Rickettsial Infections

Question 1

Rickettsiae

Answer 1

• small, G- coccobacilli, obligate intracellular pathogens
• replicate by binary fission
• target endothelial cell of capillaries and other small blood vessels to produce necrotizing vasculitis

Question 2

Rocky Mountain Spotted Fever

Answer 2

• Rickettsia rickettsii
• transmitted to humans by tick bites
• systemic vasculitis with HA, fever, rash
• spreads to vascular smooth muscle and endothelium of larger vessels
• can lead to DIC, loss of vascular fluid, shock

Question 3

Epidemic (Louse-Borne) Typhus

Answer 3

• Rickettsia prowazekii
• replicates within louse and transmitted to human via louse feces
• can establish latent infection and prodice Brill-Zinsser disease many years after primary infection
• vasculitis

Question 4

Endemic (murine) typhus

Answer 4

• Rickettsia typhi
• milder then epidemic typhus
• flea rat flea life cycle can be spread to humans

Question 5

Scrub Typhus

Answer 5

• Rickettsia tsutsugamushi
• acute febrile illness with rodents as natural reservoir
• vesicle forms at inoculation site and ulcerates with eschar. This heals then HA, fever, pneumonia, rash, lymphadenopathy, hepatosplenomegaly

Question 6

Q fever

Answer 6

• Coxiella burnetii, G- coccobacillus
• enters cells passively with phagocytosis by macrophages
• no vasculitis so no rash
• cattle, sheep, and goats are normal reservoirs (often seen in herders, ranchers, vets, slaughterhouse or dairy workers)
• inhaled and spread through monocytes and macrophages
• predominantly involves lungs and liver