The Anopheles maculipennis complex (Diptera: Culicidae) in Germany: an update following recent monitoring activities

Malaria in a metropolitan region of Southern Germany: past, present and future perspectives on a protozoan infection with the potential of re-appearance in Central Europe

BACKGROUND

Malaria occurred endemically in Germany until the twentieth century. Climate change and globalization are known to promote the spreading of malaria. Erlangen is a city with just under 120,000 inhabitants located in the Nürnberg metropolitan region, Federal State of Bavaria, Southern Germany. Historical findings, current climate data, microbiological data (local and state level) and vector surveillance data are used to estimate the risk of re-emergence and autochthonous transmission of malaria in the area of Erlangen.

METHODS

Historical data was obtained by searching literature. Climatic data were retrieved from the German Climate Data Centre. Data on reported (supra-)regional infections were obtained from the Robert-Koch Institute. Cases of malaria diagnosed at the Institute of Clinical Microbiology, Immunology and Hygiene (University Hospital Erlangen) complement this data. The citizen science project "Mückenatlas" (Mosquito Atlas), the German mosquito database (CULBASE) and the company Biogents AG provided mosquito surveillance data.

RESULTS

Malaria was highly endemic in Erlangen in the nineteenth century, with 18% of hospitalized patients suffering from this disease in 1860, but disappeared during the first half of the twentieth century. After the end of World War II, autochthonous 'malaria tertiana' (tertian malaria) occurred in neighbouring Nürnberg, demonstrating the regional malaria potential. In recent decades, the average monthly temperature increased by 1.6 °C. In Erlangen and the surrounding area, three potential vectors of tertian malaria parasites are prevalent (Anopheles messeae, Anopheles maculipennis sensu stricto, and Anopheles plumbeus). In addition, Anopheles daciae, which has unknown potential of Plasmodium transmission, and Anopheles claviger sensu lato have been detected. In recent years, malaria diagnosed in Erlangen mainly resulted from travelling to Africa. Plasmodium vivax accounted for only a small proportion of these cases (2010-2023: n = 5, 17%).

CONCLUSION

Future autochthonous transmission of malaria parasites in Erlangen is possible, although re-establishment of a natural transmission cycle is currently unlikely. In order to avoid unexpected autochthonous malaria, surveillance and prevention measures should be considered. Patients with fever after visiting endemic areas need to be analysed for Plasmodium infection.

Mosquitoes (Diptera: Culicidae) of Poland: An Update of Species Diversity and Current Challenges

This article presents the current state of knowledge of mosquito species (Diptera: Culicidae) occurring in Poland. In comparison to the most recently published checklists (1999 and 2007), which listed 47 mosquito species, four species (Aedes japonicus, Anopheles daciae, Anopheles hyrcanus, and Anopheles petragnani) are added to the Polish fauna. Our new checklist of Polish mosquito fauna includes 51 species of mosquitoes from five genera: Aedes (30), Anopheles (8), Coquillettidia (1), Culiseta (7), and Culex (5). Aspects of the ecology and biology of the Polish mosquito fauna, with particular emphasis on newly recorded species, are discussed.

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.

Airport Malaria in Non-Endemic Areas: New Insights into Mosquito Vectors, Case Management and Major Challenges

Despite the implementation of preventive measures in airports and aircrafts, the risk of importing Plasmodium spp. infected mosquitoes is still present in malaria-free countries. Evidence suggests that mosquitoes have found a new alliance with the globalization of trade and climate change, leading to an upsurge of malaria parasite transmission around airports. The resulting locally acquired form of malaria is called Airport malaria. However, piecemeal information is available, regarding its epidemiological and entomological patterns, as well as the challenges in the diagnosis, treatment, and prevention. Understanding these issues is a critical step towards a better implementation of control strategies. To cross reference this information, we conducted a systematic review on 135 research articles published between 1969 (when the first cases of malaria in airports were reported) and 2020 (i.e., 51 years later). It appears that the risk of malaria transmission by local mosquito vectors in so called malaria-free countries is not zero; this risk is more likely to be fostered by infected vectors coming from endemic countries by air or by sea. Furthermore, there is ample evidence that airport malaria is increasing in these countries. From 2010 to 2020, the number of cases in Europe was 7.4 times higher than that recorded during the 2000-2009 decade. This increase may be associated with climate change, increased international trade, the decline of aircraft disinsection, as well as delays in case diagnosis and treatment. More critically, current interventions are weakened by biological and operational challenges, such as drug resistance in malaria parasites and vector resistance to insecticides, and logistic constraints. Therefore, there is a need to strengthen malaria prevention and treatment for people at risk of airport malaria, and implement a rigorous routine entomological and epidemiological surveillance in and around airports.

