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.

Anopheles daciae, a new country record for Finland

Mosquitoes (Diptera: Culicidae) were collected throughout Finland between 2013 and 2018 to determine species distributions. During the course of molecular identifications of specimens belonging to the Anopheles maculipennis complex, ribosomal internal transcribed spacer 2 sequences and link-reared specimens revealed the presence of Anopheles daciae Linton, Nicolescu & Harbach (n = 37), a new country record, as well as Anopheles messeae Falleroni (n = 19) in the collections. Although the sample size is low, distinctions are apparent in the distributions of these two species, with An. daciae present in south-eastern and central Finland, including the regions of Kanta-Häme, Pirkanmaa, Pohjois-Pohjanmaa, Päijät-Häme and Satakunta, and An. messeae present in the southern and south-eastern regions of Åland (Ahvenanmaa), Etelä-Savo, Kanta-Häme, Kymenlaakso, Päijät-Häme, Satakunta, Uusimaa and Varsinais-Suomi. All reports of An. messeae in Finland prior to 2018 should therefore be recognized as potentially being either An. messeae or An. daciae. Because these species are potential vectors of malarial protozoa, it is important to have full knowledge of their distributions across Europe, particularly in the face of climate warming.

Species composition, geographical distribution and seasonal abundance of the Anopheles maculipennis complex along the Upper Rhine, Germany

Between May and September 2016, mosquitoes were collected on a biweekly basis at 55 locations with CO₂-baited encephalitis vector surveillance traps along the Upper Rhine, Germany, to evaluate the species composition, geographical distribution and abundance of the Anopheles maculipennis complex, some members of this complex being considered vectors of historical malaria in Germany. A total of 2115 Anopheles maculipennis complex specimens were collected during the season, of which a sample of 1252 individuals was determined to species level by amplification of species-specific internal transcribed spacer 2 (ITS2) sequences. A total of 856 individuals of Anopheles daciae (68.37%), 394 Anopheles messeae (31.47%) and 2 Anopheles maculipennis s.s. (0.16%) were recorded. The number and proportion of A. daciae was remarkably higher in the northern meandering zone of the Upper Rhine (843 specimens, 79.90%), than in the more canalised southern furcation zone where A. messeae with 183 collected specimens represented 92.89% of 197 classified individuals. The average number of collected A. maculipennis s.l. individuals per trapping site was 38.45, equalling 0.64% of the total mosquito collection. Despite an increase in imported malaria cases, this comparatively low abundance of A. maculipennis s.l. may indicate a low risk of endemic malaria transmission by members of the A. maculipennis complex today. The proportionally dominance of A. daciae suggests that this species could be suspected the main historical vector of malaria in the Upper Rhine region. Sequence analyses of the ITS2 fragment revealed intraindividual polymorphisms within 3 of 5 diagnostic nucleotides in all specimens of A. daciae, raising the question if additional loci should be considered, to gain further insight into the taxonomical relation to A. messeae.

Distribution of Anopheles daciae and other Anopheles maculipennis complex species in Serbia

Malaria is one of the most severe health problems facing the world today. Until the mid-twentieth century, Europe was an endemic area of malaria, with the Balkan countries being heavily infested. Sibling species belonging to the Anopheles maculipennis complex are well-known as effective vectors of Plasmodium in Europe. A vast number of human malaria cases in the past in the former Yugoslavia territory have stressed the significance of An. maculipennis complex species as primary and secondary vectors. Therefore, the present study evaluates the species composition, geographic distribution and abundance of these malaria vector species. Mosquitoes were collected in the northern Serbian province of Vojvodina and analysed by PCR-RFLP, multiplex PCR and sequencing of the ITS2 intron of genomic rDNA. Four sibling species of the An. maculipennis complex were identified. Both larvae and adults of the recently described species An. daciae were identified for the first time in Serbia. In 250 larval samples, 109 (44%) An. messeae, 90 (36%) An. maculipennis s.s., 33 (13%) An. daciae and 18 (7%) An. atroparvus were identified. In adult collections, 81 (47%) An. messeae, 55 (32%) An. daciae, 33 (19%) An. maculipennis s.s., and 3 (2%) An. atroparvus were recorded. The most abundant species in Vojvodina was An. messeae, whereas An. atroparvus was confirmed a rare species in all parts. Since this species is a potentially, highly competent malarial vector, low population density could be crucial to prevent a new establishment of endemic malaria transmission in Serbia.

