Brucellae are bacteria that do not form spores but are resistant nevertheless. Among other things, they can survive outside the host in chilled raw milk or yoghurt for several days and in water at room temperature for several weeks to months. Brucella can cause infections in both humans and animals. However, not all species are pathogenic to humans. The Brucella species Brucella melitensis (sheep and goat brucellosis) and Brucella abortus (bovine brucellosis) are responsible for most infections in humans. Brucella suis, the pathogen responsible for swine brucellosis, is detected much less frequently in humans.

Infections caused by Brucella are referred to as brucellosis. Worldwide, brucellosis is among the most common bacterial infections that can be transmitted from animals to humans (“zoonoses”). Affected persons suffer from influenza-like symptoms including fever, shivering, loss of appetite and fatigue. Undulating fever phases over a longer period of time is a typical symptom of untreated brucellosis. The probability of dying from an untreated brucella infection is low (less than 2%). However, chronic brucellosis can lead to diseases of the organs, such as endocarditis.

Brucellosis is transmitted to humans predominantly from sheep, goats, cattle and, more rarely, pigs. The pathogens are either transmitted directly from animals to humans or via animal-derived foods. Human-to-human infection is very rare.

Brucella can be transmitted to humans through raw foods derived from infected animals. Most infections are caused by the consumption of raw goat or sheep milk or by cheese or other products made from raw milk.

The number of patients ill with brucellosis depends on the extent to which the production animals of a country are affected by Brucella. In Germany, cattle, sheep and goat populations, are considered to have been free of Brucella since 2000. In pig populations, Brucella outbreaks occur sporadically.

However, this is caused by bacteria of the Brucella suis species, which only rarely lead to human infection. Brucella suis Biovar 2 is primarily found in wild boar and hares, but can also be transmitted to humans and domestic pigs. Brucellosis is a notifiable disease. From 2001 to 2022, between 20 and 60 cases of brucellosis were reported in Germany each year. In 2023, 71 cases of newly infected persons were reported. Most of the patients had contracted the infection during a stay in an endemic area abroad. In most cases, the consumption of raw goat milk or raw sheep milk was the cause of the infection.

Brucellosis is notably found in the Mediterranean area, on the Arabian Peninsula, in the Middle East, in Africa and in Central and South America. Worldwide, up to 500,000 cases of newly diagnosed patients are reported every year.

The most important measure to prevent Brucella infections in the long term is to control brucellosis in animal populations. In northern and central Europe, Brucella in animals has been almost eradicated through consistent surveillance and control. The number of infected humans in those countries is correspondingly low. In some countries bordering on the Mediterranean, Brucella continue to be frequently found in animal populations. Within Europe, Portugal, Spain, the South of Italy, Greece and Turkey in particular are affected.

Consumers can protect themselves from Brucella infection from food by refraining from consuming raw milk and meat. Food should be heated to 72 °C for at least two minutes. This recommendation is particularly relevant for raw goat and sheep milk and raw milk products derived therefrom such as cheese produced in endemic areas. This recommendation not only applies when travelling to these areas but also to the consumption of foods that are exported from these regions, for example to Germany.