Evaluation of the vector competence for Batai virus of native Culex and exotic Aedes species in Central Europe

BACKGROUND

Batai virus (BATV) is a zoonotic arbovirus of veterinary importance. A high seroprevalence in cows, sheep and goats and infection in different mosquito species has been observed in Central Europe. Therefore, we studied indigenous as well as exotic species of the genera Culex and Aedes for BATV vector competence at different fluctuating temperature profiles.

METHODS

Field caught Culex pipiens biotype pipiens, Culex torrentium, Aedes albopictus and Aedes japonicus japonicus from Germany and Aedes aegypti laboratory colony were infected with BATV strain 53.3 using artificial blood meals. Engorged mosquitoes were kept under four (Culex species) or three (Aedes species) fluctuating temperature profiles (18 ± 5 °C, 21 ± 5 °C, 24 ± 5 °C, 27 ± 5 °C) at a humidity of 70% and a dark/light rhythm of 12:12 for 14 days. Transmission was measured by testing the saliva obtained by forced salivation assay for viable BATV particles. Infection rates were analysed by testing whole mosquitoes for BATV RNA by quantitative reverse transcription PCR.

RESULTS

No transmission was detected for Ae. aegypti, Ae. albopictus or Ae. japonicus japonicus. Infection was observed for Cx. p. pipiens, but only in the three conditions with the highest temperatures (21 ± 5 °C, 24 ± 5 °C, 27 ± 5 °C). In Cx. torrentium infection was measured at all tested temperatures with higher infection rates compared with Cx. p. pipiens. Transmission was only detected for Cx. torrentium exclusively at the highest temperature of 27 ± 5 °C.

CONCLUSIONS

Within the tested mosquito species, only Cx. torrentium seems to be able to transmit BATV if the climatic conditions are feasible.

Using geometric wing morphometrics to distinguish Aedes japonicus japonicus and Aedes koreicus

BACKGROUND

Aedes japonicus japonicus (Theobald, 1901) and Aedes koreicus (Edwards, 1917) have rapidly spread in Europe over the last decades. Both species are very closely related and occur in sympatry. Females and males are difficult to distinguish. However, the accurate species discrimination is important as both species may differ in their vectorial capacity and spreading behaviour. In this study, we assessed the potential of geometric wing morphometrics as alternative to distinguish the two species.

METHODS

A total of 147 Ae. j. japonicus specimens (77 females and 70 males) and 124 Ae. koreicus specimens (67 females and 57 males) were collected in southwest Germany. The left wing of each specimen was removed, mounted and photographed. The coordinates of 18 landmarks on the vein crosses were digitalised by a single observer. The resulting two-dimensional dataset was used to analyse the differences in the wing size (i.e. centroid size) and wing shape between Ae. j. japonicus and Ae. koreicus using geometric morphometrics. To analyse the reproducibility of the analysis, the landmark collection was repeated for 20 specimens per sex and species by two additional observers.

RESULTS

The wing size in female Ae. koreicus was significantly greater than in Ae. j. japonicus but did not differ significantly for males. However, the strong overlap in wing size also for the females would not allow to discriminate the two species. In contrast, the wing shape clustering was species specific and a leave-one-out validation resulted in a reclassification accuracy of 96.5% for the females and 91.3% for the males. The data collected by different observers resulted in a similar accuracy, indicating a low observer bias for the landmark collection.

CONCLUSIONS

Geometric wing morphometrics provide a reliable and robust tool to distinguish female and male specimens of Ae. j. japonicus and Ae. koreicus.

Interaction of Mesonivirus and Negevirus with arboviruses and the RNAi response in Culex tarsalis-derived cells

BACKGROUND

Mosquito-specific viruses (MSVs) comprise a variety of different virus families, some of which are known to interfere with infections of medically important arboviruses. Viruses belonging to the family Mesoniviridae or taxon Negevirus harbor several insect-specific viruses, including MSVs, which are known for their wide geographical distribution and extensive host ranges. Although these viruses are regularly identified in mosquitoes all over the world, their presence in mosquitoes in Germany had not yet been reported.

METHODS

A mix of three MSVs (Yichang virus [Mesoniviridae] and two negeviruses [Daeseongdong virus and Dezidougou virus]) in a sample that contained a pool of Coquillettidia richiardii mosquitoes collected in Germany was used to investigate the interaction of these viruses with different arboviruses in Culex-derived cells. In addition, small RNA sequencing and analysis of different mosquito-derived cells infected with this MSV mix were performed.

RESULTS

A strain of Yichang virus (Mesoniviridae) and two negeviruses (Daeseongdong virus and Dezidougou virus) were identified in the Cq. richiardii mosquitoes sampled in Germany, expanding current knowledge of their circulation in central Europe. Infection of mosquito-derived cells with these three viruses revealed that they are targeted by the small interfering RNA (siRNA) pathway. In Culex-derived cells, co-infection by these three viruses had varying effects on the representative arboviruses from different virus families (Togaviridae: Semliki forest virus [SFV]; Bunyavirales: Bunyamwera orthobunyavirus [BUNV]; or Flaviviridae: Usutu virus [USUV]). Specifically, persistent MSV co-infection inhibited BUNV infection, as well as USUV infection (but the latter only at specific time points). However, the impact on SFV infection was only noticeable at low multiplicity of infection (MOI 0.1) and at specific time points in combination with the infection status.

