Abstract
Burkholderia (formally Pseudomonas) pseudomallei, the
causative agent of melioidosis, has caused considerable mortalities in cetaceans at Ocean Park
especially in the 1970s and 80s. The bacterium is mainly indigenous to South-East Asia and
Northern Australia although it is sporadically isolated from Europe, Central & South America,
Africa, Middle East and India.1
Melioidosis affects a wide range of species with a preponderance of
infections occurring during the rainy or wet season. In the earlier years of the park, the
clinical syndrome was an acute septicemia resulting in sudden death. In recent years the disease
has presented as a more chronic and debilitating syndrome, characterized by abscess formation in
virtually any organ system. Research carried out since the early 1980s at Ocean Park have
included epidemiological studies, serological examinations, specific media for isolation of the
bacterium, appropriate and effective therapy and a protein-polysaccharide vaccine3
which has been used at the park since 1987.
Burkholderia pseudomallei is a gram-negative, nonacid fast,
non-spore-bearing rod which shows characteristic bipolar staining. The organism has been isolated
from aerosol adjacent to the cetacean holding facilities during typhoons and can infect its host
via the respiratory route, ingestion or wounds and abrasions. It may remain quiescent in infected
individuals for many years and factors that reactivate dormancy probably include environmental
variables, stress and immunological status.2 Burkholderia pseudomallei could be
a serious threat to cetaceans in endemic areas and awareness of this disease is important
although it appears that improvements in facilities, husbandry practices and the implementation
of a preventative medicine program have decreased the prevalence of the disease at Ocean
Park.
Acknowledgements
The authors wish to thank the staff of Ocean Park Laboratory for their
contribution to this work.
References
1. Dance, D.A.B. 1991. Melioidosis: the tip of the iceberg?.
Clinical Microbiology Reviews 4(l):52-60.
2. Leelarasamee, A., and S. Bovornkitti. 1989. Melioidosis: Review
and Update. Reviews of Infectious Diseases 1 1(3):413-425.
3. Vedros, N. A., D. Chow, and E. Liong. 1988. Experimental vaccine
against Pseudomonas pseudomallei infections in captive cetaceans. Disease of Aquatic
Organisms 5:1570-161.