Rickettsiae (Murray 3rd Ed pp 352)

Rickettsiae is a separate family, but has similar characteristics to Chlamydia in that: aerobic, gram –ve bacilli and are obligate intracellular pathogens. The natural reservoirs are arthropods. The peptidoglycan layer is minimal and non-functional. They multiple in the cytoplasm, or nucleus of host cell. Rickettsiae has the four genera: Rickettsia, Orientia, Coxiella, & Ehrlichia.

Diseases (Murray 3^rd Ed pp 355)

There are five main groups of diseases and each of the groups of diseases are caused by different genera. The typhus group is caused by Rickettsia spp. The Rocky mountain spotted fever is caused Rickettsia spp. Scrub typhus is caused by Orienta tsutsugamushi. Q fever is caused by Coxiella burnetti. Ehrliciosis is caused by Ehrlichia canis. Look in notes for a list of diseases and the organisms that cause it.

Diagnosis (Murray 3^rd Ed pp 355)

Ricketsiae species stain poorly with gram stain but they can be stained using Giemsa stains. Isolation of bacteria can be prepared but is considered to be a hazardous procedure. You can also do serology tests, specific CFT or IHA – but usually rely on Weil-Felix Test using differential agglutination of Proteus antigens. You need a rising titre – up to four fold increase (anything <>

Treatment (Murray 3^rd Ed pp 356)

Rickettsiae are susceptible to tetracyclines and chloramphenicol. Ciprofloxacin has been reported to be effective against Queensland spotted fever. Rifampicin is effective against Q Fever.

Immunisation (Refer to notes)

You can get a COX vaccine (dead). You can also have a E-strain vaccine (live attenuated). Q fever vaccine is available.

Category: Microbiology Notes