CONCLUSIONS

Taken together, these results are important findings that will lead to a better understanding of the complex interactions of MSVs, mosquitoes and arboviruses.

Genetic diversity and wing geometric morphometrics among four populations of Aedes aegypti (Diptera: Culicidae) from Benin

BACKGROUND

The impact of the arbovirus vector Aedes aegypti is of major concern for global public health as the viruses that it transmits affect millions of people each year worldwide. Originating in Africa, Ae. aegypti has now spread throughout much of the world. While the genetic makeup of Ae. aegypti in the New World has been extensively studied, there is limited knowledge on its genetic diversity in Africa, particularly at a microgeographical level.

METHODS

We investigated mitochondrial cytochrome oxidase I of four Ae. aegypti populations from Benin and employed wing morphometric analyses as a cost-effective and reliable tool to explore population structure. Our sampling encompassed various areas of Benin, from the southern to the northern borders of the country, and included urban, semi-urban, and sylvatic sites.

RESULTS

We observed a notable level of genetic diversity (haplotype diversity of 0.8333) and nucleotide diversity (0.00421986), and identified seven distinct haplotypes. Sylvatic and semi-urban sites exhibited a greater number of haplotypes compared to urban sites. Utilizing 18 wing landmarks, we calculated the centroid size, which revealed significant variation among the three landscape types. However, principal component analysis, employed to assess wing shape variation, did not demonstrate significant differences between populations based on landscape type.

CONCLUSIONS

Our findings indicate substantial genetic and morphological diversity among Ae. aegypti populations in Benin, and provide insight into important biological characteristics of these populations with respect to their potential to transmit viruses. To the best of our knowledge, this is the first study undertaken in Africa to integrate genetics with morphology to analyse the population structure of the major arbovirus vector Ae. aegypti.

Arbovirus Epidemiology: The Mystery of Unnoticed Epidemics in Ghana, West Africa

It is evident that all the countries surrounding Ghana have experienced epidemics of key arboviruses of medical importance, such as the recent dengue fever epidemic in Burkina Faso. Therefore, Ghana is considered a ripe zone for epidemics of arboviruses, mainly dengue. Surprisingly, Ghana never experienced the propounded deadly dengue epidemic. Indeed, it is mysterious because the mosquito vectors capable of transmitting the dengue virus, such as Aedes aegypti, were identified in Ghana through entomological investigations. Additionally, cases may be missed, as the diagnostic and surveillance capacities of the country are weak. Therefore, we review the arbovirus situation and outline probable reasons for the epidemic mystery in the country. Most of the recorded cases of arbovirus infections were usually investigated via serology by detecting IgM and IgG immunoglobulins in clinical samples, which is indicative of prior exposure but not an active case. This led to the identification of yellow fever virus and dengue virus as the main circulating arboviruses among the Ghanaian population. However, major yellow fever epidemics were reported for over a decade. It is important to note that the reviewed arboviruses were not frequently detected in the vectors. The data highlight the necessity of strengthening the diagnostics and the need for continuous arbovirus and vector surveillance to provide an early warning system for future arbovirus epidemics.

First Detection of the Invasive Mosquito Vector Aedes albopictus (Diptera: Culicidae) in Benin, West Africa, 2021

Aedes albopictus (Skuse) is native to Southeast Asia and has colonized tropical and temperate regions worldwide in the last three to four decades. In Africa, data on its distribution is incomplete. Most studies having focused on the abundance, competition to other species, and phylogenetics of this vector are from the central African region. Here, we report the first detection of Ae. albopictus in Benin, West Africa. A total of 13 specimens were collected during the study period in 2021. The phylogenetic analysis of a cytochrome oxidase c subunit I gene fragment revealed a close relationship to populations from tropical India. Because of its close geographical proximity to areas where it has been found, it is assumed that the species was introduced several years before and is currently widely distributed in Benin. Additional studies are needed to explore its distribution, expansion range, and competitive effects on native species.

Mosquito-Associated Viruses and Their Related Mosquitoes in West Africa

Mosquito-associated viruses (MAVs), including mosquito-specific viruses (MSVs) and mosquito-borne (arbo)viruses (MBVs), are an increasing public, veterinary, and global health concern, and West Africa is projected to be the next front for arboviral diseases. As in-depth knowledge of the ecologies of both western African MAVs and related mosquitoes is still limited, we review available and comprehensive data on their diversity, abundance, and distribution. Data on MAVs’ occurrence and related mosquitoes were extracted from peer-reviewed publications. Data on MSVs, and mosquito and vertebrate host ranges are sparse. However, more data are available on MBVs (i.e., dengue, yellow fever, chikungunya, Zika, and Rift Valley fever viruses), detected in wild and domestic animals, and humans, with infections more concentrated in urban areas and areas affected by strong anthropogenic changes. Aedes aegypti, Culex quinquefasciatus, and Aedes albopictus are incriminated as key arbovirus vectors. These findings outline MAV, related mosquitoes, key knowledge gaps, and future research areas. Additionally, these data highlight the need to increase our understanding of MAVs and their impact on host mosquito ecology, to improve our knowledge of arbovirus transmission, and to develop specific strategies and capacities for arboviral disease surveillance, diagnostic, prevention, control, and outbreak responses in West Africa.

