Infection with Coxiella burnetii (Q fever)

Most infected cattle, sheep and goats show no signs. When disease appears it is reproductive: abortions late in pregnancy, sometimes as sporadic cases and sometimes as abortion storms in a flock or herd, together with stillbirths and dead or weak newborns. Affected females usually recover without complications. In cattle, metritis and infertility have been linked to infection, but these signs are too non-specific to support a clinical diagnosis. In camels, seropositivity has been associated with a history of abortion. People develop flu-like fever, chills, fatigue and muscle pain, pneumonia or hepatitis, and occasionally chronic endocarditis.

Q fever (coxiellosis) is caused by Coxiella burnetii, a Gram-negative obligate intracellular bacterium of the order Legionellales that is adapted to live inside the phagolysosome of phagocytic cells. Its developmental cycle includes small, dense, spore-like forms that survive outside the host and accumulate in the environment. Organisms isolated from animals are in the virulent phase I, carrying full-length lipopolysaccharide; laboratory passage produces the attenuated phase II. In domestic ruminants infection persists for years and probably for life. In pregnant females the bacterium is associated with late abortion, premature or weak offspring, and it may contribute to metritis and infertility in cattle; very large numbers of organisms are released with birth products.

The infection occurs worldwide except New Zealand. Cattle, sheep and goats are the main reservoirs, but cats, dogs, rabbits, birds, wildlife and ticks can be involved. In North Africa, the Middle East and neighbouring Sahel states, surveys report markedly higher seroprevalence in dromedary camels than in other ruminants: camel-herd figures reach more than 60% in Egypt and Sudan, around 50 to 60% in Saudi Arabia, and single surveys report 70 to 80% in Algeria and Chad, though individual studies within the same countries fall much lower. The camel tick Hyalomma dromedarii has been found infected. Animals shed the organism in placenta, birth fluids, vaginal mucus, milk, urine and faeces, often while appearing healthy, with shedding peaking at parturition. People are infected mainly by inhaling contaminated dust or aerosols; veterinarians, farm, dairy and abattoir workers are at risk, as are raw milk drinkers. It is a WOAH-listed zoonosis.

Q fever must be distinguished from the other infectious causes of late abortion, stillbirth and weak offspring in ruminants, which it cannot be separated from on clinical grounds. Acid-fast-type stains of placenta or vaginal smears (Stamp, modified Ziehl-Neelsen, Gimenez) give only presumptive evidence because they lack specificity. Confirmation relies on PCR, now the test of choice, on placenta, vaginal discharge or fetal organs, supported by herd-level ELISA serology.

Placenta and pregnant uterus, fetus, mammary gland (milk), reproductive tract (metritis, infertility in cattle); in humans lungs, liver and heart valves

Inactivated phase I vaccine, repeated annually in at-risk areas; segregated kidding areas, removal of placentas and birth material, manure and shearing management, tick and reservoir control, movement controls; avoid raw milk.

Aborting ruminants usually recover without complications, but infection persists for years, probably for life, with repeated shedding. In people the acute form resolves with antibiotics; untreated chronic infection can be severe to fatal.