TDK conference 2011

The West Nile virus mainly infects birds, horses and humans. Outcomes of the infection range from light uncharacteristic symptoms to serious disorders of the nervous system. Horses whose nervous system has been affected by the virus have been registered since 2007 in Hungary. The WNV vaccine (Duvaxyn-WNV) has been available here since 2009.

In our current study we examined the immune response given to this vaccination by measuring the quantity of the IgG and IgM antibodies in the vaccinated horses. Based on the documentation of the vaccine, our expectation was that the large majority (96%+) of the vaccinated horses will produce satisfactory amounts of IgG. It was also expected that the IgM production, which occurs when the animals are naturally infected by WNV, should not happen as a response to the vaccination.

Blood samples of 268 horses have been collected during the research. We have categorized the animals based on their vaccination history. We examined separately the groups which have been vaccinated for the first, second or third time this year respectively. There has also been a separate group of horses who received no vaccination at all, but been subject to serological testing. The primary vaccination course for the horses who were vaccinated for the first time this year, consisted of two doses 3-5 weeks apart. The animals that have been vaccinated in the previous years received one booster vaccination. Samples have been taken prior to every injection as well as 3-5 weeks after the last one. We used a hamegglutination inhibition test procedure to determine the antibody-titer in the samples.

Close to one-third of the horses who have never been vaccinated before turned out to be seropositive. Prior to the booster vaccination, 12.5% of the horses who were vaccinated during the last year for the first time were seronegative, and all of the horses who have been vaccinated for the last two years were seropositive. We have detected an increase of the IgM antibody titer in 7 cases. Out of the entire population there were three cases where we found no increase of either the IgG or the IgM antibodies.

In the examined population, only 1.4% of the animals showed no immune response to the vaccination, which met our original expectations. However, contrary to the expectations, we found that IgM antibodies can be produced as a result of the vaccination, which makes identification of the animals who had been naturally infected more difficult.