Undulant fever (chronic brucellosis)

Brucellosis is a generalised infection of Man involving primarily the reticuloendothelial system, caused by the Brucella species (Gram-negative rod).

Brucella abortis usually infects cows and is the usual organism causing human infection in the UK. B. melitensis is more common in the Mediterranean region and affects goats (1)

Brucella suis is a species found in swine, which is capable of producing severe disease in man.

Brucella ceti and Brucella pinnipedialis are found in marine mammals.

Brucella canis (B. canis) has not been regarded as endemic in the UK (2)

• however, since summer 2020, there has been an increase in the number of reports of B. canis infection in dogs, the majority of which have been in dogs directly imported into the UK from Eastern Europe
  • B. canis is principally viewed as an infection of dogs, although other UK-living carnivores such as cats and foxes may be able to be infected if in close contact with an infected dog or its immediate environment
    • human infections can occur through direct contact with contaminated secretions from infected dogs, or as a result of laboratory exposure particularly to bacterial culture

Generally, infection is contracted from animals. Transmission of infection from humans rarely, if ever, occurs (1).

Yearly incidence rates range from 0.3 cases per million in the United Kingdom and most parts of the United States to above 1 case per 1000 in endemic regions, where the disease represents a considerable and increasing health burden (1).

Reference:

• (1) Pappas G, Papadimitriou P, Akritidis N, Christou L, Tsianos EV. The new global map of human brucellosis. Lancet Infect Dis 2006;6:91-9
• (2) UK Health Security Agency (September 2023). Human Animal Infections and Risk Surveillance (HAIRS) risk assessment: Brucella canis.