Experimental Infection of Cliff Swallows (Petrochelidon pyrrhonota) with Varying Doses of West Nile Virus

Abstract

Abstract. Cliff swallows ( Petrochelidon pyrrhonota ) were inoculated with differing doses of West Nile virus (WNV) to evaluate their potential role as reservoir hosts in nature. Swallows often nest in large colonies in habitats and months associated with high mosquito abundance and early WNV transmission in North America. Additionally, cliff swallow diet consists of insects, including mosquitoes, leading to an additional potential route of WNV infection. The average peak viremia titer among infected cliff swallows was 10 6.3 plaque-forming units (PFU)/mL serum and the reservoir competence index was 0.34. There was no correlation between dose and probability of becoming infected or viremia peak and duration. Oral shedding was detected from 2 to 14 days post-inoculation with an average peak titer of 10 4.4 PFU/swab. These results suggest that cliff swallows are competent reservoir hosts of WNV and therefore, they may play a role in early seasonal amplification and maintenance of WNV.

Surveillance Potential of Non-Native Hawaiian Birds for Detection of West Nile Virus

“…27,32,34,36 Also consistent with previous reports, peak viremias were lower in species not exhibiting severe clinical disease. 27,34,37,38 For most species tested, infection peaked on days 2-3, which has been reported by others, but for JASP infection peaked later, between 5 and 7 days (Figure 1). The proportion of JASP orally shedding WNV was also lower than the other species with mortality, suggesting that the disease process may have been delayed in JASP as compared with the other species.…”

“…However, the reverse was observed for SPDO in which the viremia for birds infected with the low challenge was significantly higher than those infected with the 10 5 WNV challenge. Other studies have also used more than a single WNV challenge level and have reported contrasting results: Oesterle and others 34 used four challenge levels of WNV that varied over 3 log units and reported no differences between groups of cliff swallows (Petrochelidon pyrrhonota) in viremia or oral shedding of virus. Similarly, clear differences in survival and peak viremia were not reported in HOFI or peak viremia in mourning doves challenged with WNV doses ranging from 10 < 0.3 to 10 4.3 .…”

Experimental Exposure of Swallow Bugs (Hemiptera: Cimicidae) to West Nile Virus

“…Cliff swallows nest synchronously in large colonies (Brown and Brown 1995) often over water, where some mosquito species (e.g., Culex tarsalis) are relatively abundant (Brown and Sethi 2002). These birds are most likely reservoir competent for WNV in nature (average peak viremia of experimentally inoculated swallow was 10 6.3 PFU/ml serum; Oesterle et al 2009), and in 2003, 22% of cliff swallow nestlings tested oral swab positive for WNV RNA (our unpublished data). In addition, there was a high rate of natural exposure (20 Ð 40%) among freeranging adult cliff swallows in northern Colorado from 2004 to 2007 (our unpublished data).…”

“…The geographic distribution of cliff swallows and swallow bugs overlaps with the expanding endemic range of West Nile virus (WNV; family Flaviviridae, genus Flavivirus) in North America. Additionally, cliff swallows develop West Nile viremia titers sufÞcient to infect mosquitoes (Oesterle et al 2009) and have a high rate of exposure to the virus in some geographic areas (our unpublished data).…”

“…Given the parasitic nature of swallow bugs and WNV reservoir competence of cliff swallows (Oesterle et al 2009), swallow bugs most likely ingest infectious WNV blood meals when feeding on viremic cliff swallows. However, limited, yet conßicting information exists regarding the ability of swallow bugs to become infected with and transmit WNV; Sixl et al (1989) demonstrated WNV seroconversion in mice in the presence of swallow bugs, whereas Oesterle et al (2010) failed to document WNV transmission from swallow bugs to cliff swallow nestlings in an experimental trial.…”