Belgian Anopheles plumbeus Mosquitoes Are Competent for Japanese Encephalitis Virus and Readily Feed on Pigs, Suggesting a High Vectorial Capacity

Anopheles plumbeus, a day-active mosquito known to feed aggressively on humans, was reported as a nuisance species near an abandoned pigsty in Belgium. Since Japanese encephalitis virus (JEV) is an emerging zoonotic flavivirus which uses pigs as amplification hosts, we investigated (1) whether An. plumbeus would feed on pigs and (2) its vector competence for JEV, to investigate whether this species could be a potential vector. Three- to seven-day-old F0-generation adult mosquitoes, emerged from field-collected larvae, were fed on a JEV genotype 3 Nakayama strain spiked blood meal. Blood-fed mosquitoes were subsequently incubated for 14 days at two temperature conditions: a constant 25 °C and a 25/15 °C day/night temperature gradient. Our results show that An. plumbeus is a competent vector for JEV at the 25 °C condition and this with an infection rate of 34.1%, a dissemination rate of 67.7% and a transmission rate of 14.3%. The vector competence showed to be influenced by temperature, with a significantly lower dissemination rate (16.7%) and no transmission when implementing the temperature gradient. Moreover, we demonstrated that An. plumbeus readily feeds on pigs when the opportunity occurs. Therefore, our results suggest that Belgian An. plumbeus mosquitoes may play an important role in the transmission of JEV upon an introduction into our region if temperatures increase with climate change.

Updated occurrence and bionomics of potential malaria vectors in Europe: a systematic review (2000-2021)

Despite the eradication of malaria across most European countries in the 1960s and 1970s, the anopheline vectors are still present. Most of the malaria cases that have been reported in Europe up to the present time have been infections acquired in endemic areas by travelers. However, the possibility of acquiring malaria by locally infected mosquitoes has been poorly investigated in Europe, despite autochthonous malaria cases having been occasionally reported in several European countries. Here we present an update on the occurrence of potential malaria vector species in Europe. Adopting a systematic review approach, we selected 288 papers published between 2000 and 2021 for inclusion in the review based on retrieval of accurate information on the following Anopheles species: An. atroparvus, An. hyrcanus sensu lato (s.l.), An. labranchiae, An. maculipennis sensu stricto (s.s.), An. messeae/daciae, An. sacharovi, An. superpictus and An. plumbeus. The distribution of these potential vector species across Europe is critically reviewed in relation to areas of major presence and principal bionomic features, including vector competence to Plasmodium. Additional information, such as geographical details, sampling approaches and species identification methods, are also reported. We compare the information on each species extracted from the most recent studies to comparable information reported from studies published in the early 2000s, with particular reference to the role of each species in malaria transmission before eradication. The picture that emerges from this review is that potential vector species are still widespread in Europe, with the largest diversity in the Mediterranean area, Italy in particular. Despite information on their vectorial capacity being fragmentary, the information retrieved suggests a re-definition of the relative importance of potential vector species, indicating An. hyrcanus s.l., An. labranchiae, An. plumbeus and An. sacharovi as potential vectors of higher importance, while An. messeae/daciae and An. maculipennis s.s. can be considered to be moderately important species. In contrast, An. atroparvus and An. superpictus should be considered as vectors of lower importance, particularly in relation to their low anthropophily. The presence of gaps in current knowledge of vectorial systems in Europe becomes evident in this review, not only in terms of vector competence but also in the definition of sampling approaches, highlighting the need for further research to adopt the appropriate surveillance system for each species.

Oviposition of Aedes japonicus japonicus (Diptera: Culicidae) and associated native species in relation to season, temperature and land use in western Germany

BACKGROUND

Aedes japonicus japonicus, first detected in Europe in 2000 and considered established in Germany 10 years later, is of medical importance due to its opportunistic biting behaviour and its potential to transmit pathogenic viruses. Its seasonal phenology, temperature and land use preference related to oviposition in newly colonised regions remain unclear, especially in the context of co-occurring native mosquito species.

METHODS

Focussing on regions in Germany known to be infested by Ae. japonicus japonicus, we installed ovitraps in different landscapes and their transition zones and recorded the oviposition activity of mosquitoes in relation to season, temperature and land use (arable land, forest, settlement) in two field seasons (May-August 2017, April-November 2018).

