Q fever is a disease caused by the bacterium Coxiella(C.) burnetii. These bacteria are very resistant, their spores can survive in the environment for up to two years. It is a zoonosis (= an infectious disease transmissible from animal to human).

Q fever is distributed worldwide with the exception of New Zealand and Antarctica

Sheep, goats, cattle, wild mammals, birds, ticks

In natural herds, Coxiella burnetii circulates between wild mammals, birds, and ticks. Domestic and farm animals become infected through excreta containing the pathogen, such as aborted material or milk, but tick feces can also play a role. Coxiellen can be transmitted from animals to humans by direct contact or through the respiratory tract by inhalation of dust or droplets containing Coxiella.

2 to 3 weeks, depending on the infectious dose also shorter

Infected animals often show no symptoms after coxial infection. In sheep, goats, and cattle, infection can cause abortions or the newborns are weak and barely viable. In humans, the disease can vary greatly in severity and duration.

Drug treatment of Q fever is done with certain antibiotics.

There is the possibility of vaccination for active immunization in cattle, goats and sheep to reduce the risk of symptomatic disease and pathogen shedding.

In Austria, the occurrence of Q fever in cattle, sheep, goats, buffalo and bison must be reported in accordance with the Animal Health Act (AHL).

Q fever was first described in 1937 in Queensland, Australia. The causative agent of Q fever is an obligate intracellular, pleomorphic gram-negative bacterium called Coxiella burnetii. The bacterium is highly resistant to chemical (e.g. formaldehyde) and physical influences (UV radiation, increased temperature, dehydration). The ability to form permanent forms in the form of spores and the high resistance to desiccation enable it to survive for years outside organisms in dust, hay, wool, etc..

The survival time of C. burnetii (Runge & Ganter 2008) is

• in dust and wool at 20 °C storage 7-9 months, at 4 °C 1-2 years
• 42 days in butter and soft cheese at 20 °C
• in meat at 4 °C one month
• in raw milk at 4-6 °C 90-273 days
• in dried milk at room temperature 40 months, at -20 °C 2 years, at +70 °C 15 seconds, in 70 per cent ethanol 30 minutes

Coxiellae occur in 3 different forms: small cells (small cell variant, SCV), which are highly infectious; large cells (large cell variant, LCV), which develop in cell cultures and are less infectious; spore-like particles (SLP), which are infectious and very resistant to environmental influences (Gürtler et al. 2013).

C. burnetii has a broad host spectrum - the infection has predominantly been diagnosed in sheep, goats, cattle and wild ruminants. Progression: mostly inapparent colonisation of genitalia and udder, occurrence of frequent abortions in herds, postpartum behaviour, udder inflammation. Cats, dogs, rabbits and birds can also be reservoir hosts.

Transmission

In natural herds, C. burnetii circulates between wild mammals, birds and ticks. Ticks are a reservoir and an important vector, but not the main source of infection for farm animals. The main source is infected afterbirths following abortions in sheep and goats. Ticks remain infected throughout their lives and can also pass the pathogen on to their offspring.

There are two independent infection cycles: the first is a natural infection involving ticks and wild animals, during which domestic animals can become infected. This infection cycle is linked to the presence of certain tick species. A cycle develops between the larvae, nymphs and rodents which, when adult ticks appear, infects larger host animals (e.g. red deer, foxes, sheep, goats and cattle). Spring and the summer-autumn period are known as seasonal risk periods due to the host transitions of adult ticks. The second cycle is an arthropod-independent domestic animal cycle. The chain of infection among warm-blooded animals is maintained in this cycle without an intermediate host. Transmission occurs through abort material, excrement and faeces; transmission via the respiratory tract through dust and droplet aerosols is also possible. In pets, coxiella can also be spread passively via tick faeces containing the pathogen (in the fleece, recognisable by dark discolouration).

Coxiellae reach the uterus and mammary gland via the bloodstream, where they can remain for a long time without the infected animal showing any symptoms. The infection can be reactivated during pregnancy, and the uterus and mammary glands in particular can harbour the pathogen for years. Both organs produce and excrete considerable quantities of pathogens. Coxiellae are also excreted intermittently with the milk. Birth products (e.g. afterbirth, amniotic fluid, lochia) and the newborns contaminated with them are highly infectious. Dried fruit skins that remain on the pasture can lead to months of contamination of the area.

