Limits...
West Nile Virus: High Transmission Rate in North-Western European Mosquitoes Indicates Its Epidemic Potential and Warrants Increased Surveillance.

Fros JJ, Geertsema C, Vogels CB, Roosjen PP, Failloux AB, Vlak JM, Koenraadt CJ, Takken W, Pijlman GP - PLoS Negl Trop Dis (2015)

Bottom Line: We found that NWE mosquitoes are highly competent for both WNV lineages, with transmission rates up to 25%.Compared to NA mosquitoes, transmission rates for lineage 2 WNV were significantly elevated in NWE mosquitoes due to better virus dissemination from the midgut and a shorter extrinsic incubation time.This emphasizes the need for intensified surveillance of virus activity in current WNV disease-free regions and warrants increased awareness in clinics throughout Europe.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Virology, Wageningen University, Wageningen, The Netherlands.

ABSTRACT

Background: West Nile virus (WNV) is a highly pathogenic flavivirus transmitted by Culex spp. mosquitoes. In North America (NA), lineage 1 WNV caused the largest outbreak of neuroinvasive disease to date, while a novel pathogenic lineage 2 strain circulates in southern Europe. To estimate WNV lineage 2 epidemic potential it is paramount to know if mosquitoes from currently WNV-free areas can support further spread of this epidemic.

Methodology/principal findings: We assessed WNV vector competence of Culex pipiens mosquitoes originating from north-western Europe (NWE) in direct comparison with those from NA. We exposed mosquitoes to infectious blood meals of lineage 1 or 2 WNV and determined the infection and transmission rates. We explored reasons for vector competence differences by comparing intrathoracic injection versus blood meal infection, and we investigated the influence of temperature. We found that NWE mosquitoes are highly competent for both WNV lineages, with transmission rates up to 25%. Compared to NA mosquitoes, transmission rates for lineage 2 WNV were significantly elevated in NWE mosquitoes due to better virus dissemination from the midgut and a shorter extrinsic incubation time. WNV infection rates further increased with temperature increase.

Conclusions/significance: Our study provides experimental evidence to indicate markedly different risk levels between both continents for lineage 2 WNV transmission and suggests a degree of genotype-genotype specificity in the interaction between virus and vector. Our experiments with varying temperatures explain the current localized WNV activity in southern Europe, yet imply further epidemic spread throughout NWE during periods with favourable climatic conditions. This emphasizes the need for intensified surveillance of virus activity in current WNV disease-free regions and warrants increased awareness in clinics throughout Europe.

No MeSH data available.


Related in: MedlinePlus

Growth kinetics of lineage 1 and 2 WNV strains.(A) Human Hela, (B) avian DF-1 (duck fibroblasts) and (C) mosquito CT (Culex tarsalis) cells infected with WNV-lin2 (red) or WNV-lin1 (blue) isolates at a multiplicity of infection of 1. Medium was harvested at the indicated days post infection and used in end point dilution assays. Error bars represent the standard error of the mean.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4520649&req=5

pntd.0003956.g001: Growth kinetics of lineage 1 and 2 WNV strains.(A) Human Hela, (B) avian DF-1 (duck fibroblasts) and (C) mosquito CT (Culex tarsalis) cells infected with WNV-lin2 (red) or WNV-lin1 (blue) isolates at a multiplicity of infection of 1. Medium was harvested at the indicated days post infection and used in end point dilution assays. Error bars represent the standard error of the mean.

Mentions: Culex pipiens mosquitoes from NWE (The Netherlands), and a NA Culex pipiens colony [20] were infected with either the novel pathogenic lineage 2 WNV isolate (WNV-lin2) from Greece’10 or lineage 1 isolate (WNV-lin1), New York ‘99. The vector competence of NA mosquitoes for WNV-lin1 has been well-described [20] and serves as a reference for the infection and transmission rates of WNV. The WNV-lin2 and WNV-lin1 isolates displayed similar growth kinetics in human, avian and mosquito cell cultures (Fig 1A–1C). Infectious blood meals containing 1.4*108 TCID50/ml of either WNV-lin2 or WNV-lin1 isolates were fed to the NWE and NA Culex pipiens mosquitoes. Fully engorged females were selected and kept at an ambient temperature of 23°C. Immediately after completion of the blood meal, a subset of fully engorged females was tested for the presence of infectious WNV to confirm that both mosquito populations had ingested equal amounts of infectious virus particles (Fig 2A). Infection with either WNV isolate did not influence mosquito survival during the course of the experiments (Fig 2B). After 14 days, saliva was collected from a large and random subset of the mosquitoes. Both the isolated saliva as well as all the mosquito bodies were examined for the presence of WNV (schematic representation of the experiment, Fig 3A). The combined results from five independent experiments are summarized in Table 1 (infection rates, bodies) and 2 (transmission rates, saliva). Both the NWE and NA mosquitoes were equally susceptible to infection, but with significant differences in the infection rates between the WNV-lin2 and WNV-lin1 isolates (Table 1, P<0.05).


