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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Endemic Poultry Viral Diseases Research » Research » Publications at this Location » Publication #376832
Research Project: Genetic and Biological Determinants of Avian Herpesviruses Pathogenicity, Transmission, and Evolution to Inform the Development of Effective Control Strategies

Location: Endemic Poultry Viral Diseases Research

Title: Pathogen transmission from vaccinated hosts can cause dose-dependent reduction in virulence

Author
item BAILEY, RICHARD - Roslin Institute
item Cheng, Hans
item CHASE-TOPPING, MARGO - Roslin Institute
item Mays, Jody
item ANACLETO, OSVALDO - Roslin Institute
item Dunn, John
item DOESCHL-WILSON, ANDREA - Roslin Institute

Submitted to: PLoS Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2020
Publication Date: 3/5/2020
Citation: Bailey, R.I., Cheng, H.H., Chase-Topping, M., Mays, J.K., Anacleto, O., Dunn, J.R., Doeschl-Wilson, A. 2020. Pathogen transmission from vaccinated hosts can cause dose-dependent reduction in virulence. PLoS Biology. 18(3):e3000619. https://doi.org/10.1371/journal.pbio.3000619.
DOI: https://doi.org/10.1371/journal.pbio.3000619

Interpretive Summary: Vaccines used for Marek's disease, as well as many other vaccines for livestock and humans are considered leaky, such that they prevent disease but do not prevent infection or onward transmission. One aspect that has not been clearly demonstrated is the downstream effect of vaccination on contact individuals. Here, we used transmission experiments involving Marek’s disease virus in chickens to show that vaccination with a leaky vaccine substantially reduces viral load in both vaccinated individuals and unvaccinated contact individuals they infect. Consequently, contact birds are less likely to develop disease symptoms or die, show less severe symptoms, and shed less infectious virus themselves, when infected by vaccinated birds. These results highlight that vaccination with a leaky vaccine can have positive consequences in controlling the spread and symptoms of disease.

Technical Abstract: Many livestock and human vaccines are leaky because they block symptoms but do not prevent infection or onward transmission. This leakiness is concerning because it increases vaccination coverage required to prevent disease spread and can promote evolution of increased pathogen virulence. Despite leakiness, vaccination may reduce pathogen load, affecting disease transmission dynamics. However, the impacts on post-transmission disease development and infectiousness in contact individuals are unknown. Here, we use transmission experiments involving Marek disease virus (MDV) in chickens to show that vaccination with a leaky vaccine substantially reduces viral load in both vaccinated individuals and unvaccinated contact individuals they infect. Consequently, contact birds are less likely to develop disease symptoms or die, show less severe symptoms, and shed less infectious virus themselves, when infected by vaccinated birds. These results highlight that even partial vaccination with a leaky vaccine can have unforeseen positive consequences in controlling the spread and symptoms of disease.