Coxiella burnetii: Habitat, mode of transmission, pathogenesis, clinical diseases, lab diagnosis and treatment
- Coxiella burnetii is the smaller than other Rickettsia and passes through porcelain filter.
- Formally Coxiella burnetii is classified as Rickettsia burneti.
- It causes Q- fever
- C. burnetii is pleomorphic, small rod ( 0.4-1.4 µm long and 0.2 -0.4µm wide) or sphere (0.3-0.4µm) in diameter.
- The organism is generally considered to be gram negative although it appears to be gram positive when alcoholic iodine is used as mordant.
- C. burnetii is the only Rickettsia that shows phase variation.
- It contains two distinct plasmids.
- Natural reservoir hosts are cows, goats, sheeps, rodents, wild mammalss and several species of birds.
- C. burnetii also inhabitat several species of ticks
Mode of transmission:
- Human get infected with Coxiella burnetii by inhalation of contaminated aerosols.
- By the bite of infected ticks
- By direct contact; by handling infected animals and birds
- By consuming contaminated raw milk.
- Coxiella burnetii causes Q-fever which is also known as Red River Fever and Nine mile fever.
- Human get infected to C. burnetii by inhalation of contaminated aerosol. The organism parasitizes and remains viable inside alveolar macrophage. It also infects histiocytes of spleen and kupffer cell of liver and causes the enlargement of the organs.
- Most of time Infection may be asymptomatic or sub clinical.
- Incubation period: about 2 weeks.
- Fever, and influenza like syndrome which lasts for 4-7 days.
- In some patients bronchopneumonia, thrombophlebitis, pulmonary embolism and endocarditis may occurs.
- Q fever: it is characterized by influenza like syndrome, high fever, headache, body pain and occasionally slight rashes on body.
- Serious complication of Q-fever: pneumonitis, chronic infective endocarditis and liver disease
Specimen: blood, sputum and urine
1. Detection of Coxiella antigen :
- Direct immune-fluorescent test
- DNA- probe
- weil-Felix test: negative weil-felix OX19, OX2 and OXK
- complement fixation test (CFT)
- Culture on yolk sac of chick embryo
- Tetracycline is effective for C. burnetii