TDK conference 2020

Explosive increase in West Nile Virus infection in horses

témavezető: Süli (prophyl), KKO

West Nile Virus (WNV) can cause nervous system disorders in humans, birds and horses. Since the first Hungarian detection of the virus in horses in 2007 Hungary continuously reports WNV encephalomyelitis outbreaks among equids. Last year, in the 2018 outbreak season, there was a drastic increase in the number of both human and equine cases in whole Europe.

Our aim was to perform a serosurvey among clinically healthy horses to evaluate WNV transmission activity.

After the 2018 outbreak we have performed two distinct serosurvey in Hungary. In the first survey two commercial competition enzyme-linked immunosorbent assays (Ingenasa and ID Vet) were used to detect seroconversion in non-symptomatic horses. We have tested 162 horses in a south Hungarian county, 90 of them were tested with both kits simultaneously. 101 samples were positive on either tests, while one test showed 56,67% positivity, the other 62,22%.

During the second survey we have collected blood samples from clinically healthy horses all over the country and by testing further 112 horses with IgG ELISA we got 72,3% positivity. The 72 positive samples were further tested with virus neutralisation (VN) for WNV and in 94,5 % of cases the two test gave similar results. In those 4 cases where the IgG results were positive but VN titres were negative we have performed VN test for usutu virus. None of the samples tested positive for usutu virus.

Discrepancies between the results can be explained by different sensitivites of the tests or different level of false positive cross-reactions for Flaviviruses. Since other Flaviviruses (usutu, tick-borne encephalitis, Japanese encephalitis, Dengue) possibly circulating in the area more specific examination protocols, like parallel VN test, are needed to fully evaluate the epidemiological situation. Previously, in 2011 and 2014, we have performed serosurveys in clinically healthy horses with seropositivity of 25,7% and 15,8% respectively. Number of equine neurological cases increased from 16 in 2008, to 56 in 2016, and to 91 last year. This increase of viral activity was also reflected in our serosurveys. The very high seropositivity of 62,22% and 72,3% reflects that a massive number of horses have been infected during the 2018 transmission season which makes large scale WNV outbreaks in the following years less likely. Since seroconversion from natural infection means protection from the disease, vaccination strategies should be planned accordingly.

Köszönetnyilvánítás: dr. Forgách Petra (Járványtan, ÁTE), dr. Nagy Anna (OEK), dr. Malik Péter (NÉBIH), NKB pályázat (ÁTE)