Also known as
Query or Queensland fever, abattoir fever, Coxiellosis
Q fever is a bacterial infection affecting many animal species as well as humans, caused by Coxiella burnetii, an intracellular, rickettsial organism that can survive in a dried condition for long periods but require living cells for growth. Rickettsial diseases are often spread by ticks and can vary greatly in severity from self-limiting mild illnesses to severe life-threatening diseases. Q fever is a bit different from most other rickettsial diseases in that no tick vector is needed for transmission to animals or humans.
Infection of sheep and goats is nearly worldwide (except for New Zealand) and thought to be endemic (naturally occurring) on most continents. The rickettsial organism cycles in a wide variety of wildlife species and their external parasites.
This disease occurs in humans and can be quite serious, but is less pathogenic for domestic livestock—though there have been instances of severe infections causing abortion in sheep and goats.
In livestock, the infection is usually subclinical but may cause abortion outbreaks in goats and less commonly in sheep. Susceptible pregnant females develop inflammation of the placenta and tissue death, which results in abortion, whereas non-pregnant females do not show clinical signs.
Some sheep and goats abort without apparent clinical signs; others show depression and lack of appetite 1 to 2 days before aborting. After the initial abortions or infections, the animals have enough immunity to prevent subsequent abortion but can remain sub-clinically infected (no signs) for life.
After infection is established, the female can carry the organism indefinitely, sporadically shedding these pathogens in her milk and at each birth.
The disease is common in most areas where cattle, sheep, and goats are kept. In the U.S., testing has shown that many ruminant animals have antibodies to C. burnetii. Bulk tank milk sampling of cow dairies has found the organism at 77% to 90% of farms. In a comprehensive study conducted in Canada, 48.6% of sheep operations and 63.2% of goat operations had at least one positive animal. Prevalence in humans who handle animals—veterinarians, sheep and goat farmers--is also high.
In cattle, experimental infections have sometimes resulted in a few abortions but lack of appetite was the only consistent clinical sign.
- Lack of appetite
- abortion (rarely)
In a susceptible animal, this bacterium has an affinity for placental tissue, and is shed in birthing fluids and membranes, as well as in milk, urine and feces. Disease is transmitted to animals and humans through inhalation of the organism.
Contact with droplets or fomites (inanimate objects, such as gloves, coveralls, rags, etc.) may also result in transmission. Ingestion might be a possible route of spread, through consumption of contaminated, unpasteurized dairy products.
Although direct exposure to animals that are giving birth, or their birthing products, poses the highest risk for infection, the organism’s ability to persist in the environment may result in continued risk for infection weeks to months after the birthing event. Grazing contaminated pastures, and tick bites are other possible sources of infection.
Q fever can be transmitted to humans by inhaling dried particles from the environment (wind dispersion of dust contaminated with bacteria—from sites where sheep, goats or cattle are kept) and through contact with infected animals, particularly placentas and birthing fluids, but also other animal products like wool.
Farmers and veterinarians are at risk while assisting birthing. Slaughterhouse workers are at risk from contact with infected carcasses, hair, and wool. Transmission may also occur by consumption of unpasteurized milk. Handling infected tissue poses a threat to laboratory personnel. Q fever has also been seen in personnel and human patients in medical institutions where sub-clinically infected sheep were used for research.
The disease in humans produces influenza-like symptoms. Most 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.
Ticks may transmit the disease among domestic ruminants but are not thought to play an important role in transmission of disease to people.
Q fever in humans is a notifiable disease in the U.S. because of its status as a possible bioterrorism agent; reporting requirements for this disease in animals vary by state.
Vaccination is effective in preventing shedding of the rickettsial pathogen in cow’s milk, and in ewes helps reduce the number of rickettsia shed in the placenta at lambing. Vaccination has prevented infection when administered to uninfected calves and has improved fertility and reduced shedding in previously infected animals.
Although human and animal vaccines have been developed, none are commercially available in the United States. Also, lack of knowledge about shedding patterns among ruminants makes definitive determination of Q fever shedding status difficult.
Prevention efforts focus on minimizing contact with animals that may be shedding C. burnetii in body secretions and excretions.
It may not be practical or possible to eliminate the risk of Q fever in a typical farm setting, but the risk for spread can be decreased by proper sanitation (good hygiene, especially when working with birthing animals); segregated kidding/lambing areas; removal of risk material from birthing areas (placentas, birthing fluids, aborted fetuses, contaminated bedding, manure); good manure management; control of ticks on livestock; and restriction of moving heavily pregnant animals off the farm (or any females that are close to giving birth, or having given birth within the past two weeks).
Often no treatment is given since antibiotics don’t have a lot of effect on the rickettsial pathogen, but some veterinarians recommend use of tetracyclines. Treatment of pregnant animals with tetracycline may reduce the risk of further abortions, but is unlikely to eliminate the problem.