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Evidence for co-evolution of West Nile Virus and house sparrows in North America.

Duggal NK, Bosco-Lauth A, Bowen RA, Wheeler SS, Reisen WK, Felix TA, Mann BR, Romo H, Swetnam DM, Barrett AD, Brault AC - PLoS Negl Trop Dis (2014)

Bottom Line: West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999.Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99.These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.

View Article: PubMed Central - PubMed

Affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.

ABSTRACT
West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999. House sparrows (HOSPs; Passer domesticus) are a highly competent host for WNV that have contributed to the rapid spread of WNV across the U.S.; however, their competence has been evaluated primarily using an early WNV strain (NY99) that is no longer circulating. Herein, we report that the competence of wild HOSPs for the NY99 strain has decreased significantly over time, suggesting that HOSPs may have developed resistance to this early WNV strain. Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99. These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.

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HOSP reservoir competence for WNV.Points represent individual birds. Birds inoculated with East Coast viruses are designated in blue; birds inoculated with WN02 viruses are green; and birds inoculated with SW03 viruses are purple. (A) Reservoir competence index calculated for individual birds inoculated with one of the 12 WNV isolates, and the mean competence for each WNV genotype. ‡Previous calculations of reservoir competence indices for blue jay, HOSP, and Canada goose with NY99 [5] are shown in dashed lines for comparison. (B) Linear regression analysis of reservoir competence for individual birds inoculated with WNV, stratified by year of virus collection. 95% confidence intervals are shown by dotted lines.
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pntd-0003262-g003: HOSP reservoir competence for WNV.Points represent individual birds. Birds inoculated with East Coast viruses are designated in blue; birds inoculated with WN02 viruses are green; and birds inoculated with SW03 viruses are purple. (A) Reservoir competence index calculated for individual birds inoculated with one of the 12 WNV isolates, and the mean competence for each WNV genotype. ‡Previous calculations of reservoir competence indices for blue jay, HOSP, and Canada goose with NY99 [5] are shown in dashed lines for comparison. (B) Linear regression analysis of reservoir competence for individual birds inoculated with WNV, stratified by year of virus collection. 95% confidence intervals are shown by dotted lines.

Mentions: Infectiousness of WNV-infected HOSPs for mosquitoes is a combination of both the magnitude and duration of viremia. In the absence of performing vector competence studies for all of the viruses assessed, the mean reservoir competence index for each viral isolate in HOSPs was generalized by predicting the proportion of mosquitoes likely to become infected using linear regression analysis based on previously published data [4], [6], [33], [34]. With these calculations, an index value of 1.0 would indicate that 100% of mosquitoes feeding on a host for 1 day would be predicted to become infected by the host, though it does not predict the number of mosquitoes that would transmit WNV or the effects on mosquito survival. The mean competence index for HOSPs infected with WNV isolates from the WN02 genotype was 2.4, compared to 1.1 for the East Coast genotype (Fig. 3a), indicating that 120% more mosquitoes would be predicted to become infected after feeding on HOSPs infected with a WN02 isolate compared to mosquitoes feeding on HOSPs infected with an East Coast isolate. The mean HOSP competence index for the SW03 genotype was 1.9 (Fig. 3a), meaning that 73% more mosquitoes would become infected after feeding on HOSPs infected with a SW03 isolate than mosquitoes feeding on HOSPs infected with an East Coast isolate, and 26% more mosquitoes would become infected from feeding on HOSPs infected with a WN02 isolate compared to feeding on HOSPs infected with a SW03 isolate. These results were compared to previously published WNV competence indices for birds inoculated with the NY99 strain of WNV. Species of the avian order Anseriformes, such as the Canada goose (Branta canadensis), have WNV competence indices close to 0 and are considered non-competent hosts [5], [6]. Estimates for passerines suggest competence indices of at least 1, with HOSPs having values between 1 and 1.5, and members of the Corvidae family, such as the blue jay (Cyanocitta cristata), having values between 1.5 and 2.5 [5], [6]. HOSPs inoculated with 6 of the 12 tested WNV isolates, including NY99, had competence indices within the typical range of HOSPs (NY99, NY2001, TX114, TX2600, TX6115, M19433; Fig. 3a). However, HOSPs inoculated with 6 other isolates had competence indices greater than 2, which is more similar to the range for corvids (AR7465, TX8759, TX7191, TX8779, AR6572, TX2689; Fig. 3a). When the reservoir competence indices were stratified by year of viral isolate collection, a significant association between year and index value was observed (Fig. 3b, p<0.05) with an average increase in reservoir competence of 0.09 per year (95% CI: 0.05 to 0.15). The WNV competence of HOSPs trapped in 2012–2013 for viruses collected over 13 years varied between 1.1 and 2.6, or a 140% increase in predicted mosquito infectivity.


