Indoor development of Aedes aegypti in Germany, 2016

AEDES ALBOPICTUS IN-HOUSE WINTER BREEDING IN GERMANY-A CASE STUDY

In February 2024, a resident of Mannheim, Germany, collected aggressively attacking mosquitoes in her home and forwarded them to the "Mueckenatlas" citizen science recording scheme. The specimens turned out to be Aedes albopictus. Upon discussing the situation and consultation on the biology of the Asian tiger mosquito, the submitter found numerous developmental stages in the water of a flowerpot with an orchid in her living room. The occurrence of adult tiger mosquitoes during wintertime in Central Europe has never been described before and is probably just an indoor phenomenon. Ideal conditions provided and continued indoor breeding and activity might be an exceptional way for the species to overwinter.

Invasive mosquito vectors in Europe: From bioecology to surveillance and management

Invasive mosquitoes (Diptera: Culicidae) play a key role in the spread of a number of mosquito-borne diseases worldwide. Anthropogenic changes play a significant role in affecting their distribution. Invasive mosquitoes usually take advantage from biotic homogenization and biodiversity reduction, therefore expanding in their distribution range and abundance. In Europe, climate warming and increasing urbanization are boosting the spread of several mosquito species of high public health importance. The present article contains a literature review focused on the biology and ecology of Aedes albopictus, Ae. aegypti, Ae. japonicus japonicus, Ae. koreicus, Ae. atropalpus and Ae. triseriatus, outlining their distribution and public health relevance in Europe. Bioecology insights were tightly connected with vector surveillance and control programs targeting these species. In the final section, a research agenda aiming for the effective and sustainable monitoring and control of invasive mosquitoes in the framework of Integrated Vector Management and One Health is presented. The WHO Vector Control Advisory Group recommends priority should be given to vector control tools with proven epidemiological impact.

Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission

Aedes aegypti is a ubiquitous vector of arboviruses mostly in urbanised areas throughout the tropics and subtropics and a growing threat beyond. Control of Ae. aegypti is difficult and costly, and no vaccines are available for most of the viruses it transmits. With practical control solutions our goal, ideally suitable for delivery by householders in affected communities, we reviewed the literature on adult Ae. aegypti biology and behaviour, within and close to the human home, the arena where such interventions must impact. We found that knowledge was vague or important details were missing for multiple events or activities in the mosquito life cycle, such as the duration or location of the many periods when females rest between blood feeding and oviposition. The existing body of literature, though substantial, is not wholly reliable, and evidence for commonly held "facts" range from untraceable to extensive. Source references of some basic information are poor or date back more than 60 years, while other information that today is accepted widely as "fact" is not supported by evidence in the literature. Many topics, e.g., sugar feeding, resting preferences (location and duration), and blood feeding, merit being revisited in new geographical regions and ecological contexts to identify vulnerabilities for exploitation in control.

Past, present and future distribution of the yellow fever mosquito Aedes aegypti: The European paradox

The global distribution of the yellow fever mosquito Aedes aegypti is the subject of considerable attention because of its pivotal role as a biological vector of several high profile disease pathogens including dengue, chikungunya, yellow fever, and Zika viruses. There is also a lot of interest in the projected future species' distribution. However, less effort has been focused on its historical distribution, which has changed substantially over the past 100 years, especially in southern Europe where it was once widespread, but largely disappeared by the middle of the 20th century. The present work utilises all available historical records of the distribution of Ae. aegypti in southern Europe, the Near East within the Mediterranean Basin and North Africa from the late 19th century until the 1960's to construct a spatial distribution model using matching historical climatic and demographic data. The resulting model was then implemented using current climate and demographic data to assess the potential distribution of the vector in the present. The models were rerun with several different assumptions about the thresholds that determine habitat suitability for Ae. aegypti. The historical model matches the historical distributions well. When it is run with current climate values, the predicted present day distribution is somewhat broader than it used to be particularly in north-west France, North Africa and Turkey. Though it is beginning to reappear in the eastern Caucasus, this 'potential' distribution clearly does not match the actual distribution of the species, which suggests some other factors are responsible for its absence. Future distributions based on the historical model also do not match future distributions derived from models based only on present day vector distributions, which predict little or no presence in the Mediterranean Region. At the same time, the vector is widespread in the USA which is predicted to consolidate its range there in future. This contradiction and the implication for possible re-invasion of Europe are discussed.

