Buggy Creek virus (family Togaviridae, genus Alphavirus, BCRV) is an alphavirus within the western equine encephalitis virus complex whose primary vector is the swallow bug, Oeciacus vicarius Horvath (Hemiptera: Cimicidae), an ectoparasite of the colonially nesting cliff swallow, Petrochelidon pyrrhonota, that is also a frequent host for the virus. We investigated ecological correlates of BCRV infection in 100-bug pools at 14 different swallow colony sites in southwestern Nebraska from summer 2004, by using plaque assay on Vero cells to identify cytopathic virus and reverse transcription-polymerase chain reaction to identify noncytopathic viral RNA. We found 26.7% of swallow bug pools positive for BCRV, with 15.6% showing cytopathic ("infectious") virus and 11.0% noncytopathic ("noninfectious") viral RNA. The prevalence of cytopathic BCRV increased with cliff swallow colony size in the current year; the percentage of noncytopathic samples at a site did not vary with colony size in the current year but increased with the previous year's colony size at a site. Active colony sites (those used by swallows) had higher percentages of cytopathic BCRV in bug pools than at inactive colony sites, but the reverse held for noncytopathic viral RNA. Nests that were occupied by birds at some time in the season had more pools with cytopathic BCRV than did inactive nests. Colonies used by birds for the first or second time had less virus in bugs than did sites that had had a longer history of bird use. The percentage of pools with BCRV was affected by whether bugs were clustering at nest entrances or distributed elsewhere on a nest. The prevalence of cytopathic samples decreased at inactive colony sites and increased at active sites over the course of the summer, whereas the reverse pattern held for noncytopathic samples. Noncytopathic bug pools seem to reflect infection patterns from a previous year. The results suggest that the birds play an important role in amplification of the virus and that the spatial foci of BCRV occurrence can be predicted based on characteristics of cliff swallow colonies and the cimicid bugs that are associated with them.

Determining the effect of an invasive species on enzootic pathogen dynamics is critical for understanding both human epidemics and wildlife epizootics. Theoretical models suggest that when a naive species enters an established host-parasite system, the new host may either reduce ('dilute') or increase ('spillback') pathogen transmission to native hosts. There are few empirical data to evaluate these possibilities, especially for animal pathogens. Buggy Creek virus (BCRV) is an arthropod-borne alphavirus that is enzootically transmitted by the swallow bug (Oeciacus vicarius) to colonially nesting cliff swallows (Petrochelidon pyrrhonota). In western Nebraska, introduced house sparrows (Passer domesticus) invaded cliff swallow colonies approximately 40 years ago and were exposed to BCRV. We evaluated how the addition of house sparrows to this host-parasite system affected the prevalence and amplification of a bird-associated BCRV lineage. The infection prevalence in house sparrows was eight times that of cliff swallows. Nestling house sparrows in mixed-species colonies were significantly less likely to be infected than sparrows in single-species colonies. Infected house sparrows circulated BCRV at higher viraemia titres than cliff swallows. BCRV detected in bug vectors at a site was positively associated with virus prevalence in house sparrows but not with virus prevalence in cliff swallows. The addition of a highly susceptible invasive host species has led to perennial BCRV epizootics at cliff swallow colony sites. The native cliff swallow host confers a dilution advantage to invasive sparrow hosts in mixed colonies, while at the same sites house sparrows may increase the likelihood that swallows become infected.

This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in Natural Resources by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln. Abstract. Most arthropod-borne viruses (arboviruses) show distinct serological subtypes or evolutionary lineages, with the evolution of different strains often assumed to reflect differences in ecological selection pressures. Buggy Creek virus (BCRV) is an unusual RNA virus (Togaviridae, Alphavirus) that is associated primarily with a cimicid swallow bug (Oeciacus vicarius) as its vector and the Cliff Swallow (Petrochelidon pyrrhonota) and the introduced House Sparrow (Passer domesticus) as its amplifying hosts. There are two sympatric lineages of BCRV (lineages A and B) that differ from each other by .6% at the nucleotide level. Analysis of 385 BCRV isolates all collected from bug vectors at a study site in southwestern Nebraska, USA, showed that the lineages differed in their peak times of seasonal occurrence within a summer. Lineage A was more likely to be found at recently established colonies, at those in culverts (rather than on highway bridges), and at those with invasive House Sparrows, and in bugs on the outsides of nests. Genetic diversity of lineage A increased with bird colony size and at sites with House Sparrows, while that of lineage B decreased with colony size and was unaffected by House Sparrows. Lineage A was more cytopathic on mammalian cells than was lineage B. These two lineages have apparently diverged in their transmission dynamics, with lineage A possibly more dependent on birds and lineage B perhaps more a bug virus. The long-standing association between Cliff Swallows and BCRV may have selected for immunological resistance to the virus by swallows and thus promoted the evolution of the more bug-adapted lineage B. In contrast, the recent arrival of the introduced House Sparrow and its high competence as a BCRV amplifying host may be favoring the more bird-dependent lineage A.

Predicting the spatial foci of zoonotic diseases is a major challenge for epidemiologists and disease ecologists. Migratory birds are often thought to be responsible for introducing some aviozoonotic pathogens such as West Nile and avian influenza viruses to a local area, but most information on how bird movement correlates with virus prevalence is anecdotal or indirect. We report that the prevalence of Buggy Creek virus (BCRV) infection in cimicid swallow bugs (Oeciacus vicarius), the principal invertebrate vector for this virus, was directly associated with the likelihood of movement by cliff swallows (Petrochelidon pyrrhonota), an amplifying host for the virus, between nesting colonies. The prevalence of BCRV in bugs was also directly correlated with the number of swallows immigrating into a site. Birds that move into a site are often transient individuals that may have more often encountered virus elsewhere. These results indicate that the magnitude and direction of daily bird movement in a local area can accurately predict transmission foci for this virus and provide rare quantitative evidence that birds can play a critical role in the dispersal of certain vector-borne viruses.

A largely unanswered question in the study of arboviruses is the extent to which virus can overwinter in adult vectors during the cold winter months and resume the transmission cycle in summer. Buggy Creek virus (BCRV; Togaviridae, Alphavirus) is an unusual arbovirus that is vectored primarily by the swallow bug (Hemiptera: Cimicidae: Oeciacus vicarius) and amplified by the ectoparasitic bug's main avian hosts, the migratory cliff swallow (Petrochelidon pyrrhonota) and resident house sparrow (Passer domesticus). Bugs are sedentary and overwinter in the swallows' mud nests. We evaluated the prevalence of BCRV and extent of infection in swallow bugs collected at different times in winter (October-early April) in Nebraska and explored other ecological aspects of this virus's overwintering. BCRV was detected in 17% of bug pools sampled in winter. Virus prevalence in bugs in winter at a site was significantly correlated with virus prevalence at that site the previous summer, but winter prevalence did not predict BCRV prevalence there the following summer. Prevalence was higher in bugs taken from house sparrow nests in winter and (in April) at colony sites where sparrows had been present all winter. Virus detected by reverse transcription (RT)-polymerase chain reaction in winter was less cytopathic than in summer, but viral RNA concentrations of samples in winter were not significantly different from those in summer. Both of the BCRV lineages (A, B) overwintered successfully, with lineage A more common at sites with house sparrows and (in contrast to summer) generally more prevalent in winter than lineage B. BCRV's ability to overwinter in its adult vector probably reflects its adaptation to the sedentary, long-lived bug and the ecology of the cliff swallow and swallow bug host-parasite system. Its overwintering mechanisms may provide insight into those of other alphaviruses of public health significance for which such mechanisms are poorly known.