Evidence for co-evolution of West Nile Virus and house sparrows in North America.

Duggal NK, Bosco-Lauth A, Bowen RA, Wheeler SS, Reisen WK, Felix TA, Mann BR, Romo H, Swetnam DM, Barrett AD, Brault AC - PLoS Negl Trop Dis (2014)

HOSP reservoir competence for WNV.Points represent individual birds. Birds inoculated with East Coast viruses are designated in blue; birds inoculated with WN02 viruses are green; and birds inoculated with SW03 viruses are purple. (A) Reservoir competence index calculated for individual birds inoculated with one of the 12 WNV isolates, and the mean competence for each WNV genotype. ‡Previous calculations of reservoir competence indices for blue jay, HOSP, and Canada goose with NY99 [5] are shown in dashed lines for comparison. (B) Linear regression analysis of reservoir competence for individual birds inoculated with WNV, stratified by year of virus collection. 95% confidence intervals are shown by dotted lines.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4214623&req=5

pntd-0003262-g003: HOSP reservoir competence for WNV.Points represent individual birds. Birds inoculated with East Coast viruses are designated in blue; birds inoculated with WN02 viruses are green; and birds inoculated with SW03 viruses are purple. (A) Reservoir competence index calculated for individual birds inoculated with one of the 12 WNV isolates, and the mean competence for each WNV genotype. ‡Previous calculations of reservoir competence indices for blue jay, HOSP, and Canada goose with NY99 [5] are shown in dashed lines for comparison. (B) Linear regression analysis of reservoir competence for individual birds inoculated with WNV, stratified by year of virus collection. 95% confidence intervals are shown by dotted lines.
Mentions: Infectiousness of WNV-infected HOSPs for mosquitoes is a combination of both the magnitude and duration of viremia. In the absence of performing vector competence studies for all of the viruses assessed, the mean reservoir competence index for each viral isolate in HOSPs was generalized by predicting the proportion of mosquitoes likely to become infected using linear regression analysis based on previously published data [4], [6], [33], [34]. With these calculations, an index value of 1.0 would indicate that 100% of mosquitoes feeding on a host for 1 day would be predicted to become infected by the host, though it does not predict the number of mosquitoes that would transmit WNV or the effects on mosquito survival. The mean competence index for HOSPs infected with WNV isolates from the WN02 genotype was 2.4, compared to 1.1 for the East Coast genotype (Fig. 3a), indicating that 120% more mosquitoes would be predicted to become infected after feeding on HOSPs infected with a WN02 isolate compared to mosquitoes feeding on HOSPs infected with an East Coast isolate. The mean HOSP competence index for the SW03 genotype was 1.9 (Fig. 3a), meaning that 73% more mosquitoes would become infected after feeding on HOSPs infected with a SW03 isolate than mosquitoes feeding on HOSPs infected with an East Coast isolate, and 26% more mosquitoes would become infected from feeding on HOSPs infected with a WN02 isolate compared to feeding on HOSPs infected with a SW03 isolate. These results were compared to previously published WNV competence indices for birds inoculated with the NY99 strain of WNV. Species of the avian order Anseriformes, such as the Canada goose (Branta canadensis), have WNV competence indices close to 0 and are considered non-competent hosts [5], [6]. Estimates for passerines suggest competence indices of at least 1, with HOSPs having values between 1 and 1.5, and members of the Corvidae family, such as the blue jay (Cyanocitta cristata), having values between 1.5 and 2.5 [5], [6]. HOSPs inoculated with 6 of the 12 tested WNV isolates, including NY99, had competence indices within the typical range of HOSPs (NY99, NY2001, TX114, TX2600, TX6115, M19433; Fig. 3a). However, HOSPs inoculated with 6 other isolates had competence indices greater than 2, which is more similar to the range for corvids (AR7465, TX8759, TX7191, TX8779, AR6572, TX2689; Fig. 3a). When the reservoir competence indices were stratified by year of viral isolate collection, a significant association between year and index value was observed (Fig. 3b, p<0.05) with an average increase in reservoir competence of 0.09 per year (95% CI: 0.05 to 0.15). The WNV competence of HOSPs trapped in 2012–2013 for viruses collected over 13 years varied between 1.1 and 2.6, or a 140% increase in predicted mosquito infectivity.

Bottom Line: West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999.Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99.These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.

View Article: PubMed Central - PubMed

Affiliation: Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.

ABSTRACT
West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999. House sparrows (HOSPs; Passer domesticus) are a highly competent host for WNV that have contributed to the rapid spread of WNV across the U.S.; however, their competence has been evaluated primarily using an early WNV strain (NY99) that is no longer circulating. Herein, we report that the competence of wild HOSPs for the NY99 strain has decreased significantly over time, suggesting that HOSPs may have developed resistance to this early WNV strain. Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99. These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.

Show MeSH
Related in: MedlinePlus