The Washington Animal Disease Diagnostic Laboratory at Washington State University (WSU-WADDL) has received an increased number of inquiries about Q fever in recent years. The questions fall into three distinct areas and include:
- testing of dairy goats for the infection to be in compliance with the Washington state requirements placed on raw milk dairies (RCW 16.36.040 and WAC 16-89-170)
- testing of goats and sheep prior to sale, and/or breeding (biosecurity profiling)
- disease investigation to determine the cause(s) of pregnancy loss or low reproductive performance.
This information sheet is intended to answer some of the most common questions about Q fever.
What is Q fever?
Query or Queensland fever (Q fever) is a bacterium causing infection in a variety of domestic animal species, primarily goats, sheep, and cattle. Q fever also affects people and is an important zoonosis. Q fever is caused by Coxiella burnetii, an obligate, intracellular organism that can survive in a dried condition for extended periods.
How widespread is Q fever?
Coxiella burnetii is worldwide in geographical distribution and is thought to be endemic in most continents. C. burnetii cycles in a wide variety of wildlife species and their ectoparasites, which acts as reservoirs of infection in addition to being long-lived in the environment. WADDL investigated the serologic prevalence of Q fever infection in 2013 in Washington state and detected antibody in roughly 9% of goat herds tested.
What are the clinical signs of Q fever?
In livestock, the infection is usually subclinical. However, disease occurs most frequently in the form of abortion outbreaks in goats and sheep. Susceptible pregnant females develop necrotizing placentitis (inflammation and necrosis of the placenta), which results in late-term abortion. Some ewes and does abort without apparent clinical signs, whereas others show anorexia and depression 1 to 2 days before aborting.
How is Q fever maintained and transmitted in livestock?
C. burnetii has an affinity for the placenta, and high concentrations (approximately 100 million infectious particles) have been reported per gram of placental tissue. It can also persist in the mammary gland, supramammary lymph nodes, and the uterus. After the infection is established, the female can harbor the organism indefinitely, sporadically shedding at parturition in birthing fluids and membranes, as well as in milk, urine, and feces.
C. burnetii is typically acquired by susceptible animals through direct contact, either by inhalation or ingestion of the organism. Transmission can also be via aerosols, droplets, or fomites (inanimate objects, such as gloves, coveralls, rags, etc.). Although direct exposure to parturient animals or their birthing products poses the highest risk for infection, the organism’s ability to persist in the environment may result in a continued risk for infection weeks to months after the birthing event. Grazing contaminated pastures and tick bites are other possible sources of infection.
Can Q fever be transmitted to humans?
Q fever can be transmitted to human beings by inhalation of desiccated aerosol particles from the environment and through contact with infected animals, particularly placentas and birthing fluids. The organism can also be transmitted in raw milk, highlighting the importance of pasteurization. Most human cases have a history of contact with infected cattle, sheep, or goats.
How can Q fever infection and disease be prevented?
Although human and animal vaccines for C. burnetii have been developed, they are not commercially available for use in the U.S. Also, variable shedding patterns among ruminants make definitive determination of Q fever shedding status difficult. Therefore, prevention efforts must focus on minimizing contact with animals that may be shedding C. burnetii in body secretions and excretions. Although it is not possible to eliminate the risk of Q fever in a typical farm setting, the risk for spread can be decreased by:
- Proper sanitation – good hygiene, especially when working with parturient animals
- Segregated kidding/lambing areas
- Removal of risk material from birthing areas (birthing products/fluids, contaminated bedding, manure)
- Good manure management
- Control of ticks on livestock
- Restriction of moving peri-parturient animals (close to birthing or giving birth within the past two weeks) off the farm
For more information, see “Best Practices to Control Q Fever” on the Washington State Department of Agriculture website.
How is Q fever abortion diagnosed in the laboratory?
Diagnosis of Q fever abortion requires laboratory testing of aborted fetuses and placenta from aborting does or ewes. Diagnosis is based on identification of lesions in the placenta (gross and microscopic pathology) together with identification of the organism by non-culture methods. Culturing of C. burnetii in the laboratory is not feasible because of the particularly contagious potential of the organism in laboratory cultures to laboratory technicians. Therefore, diagnosis of Q fever abortion at WSU-WADDL is based upon special non-culture methods such as immunohistochemistry to visually identify C. burnetii under the microscope within the formalin-fixed infected placenta.
Instructions on the optimal tissues to submit to WADDL for diagnosis of Q fever abortion or other causes of abortion are available on our Abortion Diagnosis page.
Is there a diagnostic test for Q fever infection in an animal with subclinical infection (no clinical abortion)?
Unfortunately, reliable identification of non-aborting, individual infected animals is problematic. Currently, available serology tests for Q fever identify a host immune response (antibodies) to C. burnetii infection to indicate a previous or current infection. However, studies have demonstrated serologically negative animals may shed the organism and serologically positive animals may have undetectable shedding or intermittent shedding. Therefore, it is not recommended to use the serologic assay to identify infected animals as it could both under- and over-estimate risk. Ultimately, Q fever serological assays are designed for herd or flock use and some scientific publications advocate interpretation of serological tests with a minimum of six animals tested. Again, serological assays are suitable for screening herds or flocks and not for individual animal status determination. Lastly, use of the serologic test in milking animals will not determine if raw milk is free of the Q fever bacteria and safe to drink.
WSU-WADDL uses a commercially available ELISA for Q fever serology (“CHEKIT-Q-FEVER”; IDEXX Laboratories). In selected cases, WADDL may also send samples to a USDA national reference laboratory, which uses the complement fixation test (CFT) assay. Sera is tested at 1:10 and 1:20 and are reported as detected or not detected. The CFT is also a herd-level surveillance test.
PCR may be attempted from a variety of samples, but false negatives may be possible due to low or no active shedding. Currently, this is a send-out test.
What type of sample is needed for C. burnetii ELISA testing?
For most individual tests, 3 ml of blood is sufficient. If sending serum only, we recommend 1 ml for testing. If you are requesting multiple tests in addition to Q fever, we recommend 5-7 ml of blood per animal. If less than 3 ml of blood or 1 ml of serum is available, contact the laboratory to determine if there is enough sample for testing.
How do I submit a sample?
Please refer to Sample submissions.
Who should I contact for further information on C. burnetii infections and Q fever?
You can also contact the consulting microbiologist at WADDL by calling 509-335-9696.
Page revised November 2022