PUBLIC HEALTH CONCERN
Brucellosis is an old disease with low mortality in humans (less than 2% of untreated cases). Yet human brucellosis remains the commonest zoonotic disease worldwide, with more than 500,000 new cases annually1-16).
It is associated with substantial residual disability and is an important cause of travel-associated morbidity. The occurrence of the disease in humans is largely dependent on the occurrence of brucellosis in an animal reservoir, including wildlife. Today, the disease in humans is mainly occupational (abattoir, animal industry, hunters and health workers). Symptoms such as undulant fever, tiredness, night sweats, headaches and chills may continue for as long as 3 months before the illness becomes so severe and debilitating as to require medical attention.In contrast to B. suis biovars 1, 3 and 4, B. suis biovar 2 has rarely been isolated from humans, and its zoonotic role is questioned. Zoonotic concern regarding marine mammal strains was initially raised following the recovery of a cetacean strain of Brucella from a laboratory worker in the UK who had seroconverted after suffering from headaches, lassitude and severe sinusitis(49). In April 2003, the first report of community-acquired human infections with marine mammal- associated Brucella spp. was published. The authors described the identification of these strains in two patients with neurobrucellosis and intracerebral granulomas. It became apparent that all three reported cases of natural human infection associated with Brucella spp. from marine mammals(50,51) were associated with strain type 27 (ST27)(52). Unfortunately the natural host of ST27 (first isolated from a captive dolphin in the USA) has not been identified, although there is molecular evidence of the presence of this genotype in minke whales (Balaneoptera acurostrata) from the Pacific Ocean(53).
In Norway and Greenland, there is a long tradition of consumption of meat from harp seals, hooded seals and minke whales — all species to be found infected with Brucella spp. In spite of this, brucellosis has not been reported in humans at risk (whale- and seal-hunters, veterinarians, other marine mammal meat handlers or consumers). Marine mammal Brucella were tested for their ability to infect human and murine macrophage cells. The study showed that some B. ceti and B. pinnipedialis isolates were virulent in these models of infection, whereas other isolates were not. In fact, all the B. pinnipedialis isolated from hooded seals did not show any ability to infect human and murine macrophage cells(46), which may be an explanation for the absence of human infection with hooded seal B. pinnipedialis.