A standard photomap of the ovarian nurse cell chromosomes for the dominant malaria vector in Europe and Middle East Anopheles sacharovi

Phylogenomics revealed migration routes and adaptive radiation timing of Holarctic malaria mosquito species of the Maculipennis Group

BACKGROUND

Phylogenetic analyses of closely related species of mosquitoes are important for better understanding the evolution of traits contributing to transmission of vector-borne diseases. Six out of 41 dominant malaria vectors of the genus Anopheles in the world belong to the Maculipennis Group, which is subdivided into two Nearctic subgroups (Freeborni and Quadrimaculatus) and one Palearctic (Maculipennis) subgroup. Although previous studies considered the Nearctic subgroups as ancestral, details about their relationship with the Palearctic subgroup, and their migration times and routes from North America to Eurasia remain controversial. The Palearctic species An. beklemishevi is currently included in the Nearctic Quadrimaculatus subgroup adding to the uncertainties in mosquito systematics.

RESULTS

To reconstruct historic relationships in the Maculipennis Group, we conducted a phylogenomic analysis of 11 Palearctic and 2 Nearctic species based on sequences of 1271 orthologous genes. The analysis indicated that the Palearctic species An. beklemishevi clusters together with other Eurasian species and represents a basal lineage among them. Also, An. beklemishevi is related more closely to An. freeborni, which inhabits the Western United States, rather than to An. quadrimaculatus, a species from the Eastern United States. The time-calibrated tree suggests a migration of mosquitoes in the Maculipennis Group from North America to Eurasia about 20-25 million years ago through the Bering Land Bridge. A Hybridcheck analysis demonstrated highly significant signatures of introgression events between allopatric species An. labranchiae and An. beklemishevi. The analysis also identified ancestral introgression events between An. sacharovi and its Nearctic relative An. freeborni despite their current geographic isolation. The reconstructed phylogeny suggests that vector competence and the ability to enter complete diapause during winter evolved independently in different lineages of the Maculipennis Group.

CONCLUSIONS

Our phylogenomic analyses reveal migration routes and adaptive radiation timing of Holarctic malaria vectors and strongly support the inclusion of An. beklemishevi into the Maculipennis Subgroup. Detailed knowledge of the evolutionary history of the Maculipennis Subgroup provides a framework for examining the genomic changes related to ecological adaptation and susceptibility to human pathogens. These genomic variations may inform researchers about similar changes in the future providing insights into the patterns of disease transmission in Eurasia.

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.

New Cytogenetic Photomap and Molecular Diagnostics for the Cryptic Species of the Malaria Mosquitoes Anopheles messeae and Anopheles daciae from Eurasia

The Eurasian malaria vector Anopheles messeae is a widely spread and genetically diverse species. Five widespread polymorphic chromosomal inversions were found in natural populations of this mosquito. A cryptic species, Anopheles daciae, was differentiated from An. messeae by the presence of several nucleotide substitutions in the Internal Transcribed Spacer 2 (ITS2) region of ribosomal DNA. However, because of the absence of a high-quality reference cytogenetic map, the inversion polymorphisms in An. daciae and An. messeae remain poorly understood. Moreover, a recently determined heterogeneity in ITS2 in An. daciae questioned the accuracy of the previously used Restriction Fragment Length Polymorphism (RFLP) assay for species diagnostics. In this study, a standard-universal cytogenetic map was constructed based on orcein stained images of chromosomes from salivary glands for population studies of the chromosomal inversions that can be used for both An. messeae and An. daciae. In addition, a new ITS2-RFLP approach for species diagnostics was developed. Both methods were applied to characterize inversion polymorphism in populations of An. messeae and An. daciae from a single location in Western Siberia in Russia. The analysis demonstrates that cryptic species are remarkably different in their frequencies of chromosomal inversion variants. Our study supports previous observations that An. messeae has higher inversion polymorphism in all autosomes than the cryptic species An. daciae.

The Development of Cytogenetic Maps for Malaria Mosquitoes

Anopheline mosquitoes are important vectors of human malaria. Next-generation sequencing opens new opportunities for studies of mosquito genomes to uncover the genetic basis of a Plasmodium transmission. Physical mapping of genome sequences to polytene chromosomes significantly improves reference assemblies. High-resolution cytogenetic maps are essential for anchoring genome sequences to chromosomes as well as for studying breakpoints of chromosome rearrangements and chromatin protein localization. Here we describe a detailed pipeline for the development of high-resolution cytogenetic maps using polytene chromosomes of malaria mosquitoes. We apply this workflow to the refinement of the cytogenetic map developed for Anopheles beklemishevi.