Low Pathogenic Influenza in Birds

Avian Influenza viruses (AIV) are commonly found in wild waterfowl, shorebirds and gulls around the world. These Avian Influenza viruses are divided into high pathogenic (HP) and low pathogenic (LP) avian influenza viruses. A HP infection will usually result in high numbers of diseased and dead birds, a LP infection is considered rather harmless to the birds themselves. They may however shed huge amounts of viruses with their droppings and can create epidemics in other species, such as chickens.
[Image: Arthur Grosset]
While these infections do not cause significant disease among wild birds, there is evidence of subclinical signs of low pathogenic (LP) AIV infection in free living waterfowl, such as lower body mass[1], delayed migration (leaving their wintering site more than a month after uninfected animals), travelling shorter distances, and fuelling and feeding at reduced rates[2].

This research clearly shows that even low pathogenic infections in migratory birds will eventually result in higher rates of mortality because these malnourished and weaker birds are more likely to fall victim to predatory birds or starvation. Which means that, while these birds do not look ill, they certainly are weakened by the Influenza A viruses.

[1] Latorre-Margalef et al: Effects of influenza A virus infection on migrating mallard ducks in Proceedings, Biological Sciences - 2009
[2] Van Gils et al: Hampered foraging and migratory performance in swans infected with low-pathogenic avian influenza A virus in PLoS One - 2007

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