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Vector competence of Swedish Culex pipiens mosquitoes for Usutu virus.

ABSTRACT: Usutu virus (USUV) is an emerging mosquito-borne flavivirus with increasing prevalence in Europe. Understanding the role of mosquito species in USUV transmission is crucial for predicting and controlling potential outbreaks. This study aimed to assess the vector competence of Swedish Culex pipiens for USUV. The mosquitoes were orally infected with an Italian strain of USUV (Bologna 2009) and infection rates (IR), dissemination rates (DR), and transmission rates (TR) were evaluated over 7 to 28 days post-infection. The study revealed that Swedish Cx. pipiens are susceptible to USUV infection, with a gradual decrease in IR over time. However, the percentage of mosquitoes with the ability to transmit the virus remained consistent across all time points, indicating a relatively short extrinsic incubation period. Overall, this research highlights the potential of Swedish Cx. pipiens as vectors for USUV and emphasizes the importance of surveillance and monitoring to prevent future outbreaks of mosquito-borne diseases.

SUBMITTER: Krambrich J

PROVIDER: S-EPMC10945277 | biostudies-literature | 2024 Jun

REPOSITORIES: biostudies-literature

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Vector competence of Swedish <i>Culex pipiens</i> mosquitoes for Usutu virus.

Krambrich Janina J Bole-Feysot Emma E Höller Patrick P Lundkvist Åke Å Hesson Jenny C JC

One health (Amsterdam, Netherlands) 20240309

Usutu virus (USUV) is an emerging mosquito-borne flavivirus with increasing prevalence in Europe. Understanding the role of mosquito species in USUV transmission is crucial for predicting and controlling potential outbreaks. This study aimed to assess the vector competence of Swedish <i>Culex pipiens</i> for USUV. The mosquitoes were orally infected with an Italian strain of USUV (Bologna 2009) and infection rates (IR), dissemination rates (DR), and transmission rates (TR) were evaluated over 7 ...[more]

PMID: 38500563

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Project description:BackgroundInfectious blood meal experiments have been frequently performed with different virus-vector combinations to assess the transmission potential of arthropod-borne (arbo)viruses. A wide variety of host blood sources have been used to deliver arboviruses to their arthropod vectors in laboratory studies. The type of blood used during vector competence experiments does not always reflect the blood from the viremic vertebrate hosts in the field, but little is known about the effect of blood source on the experimental outcome of vector competence studies. Here we investigated the effect of avian versus human blood on the infection and transmission rates of the zoonotic Usutu virus (USUV) in its primary mosquito vector Culex pipiens.MethodsCx. pipiens biotypes (pipiens and molestus) were orally infected with USUV through infectious blood meals containing either chicken or human whole blood. The USUV infection and transmission rates were determined by checking mosquito bodies and saliva for USUV presence after 14 days of incubation at 28 °C. In addition, viral titers were determined for USUV-positive mosquito bodies and saliva.ResultsHuman and chicken blood lead to similar USUV transmission rates for Cx. pipiens biotype pipiens (18% and 15%, respectively), while human blood moderately but not significantly increased the transmission rate (30%) compared to chicken blood (17%) for biotype molestus. USUV infection rates with human blood were consistently higher in both Cx. pipiens biotypes compared to chicken blood. In virus-positive mosquitoes, USUV body and saliva titers did not differ between mosquitoes taking either human or chicken blood. Importantly, biotype molestus had much lower USUV saliva titers compared to biotype pipiens, regardless of which blood was offered.ConclusionsInfection of mosquitoes with human blood led to higher USUV infection rates as compared to chicken blood. However, the blood source had no effect on the vector competence for USUV. Interestingly, biotype molestus is less likely to transmit USUV compared to biotype pipiens due to very low virus titers in the saliva.

Project description:BackgroundUsutu virus (USUV) is a rapidly spreading zoonotic arbovirus (arthropod-borne virus) and a considerable threat to the global avifauna and in isolated cases to human health. It is maintained in an enzootic cycle involving ornithophilic mosquitoes as vectors and birds as reservoir hosts. Despite massive die-offs in wild bird populations and the detection of severe neurological symptoms in infected humans, little is known about which mosquito species are involved in the propagation of USUV.MethodsIn the present study, the vector competence of a German (i.e. "Central European") and a Serbian (i.e. "Southern European") Culex pipiens biotype molestus laboratory colony was experimentally evaluated. For comparative purposes, Culex torrentium, a frequent species in Northern Europe, and Aedes aegypti, a primarily tropical species, were also tested. Adult female mosquitoes were exposed to bovine blood spiked with USUV Africa 2 and subsequently incubated at 25 °C. After 2 to 3 weeks saliva was collected from each individual mosquito to assess the ability of a mosquito species to transmit USUV.ResultsCulex pipiens biotype molestus mosquitoes originating from Germany and the Republic of Serbia and Cx. torrentium mosquitoes from Germany proved competent for USUV, as indicated by harboring viable virus in their saliva 21 days post infection. By contrast, Ae. aegypti mosquitoes were relatively refractory to an USUV infection, exhibiting low infection rates and lacking virus in their saliva.ConclusionsConsistent with the high prevalences and abundances of Cx. pipiens biotype molestus and Cx. torrentium in Central and Northern Europe, these two species have most likely played a historic role in the spread, maintenance, and introduction of USUV into Germany. Identification of the key USUV vectors enables the establishment and implementation of rigorous entomological surveillance programs and the development of effective, evidence-based vector control interventions.

Project description:BackgroundUsutu virus (USUV) is an emerging zoonotic virus originally from sub-Saharan Africa. It has been introduced into Europe on multiple occasions, causing substantial mortality within the Eurasian blackbird (Turdus merula) population. It is transmitted by the mosquito species Culex pipiens in Europe and Africa. Vector competence studies indicate that European strains of USUV are readily transmitted by indigenous Cx. pipiens. However, there is limited information on the ability of an African strain to infect European mosquitoes.MethodsWe evaluated the ability of African strain SAAR-1776 to infect two lines of Cx. pipiens colonised within the United Kingdom (UK). Mosquitoes were fed blood meals containing this virus and maintained at 25 °C for up to 21 days. Individual mosquitoes were tested for the presence of virus in the body, legs and an expectorate saliva sample. Changes to the consensus of the virus genome were monitored in samples derived from infected mosquitoes using amplicon based next generation sequencing.ResultsInfection, dissemination and the presence of virus in saliva in one mosquito line was observed, but no evidence for dissemination in the second mosquito line. This suggests a strong barrier to infection in UK Cx. pipiens for this strain of USUV. When comparing the genome of input virus within the blood meal with USUV recovered from an infected mosquito, we observed limited changes in the consensus genome sequence.ConclusionsThe evaluation of vector competence of UK populations of Cx. pipiens for Usutu virus suggests a limited susceptibility to infection with USUV strain SAAR-1776 of African origin. However, within a single mosquito there was complete dissemination and expectoration of USUV, indicating that infection, and potentially transmission, is possible. Sequence changes were observed that may represent early adaption to the mosquito host and could reflect the early events of USUV establishment in European mosquito populations.

Dataset Information

Vector competence of Swedish Culex pipiens mosquitoes for Usutu virus.

Publications

Vector competence of Swedish <i>Culex pipiens</i> mosquitoes for Usutu virus.

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