Rickettsia Flashcards
Rickettsia
Morphology
Habitat
Transmission
A small 0.2-0.4 uM, gram negative, non-motile.
Has a permeable cell wall that is weak and pleomorphic, and no capsule
Obligate intracellular ATP parasite
Rodents are reservoir and the vector of transmission is fleas, ticks, lice.
Prefer to attack endothelial cells of the blood vessels.
Rickettsia
Virulence factors and Antigens
Rickettsia shares some antigens with Proteus vulgaris: OX-2, OX-19, and OX-K.
What are the two species of Ricketssia that cause spotted fevers?
What diseases do they cause?
How are they transmitted?
Rickettsia rickettsii - Rocky mountain spotted fever
Transmitted by ticks over 6-8 hours of attachment.
Fever, conjuntivitis, severe headache,
Red spotted rash (petechia) appearing on the wrists, palms, ankles, and soles feet, then moving to the trunk
Treat with doxycycline and chlormaphenicol (macrolide)
Rickettsia akari - Rickettsial Pox
Transmitted by mites that can be found on house mice.
Rickettsialpox - mild, self limiting fever and headache, and a blister that forms at the bite site.
Treat with doxycycline (tetracycline)
Rickettsia
Culture
Can only be cultured in living cells, is kept in innoculated embrionated eggs, lab animals, or tissue culture
Direct smear can be stained with Giemsa stain showing intracellular bacteria.
What are the major pathogenic species of Rickettsia? (4)
What are the names of the diseases the cause?
- R. rickettsii -* Rocky mountain spotted fever
- R. akari* - Ricketsialpox
- R. prowazekii* - Epidemic typhus
- R. typhi* - Endemic typhus
R. prowazekii
Transmission
Clinical disease
Causes Epidemic Typhus
Spread human to human by lice
Sudden onset fever, myalgia, spotted rash on the trunk, and organ failure
A patient may recover, but then still have a latent asymptomatic infection, which then re-emerges as Brill-Zinsser Disease, The same disease in a milder form, but with no skin rash
Rickettsia typhi
Clinical disease
Transmission
Causes Murine Typhus or Endemic Typhus
Transmitted by a flea, and not human-to-human
Causes same disease (Typhus) as R. prowazekii but in a milder form.
Headache, Fever, Trunk rash, Delerium, Coma
Rickettsia tsutsugamushi
Clinical Disease
Causes: Scrub typhus, found in Asia and the pacific.
Spread by mite larvae.
High fever, headache, and scab at the bite site.
The bacterium itself has been re-classified as Orientia tsutsugamushi, and is actually of a serparate genus than Rickettsia, but is still in the family Rickesttsiae.
`Rickettsia diseases
Diagnosis
Weil-Felix reaction: Uses the cross reactin Proteus vulgaris antigens: OX-2, OX-19, and OK-K
Latex bead agglutination test, coated with these antigen.
Different specific Rickettsia species prodeuce a different specific antibody responses, usually to just one or tow of these specific antigens.
