Outbreaks of West Nile virus in captive waterfowl in Ontario, Canada

Abstract

The detrimental effects of West Nile virus (WNV) have been well characterized in several taxonomic groups of North American birds, such as corvids and raptors. Relatively less is known about the virus' effects in waterfowl species, many of which are abundant in North America and occupy habitats, for example wetlands and marshes, likely to harbour dense mosquito populations. In two successive years, outbreaks of WNV-associated disease were observed in waterfowl at a rehabilitation centre. In the present report, clinical and pathological findings are provided for seven mallards (Anas platyrhynchos) and one Canada goose (Branta canadensis) that developed acute disease and either died or were killed humanely. The most severe and consistent microscopic lesion in mallards was myocardial degeneration and coagulative necrosis consistent with acute heart failure. The Canada goose had necrotizing myocarditis. Other lesions included pulmonary perivascular oedema, lymphoplasmacytic hepatitis, and splenic and bursal lymphoid depletion. WNV infection was confirmed using reverse transcriptase-polymerase chain reaction and immunohistochemical staining. Myofibres within all cardiac muscle layers had positive immunohistochemical staining, as did blood vessel walls in the heart and spleen. These results suggest that juvenile mallards are highly susceptible to fatal WNV-associated cardiac failure, and confirm that adult Canada geese are susceptible to fatal WNV-associated disease. The synchronous timing of clinical disease and death in these waterfowl are consistent with WNV mosquito-borne infections within a WNV transmission focus during the summer (July and August) of 2012 and 2013.

West Nile Virus Infection in Ruffed Grouse (Bonasa umbellus): Experimental Infection and Protective Effects of Vaccination

“…This pattern was also observed with natural WNV infections in juvenile birds, including domestic geese ( Anser anser domesticus ), Rouen ducks, and mallards ( Anas platyrhynchos ). 1,7,32 Experimentally infected American crows also had multisystemic WNV disease, including acute myocardial degeneration with minimal lesions in the central nervous system. 24 Brain lesions were more severe and widely distributed in naive, inoculated, subclinically infected ruffed grouse on 14 DPI vs those euthanized at earlier time points (7–8 DPI) due to morbidity, suggesting that encephalitis may be a more chronic manifestation of WNV infection in ruffed grouse.…”

“…13,20 For example, juvenile birds (as used in the present study) may be more susceptible to clinical disease and higher viremia titers associated with WNV infection. 1,7,23 Although fully mature ruffed grouse may have lower susceptibility to WNV-associated morbidity and mortality, the juvenile life stage corresponds to the peak months of WNV transmission in much of the eastern United States. In addition, population studies in the Appalachian region identify productivity (ie, chick survival and fecundity) as the most influential demographic factor on population growth; 9 thus, WNV and other potential challenges to juvenile survival and productivity should be recognized and considered in population management strategies.…”

Comparative Pathology of West Nile Virus in Humans and Non-Human Animals

“…Lesions in naturally infected birds have been previously reviewed in detail by Gamino and Höfle [95]. This chart has been modified to include the most recent literature as well as pathologic findings in birds experimentally infected with WNV (Table 1) [106][107][108][109][110][111][112][113][114][115][116]. Ocular lesions are seen in raptors (red-tailed hawks, Cooper s hawks, bald eagles, golden eagles, goshawks) and owls (great horned owls, barred owls) and range from lymphoplasmacytic pectenitis and chorioretinal inflammation and scarring to generalized endophthalmitis [110,[116][117][118][119].…”

Pathogenicity of West Nile Virus Lineage 1 to German Poultry

“…The role of WNV for domestic poultry, such as chickens, ducks, and geese, is also not fully understood. WNV outbreaks amongst captive waterfowl have been described in Israel [ 28 ] and North America [ 29 , 30 , 31 , 32 ], with high seropositivity in domestic geese ( Anser anser domesticus ) and Canada geese ( Branta canadensis ) in the outbreak in 1999 [ 33 ]. However, it is unclear whether domestic ducks ( Anas platyrhynchos domesticus ) and geese can produce viremia levels that are high enough to infect mosquitoes.…”