Q fever (coxiellosis) is an infection caused by Coxiella burnetii bacteria that rarely causes noticeable illness in animals. It can be passed from animals to people, however. Transmission to people usually occurs by direct or indirect contact with the bacteria that are shed in large numbers in the placenta and birth fluids of ruminants such as cattle, sheep, and goats. Other wild and domestic animals, including cats, can also play a role in the spread of infection to humans.
There are two major patterns of transmission. In one, the organism circulates between wild animals and their skin parasites, mainly ticks. The other transmission pattern occurs in domestic animals (mainly ruminants, where the presence of this bacteria is common). People can become infected by direct contact with the bacteria in birth fluids or materials, such as soil or bedding, that were contaminated during the delivery. The organism is also found in milk, urine, and feces of infected animals. Transmission may occur by aerosolization of the bacteria attached to dust particles that are inhaled into the lungs or by ingestion of contaminated milk. Fortunately, high-temperature pasteurization kills the bacteria in infected milk.
The Q fever bacteria usually do not cause signs of illness in infected animals. They have occasionally been implicated as the cause for a loss of pregnancy. Infected cats that contract the illness may show vague signs, such as fever, lethargy, and lack of appetite lasting several days.
Infected animals may or may not be treated with antibiotics, because antibiotics may not completely eliminate the bacteria. Vaccines for people and animals have been developed but are not commercially available in the United States. Q fever in humans is typically treated with an antibiotic and must be reported to public health officials. Reporting requirements for infected animals vary by state.
Also see professional content regarding coxiellosis.