West Nile virus (WNV) mainly infects birds, horses and humans. Outcomes of the infection range from light uncharacteristic signs to fatal neurologic disease. The main objectives of the present study were to measure serum IgG and IgM antibodies in naturally exposed and vaccinated horses and to compare results of hemagglutination-inhibition test (HIT), enzyme-linked immunosorbent assay (ELISA) and plaque reduction neutralization test (PRNT).
Altogether 224 animals were tested with HIT for WNV antibodies and 41 horses were simultaneously examined with ELISA and PRNT. After primary screening for WNV antibodies, horses were vaccinated. Samples were taken immediately before and 3-5 weeks after each vaccination. McNemar chi-squared and percent agreement tests were used to detect concordance between HIT, ELISA and PRNT.
Analyses by HIT confirmed the presence of WNV antibodies in 27/105 (25.71 %) from naturally exposed horses. Sera from 57/66 (86.36%) vaccinated animals were positive before the first booster and from 11/11 (100%) before the second booster. HIT was less sensitive when detecting IgG antibodies. We could detect post vaccination IgM in 13 cases with MAC-ELISA and in 7 cases with HIT.
WNV is endemic in Hungary causing regular natural infections. Protective antibodies could not be measured in each individual case 12 months after primary injections; protection is more reliable after the first yearly booster. Based on our findings it was not be possible to differentiate infected horses from recently vaccinated horses using IgM antibody capture ELISA (MAC-ELISA). HIT does not substitute ELISA or PRNT when detecting IgG, but was useful tool in this study to gain statistical information about the tendencies within a fixed population of horses