Phlebotomine sand flies in Southwest Germany: an update with records in new locations

Background

Vector-borne diseases (VBD) are of growing global importance. Sand flies are potential vectors for phleboviruses (family Phenuiviridae) including Toscana virus (TOSV), Sicilian virus, Sandfly fever, Naples virus, and Leishmania parasites in Europe. To date, only two phlebotomine species have been recorded for Germany: Phlebotomus perniciosus and Phlebotomus mascittii. This study updates the distribution and abundance of the two occurring species.

Methods

An entomological field study was carried out during 2015–2018 to assess the abundance of sand flies in Southwest Germany within the federal states Baden-Wuerttemberg (BW) and Rhineland-Palatinate (RLP). A total of 176 collection sites were examined using CDC light traps.

Results

A total of 149 individuals of P. mascittii were collected. During 2015–2018, P. mascittii was found at all sites known positive from previous studies and was detected at 15 additional sites previously unknown for the presence of sand flies. Although the environment has changed considerably in 30 years, no significant difference in sand fly dynamics and distribution was found. Phlebotomus perniciosus has only been trapped once since 2001.

Conclusions

This study showed that sand flies occur in different areas in Southern Germany where they had not been recorded previously. Therefore, it can be assumed that they are more widespread than expected. In addition, sand flies could be found over several years at the same trapping sites, indicating population stability. This supports the need for continued surveillance of possible vector populations and urgent clarification of the vector competence of P. mascittii.

Blood-meal analysis of Culicoides (Diptera: Ceratopogonidae) reveals a broad host range and new species records for Romania

BACKGROUND

Culicoides biting midges are potential vectors of different pathogens. However, especially for eastern Europe, there is a lack of knowledge on the host-feeding patterns of this vector group. Therefore, this study aimed to identify Culicoides spp. and their vertebrate hosts collected in a wetland ecosystem.

METHODS

Culicoides spp. were collected weekly from May to August 2017, using Biogents traps with UV light at four sites in the Danube Delta Biosphere Reserve, Romania. Vectors and hosts were identified with a DNA barcoding approach. The mitochondrial cytochrome c oxidase subunit 1 was used to identify Culicoides spp., while vertebrate hosts were determined targeting cytochrome b or 16S rRNA gene fragments. A maximum likelihood phylogenetic tree was constructed to verify the biting midge identity against other conspecific Palaearctic Culicoides species. A set of unfed midges was used for morphological confirmation of species identification using slide-mounted wings.

RESULTS

Barcoding allowed the species identification and detection of corresponding hosts for 1040 (82.3%) of the 1264 analysed specimens. Eight Culicoides spp. were identified with Culicoides griseidorsum, Culicoides puncticollis and Culicoides submaritimus as new species records for Romania. For 39 specimens no similar sequences were found in GenBank. This group of unknown Culicoides showed a divergence of 15.6-16.3% from the closest identified species and clustered in a monophyletic clade, i.e. a novel species or a species without reference sequences in molecular libraries. For all Culicoides spp., nine mammalian and 24 avian species were detected as hosts. With the exception of C. riethi (n = 12), at least one avian host was detected for all Culicoides spp., but this host group only dominated for Culicoides kibunensis and the unknown Culicoides sp.. The most common host group were mammals (n = 993, 87.6% of all identified blood sources) dominated by cattle (n = 817, 70.6%).

CONCLUSIONS

Most Culicoides spp. showed a broad host-feeding pattern making them potential bridge vectors. At the same time, new records of biting midge species for Romania, as well as a potentially unknown Culicoides species, highlight the lack of knowledge regarding the biting midge species and their genetic diversity in eastern Europe.

Ecology of West Nile Virus in the Danube Delta, Romania: Phylogeography, Xenosurveillance and Mosquito Host-Feeding Patterns

The ecology of West Nile virus (WNV) in the Danube Delta Biosphere Reserve (Romania) was investigated by combining studies on the virus genetics, phylogeography, xenosurveillance and host-feeding patterns of mosquitoes. Between 2014 and 2016, 655,667 unfed and 3842 engorged mosquito females were collected from four sampling sites. Blood-fed mosquitoes were negative for WNV-RNA, but two pools of unfed Culex pipiens s.l./torrentium collected in 2014 were tested positive. Our results suggest that Romania experienced at least two separate WNV lineage 2 introductions: from Africa into Danube Delta and from Greece into south-eastern Romania in the 1990s and early 2000s, respectively. The genetic diversity of WNV in Romania is primarily shaped by in situ evolution. WNV-specific antibodies were detected for 19 blood-meals from dogs and horses, but not from birds or humans. The hosts of mosquitoes were dominated by non-human mammals (19 species), followed by human and birds (23 species). Thereby, the catholic host-feeding pattern of Culex pipiens s.l./torrentium with a relatively high proportion of birds indicates the species’ importance as a potential bridge vector. The low virus prevalence in combination with WNV-specific antibodies indicate continuous, but low activity of WNV in the Danube Delta during the study period.

