Rickettsia and friends

The triad of Rickettsial disease: fever, headache, and rash. "Undifferentiated febrile illness" or "flu-like illness." Rickettsiae grow intracellularly, like inside endothelial cells (this includes all of genus Rickettsia, Coxiella burnetii, and Ehrlichia, but NOT Bartonella, which can be cultured on agar). Need to T-mediated cellular immunity to clear these infections. Go from cell to cell (using actin tail); part of its adaptation to evade host response by always being intracellular.

Epidemic typhus -- Rickettsia prowazekii -- vector: louse -- fever, headache, delayed rash: small pink macules on trunk, sparing palms, soles, and face; increased risk of vessel thrombosis, gangrene of feet or hands. Can be fatal. Flying squirrels a reservoir in southern U.S. Has a latent form, which can cause Brill-Zinsser disease, characterized by fever and headache (no rash) and early rise in IgG titer specific for Rickettsia prowakezii.

Endemic typhus -- Rickettsia typhi -- vector: rat flea, associated with rodents (duh) -- fever, headache, maculopapular rash. Milder than epidemic typhus. Don't want to just kill rats, but both rats and fleas.

Rocky Mountain Spotted fever -- Rickettsia rickettsiae -- vector: wood tick (Dermacentor andersoni), dog tick (Dermacentor variabilis) -- fever, headache, rash on palms, soles, wrists, ankles and later on trunk; conjunctivitis; vessel thrombosis: edema. Early removal of tick will prevent infection. Reservoir in southeastern U.S.

** Vessel thrombosis characteristic of both Rocky Mountain Spotted fever and epidemic typhus (most severe, can cause gangrene).

Scrub typhus (walking through scrub in Thailand) -- Rickettsia tsutsugamushi -- vector: chiggers (larvae of mites) -- fever, headache, scab at bite site, maculopapular rash.

** Treat all rickettsial diseases with doxycycline and chloramphenicol (only latter for pregnant women, slight risk of aplastic anemia, versus bone development insult with tetracylines).

Human ehrlichiosis -- tick-borne, "Rocky Mountain SPOTLESS Fever."

Human Monocytic Ehrlichiosis -- Ehrlichia chaffeensis -- vector: tick-borne (Lone Star tick), carried on white-tailed deer -- think hunters in Missouri. Morula in monocytes with replicating bacteria -- can see on blood smear. Perivascular lymphohistiocytic infiltrates WITHOUT vasculitis (distinguishes from Rickettsia), noncaseating granulomas.

Human Granulocytic Anaplasmosis -- Anaplasma phagocytophilum -- vector: tick-borne (Ixodes tick), carried on white-footed mice (small mammals). Morula in PMNs. Clinically indistinguishable from human monocytic ehrlichiosis -- need PCR.

** Ixodes tick also transmits Borrelia burgdorferi (Lyme disease), Babesia (parasite) and Francisella tularensis, and human granulocytic anaplasmosis.

Q fever -- Coxiella burnetii -- endospore form found in non-pasteurized milk products, cow hides, dried placental remnants (no arthropod vector!) -- can be inhaled into lungs, caused a pneumonia similar to Mycoplasma. Can be asymptomatic, cause granulomatous hepatitis "donut hole granuloma" -- lipid droplet in middle, or "culture negative" subacute endocarditis. Only rickettsial disease with pneumonia AND no rash. Obligate intracellular and steals ATP like Rickettsia, Chlamydia.

Cat scratch disease -- Bartonella hensalae -- Local lymphadenopathy, low-grade fever malaise, self-limited disease; associated with bacillary angiomatosis (proliferation of small blood vessels in skin and organs of AIDS patients -- can also be caused by B. quintana), also may be complicated by bacteremia and "culture-negative" subacute endocarditis.

Trench fever -- Bartonella quintana -- vector: lice-born like Rickettsia prowakezii, causes high fevers, headache, back and leg pains; characterized by multiple relapses (quintana -- every 5 days); usually resolves, not fatal.

Oroya fever -- B. bacilliformis -- severe hemolytic anemia, vascular skin warts called verruga peruana (related to bacillary angiomatosis -- something about Bartonella). Transmitted by sand fly, which also transmits Leishmaniasis. Organisms adherent to blood cells (very small gram negative rods).

Leptospira interrogans -- long, thin, aerobic spirochete -- found in urine of animals, can penetrate abraded skin and mucous membranes, especially if you swim in contaminated water. Biphasic illness: (1) leptospiremic phase, invades blood and CSF, causing fever, headache, malaise, and severe muscle aches, red conjunctiva, and photophobia; resembles Rickettsial symptoms; followed by 1 week afebrile period; (2) immune phase correlates with IgM antibodies, can now culture from urine, meningismus, elevated CSF white blood count. Can also cause Weil's disease: hepatitis with jaundice (but normal transaminases!), renal failure, mental status changes, hemorrhage in many organs.