Status of Humoral Immunity against Newcastle Disease Virus in Commercial Poultry Farms in Ethiopia

Vaccination is the method of choice for control of Newcastle disease in developing countries. A cross-sectional survey was conducted in six commercial poultry farms to assess their immune status against Newcastle disease in Ethiopia. In addition, follow up study was carried out in 210-day old chickens belonging to Rose, Lohmann brown and Sasso breeds to compare their response to HB1 and La Sota vaccines. Blood samples were collected from 75-day-old chickens (25 chickens from each breed) to assess the level of maternally derived antibody titer before vaccine was given. Blood samples were collected fortnightly after the first and booster vaccinations. Haemagglutination inhibition assay was used to assess the level of antibody in serum samples collected. Only two of the six farms investigated maintained good flock immunity (≥85% level of protection) with low percentage geometric coefficient of variation (4.9%-14.4%). The maternally derived antibody titre was significantly higher in Sasso breeds (134.4±1.14) followed by Ross (92.2±1.14) and Lohmann brown (68.6±1.35). The level of anti-Newcastle disease virus antibody after the first vaccination was 24.6±1.2 in Lohmann brown, 29.3±2 in Sasso and 34.5±1.1 in Ross breeds. The antibody titer was 30.9±1.3 in Lohmann brown, 29.4±1.2 in Sasso and 33.1±1.2 in Ross breeds after booster vaccination. In conclusion the maternally derived antibody level was sufficient to protect chickens from infection during early age but the flock immunity and post vaccination antibody level was low suggesting the investigation of alternative vaccination schedules for better prevention and control of Newcastle disease than the current one (day 0, day 7 and day 21).