infection involves feeding and defecation by louse
4. Fever, headache, and rash with high mortality rate
5. Louse control is primary prevention
b. Endemic (Murine) Typhus
1. Caused by Rickettsia typhi
2. Transmitted by rat fleas
3. Resembles typhus but less severe
4. R. typhi shares antigens with R. prowazekii
c. Scrub Typhus
1.
2.
3.
4.
5.
Found in the predominantly in the Far East, China and India
Causative organism is Orientia tsutsugamushi
Transmitted by rodent mite larvae (chiggers)
Local eschar followed by fever, headache, rash, and lymphadenopathy
Serologic diagnosis by indirect fluorescent antibody (IFA) test
COXIELLA BURNETTI
I. BACTERIOLOGY
1. Multiplies in phagolysosome and resists lysosomal enzymes
2. Resistant to drying
II. COXIELLA INFECTION: Q FEVER
1. Transmission usually by inhalation; occasionally by ingestion of unpasteurized
milk
2. Occupational exposure in abattoirs and research facilities
III. Q FEVER: CLINICAL ASPECTS
1. Systemic infection without rash
2. Pneumonia and endocarditis may occur
3. Diagnosis is serologic
EHRLICHIA
1. Several species of white blood cell (WBC)–associated bacteria that cause
human disease
2. Human monocytic ehrlichiosis (HME) due to Ehrlichia chaffeensis
3. Human granulocytic anaplasmosis (HGA) due to Anaplasma phagocytophilum.
4. HME is transmitted by deer ticks and the white-tailed deer is the animal
reservoir
5. HGA is transmitted by Ixodes ticks as is Lyme disease and the animal reservoir
is small mammals
6. Findings are clinically similar to RMSF
7. Intracytoplasmic inclusions (morulae) in monocytes or granulocytes
8. Treatment is doxycycline
BARTONELLA
1. Bartonella can be cultured on artificial media
2. Bartonella quintana causes trench fever
3. B. quintana reservoir is in humans, and its vector is the body louse
4. Bartonella bacilliformis is the cause of acute Oroya fever and verruga peruana
infections are seen only in South America in the distribution of its sandfly vector.
5. Bartonella henselae, has been associated with cat scratch disease, a febrile
lymphadenitis transmitted by cat scratches or
6. Cat scratch disease is common in children
7. B. henselae and B. quintana have been cultured from AIDS patients with
bacillary angiomatosis, a proliferative disease of small blood vessels of the skin
and viscera