forced-salivation-as-method-to-analyze-vector-competence

Forced Salivation As a Method to Analyze Vector Competence of Mosquitoes

Vector competence is defined as the potential of a mosquito species to transmit a mosquito-borne virus (mobovirus) to a vertebrate host. Viable virus ...

Bernhard Nocht Institute for Tropical Medicine

German Centre for Infection Research (DZIF)

The interplay between arthropod-borne (arbo) viruses and their vectors is usually complex and often exert unique relationships. Aedes japonicus japonicus (Hulecoeteomyia japonica or Ochlerotatus japonicus japonicus), an invasive mosquito species with laboratory proven vector competence for a number of emerging viruses has been newly introduced to Germany and is currently expanding its range throughout the country. On the other hand, West Nile virus (WNV), an emerging arbovirus originating from Africa, is already circulating in several European countries and might soon be introduced to Germany. Because newly introduced and rapidly expanding vector species pose a potential risk for public health in Germany, we assessed the vectorial capacity of German Ae. j. japonicus populations for WNV and Japanese encephalitis virus (JEV). The results indicate that German Ae. j. japonicus are susceptible for JEV but are refractory to infection with WNV. Of 67 Ae. j. japonicus females challenged by feeding of WNV-containing blood, none had measurable amounts of WNV-RNA (0% infection rate) on day 14 post-infection. In contrast, all females challenged with JEV were positive for JEV-RNA (100% infection rate) on day 14 post-infection. The reason for WNV resistance remains to be determined but is independent from co-infection with other flaviviruses or the presence of endosymbiotic Wolbachia, since we found no evidence for other flavivirus infections within 1,033 tested A. j. japonicus females from the sampling region, nor detectable Wolbachia infection within 30 randomly selected individuals.

Aedes japonicus japonicus (Diptera: Culicidae) from Germany have vector competence for Japan encephalitis virus but are refractory to infection with West Nile virus.

Culex pipiens sensu lato (L.) and Culex torrentium Martini, 1925 are two widely distributed mosquito species in Europe. Due to difficulties in morphological discrimination, the current knowledge on differences in the breeding ecology is fragmentary. Therefore, this study evaluated the relation between the presence-absence of both species at various types of breeding habitats in response to physico-chemical parameters, using a recently developed molecular assay that allows reliable species-specific typing of larvae and pupae. The results revealed that the two species often occur in sympatry at the studied breeding sites, and there were no substantial differences concerning presence-absence of the two species with regard to the various environmental parameters investigated. 

Physico-Chemical Characteristics of Culex pipiens sensu lato and Culex torrentium (Diptera: Culicidae) Breeding Sites in Germany.

Mosquitoes collected in Germany in 2016, including Culex pipiens pipiens biotype pipiens, Culex torrentium and Aedes albopictus, as well as Culex pipiens pipiens biotype molestus (in colony since 2011) were experimentally infected with Zika virus (ZIKV) at 18 °C or 27 °C. None of the Culex taxa showed vector competence for ZIKV. In contrast, Aedes albopictus were susceptible for ZIKV but only at 27 °C, with transmission rates similar to an Aedes aegypti laboratory colony tested in parallel.

Experimental transmission of Zika virus by mosquitoes from central Europe.

West Nile virus (WNV), a  with an avian primary host, is already widespread in Europe and might also pose an infection risk to Germany, should competent mosquito vectors be present. Therefore, we analysed the ability of WNV to infect German  mosquitoes with special emphasis on field collected specimens of  and  biotype . We collected egg rafts of  mosquitoes over two subsequent seasons at two geographically distinct sampling areas in Germany and differentiated the samples by molecular methods. Adult females, reared from the various egg rafts, were challenged with WNV by feeding of artificial blood meals. WNV infection was confirmed by real-time RT-PCR and virus titration. The results showed that field collected .  biotype  and .  mosquitoes native to Germany are susceptible to WNV infection at 25 °C as well as 18 °C incubation temperature. .  mosquitoes, which have not been established as WNV vector so far, were the most permissive species tested with maximum infection rates of 96% at 25 °C. Furthermore, a disseminating infection was found in up to 94% of tested .  biotype  and 100% of . . Considering geographical variation of susceptibility, .  biotype  mosquitoes from Southern Germany were more susceptible to WNV infection than corresponding populations from Northern Germany. All in all, we observed high infection and dissemination rates even at a low average ambient temperature of 18 °C. The high susceptibility of German  populations for WNV indicates that an enzootic transmission cycle in Germany could be possible.

Mayke Leggewie

Bernhard Nocht Institute for Tropical Medicine

Forced Salivation As a Method to Analyze Vector Competence of Mosquitoes