Wellfleet Bay virus epidemiology in the common eider
Ballard, Jennifer Renee
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Wellfleet Bay virus (WFBV) is an orthomyxovirus associated with recurrent mortality in common eiders (Somateria mollissima) in Massachusetts. Experimentally, WFBV was transmitted by oral, tracheal, and intradermal routes. Significant clinical disease occurred in one bird of 30, though lethargy and stunted growth were present in most infected individuals. Antibodies were detected by 6 days post inoculation (DPI), and virus was isolated from multiple tissues until 8 DPI. Intermittant viral shedding was detected until 8 DPI, but direct transmission to sham-inoculated birds cohoused with infected individuals did not occur. A longitudinal seroprevalence study was conducted in common eiders from six locations, two representing the northern subspecies (S. m. borealis) and five from the American subspecies (S. m. dresseri). Antibodies were not detected in the northern subspecies. In the American subspecies, the Massachusetts population had a higher seroprevalence than all other locations, and thus, Massachusetts appears to be an epicenter of WFBV exposure. Seventy-nine common eider carcasses were submitted for postmortem examination. Twenty-four birds were WFBV positive, 26 were WFBV suspects, 25 were negative, and 4 had antibodies indicating previous exposure without evidence of active infection. Positive cases were submitted in the spring and fall. Grossly apparent foci of pallor on the liver, splenomegaly, and hepatocellular necrosis were statistically associated with WFBV detection. A combination of histologic examination; virus isolation; nested, reverse-transcription polymerase chain reaction; and serology was found to be helpful for diagnosing WFBV. Immunohistochemical staining also was useful for characterizing lesions. A seroprevalence survey was conducted in seabirds sampled in Massachusetts and New Jersey. Antibodies were detected in four species: herring gull (Larus argentatus), ring-billed gull (L. delawarensis), black scoter (Melanitta nigra), and white-winged scoter (M. fusca). Three of these are winter residents, and antibody-positive birds were detected at inland and coastal locations. This investigation has helped characterize the epidemiology of WFBV. Based on these findings, the likelihood of adverse, population-level effects due to WFBV in common eiders appears to be small, and any such effects should be limited to the Massachusetts population. However, additional research is needed to better understand this virus and its epidemiology.