Serological response and protection level evaluation in chickens exposed to grains coated with I2 Newcastle disease virus for effective oral vaccination of village chickens

Abstract

Background: Conventional Newcastle disease (ND) vaccination strategies in village chicken production settings is impractical due to shortage of cold-chain, unsuitability of vaccine administration routes and demanding trained personnel and hence affected its adoption. Results from earlier works elsewhere showed that the heat stable vaccines such as NDI2 are thought to be promising for village chickens. This study investigated the suitability and efficacy of Ethiopian cereal grains as carriers for the orally administrated NDI2 vaccine in chickens.

Results: Of the 15 treatment groups, drinking water, cracked maize and parboiled barley induced significantly higher HI antibody titer than the other carrier grains and naive control. The higher mean HI titer of chickens in drinking-water, cracked maize and parboiled barley group resulted in 100 % survival rate. In general, there was an inverse relationship between chicken mortality (%) and mean HI titer. Chickens with higher HI antibody titers had better survival rate to the challenge experiment. Booster vaccination at age of day 35 and 105 induced progressively higher HI antibodies titers in all treatment groups.

Conclusions: Vaccine coated parboiled grains could be a good carrier followed by cracked grains while untreated vaccine carrier grains had lower serological responses and protection levels. The current finding gives insights on suitable vaccine delivery system in villages with weak health and transportation infrastructure, unreliable electricity, and minimally trained health workers without catching chickens individually.

Keywords: Cereal grains; Chicken; Ethiopia; Newcastle disease; Vaccination.

Fig. 1

Study design of the experimental NDI2 vaccine trial in Bovans brown chickens. Vaccine carrier groups (experimental units) were listed from No. 1 -15 in this figure. Sera collection was performed across age in days (indicator, blue color) to get 1ml sera per chick at each sampling day from wing vein until day 119. However, for chickens of barely and cracked maize group the last sampling was made on day 126, not on day 119. Vaccination was given at a rate of 107 EID50 NDV I 2 per dose per chick three times (indicator, black color). The value of vaccination by each grain carrier was measured by monitoring antibody production post vaccination in the regularly collected sera and by survival rate of the chickens post artificial inoculation of a virulent local Alemaya strain ND virus at a rate of 0.5 × 106.5 EID50 per chick of all experimental units intramuscularly at breast muscle at day129 (indicator, red color)

Fig. 2

Geometric mean (log2²) ± SE of HI antibody titer of chicken vaccinated by coating on 13 different types of grains in comparison to vaccination via water (positive control) and negative control. Red arrows labeled with V1, V2 and V3 on top indicated the day of vaccination. Maternal antibody at day old was high but reduced at day 14. One time vaccination using different carrier grains induced HI titer differently. Second and third round vaccination (booster) upgraded the induction of HI titer significantly (p< 0.05) but at varying level depending on the types of grain used as vaccine carrier

Fig. 3

The inverse relationship between chicken mortality rate (%) vs. mean HI titre (left y-axis) and % of chicken with HI titre above cut-off value (right y-axis). Each bullet points represented each treatment group of the 15 treatments. Each bullet points represents each treatment group of the 15 treatments

Fig. 4

Kaplan-Meier survival analysis of chickens vaccinated by NDI2 via different grain carriers as assessed before and after ND virus challenge by virulent strain at age of day 129. Morbidity was started on day 3 and severe mortality prevailed up to 14 days post challenge during 30 days of follow up. Vaccination using any type of vaccine carrier grain had an impact better than the naïve for survival rate of the chickens. However, different vaccine carrier grains had different survival rates in the range of 35.7 - 100% whilst 20% in naïve. The survival rate was significantly different among the treatment groups (Log-rank = 77.3498, D.F. = 14, p < 0.0000). For example, oral vaccination using water, parboiled barley and cracked maize induced 100% survival until end of the experimental period i.e. week 21