Laboratory Diagnosis, Treatment and Prevention of Coxiella burnetii


Coxiella burnetii is a bacterium that causes Q fever, a zoonotic disease that can affect humans and animals. Q fever can manifest as a mild or severe flu-like illness, pneumonia, hepatitis, or chronic infections such as endocarditis and osteomyelitis.

C. burnetii is an obligate intracellular pathogen, meaning that it can only survive and multiply within host cells. It has a unique biphasic developmental cycle that involves two forms: a small cell variant (SCV) and a large cell variant (LCV). The SCV is the infectious form that is resistant to environmental stresses and can persist in soil, dust, water, and animal products for long periods. The LCV is the replicative form that grows within a specialized vacuole inside the host cell.

C. burnetii is also characterized by phase variation, which is a change in the expression of surface antigens. There are two phases: phase I and phase II. Phase I bacteria have a full set of antigens and are highly virulent. Phase II bacteria have lost some antigens and are less virulent. Phase variation occurs when bacteria are exposed to host immune responses or subcultured in vitro.

C. burnetii can infect a wide range of animals, such as cattle, sheep, goats, dogs, cats, rodents, birds, and ticks. The main reservoirs of infection are domestic ruminants, which can shed large amounts of bacteria in their milk, urine, feces, and placenta during parturition.

Humans can acquire Q fever by inhaling aerosols or dust contaminated with animal secretions or tissues, by consuming raw or unpasteurized dairy products, by direct contact with infected animals or their products, or by tick bites. The incubation period ranges from 2 to 40 days, depending on the dose and route of exposure.

Q fever is a global public health problem that affects both rural and urban areas. It is endemic in many countries and regions, such as Australia, Europe, Africa, Asia, and North America. It can cause outbreaks in occupational settings (e.g., farms, slaughterhouses, veterinary clinics) or in communities (e.g., due to windborne dispersion of contaminated dust). It can also pose a bioterrorism threat due to its high infectivity and stability in the environment.