What do sheep, dogs, seals, frogs and humans have in common? All of them can carry bacteria of the genus Brucella, some of which are responsible for brucellosis. Symptoms of this disease in humans include fever, pain and headaches. It can lead to complications, mainly neurological or articular, and may become chronic. Affected animals can suffer abortions, fertility problems and genital tract infections.
Over the last fifteen years or so, new species of Brucella have been discovered, carried by animals as diverse as frogs, foxes and marine mammals. The IDEMBRU project, coordinated by ANSES and involving nine partners from eight European countries (Germany, Bulgaria, Spain, Italy, the United Kingdom, the Netherlands, Portugal and France), sought to gain a better understanding of these new bacteria. Running for two and a half years, it was funded by the One Health European Joint Programme (EJP). Its results are currently being published.
Atypical bacteria and host species
The project partners developed molecular biology tools to identify the different Brucella species, in order to speed up diagnosis in the event of a brucellosis outbreak. These new tests are designed to identify atypical Brucella species, as well as classic Brucella infecting unusual animal species. This is because several Brucella species, known for many years to infect certain animal species, have been found in animals in which they had not previously been detected. "We discovered three dogs carrying Brucella suis", explains Claire Ponsart, project coordinator and head of the Bacterial Zoonoses unit in ANSES's Laboratory for Animal Health. "This bacterium is known to circulate in pigs, wild boar and hares, but we didn't know that dogs could also be infected."
Predicting the risk of transmission to humans
For the newly discovered Brucella species, one of the key questions is whether they pose a risk to humans. "We developed an in vitro cell infection method that gives an indication of their pathogenicity for humans. Until now, there have been few pathogenicity indicators for these bacteria, so we mainly used to rely on identifying the bacteria involved in outbreaks of infection" says Vitomir Djokic, a scientist in the Bacterial Zoonoses unit who took part in the project.
Dogs contaminated by Brucella canis: an effect of international trade
Twenty-six dogs infected in two years in France compared with two in the previous twenty: until several cases were reported in the last few years in Great Britain, Brucella canis, a species of Brucella that affects dogs, was considered to be very rare in Western Europe. These reports in Britain prompted the IDEMBRU project partners to take samples to measure the extent of this emerging threat. Cases were then found in all participating countries. In France, the disease was detected in ten breeding facilities that had imported dogs from Eastern Europe or the United States.
The increase in the number of cases of canine brucellosis in Western Europe is probably linked to the development of online animal trading. "Buying dogs abroad is legal, but no health test for brucellosis is required," explains Claire Ponsart. "Future owners should be aware that when they import their pets, they also run the risk of importing diseases."
Treatment for Brucella canis is not effective in all dogs. Infected animals are therefore considered to be capable of transmitting the disease throughout their lifetimes. As well as causing reproductive problems in dogs, the bacteria can be transmitted to humans. This phenomenon is rare, but two cases were reported in 2022, in Great Britain and the Netherlands. Brucella canis causes the same symptoms as classic brucellosis.