Drivers of spatio-temporal variation in mosquito submissions to the citizen science project 'Mückenatlas'

Intensified travel activities of humans and the ever growing global trade create opportunities of arthropod-borne disease agents and their vectors, such as mosquitoes, to establish in new regions. To update the knowledge of mosquito occurrence and distribution, a national mosquito monitoring programme was initiated in Germany in 2011, which has been complemented by a citizen science project, the ‘Mückenatlas’ since 2012. We analysed the ‘Mückenatlas’ dataset to (1) investigate causes of variation in submission numbers from the start of the project until 2017 and to (2) reveal biases induced by opportunistic data collection. Our results show that the temporal variation of submissions over the years is driven by fluctuating topicality of mosquito-borne diseases in the media and large-scale climate conditions. Hurdle models suggest a positive association of submission numbers with human population, catch location in the former political East Germany and the presence of water bodies, whereas precipitation and wind speed are negative predictors. We conclude that most anthropogenic and environmental effects on submission patterns are associated with the participants’ (recording) behaviour. Understanding how the citizen scientists’ behaviour shape opportunistic datasets help to take full advantage of the available information.

German Culex pipiens biotype molestus and Culex torrentium are vector-competent for Usutu virus

BACKGROUND

Usutu 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.

METHODS

In 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.

RESULTS

Culex 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.

CONCLUSIONS

Consistent 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.

Nine years of mosquito monitoring in Germany, 2011-2019, with an updated inventory of German culicid species

Before the background of increasingly frequent outbreaks and cases of mosquito-borne diseases in various European countries, Germany recently realised the necessity of updating decade-old data on the occurrence and spatiotemporal distribution of culicid species. Starting in 2011, a mosquito monitoring programme was therefore launched with adult and immature mosquito stages being collected at numerous sites all over Germany both actively by trapping, netting, aspirating and dipping, and passively by the citizen science project 'Mueckenatlas'. Until the end of 2019, about 516,000 mosquito specimens were analysed, with 52 (probably 53) species belonging to seven genera found, including several species not reported for decades due to being extremely rare (Aedes refiki, Anopheles algeriensis, Culex martinii) or local (Culiseta alaskaensis, Cs. glaphyroptera, Cs. ochroptera). In addition to 43 (probably 44 including Cs. subochrea) out of 46 species previously described for Germany, nine species were collected that had never been documented before. These consisted of five species recently established (Ae. albopictus, Ae. japonicus, Ae. koreicus, An. petragnani, Cs. longiareolata), three species probably introduced on one single occasion only and not established (Ae. aegypti, Ae. berlandi, Ae. pulcritarsis), and a newly described cryptic species of the Anopheles maculipennis complex (An. daciae) that had probably always been present but not been differentiated from its siblings. Two species formerly listed for Germany could not be documented (Ae. cyprius, Ae. nigrinus), while presence is likely for another species (Cs. subochrea), which could not be demonstrated in the monitoring programme as it can neither morphologically nor genetically be reliably distinguished from a closely related species (Cs. annulata) in the female sex. While Cs. annulata males were collected in the present programme, this was not the case with Cs. subochrea. In summary, although some species regarded endemic could not be found during the last 9 years, the number of culicid species that must be considered firmly established in Germany has increased to 51 (assuming Cs. subochrea and Ae. nigrinus are still present) due to several newly emerged ones but also to one species (Ae. cyprius) that must be considered extinct after almost a century without documentation. Most likely, introduction and establishment of the new species are a consequence of globalisation and climate warming, as three of them are native to Asia (Ae. albopictus, Ae. japonicus, Ae. koreicus) and three (Ae. albopictus, An. petragnani, Cs. longiareolata) are relatively thermophilic. Another thermophilic species, Uranotaenia unguiculata, which had been described for southwestern Germany in 1994 and had since been found only at the very site of its first detection, was recently documented at additional localities in the northeastern part of the country. As several mosquito species found in Germany are serious pests or potential vectors of disease agents and should be kept under permanent observation or even be controlled immediately on emergence, the German mosquito monitoring programme has recently been institutionalised and perpetuated.