RESULTS

Ae. japonicus japonicus eggs and larvae were encountered in 2017 from June to August and in 2018 from May to November, with a markedly high abundance from June to September in rural transition zones between forest and settlement, limited to water temperatures below 30 °C. Of the three native mosquito taxa using the ovitraps, the most frequent was Culex pipiens s.l., whose offspring was found in high numbers from June to August at water temperatures of up to 35 °C. The third recorded species, Anopheles plumbeus, rarely occurred in ovitraps positioned in settlements and on arable land, but was often associated with Ae. japonicus japonicus. The least frequent species, Aedes geniculatus, was mostly found in ovitraps located in the forest.

CONCLUSIONS

The transition zone between forest and settlement was demonstrated to be the preferred oviposition habitat of Ae. japonicus japonicus, where it was also the most frequent container-inhabiting mosquito species in this study. Compared to native taxa, Ae. japonicus japonicus showed an extended seasonal activity period, presumably due to tolerance of colder water temperatures. Higher water temperatures and arable land represent distribution barriers to this species. The frequently co-occurring native species An. plumbeus might be useful as an indicator for potentially suitable oviposition habitats of Ae. japonicus japonicus in hitherto uncolonised regions. The results contribute to a better understanding of mosquito ecology and provide a basis for more targeted monitoring, distribution modelling and risk management of mosquitoes.

First records of Anopheles (Anopheles) plumbeus Stephens, 1828 and Culex (Culex) torrentium Martini, 1925 (Diptera: Culicidae) in Galicia (NW Spain)

We present the first records of Anopheles (Anopheles) plumbeus Stephens, 1828 and Culex (Culex) torrentium Martini, 1925 in the autonomous region of Galicia (NW Spain), obtained through the Rede Galega de Vixilancia de Vectores (ReGaViVec). This entomological surveillance network, which was initiated in 2017 by the Xunta de Galicia in collaboration with the University of Vigo and the University of Santiago de Compostela, aims to detect the arrival of invasive vectors as well as to improve the knowledge about mosquito populations (Diptera: Culicidae) in the Galician territory. This study shows the first findings of these species in Galicia, which have been reported in six different locations throughout the region: five in the province of Pontevedra and one in the province of Lugo. The 51 captured specimens were collected at different stages of development between July and September, 2018 and 2019 by using specialized traps arranged in favorable regions for the settlement and development of culicids.

The Nuisance Mosquito Anopheles plumbeus (Stephens, 1828) in Germany-A Questionnaire Survey May Help Support Surveillance and Control

The mosquito species Anopheles plumbeus is an aggressive biter and a potential vector of malaria parasites and West Nile virus. It occurs naturally at low population densities, as its larval development is adapted to the specific water qualities found in tree holes. However, probably owing to environmental changes, it has recently been observed in several European countries to use increasingly often artificial breeding habitats that may lead to mass development and severe annoyance to humans living close by. The perception of mosquito nuisance, however, is very subjective, and breeding habitats are not always known, thus impeding targeted surveillance and control. To relate nuisance by An. plumbeus to specific environmental conditions, a questionnaire survey was carried out addressing persons who had submitted specimens of this particular mosquito species to the German citizen science project “Mueckenatlas”, an instrument of passive mosquito surveillance. The questionnaire was intended to find out whether a nuisance situation linked to An. plumbeus had existed, whether mosquito breeding habitats could be identified and whether control measures had been conducted. Despite some efforts, the participants who claimed to suffer from an An. plumbeus nuisance problem had rarely identified the source of the mosquitoes. Once control measures had been performed on abandoned manure pits, however, the nuisance problem disappeared or mosquito abundance was at least significantly reduced. Nevertheless, no significant effect of abandoned manure pits on the probability of an An. plumbeus nuisance could be demonstrated in a multivariate logistic regression model testing various variables. Instead, a significant positive effect of a disused farm nearby was found. The reason is probably that manure pits as the most frequent source of An. plumbeus mass development are often located on disused farms, without most people’s knowledge about their existence. Disused farms are therefore appropriate candidates to consider when it comes to public health issues connected to An. plumbeus such as surveillance of mass development and implementation of control measures.