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

Abstract

ABSTRACT:Wild birds are rarely found with active arbovirus infections, and relatively little is known about the patterns of viremia they exhibit under field conditions or how infection varies with date, bird age, or other factors that potentially affect transmission dynamics. Buggy Creek virus (BCRV; Togaviridae, Alphavirus) is an arbovirus associated with colonially nesting Cliff Swallows (Petrochelidon pyrrhonota) and transmitted by its vector, the hematophagous swallow bug (Oeciacus vicarius), an ectoparasite of the Cliff Swallow. Introduced House Sparrows (Passer domesticus) that have occupied swallow nests at colony sites in peridomestic settings are also exposed to BCRV when fed upon by swallow bugs. We used data from 882 nestling House Sparrows in western Nebraska from 2006 to 2008 to examine seasonal variation and age-related correlates of virus infection in the field. Over 17% of nestling House Sparrows had active infections. Prevalence was higher in 2007 than in 2008 when birds from all colony sites were analyzed, but there was no significant difference between years for sites sampled in both seasons. Buggy Creek virus prevalence was similar in early and late summer, with a peak in midsummer, coinciding with the greatest swallow bug abundance. Nestlings 10 days of age and younger were most commonly infected, and the likelihood of BCRV infection declined for older nestlings. Average viremia titers also declined with age (but did not vary with date) and were high enough at all nestling ages to likely infect blood-feeding arthropods (swallow bugs). Length of viremia for nestlings in the field was $4 days, in agreement with an earlier study of BCRV. Nestling birds offer many advantages for field studies of arbovirus amplification and transmission.

Arbovirus infection is a major determinant of fitness in House Sparrows (Passer domesticus) that invade Cliff Swallow (Petrochelidon pyrrhonota) colonies

“…An age effect may reflect development of a more effective immune system as an individual becomes older (Apanius 1998, Klasing and Lescbinsky 1999), given tbat virus titer levels and overall prevalence declined in older nestlings and adults Brown 2012). Not unexpectedly, brood size also affected EIC, 4, Predicted probability of a House Sparrow nest being successful (>1 nestling in the nest at 12 days or beyond) with distance from the nearest active Cliff Swallow nest (NNC) at Cliff Swallow colony sites in southwestern Nebraska in 2007, In some cases, the nearest Cliff Swallow nest was at a different colony site, and the dotted vertical line represents the break between within-colony distances and between-colony distances.…”

“…Nestlings do not die immediately and often maintain viremias sufficiently high to infect bloodfeeding bugs for several days (O'Brien and Brown 2012), which suggests that a viremic nestling can potentially transmit virus to large numbers of Swallow Bugs. The frequent renesting of House Sparrows at the same site, even when their previous nesting attempts failed as a result of BCRV, means that they continually produce susceptible hosts (i.e., nestlings) for most of the summer.…”

“…Because of the virus's ecological specialization to Swallow Bug vectors and Cliff Swallow nesting colonies. House Sparrows have encountered this pathogen only since they began using old Cliff Swallow nests for breeding, and in our study area this has been within the past 60 years as artificial nesting sites (bridges, culverts) were constructed near towns where House Sparrows occur , Brown et al 2012.…”

“…Nestling birds offer many advantages for studying the effects of arboviruses on vertebrate hosts (O'Brien and Brown 2012). They tend to occur in tocatty high density at certain times ofthe year (e.g., summer), especialty among colonial species.…”

Impacts of Short-Term Food Restriction on Immune Development in Altricial House Sparrow Nestlings

“…Given that resource limitation is a common feature of avian ecology, experimental food restriction studies can help us determine whether this ecological stressor impacts the reservoir capacity of nestlings for zoonotic diseases, such as West Nile virus or Buggy Creek virus (O'Brien et al 2010;O'Brien and Brown 2012;Fassbinder-Orth et al 2013). Additionally, within the field of ecological immunology, there is widespread interest in exploring how patterns of allocation may be mediated by resource availability and whether trade-offs in allocation occur between immune defenses and other processes, such as growth, when resources are limited (Lochmiller and Deerenberg 2000; Hasselquist and Nilsson 2012;Downs et al 2014).…”