Q fever is a bacterial infection that rarely causes noticeable illness in animals; it can be passed from animals to people. 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 domestic animals, including cats, can also play a role in the spread of infection to humans.

There are 2 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). 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.

The Q fever bacteria usually do not cause signs of illness in infected animals. They have occasionally been implicated in abortion. Infected animals that contract the illness may show vague signs, such as fever, lethargy, and lack of appetite lasting several days.

Infected animals can be treated with antibiotics, but complete elimination of the organism has not been reported. Vaccines for people and animals have been developed but are not commercially available in the United States. Q fever in humans must be reported to public health officials; cases of Q fever in animals need not be reported unless humans are involved.

Last full review/revision July 2011 by Otto M. Radostits, CM, DVM, MSc, DACVIM (Deceased); Eugene D. Janzen, DVM, MVS; Jodie Low Choy, BVMS; Dennis W. Macy, MS, DACVIM; Dudley L. McCaw, DVM, DACVIM (Small Animal, Oncology); Barton W. Rohrbach, VMD, MPH, DACVPM; J. Glenn Songer, PhD; Richard A. Squires, BVSc (Hons), PhD, DVR, DACVIM, DECVIM-CA, MRCVS; Bert E. Stromberg, PhD; Joseph Taboada, DVM, DACVIM; Charles O. Thoen, DVM, PhD; John F. Timoney, MVB, PhD, Dsc, MRCVS; Ian Tizard, BVMS, PhD, DACVM; Max J. Appel, DMV, PhD; David A. Ashford, DVM, MPH, DS; Stephen C. Barr, BVSc, MVS, PhD, DACVIM; J. P. Dubey, MVSc, PhD; Paul Ettestad, DVM, MS; Craig E. Greene, DVM, MS; Delores E. Hill, PhD; Johnny D. Hoskins, DVM, PhD