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J. Virol., Aug 1997, 6128-6135, Vol 71, No. 8
GB Sharp, Y Kawaoka, DJ Jones, WJ Bean, SP Pryor, V Hinshaw and RG Webster
Coinfection of wild birds by influenza A viruses is thought to be an
important mechanism for the diversification of viral phenotypes by
generation of reassortants. However, it is not known whether coinfection is
a random event or follows discernible patterns with biological
significance. In the present study, conducted with viruses collected
throughout 15 years from a wild-duck population in Alberta, Canada, we
identified three discrete distributions of coinfections. In about one-third
of the events, which involved subtypes of viruses that appear to be
maintained in this duck reservoir, coinfection occurred at rates either
close to or significantly lower than one would predict from rates of
single-virus infection. Apparently, the better adapted an influenza A virus
is to an avian population, the greater is its ability to prevent
coinfections. Conversely, poorly adapted, nonmaintained viruses were
significantly overrepresented as coinfectants. Rarely encountered subtypes
appear to represent viruses whose chances of successfully infiltrating
avian reservoirs are increased by coinfection. Mallards (Anas
platyrhynchos) and pintails (A. acuta) were significantly more likely to be
infected by a single influenza A virus than were the other species sampled,
but no species was significantly more likely to be coinfected. These
observations provide the first evidence of nonrandom coinfection of wild
birds by influenza A viruses, suggesting that reassortment of these viruses
in a natural population does not occur randomly. These results suggest that
even though infections may occur in a species, all subtypes are not
maintained by all avian species. They also suggest that specific influenza
A virus subtypes are differentially adapted to different avian hosts and
that the fact that a particular subtype is isolated from a particular avian
species does not mean that the virus is maintained by that species.
Copyright © 1997, American Society for Microbiology
Coinfection of wild ducks by influenza A viruses: distribution patterns and biological significance
Department of Hematology/Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101, USA.
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