Experimental transmission of Zika virus by Aedes japonicus japonicus from southwestern Germany

The invasive mosquito species Aedes japonicus japonicus (Ae. japonicus) is widely distributed in Central Europe and is a known vector of various arboviruses in the laboratory, including flaviviruses such as Japanese Encephalitis virus or West Nile virus. However, the vector competence of Ae. japonicus for the recently emerging Zika virus (ZIKV) has not been determined. Therefore, field-caught Ae. japonicus from Germany were orally infected with ZIKV and incubated at 21, 24, or 27 °C to evaluate the vector competence under climate conditions representative of the temperate regions (21 °C) in the species' main distribution area in Europe and of Mediterranean regions (27 °C). Aedes japonicus was susceptible to ZIKV at all temperatures, showing infection rates between 10.0% (21 °C) and 66.7% (27 °C). However, virus transmission was detected exclusively at 27 °C with a transmission rate of 14.3% and a transmission efficiency of 9.5%. Taking into account the present distribution of Ae. japonicus in the temperate regions of Central Europe, the risk of ZIKV transmission by the studied Ae. japonicus population in Central Europe has to be considered as low. Nevertheless, due to the species' vector competence for ZIKV and other mosquito-borne viruses, in combination with the possibility of further spread to Mediterranean regions, Ae. japonicus must be kept in mind as a potential vector of pathogens inside and outside of Europe.

Circulation of Dirofilaria immitis and Dirofilaria repens in the Danube Delta Biosphere Reserve, Romania

BACKGROUND

Dirofilariosis is an emerging vector-borne parasitic disease in Europe. Monitoring of wild and domestic carnivores demonstrated circulation of Dirofilaria spp. in Romania in the past. For the implementation of control measures, knowledge on the native mosquito community responsible for Dirofilaria spp. transmission is required.

METHODS

Mosquito samples originated from a longitudinal study previously performed in the Danube Delta Biosphere Reserve. Mosquito pools were screened for Dirofilaria immitis and Dirofilaria repens. The samples comprised 240,572 female mosquito specimens collected every ten days between April and September in 2014 at four different trapping sites. In addition, blood samples of 36 randomly selected dogs were collected in 2016 in each of the four mosquito sampling sites. A duplex real-time assay was used to detect the presence of one or both Dirofilaria species for each sample. This assay targets the cytochrome c oxidase subunit 1 and the 16S rRNA gene fragments to differentiate both parasites.

RESULTS

Dirofilaria immitis and D. repens were detected in mosquito pools at all four trapping sites. In the 2118 mosquito pools tested, D. immitis was identified for eight and D. repens for six of the 14 screened mosquito taxa, with a higher prevalence of D. immitis (4.53% of analysed pools) compared to D. repens (1.09%). Dirofilaria spp. were also identified in dogs from the same sampling sites with a prevalence of 30.56%. For both Dirofilaria species, the highest estimated infection rates (EIRs) were found in Anopheles maculipennis (s.l.) (D. immitis: EIR = 0.206 per 100 specimens, D. repens: EIR = 0.066 per 100 specimens). In contrast, Coquillettidia richiardii and Anopheles hyrcanus as the most frequent taxa had infection rates which were significantly lower: Cq. richiardii (D. immitis: EIR = 0.021; D. repens: EIR = 0.004); An. hyrcanus (D. immitis: EIR = 0.028; D. repens: EIR = 0.006). The number of positive pools per calendar week was positively correlated with the number of screened pools per calendar week, suggesting constant Dirofilaria spp. transmission during the observation period.

CONCLUSIONS

This study further confirms significant circulation of Dirofilaria spp. in eastern Europe, with high parasite prevalence in domestic canids and mosquitoes. Therefore, systematic monitoring studies are required to better understand the environmental risk factors for Dirofilaria transmission, allowing the implementation of effective surveillance and control measures.

Distribution of Usutu Virus in Germany and Its Effect on Breeding Bird Populations

Usutu virus (USUV) is an emerging mosquitoborne flavivirus with an increasing number of reports from several countries in Europe, where USUV infection has caused high avian mortality rates. However, 20 years after the first observed outbreak of USUV in Europe, there is still no reliable assessment of the large-scale impact of USUV outbreaks on bird populations. In this study, we identified the areas suitable for USUV circulation in Germany and analyzed the effects of USUV on breeding bird populations. We calculated the USUV-associated additional decline of common blackbird (Turdus merula) populations as 15.7% inside USUV-suitable areas but found no significant effect for the other 14 common bird species investigated. Our results show that the emergence of USUV is a further threat for birds in Europe and that the large-scale impact on population levels, at least for common blackbirds, must be considered.

