Q fever in Small Ruminants
(Query fever; Coxiella burnetii ; Coxiellosis)
The Washington Animal Disease Diagnostic Laboratory at Washington State University (WSU-WADDL) has received an increased number of inquiries about Q fever over the past few years. The questions fall into three distinct areas and include: testing of dairy goats for the infection in order to be in compliance with the Washington State requirements placed on raw milk dairies (RCW 16.36.040); testing of goats and sheep prior to sale, and/or breeding (biosecurity profiling); and 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. Where appropriate, there are web links to specific information.
If additional questions arise, Contact the Consulting Microbiologist at WADDL
Dr. James Evermann
Dr. Tim Baszler
Dr. Kerry Sondgeroth
What is Q-Fever?
Query or Queensland fever (Q fever) is a bacterial infection affecting a variety of animal species as well as human beings. Q fever is caused by Coxiella burnetii , an obligate, intracellular, rickettsial organism that can survive in a dried condition for extended periods.
Is Q-Fever widespread?
Coxiella burnetii infection of sheep and goats is nearly 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. The true incidence of Q Fever infection is unknown in the Pacific Northwest region of the USA. WSUWADDL is currently conducting a research study to determine the geographic distribution and herd prevalence of C. burnetii infection in goats in Washington state.
What are the clinical signs of Q Fever?
In livestock the disease is usually subclinical. However, occasional abortion outbreaks caused by C. burnetii have been reported in goats and, less commonly, in sheep. Susceptible pregnant females develop necrotizing placentitis (inflammation and necrosis of the placenta), which results in abortion, whereas non-pregnant females do not develop clinical signs. Some ewes and does abort without apparent clinical signs, whereas others show anorexia and depression 1 to 2 days before aborting. After the initial abortions or infections, animals become immune to abortion but can remain subclinically infected. After the infection is established, the female can carry the organism indefinitely, sporadically shedding it in milk and at parturition.
How is the infection maintained and spread?
In the susceptible animal host, the bacterium has an affinity for placenta, and high concentrations (approximately 100 million infectious particles) have been reported per gram of placental tissue. The agent is shed in birthing fluids and membranes, as well as milk, urine and feces. C. burnetii is typically acquired by susceptible animals and humans through inhalation of the organism in fine-particle aerosols. Contact with droplets or fomites (inanimate objects, such as gloves, coveralls, rags, etc) may also result in transmission. Ingestion has been proposed as a route of spread, particularly through the consumption of contaminated, unpasteurized dairy products. 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.
What is the potential for Q Fever transmission to humans?
Q fever can be transmitted to human beings primarily by inhalation of dessicated aerosol particles from the environment, and through contact with infected animals, particularly placentas and birthing fluids but also other animal products like wool. Disease in human beings is characterized by influenza-like symptoms. The majority of human cases have a history of contact with infected sheep or goats. The organism is killed by pasteurization but can be transmitted in non-pasteurized milk. All persons should wear masks and gloves when removing manure from the barn, assisting with lambing and kidding, and handling aborted fetuses.
How can Q fever infection – disease be prevented?
Although human and animal vaccines for C. burnetii have been developed, none are commercially available for use in the United States. Also, lack of knowledge on shedding patterns among ruminants makes definitive determination of Q fever shedding status difficult. Therefore, prevention efforts must focus on minimizing contact with animals that may be sheddingC. burnetii in body secretions and excretions. Although it may not be practical or possible to eliminate the risk of Q fever in a typical farm setting, the risk for spread can be decreased by 1) proper sanitation – good hygiene, especially when working with parturient animals; 2) segregated kidding/lambing areas; 3) removal of risk material from birthing areas (birthing products/fluids, contaminated bedding, manure); 4) good manure management; 5) control of ticks on livestock; and 6) restriction of moving peri-parturient animals (close to birthing or giving birth within the past two weeks) off the farm. For more information on "Best Practices to Control Q Fever" visit the Washington State Department of Agriculture website at: http://agr.wa.gov/FoodAnimal/AnimalHealth/Diseases/QFeverManagementPractices.pdf
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 (Figure 1).
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.
Figure 1. Coxiella burnetii organisms (red) within infected placenta cells (blue).
Is there a diagnostic test for Q Fever infection in an animal with subclinical infection (no clinical abortion)?
There are a number of serology tests for Q Fever in animals that identify a host immune response (antibodies) to C. burnetiiinfection indicative of a previous or current infection. However, serology tests do not indicate whether or not an infected ewe or doe may be shedding organisms. Also, serological assays are most suitable for screening herds or flocks, but the interpretation of individual animal level is difficult.
WSU-WADDL uses a commercially available ELISA for Q Fever serology ("CHEKIT-Q-FEVER"; IDEXX Laboratories). Q fever ELISA tests are preferred for practical reasons (ease of use and commercially availability of test kits) and for their higher sensitivity compared to other tests, such as complement fixation test (CFT). The supplier gives ELISA test kit cut offs. For the IDEXX CHEK-Q-FEVER test values are normalized to a kit positive control (to decrease test variability) and values less than 30% are considered negative, values greater than or equal to 40% are considered positive, and values between 30% and 40% are considered suspect. If a sample is suspect it is recommended to collect a new sample from the animal and retest. If the sample remains suspect after 2 separate test, then retest by another method (such as CFT) and investigation of the epidemiological situation in the herd should be considered. Also, remember that serological assays are designed for herd or flock use and some scientific publications advocate interpretation of serological tests with a minimum of 6 animals tested.
On selected cases (usually retests) WADDL may also send samples to a USDA national reference laboratory, which uses the complement fixation test (CFT)) assay. CF antibody titers between 1:10 and 1:40 are characteristic of past infection while titers of 1:80 or more (from a group of at least 5 animals) indicate active infection.
What is the sample of choice and the cost of serologic testing for C. burnetii at WADDL?
The lab recommends a red top tube accompanied by the appropriate WADDL accession form.
If multiple animals are being tested use the multiple animal identification sheet.
Current testing costs are listed on the WADDL website fee schedule.
Who should we contact for further information on C. burnetii infections and Q fever?
There are several websites that have good descriptions of Q fever. These are:
Bjorka, Anderson A. Notes from the field: Q fever outbreak associated with goat farms – Washington and Montana, 2011. CDC MMWR 60(40): 1393-94, 2011.
Bottcher J. et al. Insights into the dynamics of endemic Coxiella burnetii infection in cattle by application of phase –specific ELISA’s in an infected dairy herd. Vet Microbiol 151: 291-300, 2011.
Guatteo R, et al. Prevalence of Coxiella burnetii infection in domestic ruminants: a critical review. Vet Microbiol 149: 1-16, 2011.
Horigan MW, Bell MM, Pollard, TR, Sayers AR, Pritchard GC. Q fever diagnosis in domestic ruminants: comparison between complement fixation and commercial enzyme-linked immunosorbent assays. J Vet Diag Invest 23(5): 924-931, 2011
Q fever. Chapter 2.1.12. In OlE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 7th ed. P 1-13, 2010.
Rousset E, et al. Comparative diagnostic potential of three serological tests for abortive Q fever in goat herds. Vet Microbiol 124: 286-297, 2007.