Exploration of the Epidemiology of a Newly Emerging Cattle-Epizootic Hemorrhagic Disease Virus in Israel

In September 2006 an outbreak of 'Bluetongue like' disease struck the cattle herds in Israel. Over 100 dairy and beef cattle herds were affected. Epizootic hemorrhagic disease virus (EHDV) (an Orbivirusclosely related to bluetongue virus (BTV)), was isolated from samples collected from several herds during the outbreaks. Following are the aims of the study and summary of the results: which up until now were published in 6 articles in peer-reviewed journals. Three more articles are still under preparation:   1. To identify the origin of the virus: The virus identified was fully sequenced and compared with the sequences available in the GenBank. It appeared that while gene segment L2 was clustered with EHDV-7 isolated in Australia, most of the other segments were clustered with EHDV-6 isolates from South-Africa and Bahrain. This may suggest that the strain which affected Israel on 2006 may have been related to similar outbreaks which occurred in north-Africa at the same year and could also be a result of reassortment with an Australian strain (Wilson et al. article in preparation). Analysis of the serological results from Israel demonstrated that cows and calves were similarly positive as opposed to BTV for which seropositivity in cows was significantly higher than in calves. This finding also supports the hypothesis that the 2006 EHD outbreak in Israel was an incursive event and the virus was not present in Israel before this outbreak (Kedmi et al. Veterinary Journal, 2011)   2. To identify the vectors of this virus: In the US, Culicoides sonorensis was found as an efficient vector of EHDV as the virus was transmitted by midges fed on infected white tailed deer (WTD; Odocoileusvirginianus) to susceptible WTD (Ruder et al. Parasites and Vectors, 2012). We also examined the effect of temperature on replication of EHDV-7 in C. sonorensis and demonstrated that the time to detection of potentially competent midges decreased with increasing temperature (Ruder et al. in preparation). Although multiple attempts were made, we failed to evaluate wild-caught Culicoidesinsignisas a potential vector for EHDV-7; however, our finding that C. sonorensis is a competent vector is far more significant because this species is widespread in the U.S. As for Israeli Culicoides spp. the main species caught near farms affected during the outbreaks were C. imicolaand C. oxystoma. The vector competence studies performed in Israel were in a smaller scale than in the US due to lack of a laboratory colony of these species and due to lack of facilities to infect animals with vector borne diseases. However, we found both species to be susceptible for infection by EHDV. For C. oxystoma, 1/3 of the Culicoidesinfected were positive 11 days post feeding.   3. To identify the host and environmental factors influencing the level of exposure to EHDV, its spread and its associated morbidity: Analysis of the cattle morbidity in Israel showed that the disease resulted in an average loss of over 200 kg milk per cow in herds affected during September 2006 and 1.42% excess mortality in heavily infected herds (Kedmi et al. Journal of Dairy Science, 2010). Outbreak investigation showed that winds played a significant role in virus spread during the 2006 outbreak (Kedmi et al. Preventive Veterinary Medicine, 2010). Further studies showed that both sheep (Kedmi et al. Veterinary Microbiology, 2011) and wild ruminants did not play a significant role in virus spread in Israel (Kedmi et al. article in preparation). Clinical studies in WTD showed that this species is highly susceptibile to EHDV-7 infection and disease (Ruder et al. Journal of Wildlife Diseases, 2012). Experimental infection of Holstein cattle (cows and calves) yielded subclinical viremia (Ruder et al. in preparation).   The findings of this study, which resulted in 6 articles, published in peer reviewed journals and 4 more articles which are in preparation, contributed to the dairy industry in Israel by defining the main factors associated with disease spread and assessment of disease impact. In the US, we demonstrated that sufficient conditions exist for potential virus establishment if EHDV-7 were introduced. The significant knowledge gained through this study will enable better decision making regarding prevention and control measures for EHDV and similar viruses, such as BTV.