Blood donor screening for West Nile virus (WNV) revealed acute Usutu virus (USUV) infection, Germany, September 2016

Between 1 June and 31 December 2016, 13,023 blood donations from the University Hospital Aachen in Germany were routinely screened for West Nile virus (WNV) RNA using the cobas TaqScreen WNV Test. On 28 September 2016, one blood donor was tested positive. Subsequent analysis revealed an acute Usutu virus (USUV) infection. During the ongoing USUV epizootics in Germany, blood transfusion services, public health authorities and clinicians should be aware of increased human USUV infections.

Epidemic Spread of Usutu Virus in Southwest Germany in 2011 to 2013 and Monitoring of Wild Birds for Usutu and West Nile Viruses

Mosquito-borne viruses are becoming an increasing threat for Europe. One of these viruses is Usutu virus (USUV), a single-stranded RNA virus belonging to the Japanese encephalitis virus group within the family Flaviviridae. Since the occurrence of USUV among wild birds in June, 2011, infected Blackbirds (Turdus merula) have frequently been found dead in southwest Germany, cumulating in a massive die-off. Moreover, other bird species (Strigiformes) in this region have been affected. In a first study, 209 of over 600 dead birds (wild birds and birds kept in aviaries) collected from 2011 to 2013 carried USUV, more than 88% of them Blackbirds. USUV had already been detected in 2010, one year before the epizooty, in a mosquito-based surveillance program in Germany. The main epidemic area of the USUV outbreak in wild birds in southwest Germany has been similar for the last three years. In a second study during 2011 to 2013, 902 live migratory and resident birds (representing 87 bird species belonging to 14 bird orders) from four different sampling sites were bled and tested serologically and by qPCR for West Nile virus (WNV) and USUV infections. No USUV or WNV genomes were detected. Some migratory birds (mainly long-distance migrants and some partial migrants) carried neutralizing antibodies against WNV as discriminated by USUV and WNV cross-neutralization tests. Only few resident birds showed relevant USUV-specific neutralizing antibodies. The occurrence of USUV in the Upper Rhine valley area of southwest Germany is a proof of principle for the incursion and spread of other arthropod-borne (arbo)-viruses along these routes. Therefore, monitoring studies in birds and mosquitoes for the presence of arboviruses in these areas are indispensable.

Host-feeding patterns of mosquito species in Germany

Background

Mosquito-borne pathogens are of growing importance in many countries of Europe including Germany. At the same time, the transmission cycles of most mosquito-borne pathogens (e.g. viruses or filarial parasites) are not completely understood. There is especially a lack of knowledge about the vector capacity of the different mosquito species, which is strongly influenced by their host-feeding patterns. While this kind of information is important to identify the relevant vector species, e.g. to direct efficient control measures, studies about the host-feeding patterns of mosquito species in Germany are scarce and outdated.

Methods

Between 2012 and 2015, 775 blood-fed mosquito specimens were collected. Sampling was conducted with Heavy Duty Encephalitis Vector Survey traps, Biogents Sentinel traps, gravid traps, hand-held aspirators, sweep nets, and human-bait collection. The host species for each mosquito specimen was identified with polymerase chain reactions and subsequent Sanger sequencing of the cytochrome b gene.

Results

A total of 32 host species were identified for 23 mosquito species, covering 21 mammalian species (including humans) and eleven bird species. Three mosquito species accounted for nearly three quarters of all collected blood-fed mosquitoes: Aedes vexans (363 specimens, 46.8 % of all mosquito specimens), Culex pipiens pipiens form pipiens (100, 12.9 %) and Ochlerotatus cantans (99, 12.8 %). Non-human mammals dominated the host species (572 specimens, 73.8 % of all mosquito specimens), followed by humans (152, 19.6 %) and birds (51, 6.6 %). The most common host species were roe deer (Capreolus capreolus; 258 mosquito specimens, 33.3 % of all mosquito specimens, 65 % of all mosquito species), humans (Homo sapiens; 152, 19.6 %, 90 %), cattle (Bos taurus; 101, 13.0 %, 60 %), and wild boar (Sus scrofa; 116, 15.0 %, 50 %). There were no statistically significant differences in the spatial-temporal host-feeding patterns of the three most common mosquito species.

Conclusions

Although the collected blood-fed mosquito species had a strong overlap of host species, two different host-feeding groups were identified with mosquito species feeding on (i) non-human mammals and humans or (ii) birds, non-human mammals, and humans, which make them potential vectors of pathogens only between mammals or between mammals and birds, respectively. Due to the combination of their host-feeding patterns and wide distribution in Germany, Cx. pipiens pipiens form pipiens and Cx. torrentium are potentially most important vectors for pathogens transmitted from birds to humans and the species Ae. vexans for pathogens transmitted from non-human mammals to humans. Finally, the presented study indicated a much broader host range compared to the classifications found in the literature for some of the species, which highlights the need for studies on the host-feeding patterns of mosquitoes to further assess their vector capacity and the disease ecology in Europe.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1597-z) contains supplementary material, which is available to authorized users.

