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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

Higher temperatures increase WNV infection rate in Culex pipiens.Both NA (open symbols) and NWE (closed symbols) mosquitoes were orally infected with the WNV-lin2 isolate via a blood meal. Engorged mosquitoes were separated into three groups which were incubated at either 18, 23 or 28°C. The infection rate was determined 14 days post oral infections. Asterisks indicate significant differences (Fisher’s exact test P<0.05).
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pntd.0003956.g005: Higher temperatures increase WNV infection rate in Culex pipiens.Both NA (open symbols) and NWE (closed symbols) mosquitoes were orally infected with the WNV-lin2 isolate via a blood meal. Engorged mosquitoes were separated into three groups which were incubated at either 18, 23 or 28°C. The infection rate was determined 14 days post oral infections. Asterisks indicate significant differences (Fisher’s exact test P<0.05).

Mentions: As the mosquito colonies used in this laboratory study are representatives of their respective populations from the described areas, the experiments presented here show that highly WNV-competent Culex pipiens mosquitoes are present in NWE. Vector competence is, however, not only attributed to intrinsic factors, but also subjective to extrinsic factors, most notably the ambient temperature [20,27]. Because indigenous WNV activity is currently absent in NWE [11,28], but competent European bird species are present [14,15], we hypothesized that temperature limits the vector competence of European mosquitoes for WNV transmission. To test this hypothesis, we infected both NWE and NA mosquitoes with the WNV-lin2 isolate via a WNV-containing blood meal and incubated the mosquitoes at three different temperatures for 14 days post oral infections. The first temperature represented the average summer temperatures in large parts of NWE, including the origin of our NWE mosquito colony (The Netherlands; 18°C). The second temperature was an intermediate temperature (23°C), while the third temperature matched the average summer temperature of the area where WNV-lin2 was isolated (Greece; 28°C) [29]. The warmest period of the year (July and August) also corresponded with the peak in WNV amplification and transmission [8]. Higher temperatures significantly increased the percentage of WNV-infected mosquito vectors, with no apparent difference between NWE and NA mosquitoes (Fig 5, P<0.05). At 18°C, 17% (n = 29) and 19% (n = 41) of mosquitoes were infected with WNV-lin2, whereas incubation at 28°C increased the infection rates to 58% (n = 36) and 52% (n = 25) for NWE and NA mosquitoes, 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)

Higher temperatures increase WNV infection rate in Culex pipiens.Both NA (open symbols) and NWE (closed symbols) mosquitoes were orally infected with the WNV-lin2 isolate via a blood meal. Engorged mosquitoes were separated into three groups which were incubated at either 18, 23 or 28°C. The infection rate was determined 14 days post oral infections. Asterisks indicate significant differences (Fisher’s exact test P<0.05).
© Copyright Policy
Related In: Results  -  Collection

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

pntd.0003956.g005: Higher temperatures increase WNV infection rate in Culex pipiens.Both NA (open symbols) and NWE (closed symbols) mosquitoes were orally infected with the WNV-lin2 isolate via a blood meal. Engorged mosquitoes were separated into three groups which were incubated at either 18, 23 or 28°C. The infection rate was determined 14 days post oral infections. Asterisks indicate significant differences (Fisher’s exact test P<0.05).
Mentions: As the mosquito colonies used in this laboratory study are representatives of their respective populations from the described areas, the experiments presented here show that highly WNV-competent Culex pipiens mosquitoes are present in NWE. Vector competence is, however, not only attributed to intrinsic factors, but also subjective to extrinsic factors, most notably the ambient temperature [20,27]. Because indigenous WNV activity is currently absent in NWE [11,28], but competent European bird species are present [14,15], we hypothesized that temperature limits the vector competence of European mosquitoes for WNV transmission. To test this hypothesis, we infected both NWE and NA mosquitoes with the WNV-lin2 isolate via a WNV-containing blood meal and incubated the mosquitoes at three different temperatures for 14 days post oral infections. The first temperature represented the average summer temperatures in large parts of NWE, including the origin of our NWE mosquito colony (The Netherlands; 18°C). The second temperature was an intermediate temperature (23°C), while the third temperature matched the average summer temperature of the area where WNV-lin2 was isolated (Greece; 28°C) [29]. The warmest period of the year (July and August) also corresponded with the peak in WNV amplification and transmission [8]. Higher temperatures significantly increased the percentage of WNV-infected mosquito vectors, with no apparent difference between NWE and NA mosquitoes (Fig 5, P<0.05). At 18°C, 17% (n = 29) and 19% (n = 41) of mosquitoes were infected with WNV-lin2, whereas incubation at 28°C increased the infection rates to 58% (n = 36) and 52% (n = 25) for NWE and NA mosquitoes, 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