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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

Mesenteron infection barriers determine the transmission rate of WNV-lin2.Culex pipiens from either NWE (spherical symbols) or NA (square symbols) were infected with the WNV-lin2 isolate via infectious blood meals (closed symbols) or intrathoracic injections (open symbols). At the indicated times post infection, the percentages of effectively infected mosquitoes (A) or successive infectious saliva (B) were determined.
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pntd.0003956.g004: Mesenteron infection barriers determine the transmission rate of WNV-lin2.Culex pipiens from either NWE (spherical symbols) or NA (square symbols) were infected with the WNV-lin2 isolate via infectious blood meals (closed symbols) or intrathoracic injections (open symbols). At the indicated times post infection, the percentages of effectively infected mosquitoes (A) or successive infectious saliva (B) were determined.

Mentions: Efficient infection and escape from the midgut epithelial cells is necessary for dissemination of the virus to other tissues, including the salivary glands [24–26]. When the midgut was circumvented by injecting WNV-lin2 directly into the thorax, all mosquitoes from both NWE and NA became readily infected (Fig 4A, open symbols) and up to 100% of injected individuals were able to transmit WNV at day eight post injection (Fig 4B, open symbols). In contrast, infectious blood meals resulted in differential proportions of the NWE and NA mosquitoes being able to transmit WNV-lin2 (Fig 4B, closed symbols), again with NWE as a more competent vector. Strikingly, both eight and eleven days post infection, the WNV-lin2 isolate was detected in the saliva of 14% of NWE mosquitoes, compared to <3% of NA mosquitoes (Fig 4B, closed symbols, P = 0.1076 and P = 0.0259 respectively).


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)

Mesenteron infection barriers determine the transmission rate of WNV-lin2.Culex pipiens from either NWE (spherical symbols) or NA (square symbols) were infected with the WNV-lin2 isolate via infectious blood meals (closed symbols) or intrathoracic injections (open symbols). At the indicated times post infection, the percentages of effectively infected mosquitoes (A) or successive infectious saliva (B) were determined.
© Copyright Policy
Related In: Results  -  Collection

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

pntd.0003956.g004: Mesenteron infection barriers determine the transmission rate of WNV-lin2.Culex pipiens from either NWE (spherical symbols) or NA (square symbols) were infected with the WNV-lin2 isolate via infectious blood meals (closed symbols) or intrathoracic injections (open symbols). At the indicated times post infection, the percentages of effectively infected mosquitoes (A) or successive infectious saliva (B) were determined.
Mentions: Efficient infection and escape from the midgut epithelial cells is necessary for dissemination of the virus to other tissues, including the salivary glands [24–26]. When the midgut was circumvented by injecting WNV-lin2 directly into the thorax, all mosquitoes from both NWE and NA became readily infected (Fig 4A, open symbols) and up to 100% of injected individuals were able to transmit WNV at day eight post injection (Fig 4B, open symbols). In contrast, infectious blood meals resulted in differential proportions of the NWE and NA mosquitoes being able to transmit WNV-lin2 (Fig 4B, closed symbols), again with NWE as a more competent vector. Strikingly, both eight and eleven days post infection, the WNV-lin2 isolate was detected in the saliva of 14% of NWE mosquitoes, compared to <3% of NA mosquitoes (Fig 4B, closed symbols, P = 0.1076 and P = 0.0259 respectively).

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