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TDK conference 2015

Comprehensive description of equine encephalomyelitis caused by different West Nile Virus lineages
Fehér Orsolya Eszter - year 5
SzIU,Faculty of Veterinary Science, Institute for Animal Breeding, Nutrition and Laboratory Animal Science , HAS-SzIU Large Animal Clinical Research Group, National Veterinary School of Lyon (VetAgro Sup)
Supervisors: Orsolya Korbacska-Kutasi DVM, Ottó Szenci DVM, Sára Sárdi DVM


West Nile Virus (WNV) is a mosquito-borne zoonotic arbovirus belonging to the genus Flavivirus, in the family of Flaviviridae. This RNA virus causes nervous system disorders in humans, birds and horses. The virus occurs sporadically worldwide. Main mosquito vectors which conspire in the spread of the virus, belonging to the Culex genus. Among phylogenetic studies we can identify two main lineage strains of the West Nile Virus.

The aim of our study is to present a comprehensive summary of neuroinvasive diseases caused by different West Nile Virus lineage strains. We would also like to present a retrospective comparative study to summarise clinical manifestations and to determine the most common signs and findings of WNV encephalomyelitis in three different European countries. We have collected data in cooperation with the National Veterinary School of Lyon and the Facultad de Veterinaria Universidad de Córdoba to compare Hungarian lineage 2 strain cases to lineage 1 strain cases described in France and Spain. West Nile Virus neuroinvasive cases were diagnosed based on seasonality (August-November), acute neurologic clinical signs (less than 5 days) and positive serum IgM ELISA tests. Clinical and detailed nervous system examinations were performed in all cases, based on a unified neurological examination protocol.

We have recorded the data of 34 confirmed Hungarian cases from 2007 up to 2014, 39 French cases from 2004 and 84 Spanish cases between 2006 and 2013. In Hungary the highest prevalence was detected in the age category of horses between 5-10 years while in other countries there was no difference in the age groups according to the appearance of the infection. The fatality rate was nearly the same in all three countries (24-33%). Gender did not seem to affect occurrence of the neurologic signs. Ataxia was the leading clinical symptom in most of the cases (58-97%) independently of the viral lineage and country of origin. In the view of the Hungarian data, horses with front limb weakness were less likely to survive. Seventeen percentages of horses surviving lineage 2 strain caused disease showed residual symptoms.

Although there are massive similarities between the clinical manifestations caused by the two lineages, still there are some significant differences in the disease progression and characteristics. In our study we would like to draw the attention of equine practitioners that international literature data, based mainly on lineage 1 strain infections, should be followed with caution when establishing the diagnosis of a neurologic case in Hungary. Our results also help to evaluate these cases better and to give a more reliable prognosis.

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