Single nucleotide polymorphism analysis of the ITS2 region of two sympatric malaria mosquito species in Sweden: Anopheles daciae and Anopheles messeae

Four species of the Anopheles maculipennis complex have previously been recorded in Sweden. A recent addition to the complex is Anopheles daciae, which is considered to be closely related to, but distinct from Anopheles messeae. The original designation of An. daciae was based on five genetic differences (161, 165, 167, 362 and 382) in the second internal transcribed spacer (ITS) 2 of the ribosomal RNA. Further studies have shown that only two nucleotide differences (362 and 382) robustly separate the species. Thirty-three An. maculipennis complex mosquitoes were collected in the province of Uppland, Sweden. All were An. daciae but showed double peaks for three variable positions (161, 165 and 167). When cloned, the intra-individual nucleotide variation was almost exclusively fixed with either TTC or AAT, originally diagnostic for An. messae and An. daciae, respectively. To further investigate the intra-individual variation, nine An. daciae and 11 An. messeae were collected in southern Sweden and their ITS2 fragments were amplified and sequenced using Illumina MiSeq sequencing (Illumina, Inc., San Diego, CA, USA). For the diagnostic nucleotide 382 no intra-individual variation could be detected. However, although each An. daciae specimen carried several ITS2 sequence variants for the four other nucleotides, there was no intra-individual variation in the An. messeae specimens.

Laboratory colonization and maintenance of Anopheles atroparvus from the Ebro Delta, Spain

Background

Historically, Anopheles atroparvus has been considered one of the most important malaria vectors in Europe. Since malaria was eradicated from the European continent, the interest in studying its vectors reduced significantly. Currently, to better assess the potential risk of malaria resurgence on the continent, there is a growing need to update the data on susceptibility of indigenous Anopheles populations to imported Plasmodium species. In order to do this, as a first step, an adequate laboratory colony of An. atroparvus is needed.

Methods

Anopheles atroparvus mosquitoes were captured in rice fields from the Ebro Delta (Spain). Field-caught specimens were maintained in the laboratory under simulated field-summer conditions. Adult females were artificially blood-fed on fresh whole rabbit blood for oviposition. First- to fourth-instar larvae were fed on pulverized fish and turtle food. Adults were maintained with a 10% sucrose solution ad libitum.

Results

An An. atroparvus population from the Ebro Delta was successfully established in the laboratory. During the colonization process, feeding and hatching rates increased, while a reduction in larval mortality rate was observed.

Conclusions

The present study provides a detailed rearing and maintenance protocol for An. atroparvus and a publicly available reference mosquito strain within the INFRAVEC2 project for further research studies involving vector-parasite interactions.

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.

Chromosome and Genome Divergence between the Cryptic Eurasian Malaria Vector-Species Anopheles messeae and Anopheles daciae

Chromosomal inversions are important drivers of genome evolution. The Eurasian malaria vector Anophelesmesseae has five polymorphic inversions. A cryptic species, An. daciae, has been discriminated from An. messeae based on five fixed nucleotide substitutions in the internal transcribed spacer 2 (ITS2) of ribosomal DNA. However, the inversion polymorphism in An. daciae and the genome divergence between these species remain unexplored. In this study, we sequenced the ITS2 region and analyzed the inversion frequencies of 289 Anopheles larvae specimens collected from three locations in the Moscow region. Five individual genomes for each of the two species were sequenced. We determined that An. messeae and An. daciae differ from each other by the frequency of polymorphic inversions. Inversion X1 was fixed in An. messeae but polymorphic in An. daciae populations. The genome sequence comparison demonstrated genome-wide divergence between the species, especially pronounced on the inversion-rich X chromosome (mean Fst = 0.331). The frequency of polymorphic autosomal inversions was higher in An. messeae than in An. daciae. We conclude that the X chromosome inversions play an important role in the genomic differentiation between the species. Our study determined that An. messeae and An. daciae are closely related species with incomplete reproductive isolation.

