Equine herpesvirus (EHV) can cause a range of disease in equids, from respiratory infections [EHV-4] to neurologic disease [EHV-1], while other strains [e.g., EHV-9] have not been shown to cause clinical disease.6 Cross-infection of non-equid zoo species with EHV-1 is rare, but clinical disease has been reported.1,4,5,7 In 2007, a polar bear (Ursus maritimus) housed in a US zoological facility died from progressive neurologic disease in which post-mortem analysis revealed EHV-9 within its nervous tissue.2 While the affected polar bear had no direct contact with exotic equids, the same strain of virus had been detected in two Grevy’s zebras (Equus grevyi) housed within 200 feet of the bear.8 Similarly, in 2010, two polar bears from a European zoological facility developed neurologic disease, and one died.3 Post-mortem analysis on nervous tissue of the deceased bear revealed a recombinant strain of EHV-1 and -9; these bears also had no direct contact with zebras, although their enclosure was within 200 feet of an enclosure with plains zebra (Equus quagga) of unknown serologic status.3 Since these initial cases, EHV-1 has been detected in the nervous tissue of four captive black bears (Ursus americanus) that died from neurological disease.9 The present investigation was undertaken to evaluate the serologic status of EHV in US AZA institutions housing polar bears (n=32) with (n=24) and without (n=8) exotic equids in the collection to establish disease prevalence and assess risk factors for disease transmission and prevention.
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