The Role of Environmental Transmission in Recurrent Avian Influenza Epidemics ----------------------------------------------------------------------------- Abstract -------- Avian influenza virus (AIV) persists in North American wild waterfowl, exhibiting major outbreaks every 2-4 years. Attempts to explain the patterns of periodicity and persistence using simple direct transmission models are unsuccessful. Motivated by empirical evidence, we examine the contribution of an overlooked AIV transmission mode: environmental transmission. It is known that infectious birds shed large concentrations of virions in the environment, where virions may persist for a long time. We thus propose that, in addition to direct fecal/oral transmission, birds may become infected by ingesting virions that have long persisted in the environment. We design a new host-pathogen model that combines within-season transmission dynamics, between-season migration and reproduction, and environmental variation. Analysis of the model yields 3 major results. 1st, environmental transmission provides a persistence mechanism within small communities where epidemics cannot be sustained by direct transmission only (i.e., communities smaller than the critical community size). 2nd, environmental transmission offers a parsimonious explanation of the 2-4 year periodicity of avian influenza epidemics. 3rd, very low levels of environmental transmission (i.e., few cases per year) are sufficient for avian influenza to persist in populations where it would otherwise vanish. Citation: Breban R, Drake JM, Stallknecht DE, Rohani P (2009) The Role of Environmental Transmission in Recurrent Avian Influenza Epidemics. PLoS Comput Biol 5(4): e1000346. doi:10.1371/journal.pcbi.1000346 -- Communicated by: ProMEDmail Rapporteur Mary Marshall [It is nice to see a past LSU graduate student, David Stallknecht, returning to the topic of his dissertation (1989) which was on the shedding of LPAI wild viruses by migrating ducks. After presenting an analysis of the very large number of isolates he had obtained by cloacal swabbing of ducks shot by hunters, he was asked how long did the virus survive in the fresh and brackish waters where these birds fed and slept. To cut a long story short, at the right water salinity and temperature they were immortal. The moral of this story is beware of simple questions posed by your professors. The above paper is worth reading in its entirety. - Mod.MHJ] http://apex.oracle.com/pls/otn/f?p=2400:1001:791898450947259::NO::F2400_P1001_BACK_PAGE,F2400_P1001_PUB_MAIL_ID:1010,77036