West Nile Virus: High Transmission Rate in North-Western European Mosquitoes Indicates Its Epidemic Potential and Warrants Increased Surveillance.

Fros JJ, Geertsema C, Vogels CB, Roosjen PP, Failloux AB, Vlak JM, Koenraadt CJ, Takken W, Pijlman GP - PLoS Negl Trop Dis (2015)

Growth kinetics of lineage 1 and 2 WNV strains.(A) Human Hela, (B) avian DF-1 (duck fibroblasts) and (C) mosquito CT (Culex tarsalis) cells infected with WNV-lin2 (red) or WNV-lin1 (blue) isolates at a multiplicity of infection of 1. Medium was harvested at the indicated days post infection and used in end point dilution assays. Error bars represent the standard error of the mean.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4520649&req=5

pntd.0003956.g001: Growth kinetics of lineage 1 and 2 WNV strains.(A) Human Hela, (B) avian DF-1 (duck fibroblasts) and (C) mosquito CT (Culex tarsalis) cells infected with WNV-lin2 (red) or WNV-lin1 (blue) isolates at a multiplicity of infection of 1. Medium was harvested at the indicated days post infection and used in end point dilution assays. Error bars represent the standard error of the mean.
Mentions: Culex pipiens mosquitoes from NWE (The Netherlands), and a NA Culex pipiens colony [20] were infected with either the novel pathogenic lineage 2 WNV isolate (WNV-lin2) from Greece’10 or lineage 1 isolate (WNV-lin1), New York ‘99. The vector competence of NA mosquitoes for WNV-lin1 has been well-described [20] and serves as a reference for the infection and transmission rates of WNV. The WNV-lin2 and WNV-lin1 isolates displayed similar growth kinetics in human, avian and mosquito cell cultures (Fig 1A–1C). Infectious blood meals containing 1.4*108 TCID50/ml of either WNV-lin2 or WNV-lin1 isolates were fed to the NWE and NA Culex pipiens mosquitoes. Fully engorged females were selected and kept at an ambient temperature of 23°C. Immediately after completion of the blood meal, a subset of fully engorged females was tested for the presence of infectious WNV to confirm that both mosquito populations had ingested equal amounts of infectious virus particles (Fig 2A). Infection with either WNV isolate did not influence mosquito survival during the course of the experiments (Fig 2B). After 14 days, saliva was collected from a large and random subset of the mosquitoes. Both the isolated saliva as well as all the mosquito bodies were examined for the presence of WNV (schematic representation of the experiment, Fig 3A). The combined results from five independent experiments are summarized in Table 1 (infection rates, bodies) and 2 (transmission rates, saliva). Both the NWE and NA mosquitoes were equally susceptible to infection, but with significant differences in the infection rates between the WNV-lin2 and WNV-lin1 isolates (Table 1, P<0.05).

Bottom Line: We found that NWE mosquitoes are highly competent for both WNV lineages, with transmission rates up to 25%.Compared to NA mosquitoes, transmission rates for lineage 2 WNV were significantly elevated in NWE mosquitoes due to better virus dissemination from the midgut and a shorter extrinsic incubation time.This emphasizes the need for intensified surveillance of virus activity in current WNV disease-free regions and warrants increased awareness in clinics throughout Europe.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Virology, Wageningen University, Wageningen, The Netherlands.

ABSTRACT

Background: West Nile virus (WNV) is a highly pathogenic flavivirus transmitted by Culex spp. mosquitoes. In North America (NA), lineage 1 WNV caused the largest outbreak of neuroinvasive disease to date, while a novel pathogenic lineage 2 strain circulates in southern Europe. To estimate WNV lineage 2 epidemic potential it is paramount to know if mosquitoes from currently WNV-free areas can support further spread of this epidemic.

Methodology/principal findings: We assessed WNV vector competence of Culex pipiens mosquitoes originating from north-western Europe (NWE) in direct comparison with those from NA. We exposed mosquitoes to infectious blood meals of lineage 1 or 2 WNV and determined the infection and transmission rates. We explored reasons for vector competence differences by comparing intrathoracic injection versus blood meal infection, and we investigated the influence of temperature. We found that NWE mosquitoes are highly competent for both WNV lineages, with transmission rates up to 25%. Compared to NA mosquitoes, transmission rates for lineage 2 WNV were significantly elevated in NWE mosquitoes due to better virus dissemination from the midgut and a shorter extrinsic incubation time. WNV infection rates further increased with temperature increase.

Conclusions/significance: Our study provides experimental evidence to indicate markedly different risk levels between both continents for lineage 2 WNV transmission and suggests a degree of genotype-genotype specificity in the interaction between virus and vector. Our experiments with varying temperatures explain the current localized WNV activity in southern Europe, yet imply further epidemic spread throughout NWE during periods with favourable climatic conditions. This emphasizes the need for intensified surveillance of virus activity in current WNV disease-free regions and warrants increased awareness in clinics throughout Europe.

No MeSH data available.


Related in: MedlinePlus