Q Fever (Coxiellosis)

by Amy Young
July 06, 2020

What is Q Fever?

Takeaways

Q Fever is a highly contagious infection caused by the bacterium Coxiella burnetii.
Q Fever is a zoonosis, meaning that it can be passed from animals to humans.
The main reservoirs for human outbreaks are domestic small ruminants (sheep and goats)
Infected ruminants may show no clinical signs of disease, but may abort their fetuses and shed large amounts of pathogen at that time.
In humans, many cases are asymptomatic, whereas others can lead to flu-like symptoms, pneumonia or serious heart complications.

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Q Fever, also known as “query fever” or coxiellosis, is an infection caused by the bacterium Coxiella burnetii, which is ubiquitous and persistent in the environment. It is a zoonosis, meaning that it can be passed from animals to humans. Found worldwide, the features of the disease vary by geographic area. It is widespread in some regions, and some places have experienced large outbreaks.

The main reservoirs for human outbreaks are domestic ruminants, including sheep, goats, and, to a much lesser extent, cattle. Infected animals are often not visibly ill, but may abort their fetuses late in gestation or have stillborn or weak offspring. Infected sheep often have normal births but can still serve as a source of infection for humans. A series of abortions, or an “abortion storm”, can occur when a previously uninfected herd or flock becomes infected.

In humans, symptoms resemble the flu and often resolve without treatment. An infected person also may show no symptoms. In rare cases, the disease becomes chronic and can damage vital organs such as the brain, heart, and lungs. The most common serious complication is bacterial endocarditis, an inflammation of the lining of the heart, which can be fatal if left untreated. People at highest risk of infection are pregnant women, the elderly, children, and immunocompromised persons.

Q Fever is spread primarily through aerosols of body fluids, especially amniotic fluid from infected aborting ruminants and is also shed in milk and feces. The bacteria may be spread through tick bites, which is the predominant route of transmission between wild animals, such as rabbits and rodents.

Q Fever is a monitored condition in livestock and people in the United States, and cases must be reported within 30 days (https://www.cdfa.ca.gov/ahfss/animal_health/pdfs/ca_reportable_disease_list_poster.pdf).

What are the clinical signs of Q Fever?

In ruminants, the main clinical signs of Q Fever are reproductive disorders. These include abortion, infertility, stillbirth, mastitis, and metritis. Animals that are not pregnant typically do not show any clinical signs.

How is Q Fever diagnosed?

Diagnosing Q Fever can be challenging because animals can show no signs of the disease but still shed the bacteria. Serology can be used to screen herds/flocks for C. burnetti. Individual animals can be tested by PCR or immunohistochemistry of placental lesions. PCR can also be used to test birth products, milk, and feces. Culture is rarely used for diagnosis due to the highly contagious nature of the bacteria and the associated risk to laboratory personnel.

How is Q Fever treated?

There are currently no labeled therapies for livestock infected with Q Fever in the US. It is recommended to work with your veterinarian if you suspect abortions due to Q fever. In humans, antibiotics may be used to treat severe or chronic cases.

What is the prognosis for Q Fever?

The prognosis for Q Fever in most animals and humans is good; many recover without treatment or show no signs or symptoms of disease. Reproductive losses in pregnant ruminants, however, can recur, mostly frequently in goats, resulting in financial losses and potential culling of animals from the herd/flock.

How can Q Fever be prevented?

Q Fever can be prevented by avoiding high densities of animals during kidding, lambing, and calving seasons. Carcasses, aborted fetuses, and placentas should be promptly removed to minimize spread from potentially infected materials. Pregnant, infected females should be isolated from the herd. Workers should wear personal protective equipment (PPE), including gloves and masks, when handling potentially infectious animals or infected tissues. Pregnant women should avoid handling aborted materials from small ruminants or assisting with deliveries of premature or aborted lambs or goat kids due the risks to their own pregnancy associated with exposure to Coxiella and other zoonotic pathogens. Barns, especially birthing pens, should be thoroughly cleaned and disinfected with “a 10% solution of bleach, a 5% solution of hydrogen peroxide, or a 1% solution of Lysol®” (The Center for Food Security & Public Health - Q Fever Factsheet). Exposure to dust should be minimized, and spreading of manure avoided under windy conditions. Proper composting of manure will greatly reduce the load in manure. Milk should not be consumed raw; pasteurization will eliminate C. burnetii from milk.

There are currently no human or livestock vaccines for Q Fever commercially available in the U.S. When cases or outbreaks occur, the movement and sale of animals should be halted to limit the spread of infection. Since the organism is ubiquitous and long lived in the environment, culling of infected herds is typically not recommended.

Although ticks are not a common mode for the transmission of C. burnetti in livestock, they are important for transmission in wildlife. The bacterium has been isolated from both hard and soft-shelled tick species, as well as bed bugs, flies, and mites. It is important to minimize contact of domestic ruminants with wildlife and practice good tick and vector control on farms.

An ELISA antibody test is available for Q fever, which can be performed on serum, plasma, or milk samples. Data indicates that this test has an estimated 98.6% overall sensitivity and 97.1% specificity. Testing of potential herd additions prior to introduction can help keep a herd negative. However, it is important to note that this test does not determine if animals are actively shedding the bacteria, just that they have developed antibodies to C. burnetti. At the farm level, PCR testing of bulk tank milk can detect bacterial shedding.