Clinical and Pathologic Features of West Nile Virus Infection in Native North American Owls (Family Strigidae)

Abstract

Since the initial report of West Nile virus in the northeastern United States in 1999, the virus has spread rapidly westward and southward across the country. In the summer of 2002, several midwestern states reported increased cases of neurologic disease and mortality associated with West Nile virus infection in various native North American owl species. This report summarizes the clinical and pathologic findings for 13 captive and free-ranging owls. Affected species were all in the family Strigidae and included seven snowy owls (Nyctea scandiaca), four great-horned owls (Bubo virginianus), a barred owl (Strix varia), and a short-eared owl (Asio flammeus). Neurologic signs identified included head tilt, uncoordinated flight, paralysis, tremors, and seizures. Owls that died were screened for flaviviral proteins by immunohistochemical staining of formalin-fixed tissues, followed by specific polymerase chain reaction assay to confirm West Nile virus with fresh tissues when available. Microscopic lesions were widespread, involving brain, heart, liver, kidney, and spleen, and were typically nonsuppurative with infiltration by predominantly lymphocytes and plasma cells. Lesions in owls were much more severe than those previously reported in corvids such as crows, which are considered highly susceptible to infection and are routinely used as sentinel species for monitoring for the presence and spread of West Nile virus. This report is the first detailed description of the pathology of West Nile virus infection in Strigiformes and indicates that this bird family is susceptible to natural infection with West Nile virus.

Pathology and Virus Detection in Tissues of Nestling House Sparrows Naturally Infected With Buggy Creek Virus (Togaviridae)

“…The mild, nonsuppurative encephalitis found in nestlings with BCRV is similar to the brain pathology found in birds with other encephalitic avian viruses, such as EEEV in Chukars and Ring-necked Pheasants (Ranck et al, 1965;Williams et al, 2000), neurotropic velogenic Newcastle disease virus in Double-crested Cormorants (Phalacrocorax auritus; Meteyer et al, 1997), and West Nile virus in owls (Fitzgerald et al, 2003 …”

Natural and Experimental West Nile Virus Infection in Five Raptor Species

“…High death rates associated with WNV were observed in five species of Strigiformes of northern native breeding range in a captive population of owls in southern Ontario, Canada, though within this population, only 1 of 13 (8%) infected great horned owls died, while 0 of 8 infected barn owls died (Gancz et al, 2004). Considering anecdotal reports of recent die-offs in wild raptors and documented events involving captive raptors with acute neurologic signs testing positive for WNV (Fitzgerald et al, 2003;D'Agostino and Isaza, 2004), we expected to observe clinical signs in some of the experimentally infected raptors. We did observe clinical illness in raptors naturally infected with WNV that culminated in death.…”

“…Although WNV infections have been reported from 36 species of raptors in the United States through February 2005 (Table 1), estimates of morbidity and mortality are not available. Raptor species that were infected experimentally failed to develop overt disease (Komar et al, 2003), but several cases of WNV-induced disease in raptor species have been described (Garmendia et al, 2000;Steele et al, 2000;Ludwig et al, 2002;Fitzgerald et al, 2003;D'Agostino and Isaza, 2004;Gancz et al, 2004;Wü nschmann et al, 2004). More data are needed to understand the impact of WNV infection on raptor populations and the full spectrum of disease syndromes that may occur in these species.…”

West Nile Virus Detection in the Organs of Naturally Infected Blue Jays (Cyanocitta Cristata)

“…Gross hemorrhage of the brain, splenomegaly, meningoencephalitis, and myocarditis were the most prominent lesions noted in birds found dead at the beginning of the WNV epidemic (Steele et al, 2000). Subsequent studies noted similar lesions in experimentally infected blue jays, crows, chickens, and turkeys, as well as naturally infected owls (Senne et al, 2000;Swayne et al, 2000;Fitzgerald et al, 2003;Weingartl et al, 2004;Wü nschmann et al, 2004). No pathognomonic lesions for WNV have been described, however, and lesions between species are not consistent.…”