Equine Encephalosis Virus in Israel


We wish to draw your attention to an outbreak of equine encephalosis virus (EEV) in Israel. Between October 2008 and January 2009, a febrile horse disease was observed in more than 60 equine premises across the country. Clinical signs included: raised body temperatures, unrest, decreased appetite, edema of the neck, legs, lips and eyelids, accelerated pulse and breathing rates, and congested mucosae. The morbidity ranged from 2% to 100% but there were no fatalities. In the affected stables, the disease infected all breeds, ages and sexes and the duration of illness lasted from between 7 and 30 days.

The initial diagnostic investigation was performed by the Kimron Veterinary Institute (KVI), Israel, on nasal swabs, blood and serum samples from affected animals. The tests for WNV and EHV-1 were negative. Initial serological results indicated that the disease was equine viral arteritis (EAV), but no EAV virus could be isolated and PCR tests were also negative. The virus isolates and original sample material were passed on to the Veterinary Laboratories Agency (VLA) in the UK for further investigation.

Based on the clinical signs and possible suspect diagnosis, the VLA performed PCR tests for EAV, Togaviruses (Getah, WEE, EEE, VEE, Ross River), and Flaviviruses (Tick Borne Encephalitis, WN, Usutu, Louping ill, Dengue, Japanese encephalitis), with all tests being negative. Using a novel DNA array technique, with subsequent RT-PCR and sequence analysis, the virus was finally identified as EEV.

While further characterization of the virus is underway and an extended description of the investigation will be provided in due course, we feel obliged to alert the scientific community of this important disease and the implications involved. Equine encephalosis virus is member of the Orbivirus genus, thus transmitted by midges of the Culicoides family and is related to African horse sickness; all equids (horses, donkeys, zebras) being susceptible to infection. This disease has never been diagnosed in Israel or anywhere else North of Southern Africa before (van Niekerk et al., 2003). In the future, it will now be important to distinguish EEV from other diseases such as EAV and Getah, which can have similar clinical signs. In this context, we would wish to recommend further testing of equines in the region, in order to obtain a better knowledge of the distribution of this virus.