Brucellosis is caused by various bacteria of the genus Brucella. Brucella occurs worldwide and is sensitive to heat and all common disinfectants. In humans, the infectious disease caused by B. melitensis is known as Malta fever. B. abortus causes Bang's disease (Morbus Bang).

Brucella melitensis and Brucella abortus are common in domestic and farm animals worldwide with regional differences. In 2018, an outbreak caused by B . melitensis was reported in a cattle herd in Upper Austria. B. suis (Biovar 2) is rarely detected in domestic pigs and humans in Europe. Disease outbreaks were last detected in 2017 and 2024 in breeding sow farms in Upper Austria. B. canis was first detected in Austria in 2010 as an abortus pathogen in dogs on a poodle breeding farm in Upper Austria.

Cattle, sheep, goats, wild boar, hare, dog. The pathogen reservoir of B. abortus is cattle, and longstanding control programs have eradicated the pathogen in our latitudes. In the USA, infected wild bison herds are occasionally found, and in developing countries this pathogen is more common in humans and animals. The species B. melitensis occurs primarily in sheep and goats in Mediterranean countries. Wild boar and brown hares act as reservoirs for Brucella suis Biovar 2.

Transmission to humans usually occurs through food containing Brucella (raw milk and products made from it) or through direct contact with infected animals and their excretions. Direct transmission from person to person is extremely rare (in individual cases through breastfeeding or blood transfusions). The risk of infection in Austria is very low.

Usually between 5 and 60 days

Up to 90 % of all infections are asymptomatic; they can only be assessed by the detection of specific antibodies in patients and are the expression of a successful immune response. In the initial phase of acute brucellosis, patients experience non-specific, flu-like symptoms such as fatigue, mild fever, headache and aching limbs, which do not stop after 7 to 10 days, as is usually the case with influenza. After a short, symptom-free interval, flu-like symptoms may re-occur, often with evening temperature rises up to 40 °C, combined with massive sweating (the temperature returns to normal in the morning); this is often associated with a drop in blood pressure and swelling of the liver, spleen and lymph nodes. These phases last up to 5 weeks. The disease can heal spontaneously without antibiotic treatment, but without therapy it can also lead to a chronic progression with recurrent episodes of fever. Chronic progressions of the disease can lead to complications in the nervous system and internal organs.

Treatment with antibiotics

Brucellosis in cattle, pigs, sheep and goats is a notifiable animal disease. Control is focused on the isolation and culling of infected animals.

Brucellosis is a very rare infectious disease in humans. In 2023, eight laboratory-confirmed cases were reported to the Epidemiological Reporting System (EMS) (EMS, as at 17.01.2024). Interviews with patients revealed that all cases were imported, four cases from Bosnia-Herzegovina, two from Turkey and one each from Ethiopia and Thailand.

Due to the officially recognized brucellosis-free status of the Austrian cattle population as well as the sheep and goat population, foodstuffs are currently not tested for brucella in Austria. In 2021, no foodborne disease outbreak (LMbKA) caused by brucella was notified to the EMS in Austria (as of March 1, 2022). In each of 2019 and 2020, one outbreak caused by B. melitensis was reported, probably due to consumption of raw milk and sheep meat abroad.

Bovine brucellosis: In Austria, the cattle population was already recognised as officially free of brucellosis (OBF) in 1999. The bovine brucellosis testing ordinance came into force in 2008. Until 2012, comprehensive monitoring of all milk-supplying cattle farms was carried out via tank milk testing; blood tests were carried out in accordance with a risk-based sampling plan. Since 2013, the bulk milk samples from milk-supplying farms have also been selected according to a risk-based sampling plan. In 2023, 1,218 bulk milk samples from 1,214 farms were analysed. Serologically non-negative tank milk samples are verified using blood samples. 10,391 blood samples from non-milk-supplying cattle farms were tested according to a risk-based sampling plan from 1,228 farms. Brucellosis was not detected in any cattle herd. Austria's cattle population has the status "disease-free" with regard to infections with Brucella abortus, B. melitensis and B. suis.

Sheep and goat brucellosis: The Austrian sheep and goat flocks were recognised as officially free of B. melitensis (OBmF) in 2001. To maintain the recognised status, annual proof must be provided that less than 0.2% of all sheep and goat flocks are infected with ovine and caprine brucellosis. In 2023, 21,034 blood samples from 1,680 farms were analysed throughout Germany according to a risk-based sampling plan. There was no evidence of Brucella infections in sheep and goats. The Austrian sheep and goat population has the status "disease-free" with regard to infections with Brucella abortus, B. melitensis and B. suis.