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).

Putative Lineage of Novel African Usutu Virus, Central Europe

We characterized the complete genome of a putative novel Usutu virus (USUV) strain (Usutu-BONN) detected in a dead blackbird from Germany. Genomic analysis revealed several unique amino acid substitutions among the polyprotein gene. Phylogenetic analyses demonstrated that Usutu-BONN constitutes a putative novel African USUV lineage, which was probably recently introduced to central Europe.

Pilot longitudinal mosquito surveillance study in the Danube Delta Biosphere Reserve and the first reports of Anopheles algeriensis Theobald, 1903 and Aedes hungaricus Mihályi, 1955 for Romania

BACKGROUND

Mosquito-borne viruses (moboviruses) are of growing importance in many countries of Europe. In Romania and especially in the Danube Delta Biosphere Reserve (DDBR), mosquito and mobovirus surveillance are not performed on a regular basis. However, this type of study is crucially needed to evaluate the risk of pathogen transmission, to understand the ecology of emerging moboviruses, or to plan vector control programmes.

METHODS

We initiated a longitudinal mosquito surveillance study with carbon dioxide-baited Heavy Duty Encephalitis Vector Survey traps at four sampling sites to analyse the spatio-temporal pattern of the (i) mosquito species composition and diversity, (ii) functional groups of mosquitoes (oviposition sites, overwintering stage, and number of generations), and (iii) the occurrence of potential West Nile virus (WNV) vectors.

RESULTS

During 2014, a total of 240,546 female mosquitoes were collected. All species were identified using morphological characteristics and further confirmed by mitochondrial cytochrome c oxidase subunit I (COI) gene analysis of selected specimens. The two most common taxa were Coquilettidia richiardii (40.9 %) and Anopheles hyrcanus (34.1 %), followed by Culex pipiens (sensu lato) (s.l.)/Cx. torrentium (7.7 %), Aedes caspius (5.7 %), Cx. modestus (4.0 %), An. maculipennis (s.l.) (3.9 %), and Ae. vexans (3.0 %). A further seven species were less common in the area studied, including two new records for Romania: An. algeriensis and Ae. hungaricus. Phylogenetic analysis of COI gene demonstrated the evolutionary relatedness of most species with specimens of the same species collected in other European regions, except Ae. detritus and An. algeriensis, which exhibited high genetic diversity. Due to the dominance of Cq. richiardii and An. hyrcanus (75 % of all collected specimens), the overall phenology and temporal pattern of functional groups basically followed the phenology of both species. A huge proportion of the mosquito population in the course of the entire sampling period can be classified as potential WNV vectors. With 40 % of all collected specimens, the most frequent species Cq. richiardii is probably the most important vector of WNV in the DDBR.

CONCLUSION

This is the first DNA-barcoding supported analysis of the mosquito fauna in the DDBR. The detection of two new species highlights the lack of knowledge about the mosquito fauna in Romania and in the DDBR in particular. The results provide detailed insights into the spatial-temporal mosquito species composition, which might lead to a better understanding of mobovirus activity in Romania and thus, can be used for the development of vector control programs.

Mammalophilic feeding behaviour of Culex quinquefasciatus mosquitoes collected in the cities of Chetumal and Cancun, Yucatán Peninsula, Mexico

OBJECTIVE

The studie describes the blood-feeding behaviour of mosquitoes in Mexico, to understand host-vector relationships and dynamics of disease transmission.

METHODS

From September 2012 to November 2012 and in November 2013, 911 blood-fed Cx. quinquefasciatus mosquitoes were collected with aspirators inside houses in Chetumal and Cancun. Blood meals were analysed by PCR and subsequent Sanger sequencing of the cytochrome b gene.

RESULTS

93.3% of mosquitoes fed on mammals, 6.5% on birds and 0.2% on reptiles. The most frequent vertebrate hosts were humans (65.4%), dogs (23.2%), chicken (5.4%), cattle (2.2%) and cats (1.8%).

CONCLUSIONS

Cx. quinquefasciatus most frequently fed on humans and dogs in both studied cities, which is in contrast to a previous study that demonstrated lower prevalence of mammalian blood in engorged Cx. quinquefasciatus.

Insecticide resistance status in Culex quinquefasciatus in Benin

BACKGROUND

Culex quinquefasciatus, an arboviral and filarial vector, is present year round in several cities of the Republic of Benin. There is more information on the resistance status to malaria vectors compared to Culicines. It is therefore unfortunate that the international focus is on Anopheles control and not so much done against Cx. quinquefasciatus, a rather more resilient mosquito to many insecticides that deserves attention. The present study aims to assess the resistance status of Cx. quinquefasciatus to carbamates, pyrethroids and organochlorine and discuss the implications for vector control in four contrasting localities of the country.

