Abstract

An approximately 11-year-old male bottlenose dolphin (Tursiops truncatus) was acquired by a marine park in Canada in September 2000 from a facility at the Black Sea, Russia. From initial arrival through to 2005, the animal had a history of sporadic bouts of leukocytosis with neutrophilia and eosinophilia ranging as high as 34%, as well as elevated liver and muscle enzymes. There were occasional episodes of cutaneous papillomatosis localized to the peduncle and often precipitated by stress. The dolphin generally responded to various combination therapies of amoxicillin-clavulanate potassium, marbofloxacin, itraconazole, prednisone, enrofloxacin, sulfadimethazine and cimetidine. Routine microbiology and fecal parasitology over this time proved negative for significant pathogens and deep fungal screening was consistently unremarkable. This animal had been vaccinated for Erysipelothrix ERBAC® PLUS bacterin (Pfizer Animal Health) September 2005 and received a booster in October 2005.

From early December 2005 to October 2006, the dolphin exhibited increasingly more frequent episodes of abnormal behaviors, including erratic swimming, abrupt turns, jaw shattering, seizure-like activity, swimming into the sides of the tank, aggression toward people outside of the tank, and partial to complete blindness. Initial antibiotic, fluid and supportive care resulted in clinical and hematological improvement, however, the duration of antimicrobial treatments become increasing longer. After administration of ciprofloxacin for 4 weeks, bilateral symmetric hypodermal fluid-filled swellings were detected along the trunk and head and treatment ceased. In late October, a pronounced leukocytosis was detected (37,400 total count) with a profound and progressive deterioration in mental status. The dolphin would swim into objects and appeared blind. Over the course of the next 6 weeks, he was administered varying combinations of oral and intramuscular antibiotic injections of clindamycin, amikacin, timentin (ticarcillin and clavulanate potassium), difloxacin, tazocin (tazobactam and pipericillin) ceftazidime and florfenicol. Despite these aggressive treatments, the dolphin succumbed in December 2006.

Gross examination disclosed emaciation and generalized pallor, with multiple traumatic cutaneous abrasions and lacerations. The most salient internal changes included hepatomegaly, pulmonary congestion and edema with small foci of atelectasis and serosanguinous pericardial effusion. Microscopic evaluation of sampled tissues revealed rare Toxoplasma gondii throughout the cerebrum with occasional glial nodules and nonsuppurative meningitis. Marked lymphoid depletion and hemosiderosis was apparent within the spleen and select lymph nodes featured subcapsular and medullary histiocytosis and occasional cortical lymphoid depletion. Lytic necrosis was apparent within the adrenal cortex with scattered cells within the fasciulata layer that featured prominent intranuclear inclusions with marginated nuclear chromatin. Follow up polymerase chain reaction of sampled brain tissue was positive for Toxoplasma gondii. This infection likely contributed significantly to antemortem clinical signs and possibly the loss of this animal.

Without serologic evidence, it is difficult to resolve whether this animal was subclinical carrier at the time of capture and transport from Russia, or whether infection may have been recruited after arrival to Canada. As oocyst exposure may have been waterborne, there are important implications from a management perspective. Follow up serologic evaluation of enclosure mates, review of current water disinfectant procedures, and biosecurity and biocontainment protocols are imperative. Efforts are currently underway to develop a dolphin specific serologic assay, which should enhance efforts to detect, manage, and control this condition in captive animals. Antibodies to Toxoplasma gondii have been detected and microscopic lesions have previously been reported in a variety of captive and wild marine mammal species. This case is believed to be the first involving a captive bottlenose dolphin in Canada.