Abstract

Burkholderia pseudomallei is the bacterium that causes melioidosis in a variety of animal species, including man. It was first reported in marine mammals in Hong Kong in 1976. Although the number of cases has decreased over the past decade, it remains an important cause of death in marine mammals at Ocean Park,

An unusually high number of melioidosis cases occurred between July and September 2002. Four bottlenose dolphins (Tursiops aduncus), four harbor seals (Phoca vitulina) and one Californian sea lion (Zalophus californianus) were diagnosed with the disease. All cases but one were treated early and aggressively, primarily with ceftazidime, a third generation cephalosporin, and/or meropenem, a carbapenem. To institute appropriate antimicrobial therapy, we examined the pharmacokinetics of meropenem in a dolphin and determined the minimum inhibitory concentrations (MIC) of B. pseudomallei isolates. Initial injectable antimicrobial therapy was followed by maintenance oral therapy, recommended for a minimum of 20 weeks in humans. A combination of, or sole therapy with, trimethoprim sulphadiazine, chloramphenical, doxycycline, and amoxycillin-clavulonic acid were chosen for maintenance therapy. In three dolphins, we observed severe bone marrow aplasia, possibly due to high doses of trimethoprim sulphadiazine.

The outbreak resulted in three marine mammal mortalities. Prior to 2002, no definitively diagnosed case (i.e., B. pseudomallei positive culture) of melioidosis in a cetacean had been successfully treated. Most cases had been diagnosed at necropsy. All marine mammal melioidosis cases in 2002 displayed clinical signs 2-20 (mean 6.7) days following a strong monsoon and a tropical cyclone. B. pseudomallei was isolated from rainwater from all animal facilities where rainwater was collected during the tropical cyclone. Five parrots also died from melioidosis soon after the tropical cyclone. Statistical analyses demonstrate a strong correlation between the onset of clinical signs of melioidosis and inclement weather in 2002; suggesting monsoons and typhoons play a major role in exposure and mode of infection by the organism.

Acknowledgements

The authors wish to thank the Ocean Park Clinical Laboratory, Crista Rayner and the Marine Mammal Department for their technical and logistical support.