Estimation of antibodies to Newcastle disease virus in tears.

Micro-haemagglutination inhibition tests (Micro-HI) were used to measure the level of maternal IgG in the tears of chicks and also to measure the levels of HI antibodies in the tears and serum after vaccination with "F" strain of Newcastle disease virus (NDV) and in the face of an outbreak of Newcastle disease. There was a 1.4 fold difference between the maternal IgG concentration in the serum and tears. The ratio of serum IgG to lachrymal IgG after maternal transfer was 4 to 5:1 on day 4 to 9 and decreased to 2.6:1 on day 12 post-hatch. The intra-ocular vaccination of chicks with "F" strain of NDV resulted in the highest titre of HI antibodies in the tears though there was no significant difference in the response of chicks vaccinated through intranasal, oral and intravenous routes. In the face of an ND outbreak, the level of HI antibodies in the tears during the acute phase was very high and persisted at the same level for 14 days.