METHODS

Four contrasting localities of the country were selected for mosquito collection during the dry season based on their variation in agricultural production, use of insecticides and/or ecological settings. Bioassay were performed on adults collected from the field to assess the susceptibility of Cx. quinquefasciatus to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. Molecular assays were carried out to detect the presence of knock down resistance (kdr) and acetylcholinesterase (ace. 1) mutations in surviving specimens using PCR techniques.

RESULTS

WHO diagnostic tests showed high frequency of resistance in Cx. quinquefasciatus to permethrin (ranging from 4 to 24% mortality), deltamethrin (24 to 48%), DDT (4 to 12%) and bendiocarb (60 to 76%) in the four selected areas. This was consistent with the presence of target site insensitivity due to kdr and ace.1 mutations, which were significantly higher in areas where farmers used insecticides for pests control than in areas where no insecticides were used (p < 0.05.).

CONCLUSION

These findings showed that wild populations of Cx. quinquefasciatus have developed resistance against pyrethroids, organochlorine and carbamate. This situation of resistance may seriously jeopardize the efficacy of Insecticide Residual Spray (IRS) and Long-Lasting Insecticide nets (LLINs) on which, most African countries including Benin, rely to reduce malaria transmission.

Characterization of a novel circo-like virus in Aedes vexans mosquitoes from Germany: evidence for a new genus within the family Circoviridae

Over recent decades, metagenomic studies have expanded the number of newly described, often unclassified, viruses within the family Circoviridae. Using broad-spectrum circovirus and cyclovirus PCRs, we characterized a novel circo-like virus in Aedes vexans mosquitoes from Germany whose main putative ORFs shared very low amino acid identity with those of previously characterized circoviruses and cycloviruses. Phylogenetic and genetic distance analysis revealed that this new virus species defined, together with previously described mosquito- and bat faeces-derived circo-like viruses, a different genus, tentatively called Krikovirus, within the family Circoviridae. We further demonstrated that viruses of the putative genus Krikovirus all shared a genomic organization that was unique among the family Circoviridae. Further investigations are needed to determine the host range, tissue tropism and transmission route(s). This report increases the current knowledge of the genetic diversity and evolution of the members of the family Circoviridae.

Lack of evidence for the presence of Schmallenberg virus in mosquitoes in Germany, 2011

Background

In 2011, a novel orthobunyavirus of the Simbu serogroup was discovered near the German-Dutch border and named Schmallenberg virus (SBV). So far, SBV genome has been detected in various field-collected Culicoides species; however, other members of the Simbu serogroup are also transmitted by mosquitoes.

Findings

In the present study, approximately 50,000 mosquitoes of various species were collected during summer and early autumn 2011 in Germany. None of them tested positive in an SBV-specific real-time PCR.

Conclusions

The absence of SBV in mosquitoes caught in 2011 in Germany suggests that they play no or only a negligible role in the spread of the disease.

European surveillance for West Nile virus in mosquito populations

A wide range of arthropod-borne viruses threaten both human and animal health either through their presence in Europe or through risk of introduction. Prominent among these is West Nile virus (WNV), primarily an avian virus, which has caused multiple outbreaks associated with human and equine mortality. Endemic outbreaks of West Nile fever have been reported in Italy, Greece, France, Romania, Hungary, Russia and Spain, with further spread expected. Most outbreaks in Western Europe have been due to infection with WNV Lineage 1. In Eastern Europe WNV Lineage 2 has been responsible for human and bird mortality, particularly in Greece, which has experienced extensive outbreaks over three consecutive years. Italy has experienced co-circulation with both virus lineages. The ability to manage this threat in a cost-effective way is dependent on early detection. Targeted surveillance for pathogens within mosquito populations offers the ability to detect viruses prior to their emergence in livestock, equine species or human populations. In addition, it can establish a baseline of mosquito-borne virus activity and allow monitoring of change to this over time. Early detection offers the opportunity to raise disease awareness, initiate vector control and preventative vaccination, now available for horses, and encourage personal protection against mosquito bites. This would have major benefits through financial savings and reduction in equid morbidity/mortality. However, effective surveillance that predicts virus outbreaks is challenged by a range of factors including limited resources, variation in mosquito capture rates (too few or too many), difficulties in mosquito identification, often reliant on specialist entomologists, and the sensitive, rapid detection of viruses in mosquito pools. Surveillance for WNV and other arboviruses within mosquito populations varies between European countries in the extent and focus of the surveillance. This study reviews the current status of WNV in mosquito populations across Europe and how this is informing our understanding of virus epidemiology. Key findings such as detection of virus, presence of vector species and invasive mosquito species are summarized, and some of the difficulties encountered when applying a cost-effective surveillance programme are highlighted.