Transmission to humans

Q fever can be transmitted from animals to humans through direct contact or via the respiratory tract by inhalation of Coxiella-containing dust or droplets (= aerogenic transmission). Another route of infection for humans is transmission through tick faeces, e.g. in sheep fleece. Occupational groups that come into contact with infected animals, such as farmers, veterinary staff, slaughterhouse staff, shepherds, sheep shearers, but also visitors to farms are at risk. Visitors to farms should therefore be prohibited from entering premises with infected animals in order to minimise the risk of inhaling infected dust. Dust containing C. burnetii can be carried by the wind and endanger people several kilometres away. In this case, 1 to 10 coxiellae already form a human infectious dose (HID) and are sufficient for an infection.

Coxiella burnetii has not only been found in herds affected by Q fever, but has also been detected in raw milk and raw milk products (e.g. soft cheese, butter) as well as in the muscle meat and organs of infected animals. The risk of humans contracting a food-borne infection has been documented in individual cases; however, food-borne transmission plays a minor role in the incidence of infection. For precautionary reasons, raw milk from infected herds should always be subjected to heat treatment; raw milk and raw milk products from C. burnetii-positive herds must not be sold to consumers. Pasteurisation reliably destroys the pathogens.

Symptoms

The infected animals are usually only subclinically ill. In sheep, goats and cattle, an infection causes abortions or the newborns are often weak and barely viable; in cattle in particular, coxiella is also the cause of fertility problems.

Control

As it is a bacterial pathogen, treatment with antibiotics is generally possible. However, due to the long survival time of coxiellae in the environment, there is a very high probability that new infections of previously healthy animals will occur again and again.

There is an approved vaccine for active immunisation for cattle, sheep and goats. Vaccination offers the possibility of reducing the infection cycle and minimising the use of antibiotics in the long term.

The control of Q fever in livestock also focuses on preventive measures. A prerequisite for measures to prevent and control Q fever is the timely identification of infections. Some important recommendations for the identification of Q fever outbreaks are the search for possible sources of infection, the occurrence of lambing/calving, examinations for tick infestation (tick faeces in the fleece - dark discolouration in the deeper fleece, skin is inflamed or encrusted at the tick bite sites, charcoal stains on the skin, etc.). encrusted, coal dust-like particles are present in the densely furred region between the head, neck and withers) and serological and molecular biological examinations to clarify the infection process; immunohistochemical procedures and microbiological examinations.

Measures to reduce the spread of the pathogen:

• Checking new purchases for the presence of coxiella infection
• Moving the pregnant animals into the barn for lambing or calving: lambing or calving should take place in barns that are as enclosed as possible and at a sufficient distance from residential buildings
• Removal of afterbirths: Contamination of the environment with birth products from infected animals should be minimised in order to prevent airborne transmission of the pathogens. Afterbirths and stillbirths should be collected in closed, liquid-impermeable containers and disposed of properly. The containers must then be professionally disinfected
• Professional disinfection of the stables and equipment affected by the infection. Regular cleaning of the stables should not be carried out with a high-pressure jet or steam jet in the first phase, as this promotes the spread of pathogens through aerosols
• Dogs and cats should be kept away from stables with infected animals
• Do not spread contaminated bedding or manure from stables affected by the infection on agricultural land. Spores can be spread over long distances
• Controlled acaricide treatment of the herd. Tick control in the affected herds every year at the beginning of the tick season can significantly reduce the spread of the pathogen if ticks play a role in transmission
• Persons who are in stables with infected animals for shearing or other activities should observe the usual hygiene regulations (e.g. washing hands several times, protective gloves, own work clothing) and wear protective masks. Shearing in closed rooms. Disposal of contaminated wool

The diagnosis of Coxiella burnetii is possible both directly (pathogen detection) and indirectly (antibody detection).

Sample material for pathogen detection by PCR:

• Milk
• Placenta
• Abortion material
• Vaginal swab

Sample material for antibody detection by ELISA:

• Blood (plasma/serum)
• Milk (single and tank milk)