Animals + Humans = One health

What is Q Fever?

Q fever is a highly contagious zoonotic disease caused by the intracellular pathogen Coxiella burnetii. Many domesticated and wild animals including mammals, birds, reptiles and arthropods can carry C. burnetii. In most cases, the infection is asymptomatic, but abortions or stillbirths can occur in ruminants. Both symptomatic and asymptomatic animals shed C. burnetii in large quantities at parturition. Shedding can also occur in faeces, milk and urine. These organisms persist in the environment for long periods and can be spread long distances by the wind. Human outbreaks can result from the inhalation of aerosolised organisms. More often, sporadic cases occur in people who are occupationally exposed.

Where is the disease found?

Q fever has been found worldwide, except in New Zealand.

How is the disease transmitted and spread?

C. burnetii can be transmitted by aerosols or direct contact; it is also spread by ingestion. Infections in animals can persist for several years and possibly lifelong. Organisms localise in the mammary glands, supramammary lymph nodes, uterus, placenta and foetus in animals; bacteria can be shed in milk, the placenta and reproductive discharges during subsequent pregnancies and lactations. C. burnetii can also be found in the faeces and urine, and in the semen of bulls. Sexual transmission has been demonstrated in mice. Ticks may be important in transmission among wildlife, and can also spread infections to domesticated ruminants.

Most human infections are associated with cattle, sheep and goats, and often occur when the animal gives birth.

Humans are usually infected via aerosols, but transmission may also occur by the ingestion of unpasteurised milk or other contaminated material.

What is the public health risk associated with this disease?

Q Fever is a zoonosis. In humans, the incubation period for acute Q fever varies from 2 to 48 days; the typical incubation period is approximately 2 to 3 weeks. Chronic Q fever can occur from months to many years after infection. Symptomatic infections can be acute or chronic. Many cases of acute Q fever are asymptomatic or very mild, and remain unnoticed. The symptoms of acute disease are flu-like and can include high fever, chills, a headache, fatigue, malaise, myalgia, sore throat and chest pain. The illness is often self-limiting, and generally lasts from a week to more than three weeks.

Chronic Q fever is an uncommon condition that develops months or years after the acute syndrome. Endocarditis is the most commonly reported syndrome. It usually occurs in people who have pre-existing damage to the heart valves or are immunosuppressed.

Approximately 98% of cases in pregnant women seem to be asymptomatic; however, C. burnetii has been linked to premature delivery, abortion, placentitis or lower birth weight in some women. Pregnancy complications have been reported with both acute and chronic Q fever. The consequences of congenital Q fever are unknown.

What are the clinical signs of the disease?

Many species are susceptible to infection, but most species seem to be infected asymptomatically. Abortion, stillbirth, retained placenta, endometritis, infertility and small or weak offspring can be seen in sheep, goats and cattle. Most abortions occur near term. Several abortions may be followed by uncomplicated recovery, particularly in small ruminants; in other cases, the disease may recur yearly. With the exception of reproductive disease, animals are usually asymptomatic. Goats sometimes have a poor appetite and are depressed for 1 to 2 days before an abortion. Placental retention for 2 to 5 days and agalactia have also been reported. Clinical signs including fever, anorexia, mild coughing, rhinitis and increased respiratory rates occur in experimentally infected sheep but have not been reported in natural infections.

How is the disease diagnosed?

C. burnetii can be detected in vaginal discharges, the placenta, placental fluids and aborted foetuses (liver, lung or stomach contents), as well as milk, urine and faeces. Organisms are not shed continuously in milk and colostrum. In the placenta, organisms can be identified in exudates or areas of inflammation with a modified Ziehl–Neelsen, Gimenez, Stamp, Giemsa or modified Koster stain;

The presence of organisms, together with serological tests and clinical findings may be adequate for a diagnosis at the flock or herd level. Bacterial identity can be confirmed by immunohistochemistry or capture ELISA. A number of serologic tests are available; the most commonly used assays include indirect immunofluorescence, ELISA and complement fixation. Serology may be more helpful in screening herds than in individual animals.

In humans, Q fever is usually diagnosed by serology or PCR. Serologic tests can be done as early as the second week of illness; they may include immunofluorescence, ELISA, microagglutination or complement fixation.

What is being done to prevent or control this disease?

Little is known about the efficacy of antibiotic treatment in ruminants or other domestic animals. Prophylactic treatment is sometimes recommended to reduce the risk of abortion. Antibiotics may suppress rather than eliminate infections.

In a C. burnetii-free flock, introduction of new stock should be minimized, and contact with wildlife should be prevented as much as possible. Good tick control should also be practiced. Prevention may be difficult, as this organism can also be introduced on fomites or in aerosols over long distances. In an infected flock, isolating infected pregnant animals and burning or burying the reproductive membranes and placenta can decrease transmission.

Antibiotics may be given prophylactically before animals give birth.

Vaccines may prevent infections in calves, decrease shedding of organisms and improve fertility in infected animals. They do not eliminate shedding of the organism.

Most human cases are associated with exposure to ruminants, particularly when the animal has given birth. Whenever possible, the placenta from sheep, goats and cattle should be removed and destroyed immediately. Because ingestion is a potential route of exposure, unpasteurised milk and milk products should be avoided. Effective vaccines may be available for people who are occupationally exposed.

People at high risk for chronic Q fever, such as those who are immunosuppressed, should consider staying away from susceptible ruminants, particularly parturient ruminants. It may be advisable to avoid all animals that have recently given birth, as cases have also resulted from exposure to cats and other species.