Direct transmission from person to person is extremely rare (in individual cases through breastfeeding or blood transfusions) and occurs only in exceptional cases. It has essentially only been observed in infants through the milk of infected mothers. Brucella can be transmitted directly through contact with diseased animals or indirectly through contaminated food. Bovine brucellosis is enzootic in the herd. It poses a risk to human health, particularly to those in direct contact (farmers, veterinarians, slaughterhouse staff). Raw milk (unpasteurised milk or products made from it, such as butter made from raw milk and raw milk cheese) and raw meat from infected animals pose the greatest risk of transmission. In addition to the gastrointestinal tract, the pathogen can be absorbed into the body by several other routes, including the conjunctiva, the respiratory tract and injured skin. After entering the body, brucella are taken up by cells of the monocyte-macrophage system and transported to the nearest lymph nodes. From the infested lymph nodes, the germs are disseminated first lymphogenically and then hematogenically, reaching most organs, especially the liver, spleen, and bone marrow. In the affected organs, inflammatory granulomas consisting of macrophages and lymphocytes can form due to the activation of specific T cells. From these inflammatory foci, the brucella can enter the bloodstream in spurts.

Symptoms

The incubation period of brucellosis is usually 1 to 2 months (incubation periods of 5 days to 150 days have been described in individual cases). Up to 90% of all infections are subclinical; they can only be identified by the detection of specific antibodies in the patient and are an expression of a successful immune response. In acute brucellosis, fatigue, mild fever, headache and pain in the limbs occur in the initial phase. After a short, symptom-free interval, flu-like symptoms may appear, which then do not stop after 7 to 10 days as is usual with influenza. Typical for brucellosis are evening temperature rises of up to 40 °C combined with massive sweating! The temperature returns to normal in the morning. This undulating fever is typical of brucellosis in humans. The phases last up to 5 weeks and are interrupted by remission periods of up to 2 weeks with greatly attenuated symptoms. The course of fever extends over 7-21 days and may be interrupted by 2- to 5-day fever-free intervals (undulating fever). Chronic courses of the disease can lead to complications in the nervous system and internal organs. The disease can be treated well with antibiotics.

The genus Brucella comprises 12 officially described species: Brucella abortus, Brucella suis, Brucella melitensis, Brucella canis, Brucella ovis, Brucella neotomae, Brucella ceti, Brucella pinnipedialis, Brucella microti, Brucella inopinata, Brucella papionis and Brucella vulpis.

In Austria, the cattle population has been officially recognised as free of B. abortus since 1999 and the sheep and goat populations have been officially recognised as free of B. melitensis since 2001, so the risk of infection in humans in Austria is very low. An outbreak of B. melitensis was last detected in a cattle herd in Upper Austria in 2018.

Diseases in domestic pigs caused by B. suis Biovar 2 are rarely reported in Europe. In Austria, porcine brucellosis was first detected in a breeding sow in Styria in the 1990s. In 2003, there were outbreaks in several pig farms in the Waldviertel region of Lower Austria and in 2004 there was an outbreak in the district of Schärding in Upper Austria. In 2017, an outbreak was detected on a breeding farm in the district of Grießkirchen in Upper Austria with a total of 9 contact farms, and in 2024 an outbreak was detected on a breeding sow farm in Upper Austria.

B. suis biovar 2 is widespread in Europe in wild boar and hares and can be transmitted from these wild animals to domestic pigs and humans. B. suis Biovar 2 was isolated from the head lymph nodes of 12 animals (5.2 %) from 228 wild boar shot in 2011/2012 from 8 districts in Upper Austria, Lower Austria and Burgenland. Secondary hosts of B. suis Biovar 2 are humans, cattle, rats, red foxes and deer. The red fox can serve as an indicator animal for the investigation and monitoring of natural brucellosis herds(B. suis, B. microti, B. vulpis). From June 2007 to July 2008, mandibular lymph nodes of 903 foxes from 37 districts (20 Lower Austrian, 5 Burgenland, 5 Upper Austrian and 7 Styrian districts) were examined, revealing B. suis natural herds in Lower Austria, Styria and Burgenland. While B. su is biovar 2 has only a low pathogenicity for humans (rare reports, patients with previous illnesses), B. suis biovar 1, which in Europe has so far only been detected in wild and domestic animals in Croatia, is highly pathogenic for humans.

B. microti is a newly described species that was first detected in the Czech Republic in 2000 in diseased field mice and several times in 2007 in foxes in Lower Austria. The pathogenic significance of this mouse brucellosis pathogen for other animals and humans is unclear. This species has so far only been detected in wild animals in the Czech Republic, Austria and Hungary.

