|Montiel, Enrique - Merial, Ltd|
|Cardenas Garcia, Stivalis - University Of Georgia|
|Dimitrov, Kiril - Consultant|
|Williams Coplin, Tina|
Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2017
Publication Date: 6/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5763050
Citation: Taylor, T.L., Miller, P.J., Olivier, T.L., Montiel, E., Cardenas Garcia, S., Dimitrov, K.M., Williams Coplin, T.D., Afonso, C.L. 2017. Repeated challenge with virulent Newcastle Disease Virus does not decrease the efficacy of vaccines. Avian Diseases. 61(2):245-249. doi:10.1637/11555-120816-ResNote.1.
Interpretive Summary: The virulent strains of Newcastle disease virus (NDV) often cause outbreaks in vaccinated chickens producing sickness and death; however, under experimental laboratory conditions with specific-pathogen-free chickens, vaccinated birds are usually fully protected against the same strains. The discrepancy in NDV vaccine performance between the laboratory and the field has led us to hypothesize that vaccine failure may be caused by the repeated exposure of well-vaccinated birds in the field to virulent strains of NDV that is lacking under laboratory conditions. Under the laboratory conditions we usually only challenge the birds with one dose of virulent virus. We investigated if daily, reoccurring, high-dose challenges of virulent NDV suppressed the immune system of well-vaccinated White Leghorns. We demonstrated that the repeated challenge does not affect the success of the NDV vaccines if the birds are properly vaccinated with two doses of vaccines and are given enough time to develop a sufficient antibody titer before being exposed to the virulent challenge virus.
Technical Abstract: In the field, well-vaccinated birds may be repeatedly exposed to challenges with virulent strains of Newcastle disease virus (vNDV), which may infect macrophages and cause damage to the immune system. In this study, we evaluated the hypothesis that daily challenges with high doses of vNDV may overwhelm the immune system of well-vaccinated birds leading to signs of clinical disease, with or without mortality. Day-old specific-pathogen-free (SPF) White Leghorns (n = 100) were vaccinated with a live NDV B1 vaccine (105.7 EID50/mL per bird, divided half intraocular [IO] and half intranasal [IN]), and two weeks later were inoculated with a second NDV vaccine; either a live LaSota NDV (n = 60) using the same route and a dose of 107.9 EID50/mL per bird, or an inactivated LaSota oil emulsion vaccine (n = 40), given subcutaneously. Both control groups were initially inoculated with Brain-heart infusion (BHI). Two weeks later, one control group (n = 10) received one BHI inoculation (IO/IN), a sham-live vaccine, and another control group (n = 10) received one oil emulsion with non-infected allantoic fluid, a sham-inactivated vaccine. Thirteen days after the second vaccination, all the NDV vaccinated birds (n = 100), including the control groups (n = 20), were challenged with 106.9 EID50/mL of chicken/USA(CA)/2002 (CA/02) vNDV, administered IO/IN. Half of the birds vaccinated with two live NDV vaccines (n = 30) and half of the birds vaccinated with a live and an inactivated NDV vaccine (n = 20) were challenged with the same dose (107.1 to 107.5 EID50/mL) of CA/02 each day, for nine additional days. All sham-vaccinated birds died by the fourth day post challenge. No morbidity or mortality was observed in any of the NDV-vaccinated birds, up to 14 days post-challenge. In summary, repeated high-dose challenges of vNDV was not sufficient to overcome vaccine immunity.