Can data from native mosquitoes support determining invasive species habitats? Modelling the climatic niche of Aedes japonicus japonicus (Diptera, Culicidae) in Germany

Invasive mosquito species and the pathogens they transmit represent a serious health risk to both humans and animals. Thus, predictions on their potential geographic distribution are urgently needed. In the case of a recently invaded region, only a small number of occurrence data is typically available for analysis, and absence data are not reliable. To overcome this problem, we have tested whether it is possible to determine the climatic ecological niche of an invasive mosquito species by using both the occurrence data of other, native species and machine learning. The approach is based on a support vector machine and in this scenario applied to the Asian bush mosquito (Aedes japonicus japonicus) in Germany. Presence data for this species (recorded in the Germany since 2008) as well as for three native mosquito species were used to model the potential distribution of the invasive species. We trained the model with data collected from 2011 to 2014 and compared our predicted occurrence probabilities for 2015 with observations found in the field throughout 2015 to evaluate our approach. The prediction map showed a high degree of concordance with the field data. We applied the model to medium climate conditions at an early stage of the invasion (2011–2015), and developed an explanation for declining population densities in an area in northern Germany. In addition to the already known distribution areas, our model also indicates a possible spread to Saarland, southwestern Rhineland-Palatinate and in 2015 to southern Bavaria, where the species is now being increasingly detected. However, there is also evidence that the possible distribution area under the mean climate conditions was underestimated.

Mosquitoes as Arbovirus Vectors: From Species Identification to Vector Competence

Mosquitoes and other arthropods transmit a large number of medically important pathogens, in particular viruses. These arthropod-borne viruses (arboviruses) include a wide variety of RNA viruses belonging to the Flaviviridae family (West Nile virus (WNV), Usutu virus (USUV), Dengue virus (DENV), Japanese encephalitis virus (JEV), Zika virus (ZIKV)), the Togaviridae family (Chikungunya virus (CHIKV)), and Bunyavirales order (Rift Valley fever virus (RVFV)) (please refer also to Table 9.1). Arboviral transmission to humans and livestock constitutes a major threat to public health and economy as illustrated by the emergence of ZIKV in the Americas, RVFV outbreaks in Africa, and the worldwide outbreaks of DENV. To answer the question if those viral pathogens also pose a risk to Europe, we need to first answer the key questions (summarized in Fig. 9.1):

Who could contribute to such an outbreak? Information about mosquito species resident or imported, potential hosts and viruses able to infect vectors and hosts in Germany is needed.

Where would competent mosquito species meet favorable conditions for transmission? Information on the minimum requirements for efficient replication of the virus in a given vector species and subsequent transmission is needed.

How do viruses and vectors interact to facilitate transmission? Information on the vector immunity, vector physiology, vector genetics, and vector microbiomes is needed.

Cryptic species Anopheles daciae (Diptera: Culicidae) found in the Czech Republic and Slovakia

We report the distribution of mosquitoes of the maculipennis complex in two distinct areas of the Czech Republic (Bohemia and South Moravia) and in one locality of neighbouring Slovakia with emphasis on the detection of the newly described cryptic species Anopheles daciae (Linton, Nicolescu & Harbach, 2004). A total of 691 mosquitoes were analysed using a species-specific multiplex PCR assay to differentiate between the members of the maculipennis complex. In the Czech Republic, we found Anopheles maculipennis (with a prevalence rate of 1.4%), Anopheles messeae (49.0%) and Anopheles daciae (49.6%). In Slovakia, only An. messeae (52.1%) and An. daciae (47.9%) were detected. In this study, An. daciae was documented for the first time in the two countries where it represented a markedly higher proportion of maculipennis complex species (with an overall prevalence almost reaching 50%) in comparison to previous reports from Germany, Romania and Poland. The determination of the differential distribution of maculipennis complex species will contribute to assessing risks of mosquito-borne diseases such as malaria or dirofilariasis.