Investigation of viral causes of undiagnosed neurological disease in animals and their zoonotic risk to humans in South Africa

Abstract

Every year thousands of cases of neurological disease go undiagnosed largely due to the vast number of potential causes, especially neglected are those thought to be of viral origin. The purpose of this study was to investigate the potentially novel causes of undiagnosed neurological disease in horses. An arbitrarily primed PCR was developed which allowed for the identification of unknown agents from cell culture and as well as tissue specimens. Shuni virus (SHUV) was identified in a cell culture isolate from a horse that had displayed severe neurological signs. This little known orthobunyavirus, had not been well studied since its discovery in the 1960’s and thus the focus became to further elucidate the role SHUV may play in neurological disease in South Africa. Two SHUV specific assays were developed and employed in a five year epidemiologic study. 497 horses and 143 other animals submitted to our surveillance program with febrile and neurological disease were screened for the presence of SHUV. 13 SHUV cases were identified, nine in horses and four in wildlife species. In horses symptoms ranged from mild febrile illness to severe neurological disease, where 45% of animals either died or were euthanized on humane grounds. All wildlife cases presented with paralysis, all cases proved fatal. A genome was amplified and characterised and SHUV’s (SAE 18/09) relationship to the prototype SHUV isolate and the Simbu serogroup fully clarified. Of significance was the finding that the prototype isolate’s sequence differed from SAE 18/09 at one of the M segment cleavage sites, such changes are known to affect pathogenicity. Finally due to the zoonotic potential of SHUV, a serological survey was conducted on veterinarians, to determine whether they may be at increased level of exposure due to occupational risk. WNV was used in comparison as zoonotic transmission of this virus had been documented and multiple studies conducted to analyse its sero-prevalance. 12.5% of veterinarians were found to have neutralizing antibodies to WNV and 4% to SHUV, these values correlate with what is seen in equine studies (WNV 8.7% - SHUV 1.9%), highlighting the zoonotic potential of these pathogens.