The challenge of invasive mosquito vectors in the U.K. during 2016-2018: a summary of the surveillance and control of Aedes albopictus

Mosquito-borne diseases resulting from the expansion of two key vectors, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), continue to challenge whole regions and continents around the globe. In recent years there have been human cases of disease associated with Chikungunya, dengue and Zika viruses. In Europe, the expansion of Ae. albopictus has resulted in local transmission of Chikungunya and dengue viruses. This paper considers the risk that Ae. aegypti and Ae. albopictus represent for the U.K. and details the results of mosquito surveillance activities. Surveillance was conducted at 34 points of entry, 12 sites serving vehicular traffic and two sites of used tyre importers. The most common native mosquito recorded was Culex pipiens s.l. (Diptera: Culicidae). The invasive mosquito Ae. albopictus was detected on three occasions in southern England (September 2016, July 2017 and July 2018) and subsequent control strategies were conducted. These latest surveillance results demonstrate ongoing incursions of Ae. albopictus into the U.K. via ground vehicular traffic, which can be expected to continue and increase as populations in nearby countries expand, particularly in France, which is the main source of ex-continental traffic.

The effect of global change on mosquito-borne disease

More than 80% of the global population is at risk of a vector-borne disease, with mosquito-borne diseases being the largest contributor to human vector-borne disease burden. Although many global processes, such as land-use and socioeconomic change, are thought to affect mosquito-borne disease dynamics, research to date has strongly focused on the role of climate change. Here, we show, through a review of contemporary modelling studies, that no consensus on how future changes in climatic conditions will impact mosquito-borne diseases exists, possibly due to interacting effects of other global change processes, which are often excluded from analyses. We conclude that research should not focus solely on the role of climate change but instead consider growing evidence for additional factors that modulate disease risk. Furthermore, future research should adopt new technologies, including developments in remote sensing and system dynamics modelling techniques, to enable a better understanding and mitigation of mosquito-borne diseases in a changing world.

[Zika virus infection and the nervous system]

Zika virus is an arbovirus from the family of flaviviruses, which is transmitted by the mosquito Aedes aegyptii and also by the Asian mosquito Aedes albopticus. The largest observed Zika virus epidemic is currently taking place in North and South America, in the Caribbean, southern USA and Southeast Asia. In most cases the infection is an unspecific, acute, febrile disease. Neurological manifestations consist mainly of microcephaly in newborns and Guillain-Barré syndrome but other rare manifestations have also become known in the meantime, such as meningoencephalitis and myelitis. Therefore, the Zika virus, similar to other flaviviruses, has neuropathogenic properties. In particular, the drastic increase in microcephaly cases in Brazil has induced great research activities. The virus is transmitted perinatally and can be detected in the amniotic fluid, placenta and brain tissue of the newborn. Vaccination or a causal therapy does not yet exist. The significant increase in Guillain-Barré syndrome induced by the Zika virus was observed during earlier outbreaks. In the meantime, scientifically clear connections between a Zika virus infection and these neurological manifestations have been shown. Long-term studies and animal models should be used for a better understanding of the pathomechanisms of this disease.

Emerging mosquito species in Germany-a synopsis after 6 years of mosquito monitoring (2011-2016)

Globalisation and climate change are the main drivers of invasion of non-endemic regions by mosquitoes. Mass transportation of people, animals and goods facilitate accidental long-distance displacement while climate warming supports active spread and establishment of thermophilic species. In the framework of a mosquito-monitoring programme, eight non-indigenous culicid species have been registered in Germany since 2011, with four of them being more or less efficient vectors of disease agents and another four now considered established. The eight newly emerged species include Aedes albopictus, Ae. japonicus, Ae. aegypti, Ae. koreicus, Ae. berlandi, Ae. pulcritarsis, Anopheles petragnani and Culiseta longiareolata. We here review recent findings and at the same time present new findings of specimens of non-native mosquito species in Germany.