Rickettsiae Flashcards
Rickettsia rickettsii
Disease
Rocky Mountain spotted fever.
Rickettsia rickettsii & prowazekii
Characteristics
- Obligate intracellular parasites.
- Not seen well on Gram-stained smear.
- Antigens cross-react with OX strains of Proteus vulgaris (Weil-Felix reaction).
Rickettsia rickettsii
Habitat & Transmission
- Dermacentor (dog) andersoni ticks both vector & main reservoir-> tick bite.
- Dogs and rodents reservoirs as well.
Rickettsia rickettsii
Clinical findings
- fever, severe headache, myalgias, &
prostration - rash appears 2 to 6 days later on hands & feet & trunk, beginning with macules progress to petechiae.
- delirium & coma
- Disseminated intravascular coagulation, edema, & circulatory collapse -> severe cases.
Rickettsia rickettsii & prowazekii
Pathogenesis
- Organism invades endothelial lining of capillaries-> vasculitis.
- No toxins or virulence factors identified.
Rickettsia rickettsii, prowazekii & Coxiella burnetii
Laboratory Diagnosis
- detecting antibody in serologic-> ELISA test.
- Weil-Felix test no longer used. -> cross-reaction of antigen with O antigen polysaccharide found in P. vulgaris OX-2, OX-19, & OX-K. Measures antirickettsial antibodies
in patient’s serum by ability to agglutinate Proteus. - specific rickettsial organism identified by agglutination observed with one or another of these 3 different strains of P. vulgaris.
Rickettsia rickettsii
Treatment & Prevention
- Doxycycline
- Protective clothing, prompt removal of ticks, Tetracycline effective in exposed persons & No vaccine.
Rickettsia prowazekii
Disease
Typhus
Rickettsia prowazekii
Habitat & Transmission
Humans-> bite of the human body louse (Pediculus).
Rickettsia prowazekii
Clinical Findings
- influenzalike symptoms 1 to 3 weeks after louse bite occurs.
- Between 5-9 days maculopapular
rash begins on trunk-> becomes petechial & spreads over body sparing face, palms, & soles. - Severe meningoencephalitis-> delirium & coma.
- Death-> peripheral vascular collapse or bacterial pneumonia.
- Bacteremic patient bitten, organism ingested by louse & multiplies in gut epithelium-> excreted in louse feces when biting next person & autoinoculated while scratching bite. - Infected louse dies after a few weeks-> no louse-to-louse transmission
- Brill-Zinsser disease-> symptoms similar to
epidemic typhus but less severe, of shorter
duration, & rarely fatal. - persistently infected patients source of
organism should a louse bite occur.
Rickettsia prowazekii
Treatment & Prevention
Doxycycline & killed vaccine used in military.
Coxiella burnetii
Disease
Q fever.
Coxiella burnetii
Characteristics
Obligate intracellular parasites.
Not seen on Gram-stained smear
- Phase I: virulent, isolated from patient, synthesize certain surface antigens
- Phase II: nonvirulent, produced
by repeated passage in culture, lost ability to synthesize certain surface antigens. - chronic Q fever higher antibody to phase 1 antigens than acute.
Coxiella burnetii
Habitat & Transmission
- domestic livestock-> aerosols of urine, feces, amniotic fluid, or placental tissue.
- occupations-> shepherds, abattoir employees, & farm workers; Ingestion of
cow’s milk.
Clinical Findings
- influenzalike symptoms-> pneumonia ensues
in half patients. - Pneumonia & hepatitis ->t Q fever.
- Rare rash
- chronic Q fever -> life-threatening endocarditis
