Abstract

As part of a program of investigation into strandings of marine mammals, post mortem and bacteriologic examinations of stranded and by-caught animals from around the Scottish Coast were undertaken by SAC Veterinary Science Division. This led to the isolation of Brucella sp. from a porpoise in 1991.³ Prior to 1991, all isolations of Brucella had come from terrestrial animals, but subsequently, many more marine mammal isolations have been made.

Brucellae are obligate, intracellular bacteria, each species having its own animal host, but most are recognized as significant pathogens and zoonotic agents.

Presumptive identification of marine Brucella depends upon the growth of tiny non-hemolytic colonies on Columbia sheep blood agar after 3-5 days at 37°C in 10% CO_2.

The organisms are tiny gram-negative coccobacilli which are acid fast with modified Ziehl-Neelsen stain and agglutinate with Brucella abortus antisera. Seal strains have increased CO₂ requirements and will not grow on Farrell's medium on primary culture, while the converse applies to cetacean strains.²

Serologic studies have been carried out which indicate that exposure to Brucella is relatively common in marine mammals off the United Kingdom (Table 1). Brucella has now been isolated from forty-five animals examined between 1991 and 1999. The serologic evidence suggests that Brucella infections are common in marine mammals, but Brucella associated pathology has been a relatively uncommon finding (Table 2).

The single most common lesion is sub-blubber abscesses. The abscesses are generally found below the dorsal fin and, in some cases, parasites have been found within the lesions. Other animals have had liquefactive lesions in the blubber elsewhere on the carcasses.

Brucella associated pneumonia has been found in seals. The affected animals were juvenile and in poor condition and had been in rehabilitation centers. This raises concerns of transmission to other species and zoonotic risks to staff. However, at present, there has been only one recorded incident of human infection and this occurred in a laboratory worker.¹ There have also been cases of systemic infections, but these animals also had other conditions which may have been the primary condition and predisposed the animal to the Brucella infection.

There has been one suspected abortion, an epididymitis and a spinal lesion. These findings would be more typical of those expected with Brucella infections in terrestrial mammals.

The findings suggest that marine Brucellae may be well adapted and may not be acting as significant pathogens in the marine environment. However, if the main problems caused are, in fact, infectious abortion and infertility, then such conditions would not often be found in strandings studies and would therefore be under represented.

In addition, three Stenella coeruleoalba that live-stranded in various parts of Scotland at the end of 1999 had meningitis and Brucella was isolated from their brains. Except for one which had a small Brucella blubber abscess, Brucella was not recovered from any other tissues.

There are probably several Brucella species in the marine environment with multiple biovars. There are also likely to be varying exposure rates between species and populations, so even if Brucellae are well adapted in their host species, there is potential for cross infection and disease which may be increased by anthropogenic factors.

Acknowledgments

The strandings investigations by SAC Veterinary Science Division have been conducted under contract to the UK Department of the Environment, Transport and Regions as a contribution to its coordinated program of research on the North Sea. SAC Veterinary Science Division received financial support from the Scottish Executive Rural Affairs Department.

Table 1. Results of Brucella serology for cetacean and seal serum samples.

Table 2. Brucella isolations from marine mammal necropsies 1991-1999.

References

1.  Brew SD, LL Perrett, JA Stack, AP MacMillan, NJ Staunton. 1999. Human exposure to Brucella recovered from a sea mammal. The Veterinary Record. 144:483.

2.  Foster G, KL Jahans, RJ Reid, HM Ross. 1996. Isolation of Brucella species from cetaceans, seals and an otter. The Veterinary Record. 138:583-586.

3.  Ross HM, KL Jahans, AP MacMillan, RJ Reid, PJ Thompson, G Foster. 1996. Brucella species infection in North Sea seal and cetacean populations. The Veterinary Record. 138:647-648.