title: Imperfect Vaccination Can Enhance the Transmission of Highly Virulent Pathogens.
abstract: Could some vaccines drive the evolution of more virulent pathogens? Conventional wisdom is that natural selection will remove highly lethal pathogens if host death greatly reduces transmission. Vaccines that keep hosts alive but still allow transmission could thus allow very virulent strains to circulate in a population. Here we show experimentally that immunization of chickens against Marek's disease virus enhances the fitness of more virulent strains, making it possible for hyperpathogenic strains to transmit. Immunity elicited by direct vaccination or by maternal vaccination prolongs host survival but does not prevent infection, viral replication or transmission, thus extending the infectious periods of strains otherwise too lethal to persist. Our data show that anti-disease vaccines that do not prevent transmission can create conditions that promote the emergence of pathogen strains that cause more severe disease in unvaccinated hosts.
authors.affiliation: Center for Infectious Disease Dynamics, Departments of Biology and Entomology, The Pennsylvania State University, University Park, Pennsylvania, United States of America; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Read
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Baigent
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Claire
authors.initials: C
authors.lastname: Powers
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Lydia B
authors.initials: LB
authors.lastname: Kgosana
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Luke
authors.initials: L
authors.lastname: Blackwell
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Lorraine P
authors.initials: LP
authors.lastname: Smith
authors.affiliation: Center for Infectious Disease Dynamics, Departments of Biology and Entomology, The Pennsylvania State University, University Park, Pennsylvania, United States of America; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: David A
authors.initials: DA
authors.lastname: Kennedy
authors.affiliation: School of Environmental and Rural Science, The University of New England, Armidale, Australia.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Walkden-Brown
authors.affiliation: Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
authors.forename: Venugopal K
authors.initials: VK
authors.lastname: Nair
mesh_terms: D000818:Animals; D002645:Chickens; D025922:Mardivirus / Q000235:genetics / Q000472:pathogenicity*; D008380:Marek Disease / Q000276:immunology / Q000635:transmission*; D022501:Marek Disease Vaccines / Q000009:adverse effects*; D012641:Selection, Genetic; D017201:Virus Shedding
chemical_list: D022501:Marek Disease Vaccines