Urbanization impact on mosquito community and the transmission potential of filarial infection in central Europe

BACKGROUND

Despite long-term research on dirofilariosis in Slovakia, little attention has thus far been paid to Dirofilaria vectors. The particular aim of the present study was molecular screening for filarioid parasites in two different habitats of Bratislava, the capital city of Slovakia. In addition, the effect of urbanisation on mosquito species abundance and composition, associated with the risk of mosquito-borne infections, was studied and discussed.

METHODS

Mosquitoes were identified by morphological features, and molecular methods were also used for determination of selected individuals belonging to cryptic species from the Anopheles maculipennis and Culex pipiens complexes. The presence of filarioid DNA (Dirofilaria repens, Dirofilaria immitis and Setaria spp.) was detected using standard PCR approaches and sequencing.

RESULTS

A total of 6957 female mosquitoes were collected for the study. Overall, the most abundant mosquito species was Aedes vexans, closely followed by unidentified members of the Cx. pipiens complex and the less numerous but still plentiful Ochlerotatus sticticus species. Further investigation of mosquito material revealed 4.26% relative prevalence of Dirofilaria spp., whereby both species, D. repens and D. immitis, were identified. The majority of positive mosquito pools had their origin in a floodplain area on the outskirts of the city, with a relative prevalence of 5.32%; only two mosquito pools (1.26%) were shown to be positive in the residential zone of Bratislava. Setaria spp. DNA was not detected in mosquitoes within this study.

CONCLUSIONS

The study presented herein represents initial research focused on molecular mosquito screening for filarioid parasites in urban and urban-fringe habitats of Bratislava, Slovakia. Molecular analyses within the Cx. pipiens complex identified two biotypes: Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus. To our knowledge, Dirofilaria spp. were detected for the first time in Slovakia in mosquitoes other than Ae. vexans, i.e. D. repens in Anopheles messeae and unidentified members of An. maculipennis and Cx. pipiens complexes, and D. immitis in Coquillettidia richiardii and Cx. pipiens biotype pipiens. Both dirofilarial species were found in Och. sticticus. The suitable conditions for the vectors' biology would represent the main risk factor for dirofilariosis transmission.

Distribution of individual members of the mosquito Anopheles maculipennis complex in Germany identified by newly developed real-time PCR assays

Owing to their role as vectors of malaria parasites, species of the Anopheles maculipennis complex (Diptera: Culicidae) Meigen were intensively studied in the past, but with the disappearance of malaria in Germany in the middle of the last century, the interest in this field of research declined. A comprehensive ecological analysis of the current species distribution for Germany is lacking. Between 2010 and 2013, a total of 1445 mosquitoes of the An. maculipennis complex were collected at 72 different sites in Germany. The samples comprise 722 single individuals as well as 723 individuals in 90 pools of up to 25 mosquitoes. All samples were analysed with newly developed species-specific qPCR assays for the identification of the four German species using nucleotide differences within the internal transcribed spacer 2 (ITS2) ribosomal DNA. All gathered data were used for species distribution modelling. The overall prevalence of An. messeae s.l. was highest with 98.89% of all pools; An. daciae with 6.93% of all individuals and An. messeae s.s. with 69.53%. The prevalence of the other two species was relatively low: An. maculipennis s.s. with 13.30% of all individuals (6.67% of all pools) and An. atroparvus with 1.80% of all individuals (1.11% of all pools).