A ProMED-mail post
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International Society for Infectious Diseases
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Date: 14 Apr 2009
Source: PLoS Computational Biology [edited]
<http://www.ploscompbiol.org/article/...l.pcbi.1000346>
The Role of Environmental Transmission in Recurrent Avian Influenza Epidemics
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Abstract
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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]
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