Evaluation of Potency and Efficacy of Commercial Brands of Newcastle Disease Vaccines in Nigeria

Aims: To evaluate the potency and efficacy of four commercially available brands of Newcastle disease (ND) vaccines in southwest Nigeria.

Study Design: Cross sectional survey of commercial ND (Hitchner and LaSota) for in-vitro and in-vivo analysis.

Place and Duration of Study: Vaccines were obtained from manufacturers’ representatives in southwest Nigeria while chicks were obtained from commercial hatchery, reared at the Teaching and Research Farm and analysis was carried out at Department of Veterinary Microbiology in University of Ibadan.

Methodology: Isa Brown cockerel chicks divided into five groups (A-E) comprising 60 birds each were used. Chicks in groups A-D were vaccinated primarily with four different brands (ND-Sevac®; ND-Jovac®, ND-Biovac® and ND-Fort Dodge®) of Hitchner B1 (HB1) vaccine at one-day-old (Day 1) and later with four corresponding brands of LaSota (booster) vaccine at day 21. Chicks in the fifth group which served as control received no vaccine and were used to assess the rate of maternal antibody decay. Sera were collected on days 1, 9, 16, 32, and 39 of age and the chickens were challenged with Kudu strain of ND virus (NDV) on day 33. Haemagglutination (HA) and haemagglutination inhibition (HI) tests were used to determine NDV titre and antibody levels in the vaccines and sera respectively.

Results: NDV maternal antibody level was highest (64±18.2) on day 1 and persisted to a minimum protective level (8±5.7) on day 16 before decaying to non-protective levels by day 32. All the four vaccine brands were potent with Biovac® (Vaccine C) yielding the highest NDV titres [HB1 (1536±724.1), LaSota (512±0.0)]. Also, following the administration of primary and booster (secondary) vaccinations, all the vaccines elicited protective immunity with the booster doses producing higher immune response in all the groups. However, chicks that received ND-Jovac® and ND-Biovac® were best able to overcome the effects of experimental challenge as they gave the lowest mortality rate of 33.3% with mean NDV antibody titres of 9 log2 (512±313.5) recorded seven days post-challenge. Chicks that received Sevac® and Fort Dodge®(Vaccines A and D) gave mortality rates of 55.0% and 50.0%, respectively with mean antibody titres of 7 log2 (154±57.3) post-challenge.

Conclusion: All the tested vaccines were potent and elicited protective antibody. However, ND outbreaks in vaccinated flocks in southwest Nigeria may not necessary be due to lack of potency of the vaccines but other factors such as virus strain (s) used in the production of the vaccines, vaccine storage and handling and biosecurity among others may play a role. Therefore, there is a need for routine isolation and characterization of the enzootic strain(s) of NDV in Nigeria and production of ND vaccines with such circulating strain(s) to offer optimal protection against the disease.