Abstract
We examined seroprevalence (presence of detectable antibodies in serum) for avian influenza viruses (AIV) among 4,485 birds, from 11 species of wild waterfowl in Alaska (1998–2010), sampled during breeding/molting periods. Seroprevalence varied among species (highest in eiders (Somateria and Polysticta species), and emperor geese (Chen canagica)), ages (adults higher than juveniles), across geographic locations (highest in the Arctic and Alaska Peninsula) and among years in tundra swans (Cygnus columbianus). All seroprevalence rates in excess of 60% were found in marine-dependent species. Seroprevalence was much higher than AIV infection based on rRT-PCR or virus isolation alone. Because pre-existing AIV antibodies can infer some protection against highly pathogenic AIV (HPAI H5N1), our results imply that some wild waterfowl in Alaska could be protected from lethal HPAIV infections. Seroprevalence should be considered in deciphering patterns of exposure, differential infection, and rates of AIV transmission. Our results suggest surveillance programs include species and populations with high AIV seroprevalences, in addition to those with high infection rates. Serologic testing, including examination of serotype-specific antibodies throughout the annual cycle, would help to better assess spatial and temporal patterns of AIV transmission and overall disease dynamics.
Highlights
The role of wild birds in the spread of highly pathogenic avian influenza virus (HPAIV) H5N1 has been widely debated [1], but waterfowl have consistently represented the primary reservoir of avian influenza viruses (AIV) across the globe [2]
Understanding the balance of these elements is an area of active research, but the primary concern still stands: if previous immunity results in lower HPAIV H5N1 pathogenicity, and surviving birds can migrate while infectious, they could play an important role in HPAIV H5N1 disease dynamics and infection rates
Shedding of low pathogenic avian influenza virus (LPAIV) in wild Alaska birds was found in only 0.06% of individuals sampled between 1998 and 2004 (n = 8,254 samples; [15]) and 1.7% during May 2006 and March 2007 (n = 16,797; [16]), using real-time reverse transcriptase polymerase chain reaction and virus isolation from cloacal swabs or fecal samples
Summary
The role of wild birds in the spread of highly pathogenic avian influenza virus (HPAIV) H5N1 has been widely debated [1], but waterfowl have consistently represented the primary reservoir of avian influenza viruses (AIV) across the globe [2]. Experimental inoculations with HPAIV H5N1 in waterfowl have shown that the susceptibility, development of clinical signs, and frequency of mortality varies among and within species [3,4] These results have been confirmed by relatively low mortality rates observed during some HPAIV H5N1 outbreaks and by isolation of the virus from surviving birds [5,6,7]. Understanding the balance of these elements is an area of active research, but the primary concern still stands: if previous immunity (i.e., pre-existing antibodies) results in lower HPAIV H5N1 pathogenicity, and surviving birds can migrate while infectious, they could play an important role in HPAIV H5N1 disease dynamics and infection rates
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