B. vulpis was officially described as the twelfth Brucella species in 2016. This species has so far only been isolated in Austria. In 2008, this Brucella species was isolated from macroscopically unchanged mandibular lymph nodes of 2 foxes in the Lower Austrian district of Hollabrunn. The reservoir of this pathogen and its pathogenic significance for other animal species and humans is unclear.

B. canis was first detected in Austria in 2010 as an abortus pathogen in dogs in a poodle breed in Upper Austria and is also a zoonotic agent.

B. ovis, the causative agent of infectious epididymitis in rams, is not pathogenic for humans.

Transmission and symptoms

Epidemiologically significant massive excretions occur particularly during abortions and infected normal births, but also with milk, urine, faeces and nasal secretions. Typical routes of infection are oral ingestion and transmission during mating. Infections via the skin, also through arthropods as vectors, must be taken into consideration.

Domestic pigs: In endemic areas, the possibility of transmission of B. suis Biovar 2 from wild animals to domestic pigs is particularly high when domestic pigs are kept outdoors. However, the pathogen can also be introduced into a breeding sow herd via contaminated green fodder, indirectly via carnivorous mammals such as foxes and dogs or carrion-eating birds or through the purchase of a chronically infected boar. The unsafe disposal of animal by-products from hunted wild boar and hares also represents a risk factor for introduction into the livestock population. Compliance with hygiene principles in hunting and game processing by hunters is the most important measure to prevent the introduction of the pathogen into domestic pig herds and transmission to humans.

Within a herd of domestic pigs, infection occurs particularly through contact with infected material such as abortions, afterbirths, body faeces and secretions and during mating. The incubation period is very variable (a few days to several months). In the case of infection through the mating of an infected boar, the first symptom to appear after 5-8 weeks may be increased rumination as a result of early abortions. However, abortions are possible at any stage of pregnancy. In domestic pigs, a new outbreak in sows results in frequent abortions at all stages of pregnancy, the birth of weak piglets, postpartum behaviour and uterine inflammation with possible small-node changes. In boars, testicular swelling and inflammation may occur. In general, movement disorders due to joint inflammation and abscessing changes in various organs can occur. The disease can also progress without clinical symptoms, with excretion of the pathogen lasting for years.

Cattle: Before the frequently occurring abortions, the infection is usually asymptomatic apart from a temporary rise in temperature. The animals remain pathogen excretors. Calcifications in the second half of pregnancy are the most conspicuous symptom; no signs of the disease are usually observed before the abortion. Subsequently, inflammation of the joints, tendon sheaths and bursae often occurs, less frequently clinically conspicuous udder inflammation (pathogen excretion!). After the abortion, a cow may well give birth to a normal calf again; a new calving is just as possible as sterility after the first abortion. Testicular and epididymitis are observed in bulls. Bovine brucellosis is enzootic in the herd. Infections with B. abortus rarely occur in other animal species (sheep, goats, sheep, pigs). Their occurrence is usually due to contact with infected cattle herds.

Sheep and goats: Sheep and goat brucellosis is caused by B. melitensis with its 3 biovars. The course is similar to bovine brucellosis. Animals frequently abort, give birth to weak lambs and show inflammatory changes, especially in the reproductive tract. Mastitis, inflammation of the testicles and epididymis also occur. In rams, brucellosis also occurs in the form of infectious unilateral and bilateral epididymitis accompanied by a deterioration in semen quality, which is caused by Brucella ovis. Brucella are transmitted during mating and can lead to abortions in the dam. After kidney colonisation, excretion takes place via the urine.

Dog: Infected dogs show no fever and can remain bacteraemic for years. Serological tests can be falsely negative despite bacteraemia. Brucellosis can remain undetected if clinical symptoms are absent or not recognised (infertility, pregnancy disorders, iritis, spondylodiscitis, lymphadenitis, prostatitis, epididymitis).

Control/prevention

Brucellosis in cattle, pigs, sheep and goats is a notifiable animal disease. Control is focussed on the detection, isolation and eradication of infected animals and the control of animal traffic in order to prevent the spread of the pathogen. Serological tests are used to monitor the absence of the disease.

Farmers, veterinarians, animal breeders and slaughterhouse staff must adhere strictly to hygiene regulations when handling infected animals. People in those businesses that are supplied with animals from the affected farm should also be informed about the nature of this disease and the existing risk of infection via animals, carcasses and slaughterhouse waste. In addition to the use of protective gloves, especially in obstetrics, thorough hand disinfection with an approved hand sanitiser and hand washing with soap and water are essential. Suitable ointment protection can provide additional protection against transdermal infections. Clothing and shoes must be changed after working in the barn. Surface disinfection in animal stables is advisable.