Effect of vaccination on transmission characteristics of highly virulent Newcastle disease virus in experimentally infected chickens
An experimental study was conducted to evaluate the effect of vaccines produced in Ethiopia from vaccine strains used worldwide on the transmission characteristics of velogenic Newcastle disease virus field strain after different vaccination schemes. Chickens were vaccinated with Hitchner
B1, La Sota or I-2 via the intraocular and intranasal routes. Vaccine and challenge viruses induced high antibody levels, both in inoculated and contact birds. Prime-boost vaccination protected birds against morbidity and mortality and significantly reduced the incidence of viral shedding
from chickens compared with single vaccinated and unvaccinated birds. Protection from disease and mortality was correlated with the presence of positive antibody titres (>4 log2) at day of challenge. Most of the unvaccinated and in-contact birds excreted the virus and showed
a high level of antibody titres, indicating the high infectivity of the challenge virus. The detection of the challenge virus in most of vaccinated birds demonstrated that the tested vaccination protocols cannot fully protect birds from viral infection, replication and shedding, and vaccinated–infected
birds can act as a source of infection for susceptible flocks. The high mortality observed in unvaccinated birds and their contacts confirmed the virulence of the challenge virus and indicated that this field virus strain can easily spread in an unvaccinated poultry population and cause major
outbreaks. Progressive vaccinations supported by biosecurity measures should therefore be implemented to control the disease and introduction of the virus to the poultry farms.
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Document Type: Research Article
Faculty of Veterinary Medicine, University of Gondar, Gondar, Ethiopia
Yabelo Livestock Development Agency, Oromia Bureau of Agriculture, Yabello, Ethiopia
Aklilu Lemma Institute of Pathobiology, Addis Ababa University, Addis Ababa, Ethiopia
National Animal Health Diagnostic and Investigation Center, Sebeta, Ethiopia
OIE/FAO Reference Laboratory for Avian Influenza and Newcastle Disease, Instituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Italy
Publication date: September 3, 2014
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