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

Abstract

ABSTRACT:Alphaviruses (Togaviridae) infect wild birds, but clinical illness and death attributable to virus in naturally infected birds is rarely reported, particularly for small passerine species or nestlings. Buggy Creek virus is a unique alphavirus in the Western equine encephalomyelitis virus (WEEV) complex that is vectored by the cimicid swallow bug (Oeciacus vicarius), an ectoparasite of the colonially nesting Cliff Swallow (Petrochelidon pyrrhonota) and the introduced House Sparrow (Passer domesticus). While sampling birds for Buggy Creek virus (BCRV) during the summers of 2007 and 2008, we discovered large numbers of clinically ill or dead House Sparrow nestlings. Ill nestlings exhibited ataxia, torticollis, paresis, and lethargy. Histologic examination revealed that encephalitis was the most common finding, followed by myositis, myocarditis, and hepatic changes, but pathology was highly variable. We isolated BCRV from brain tissue in most of the ill or dead nestlings, and from blood, liver, kidney, spleen, lung, feather pulp, and skin in some birds. To our knowledge, this is the first report of clinical illness, gross pathology, and histopathology for a WEEV-complex alphavirus in a field-collected passerine species.

Seasonal Variation and Age-Related Correlates of Buggy Creek Virus (Togaviridae) Infection in Nestling House Sparrows

“…The highest virus prevalence among the youngest nestlings also confirms work suggesting limited transfer of maternal antibodies to arboviruses in House Sparrows (Holden et al, 1973a;Nemeth et al, 2008). Our results indicate that most of the mortality and pathology attributable to BCRV (O'Brien et al, 2010a) occurs among House Sparrow nestlings 10 days or younger, perhaps because virus replicates to such a high degree in nestlings of those ages.…”

“…In contrast, for western equine encephalomyelitis virus (WEEV), Holden et al (1973b) found infection prevalence highest in 9-12-day-old nestling House Sparrows, which in this species would be birds approaching fledging (Anderson, 2006;Lowther and Cink, 2006). This result might be expected for a virus such as WEEV that is transmitted by a mosquito, as some studies show a mosquito feeding preference for older nestlings Griffing et al, 2007;O'Brien et al, 2010b). The decline in BCRV prevalence with age, even when using relatively sensitive RT-PCR to detect viral RNA, may reflect 1) decreasing rates of biting by swallow bugs as nestling House Sparrows become feathered and start to preen, a pattern seen in Cliff Swallows (Brown and Brown, 1995;C.…”

“…Viral RNA was extracted from bird sera by adding 25 ml of thawed serum in BA-1 diluent to 100 ml of a guanidine thiocyanate-based lysis buffer (O'Brien et al, 2008). After the addition of 400 ml of 100% ethanol, RNA was extracted using the QIAmp Viral RNA Mini Kit (Qiagen, Valencia, California, USA), following the manufacturer's protocol .…”

“…Nestlings offer several advantages for studying natural patterns of arbovirus infection and thus the potential for transmission: 1) large numbers, especially of colonially nesting species (Buescher et al, 1959;Scott et al, 1984;O'Brien et al, 2011), can be located easily and predictably; 2) immunologically naïve nestlings are readily susceptible to infection even in areas where an arbovirus is enzootic and many of the adults have antibodies to the virus (Holden et al, 1973a); 3) nestlings, especially younger ones, may be more likely than adult birds to be fed on by insect vectors because the nestlings have not developed defensive behaviors to thwart biting by arthropods (Blackmore and Dow, 1958;Scott et al, 1990); and 4) nestling birds may not have as welldeveloped immune systems as adults (Apanius, 1998;Klasing and Leschinsky, 1999;Palacios et al, 2009) and therefore may exhibit longer-lasting or higher-titer viremias, facilitating detection and increased virus transmission to uninfected arthropod vectors.…”

“…Buggy Creek virus (BCRV; Togaviridae; Alphavirus) and the similar Fort Morgan virus (FMV) commonly infect nestling House Sparrows and can cause serious pathology in nestlings (Hayes et al, 1977;Scott et al, 1984;O'Brien et al, 2010a). The principal vector for BCRV is the swallow bug (Hemiptera: Cimicidae: Oeciacus vicarius) that transmits the virus to House Sparrows when blood feeding.…”