Abstract
In the summer of 2003, numerous rabbits (Sylvilagus floridanus) were found dead on grounds of the Topeka Zoo, including the outdoor orangutan exhibit. Several rabbit carcasses were tested for various potential diseases, including tularemia (Francisella tularensis) and West Nile virus, but results were negative for pathogens.
In August, one female and one male Bornean orangutan (Pongo pygmaeus borneo), became lethargic and anorexic. Both animals were chemically restrained with medetomidine (Domitor, Pfizer Animal Health, Exton, PA 19341, USA; 0.05 mg/kg IM), and ketamine, (Ketaset, Fort Dodge Animal Health, Fort Dodge, IA 50501, USA; 3 mg/kg IM), reversed with atipamezole (Antisedan, Pfizer Animal Health, Exton, PA19341, USA; 025 mg/kg IM for physical examination and to obtain baseline clinical pathology. Abnormal laboratory findings included a leukocytosis (36 and 16.8×103/dl, respectively) characterized by neutrophilia and monocytosis, and a mild elevation of albumin (2.8 and 3.4 g/L) and LDH (1401 and 396 U/L). Both orangutans were administered IV and SC balanced electrolyte fluids, dexamethasone (Dexamethasone Sodium Phosphate, American Pharmaceutical Partners, Los Angeles, CA 90024, USA; 2 mg/kg IV), and a course of doxycycline (Doxy 100, American Pharmaceutical Partners, Los Angeles, CA 90024, USA; 5 mg/kg, PO, BID). Doxycycline was selected because of its efficacy for many bacterial diseases and as it is related to tetracycline, a drug of choice to treat tularemia.2,4
Two days later, a second adult female orangutan, died without prior clinical signs. Postmortem findings revealed a septicemia but cultured only hemolytic E. coli, Citrobacter sp., and Streptococcus pneumoniae from the lungs, liver, and spleen. Samples were again submitted for tularemia and West Nile virus. At this time, the two previously examined orangutans developed signs of pneumonia with fever (103°F/39.6°C) and coughing. Following chemical immobilization with the same anesthesia protocol used previously, both animals were administered balanced electrolyte fluids and doxycycline IV. Doxycycline was continued PO as before, and over the next few days the condition of both animals improved. Both orangutans were considered fully recovered within 17–18 days.
Despite the lack of signs characteristic of tularemia in the two surviving orangutans during the first examination and the negative results for tularemia from the rabbit carcasses, tularemia remained high as a differential diagnosis because of the history of these orangutans handling dead rabbits. The spleen of the dead orangutan was tested for tularemia by culture and immunohistochemistry while samples of the previously submitted rabbit carcasses were retested for tularemia. Laboratory results from both the orangutan and the dead rabbits were positive for Francisella tularensis. Serum samples from the two initial clinical orangutan examinations had negative serology for tularemia. However, it was suspected that these animals were sampled in early onset of the disease before potential seroconversion. Serum samples collected since the presentation have shown seroconversion to tularemia.
As result of these findings, the remaining two orangutans in this group were administered oral doxycycline for 2 weeks and a small-mesh wire fence was placed around the outdoor exhibit to prevent rabbits from entering the enclosure.
Outbreaks of tularemia in nonhuman primates are rather uncommon.2,3,5,6 Sources of infection are mainly rodents with access to holding units.2,3,5,6 The only case of tularemia in great apes was reported in a Western lowland gorilla (Gorilla gorilla gorilla) where the source of infection was never determined.1 This is the first report of tularemia in orangutans.
Literature Cited
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