Read Andrew F, Baigent Susan J, Powers Claire, Kgosana Lydia B, Blackwell Luke, Smith Lorraine P, Kennedy David A, Walkden-Brown Stephen W, Nair Venugopal K
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.
Avian Oncogenic Virus Group, The Pirbright Institute, Compton, Newbury, Berkshire, United Kingdom.
PLoS Biol. 2015 Jul 27;13(7):e1002198. doi: 10.1371/journal.pbio.1002198. eCollection 2015 Jul.
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.
某些疫苗会促使更具毒性的病原体进化吗？传统观点认为，如果宿主死亡会大幅减少传播，自然选择就会淘汰高致死性病原体。因此，能使宿主存活但仍允许传播的疫苗可能会让极具毒性的毒株在种群中传播。在此，我们通过实验表明，给鸡接种针对马立克氏病病毒的疫苗会提高更具毒性毒株的适应性，使高致病性毒株得以传播。直接接种疫苗或母体接种疫苗引发的免疫会延长宿主存活时间，但无法预防感染、病毒复制或传播，从而延长了那些原本因过于致命而无法持续存在的毒株的传染期。我们的数据表明，不阻止传播的抗病疫苗可能会创造条件，促使在未接种疫苗的宿主中引发更严重疾病的病原体毒株出现。
