The Effect of Maternal Antibodies on Clinical Response to Infection with Epizootic Hemorrhagic Disease Virus in White-Tailed Deer (Odocoileus virginianus) Fawns.

We investigated whether naturally acquired maternal antibodies to epizootic hemorrhagic disease virus serotype 2 (EHDV-2) would protect white-tailed deer (Odocoileus virginianus) fawns against infection and clinical disease following an EHDV-2 challenge. We compared viremia and clinical response in 27-47-d-old, experimentally infected fawns with and without maternally derived antibodies to EHDV-2. Mild to moderate clinical signs were observed in four seronegative (maternal antibody-negative) fawns, which were viremic from 3 to 14 d postinoculation. Individual peak blood virus titers for seronegative fawns ranged from 104.3 to 106.3 median tissue culture infective doses (TCID50)/mL. In contrast, clinical signs were not observed in seropositive (maternal antibody-positive) fawns and a transient low-level viremia (≤102.4 TCID50/mL) occurred in two of six fawns. Our results indicated that the presence of maternally derived EHDV-2 antibodies in fawns prevents or greatly reduces clinical disease and the level and duration of EHDV-2 viremia.

SUSCEPTIBILITY OF LAUGHING GULLS (LEUCOPHAEUS ATRICILLA) AND MALLARDS (ANAS PLATYRHYNCHOS) TO RUDDY TURNSTONE (ARENARIA INTERPRES MORINELLA) ORIGIN TYPE A INFLUENZA VIRUSES.

Delaware Bay, US is the only documented location where influenza A virus (IAV) is consistently detected in a shorebird species, the Ruddy Turnstone (RUTU; Arenaria interpres morinella). Although IAV in shorebirds has been well studied at this site for decades, the importance of other species in the avian community as potential sources for the IAVs that infect RUTUs each spring remains unclear. We determined the susceptibility of Mallards (Anas platyrhynchos) and Laughing Gulls (Leucophaeus atricilla), to IAVs isolated from RUTUs in order to gain insight into the potential host range of these viruses. Captive-reared gulls were challenged with RUTU-origin H6N1, H10N7, H11N9, H12N4, and H13N6 IAV, as well as Mallard-origin H6N1 and H11N9. We challenged captive-reared Mallards with the same viruses, except for H13N6. At a biologically plausible challenge dose (104 50% embryo infective doses/0.1 mL), one of five gulls challenged with both H6N1 IAVs shed virus. The remaining gulls were resistant to infection with all viruses. In contrast, all Mallards were infected and shed virus. The H12N4 Mallard challenge group was an exception with no birds infected. These results indicated that Mallards are permissive to infection with viruses originating from a shorebird host and that interspecies transmission could occur. In contrast, host adaptation of IAVs to RUTUs may compromise their ability to be transmitted back to gulls.

Prevalence of Influenza A Viruses in Ducks Sampled in Northwestern Minnesota and Evidence for Predominance of H3N8 and H4N6 Subtypes in Mallards, 2007-2016.

Long-term comprehensive studies of avian influenza virus subtypes in ducks not only contribute to understanding variations and patterns of subtype diversity, but also can be important in defining seasonal and temporal risks associated with transmission of potentially highly pathogenic H5 and H7 subtypes to domestic poultry. We analyzed influenza A virus (IAV) surveillance data from dabbling ducks collected at an important migratory stopover site in northwestern Minnesota from 2007-2016 and identified prevalence and subtype diversity throughout this period. In total, 13,228 cloacal and oropharyngeal swabs from waterfowl were tested over the 10-year period; the majority of these waterfowl were mallards sampled from late August through late September (n = 9133). From these, 1768 IAVs were isolated (19.4% mean annual prevalence, ranging from 11.0% in 2007 to 32.8% in 2011), and both hemagglutinin (HA) and neuraminidase were identified for 1588. Although subtype diversity and prevalence varied by year, H3 and H4 HA subtypes predominated in all years, accounting for 65.7% of the observed HA subtype diversity. The mechanisms driving this consistent pattern of subtype diversity and predominance are not understood but may include factors at the host, population, and virus level.

Prevalencia de virus de influenza A en patos muestreados en el noroeste de Minnesota y evidencia de predominio de los subtipos H3N8 y H4N6 en patos de collar entre los años 2007 al 2016. Los estudios exhaustivos a largo plazo de subtipos de virus de la influenza aviar en patos no solo contribuyen a comprender las variaciones y patrones de diversidad de subtipos, sino que también pueden ser importantes para definir los riesgos estacionales y temporales asociados con la transmisión de subtipos H5 y H7 potencialmente altamente patógenos para la avicultura comercial. Analizamos los datos de vigilancia del virus de la influenza A de patos chapoteadores recolectados en un sitio de descanso migratorio importante en el noroeste de Minnesota desde el año 2007 al 2016 y se identificó la prevalencia y la diversidad de subtipos a lo largo de este período. En total, 13,228 hisopos cloacales y orofaríngeos de aves acuáticas se analizaron durante el período de diez años; la mayoría de estas aves acuáticas eran patos silvestres muestreados desde finales de agosto hasta finales de septiembre (n = 9133). De estas muestras, 1768 virus de la influenza aviar fueron aislados (prevalencia anual media de 19.4%, y con un rango de 11.0% en el 2007 a 32.8% en 2011), y tanto la hemaglutinina (HA) como la neuraminidasa fueron identificadas para 1588 virus. Aunque la diversidad de subtipos y la prevalencia variaron por año, los subtipos de hemaglutinina H3 y H4 predominaron en todos los años, representando el 65.7% de la diversidad de subtipos observada para la hemaglutinina. Los mecanismos que impulsan este patrón consistente de diversidad de subtipos y predominio no se comprenden, pero pueden incluir factores a nivel del hospedador, de la población y del virus. Abbreviations: CL = cloacal; HA = hemagglutinin; IAV = influenza A virus; NA = neuraminidase; NWR = National Wildlife Refuge; RRT-PCR = real-time reverse transcriptase PCR; WMA = Wildlife Management Area.