Impact of Escherichia coli (E. coli) Isolates and Newcastle Disease Virus Cochallenge on Immune Response to LaSota Vaccination in Broilers

This study assessed the effects of co-infection of Escherichia coli (E. coli) with Newcastle disease virus (NDV) on the immune response of broiler chickens to LaSota vaccination It is a pathogen challenge and immune response study, whereby two experiments were conducted using 220 day-old broiler chicks (DOCs) to evaluate (i) how two different E. coli isolates challenge prior to LaSota vaccination would affect immune response to LaSota vaccination, and (ii) how a co-infection of the two E. coli isolates and NDV would impact on immune response after LaSota vaccination in broilers. In experiment 1, eighty DOCs were randomly assigned to four groups (A, B, C, and D) of 20 birds each, while 60 DOCs were assigned to three control groups (I, J, and K). Birds in all groups, except group J, were vaccinated with Hitchner B1 and LaSota on days 1 and 14 post-hatch (PH). On day 18, groups A and C along with groups B and D, each were challenged with 0.05ml of nutrient broth containing 1× 10^8 colony-forming units (cfu)/ml of E. coli strains code-named (Eco-1) and Eco-2 per os respectively, on day 3 prior to LaSota vaccination, while the control groups I, J and K received PBS. On day 35PH, groups A and B along with I and J (standard and negative controls) received ocular and intranasal challenge with 0.1 ml of 10^6.4 ED of NDV (kudu 113, 14 days post LaSota vaccination, 50 while the positive control, K, did not receive any treatment. In experiment 2, eighty DOCs were assigned to four groups (E, F, G, and H) of 20 birds each, with groups I, J, and K serving as controls. On day 35 PH, birds in groups E and G, along with the standard and negative controls, I and J received ocular and intranasal challenge with 0.1 ml of 10^6.4 ED of NDV (kudu 11), 14 days post LaSota 50 vaccination, and F and H were challenged with 0.05ml of nutrient broth containing 1× 10^8 colony forming units (cfu)/ml of E. coli strains code-named Eco-1 and Eco-2 per os, while the positive control, group K, received PBS. On day 38 PH, groups E and H were challenged with 0.05ml of nutrient broth containing 1× 10^8 colony-forming units (cfu)/ml of E. coli strains Eco-1 and Eco-2 per os, while the F and H received ocular and intranasal challenge with 0.1 ml of 10^6.4 ED of NDV (kudu 113, 17 days 50 post LaSota vaccination, while the control groups received PBS only. Data collect were analyzed using one-way ANOVA. Escherichia coli challenge prior to LaSota vaccination and E. coli and NDV cochallenge caused significant reduction (P<0.05) in antibody responses on days 7 and 28 respectively. The study concludes that E. coli infections and a co-challenge of both E. coli and NDV challenge reduced the immune response to LaSota vaccination in broiler chickens. To optimize vaccine efficacy, it is recommended that chickens be confirmed free of E. coli infection and free of NDV infection before LaSota vaccination