Brucellosis is an animal disease which can infect humans (zoonosis). It is caused by bacteria of the genus Brucella. This bacterial zoonosis with worldwide distribution can affect humans and most mammal species, especially wild and domestic ruminants, as well as pigs and boars (suidae).
In animals, brucellosis can cause abortion, reduced fertility and reduced milk production. In addition, animals or herds which have not been certified as brucellosis-free cannot circulate freely between countries. The disease can therefore induce major economic losses.
In humans, who can be contaminated through contact with infected animals or by consuming raw dairy products, the disease causes intermittent bouts of fever (severe night sweats in particular), pain, headaches and/or weakness. It can evolve into a chronic form of the disease, causing serious osteo-articulatory complications. The severe forms of the disease are rare, and fatalities extremely rare, even in cases where no treatment is administered.
Brucellosis is a disease with worldwide distribution and significance. Only a few countries in northern, central and eastern Europe (France, Great Britain, Scandinavian countries, the Netherlands, Belgium, Austria, Switzerland), as well as Canada, Japan, Australia and New Zealand, are free of the disease in ruminants. In Europe, the Mediterranean countries and the Balkans are still affected by the disease.
The incidence of human brucellosis is estimated by WHO at 500 000 new cases per year worldwide. In France, the disease is now rare and is essentially contracted in third-party countries where the disease is insufficiently controlled, or uncontrolled in animals, or through foods imported from these countries.
France has been officially declared bovine brucellosis-free since 2005, as defined by the European regulation, and no brucellosis outbreaks in cattle, sheep or goats were identified on the national territory from 2003 to 2012. However, two outbreaks of bovine brucellosis were confirmed in 2012 on French territory, which calls for vigilance concerning the disease (Mailles et al., 2012; Rautureau et al., 2013). The first outbreak was due to an imported cow and was promptly resolved. The second outbreak was linked to a major wild ibex reservoir discovered in a French massif (Hars et al., 2013).
In suids (pigs and boars), brucellosis infection reappeared in 1993 in an open-air pig farm. Over 70 outbreaks have been identified since then, and in most cases the infection originated in wild boar populations which occasionally came into contact with pigs raised in the open (Hars & Garin-Bastuji, 2013).
Preventing and avoiding infection
Transmission from animals to humans can occur through the alimentary route or through direct contact with an infected animal or its genital secretions, infected organs, contaminated manure or wool, etc. The Brucella species that can infect humans are mainly found in domestic pigs, cattle, sheep and goats.
People working in direct contact with infected animals – breeders, veterinarians, A.I. technicians, slaughterhouse and rendering plant personnel – are those most highly exposed to infection. Likewise, brucellosis is one of the primary infectious diseases contracted by laboratory personnel during veterinary or medical analyses.
Because of this, hygiene and safety rules must be adhered to by all those whose work brings them in contact with potentially-infected products or animals. These measures include washing hands, wearing gloves, masks and goggles, etc.
As concerns contamination through the alimentary route, the main foods responsible for human brucellosis cases are contaminated raw milk and products made from contaminated raw milk (fresh or semi-ripened cheeses, butter, ice cream), contaminated undercooked offal (liver, spleen), and fruits and vegetables grown in soil treated with contaminated manure.
Controlling food-based Brucella contamination involves either the pasteurisation or sterilisation of milk, or the use of raw milk from herds officially declared brucellosis-free.
Owing to the economic importance of brucellosis and to its risk for human health, this disease is a major concern for public health organisations in charge of human and animal health both in France and worldwide.
ANSES's Maisons-Alfort Laboratory for Animal Health is the national, European, WOAH and FAO Reference Laboratory for animal brucellosis and the National Centre of Reference for human brucellosis. It is involved in the surveillance of animals and of human cases of brucellosis in France. It coordinates the reference activities of a network of national and European laboratories. It also contributes to the creation of prevention, surveillance and eradication strategies, in conjunction with national and international public health organisations.
The role of the research conducted at ANSES involves improving:
- the tools for diagnosing this disease in animals and humans;
- epidemiological knowledge on brucellosis in all susceptible species, both domestic and wild, in order to improve both risk analysis and strategies for prevention and eradication of the disease in humans as well as in animal populations.
Expert appraisals to manage the infection of ibex in the Bargy massif
Since 2013, following the detection of brucellosis in certain ibex, ANSES has produced several expert appraisals on ibex populations in the Bargy massif (Haute-Savoie département). The objective is twofold: limit the risk of contamination in domestic animals and work towards the natural extinction of the disease in the wild population.
The strategy recommended by the Agency is based on capturing and shooting the animals that are most at risk of being infected and transmitting the disease. Capturing ibex makes it possible to monitor and control levels of infection. Infected animals are euthanised, while those not carrying the pathogen are marked before being released. For ANSES, this strategy is preferable to a mass cull of ibex that would eliminate a large number of healthy individuals. It would also make it difficult, if not impossible, to monitor the few surviving ibex and detect a possible resurgence or spread of the infection to other areas.
ANSES has renewed and clarified its recommendations following local events, such as the detection of brucellosis on a cattle farm in 2021 and the discovery of an infected female in the neighbouring Aravis massif in 2022. The recommendations always favour long-term management of local outbreaks, combining capture and targeted shooting. In the event that the disease is detected in a neighbouring area, the Agency recommends extending the surveillance and shooting strategy to the area in question.