Detection of Usutu virus infection in a healthy blood donor from south-west Germany, 2012

From September 2011 until November 2012, 31 serum samples from German patients with clinically suspected acute Usutu virus (USUV) infections were tested for USUV-specific antibodies. All samples tested negative. In addition, 4,200 serum samples from healthy blood donors from south-west Germany were collected in January 2012 and also analysed for the presence of specific antibodies. One sample tested positive for USUV-IgG and -IgM. Thus, the seroprevalence of USUV antibodies in healthy blood donors from south-west Germany was low in January 2012.

Detection of Usutu virus infection in a healthy blood donor from south-west Germany, 2012

From September 2011 until November 2012, 31 serum samples from German patients with clinically suspected acute Usutu virus (USUV) infections were tested for USUV-specific antibodies. All samples tested negative. In addition, 4,200 serum samples from healthy blood donors from south-west Germany were collected in January 2012 and also analysed for the presence of specific antibodies. One sample tested positive for USUV-IgG and -IgM. Thus, the seroprevalence of USUV antibodies in healthy blood donors from south-west Germany was low in January 2012.

Epizootic emergence of Usutu virus in wild and captive birds in Germany

This study aimed to identify the causative agent of mass mortality in wild and captive birds in southwest Germany and to gather insights into the phylogenetic relationship and spatial distribution of the pathogen. Since June 2011, 223 dead birds were collected and tested for the presence of viral pathogens. Usutu virus (USUV) RNA was detected by real-time RT-PCR in 86 birds representing 6 species. The virus was isolated in cell culture from the heart of 18 Blackbirds (Turdus merula). USUV-specific antigen was demonstrated by immunohistochemistry in brain, heart, liver, and lung of infected Blackbirds. The complete polyprotein coding sequence was obtained by deep sequencing of liver and spleen samples of a dead Blackbird from Mannheim (BH65/11-02-03). Phylogenetic analysis of the German USUV strain BH65/11-02-03 revealed a close relationship with strain Vienna that caused mass mortality among birds in Austria in 2001. Wild birds from lowland river valleys in southwest Germany were mainly affected by USUV, but also birds kept in aviaries. Our data suggest that after the initial detection of USUV in German mosquitoes in 2010, the virus spread in 2011 and caused epizootics among wild and captive birds in southwest Germany. The data also indicate an increased risk of USUV infections in humans in Germany.

Molecular detection of Setaria tundra (Nematoda: Filarioidea) and an unidentified filarial species in mosquitoes in Germany

Background

Knowledge of the potential vector role of Culicidae mosquitoes in Germany is very scanty, and until recently it was generally assumed that they are not involved in the transmission of anthroponotic or zoonotic pathogens in this country. However, anticipated changes in the course of global warming and globalization may alter their status.

Methods

We conducted a molecular mass screening of mosquitoes for filarial parasites using mitochondrial 12S rRNA-based real-time PCR.

Results

No parasites causing disease in humans such as Dirofilaria spp. were detected in about 83,000 mosquitoes tested, which had been collected in 2009 and 2010 in 16 locations throughout Germany. However, minimum infection rates of up to 24 per 1000 mosquitoes were revealed, which could be attributed to mosquito infection with Setaria tundra and a yet unidentified second parasite. Setaria tundra was found to be widespread in southern Germany in various mosquito species, except Culex spp. In contrast, the unidentified filarial species was exclusively found in Culex spp. in northern Baden-Württemberg, and is likely to be a bird parasite.

Conclusions

Although dirofilariasis appears to be emerging and spreading in Europe, the absence of Dirofilaria spp. or other zoonotic filariae in our sample allows the conclusion that the risk of autochthonous infection in Germany is still very low. Potential vectors of S. tundra in Germany are Ochlerotatus sticticus, Oc. cantans, Aedes vexans and Anopheles claviger. Technically, the synergism between entomologists, virologists and parasitologists, combined with state-of-the-art methods allows a very efficient near-real-time monitoring of a wide spectrum of both human and veterinary pathogens, including new distribution records of parasite species and the incrimination of their potential vectors.

Isolation of usutu virus in Germany

Usutu virus (USUV) is a mosquito-borne flavivirus that emerged 2001 in Austria and caused deaths in wild birds. In Germany, 70,378 female mosquitoes were captured in 2009 and 2010 and assayed for USUV. Virus was isolated in cell culture from one pool of Culex pipiens pipiens mosquitoes trapped exclusively in August 2010 in Weinheim, Germany. Subsequent phylogenetic analysis demonstrated a close relationship between the isolated USUV strain from Germany and a USUV strain from Austria, which was detected in a dead blackbird in 2004.

Isolation and phylogenetic analysis of Batai virus, Germany

A molecular survey including 16,057 mosquitoes captured in Southwest Germany during the summer of 2009 showed the presence of Batai virus (BATV) in Anopheles maculipennis sensu lato. Until this survey, there was no evidence for circulation of BATV in Germany. Analysis of partial S, M, and L segments showed that the sequences from all three segments were most closely related to BATV, indicating that the virus has not undergone reassortment. Phylogenetic analysis revealed a close relationship of the isolated BATV strain from Germany with strains from Slovakia, Ukraine, and Russia.