30th Annual Meeting of the German Society for Parasitology

Prof. Dr.

Prof.

Hibernation site patterns and survival rates of adult overwintering mosquitoes in Central Europe

Abstract text Adult overwintering mosquitoes can act as reservoir for viruses (e.g. West Nile virus) and thus may contribute to the establishment of mosquito-borne viruses in Central Europe. Knowledge on the ecology of adult overwintering mosquitoes can enhance our understanding of the mosquito population development after winter and how arboviruses persist in temperate regions. Here, we present three studies analysing mosquitoes" preferred hibernation sites and the factors influencing the winter survival in these hibernation sites. In the first study, we quantified the number of adult overwintering mosquitoes in cellars and aboveground structures such as sheds or barns. In 2016/17 and 2018/19, we searched for overwintering mosquitoes in 149 different constructions in Northwest Germany. Over both winters, 2,716 mosquitoes were collected; mosquitoes were detected in 44% of the cellars and 33% of the aboveground constructions. Culex p. pipiens Linnaeus, 1758 was the dominant species in cellars, while high numbers of Anopheles messeae Falleroni, 1926 were detected in a single barn. Only nine Culex torrentium Martini, 1925 specimens were detected, although collection data from summer would suggest that the species is highly abundant. In 2022, a second study was conducted in Poznań, Poland, where we collected overwintering mosquitoes from animal burrows and spatially close man-made constructions. In total, we detected 5,511 Culex specimens (man-made sites: 3,823, animal burrows: 1,688). While Cx. p. pipiens was again the most abundant species at the man-made hibernation sites (~90%), Cx. torrentium predominated in the animal burrows (~75%). The third study aimed to analyse the survival rates in dependence of the environmental conditions at different hibernation sites. Field-sampled overwintering Cx. p. pipiens and An. messeae were divided into groups and placed in cages at different cellars and sheds, where temperature and relative humidity was logged hourly. Mosquito wing size, lipid content and mortality rates were measured. Increasing mean temperatures at the hibernation sites (5 °C to 16 °C) but not mean relative humidity (58% to 94%) were correlated to the winter mortality rates of the mosquitoes. Larger specimens store more lipids, and in Cx. p pipiens, but not in An. messeae, survival probability of large specimens was significantly higher.

One Health/NTD/Zoonoses

Vectors and Entomology

Talk

Accuracy of the automated mosquito counting device BG-Counter 2

Abstract text The transmission of pathogens is an important capability of mosquitoes. Prevention methods such as the application of insecticides or the removal of potential breeding sites are common practice. However, the timing of their application requires exact knowledge on the spatial-temporal occurrence of the vector species. Mosquitoes are usually collected with CO2-baited traps and subsequently identified by morphological and molecular biological methods. This procedure is very time consuming, which prevents a short-term assessment of the risk of local mosquito-borne pathogen transmission. Automatic counting traps allow a timely decision-making on the prevention measures against pathogen transmission. The BG-Counter 2 (Biogents) counts insects and discriminates these by size directly in the field. Placed on CO2-baited traps, captured insects are categorized as &quot;mosquito sized&quot;, &quot;too small to be a mosquito&quot; and &quot;too large to be a mosquito&quot;. The Counter additionally measures standard environmental parameters, such as temperature and humidity. All information is transmitted to a cloud server at 15-minute intervals. In order to assess the accuracy of this counting device, traps were placed all over Germany which were run in daily and bimonthly intervals. The BG Counter 2 was attached to a CO2-trap (BG-Trap-Station) and a modified version for gravid mosquitoes. All captured mosquitoes were identified morphologically. The number of mosquitoes were compared to the output of the counter. Spearman correlation coefficients between captured and counted mosquitoes and the counting accuracy was calculated. The correlation varied greatly depending on sampling site (rs=0,33-0,72). During months with high mosquito abundances, the correlation was also the highest (rs=0,66). The lowest correlation could be seen in early spring and autumn, during low mosquito abundance months (rs=0,33). While the BG-Counter 2 can depict the general phenology well, the accuracy during low mosquito abundance is rather low.

Emerging Parasitic Diseases

Host-feeding patterns of European mosquitoes in relation to land use

Abstract text Introduction Mosquitoes (Diptera: Culicidae) are the most important arthropod vectors of pathogens. Understanding their blood-feeding behavior is an essential element to assess the vectorial capacity of a mosquito population. Therefore, this study aims to analyze mosquito spatial-temporal host-feeding patterns by barcoding blood-fed female mosquitoes. Methods Between 2012 and 2019, mosquitoes were sampled at different sites in Germany, Iran, Moldavia and Romania. Blood-fed specimens were analyzed by PCR with vertebrate specific primers and subsequently processed with Sanger sequencing. The sequences were compared to sequences from GenBank to identify the host species. The host specificity of the mosquitoes was tested by calculating the checkerboard score (C-score). In addition, land use information based on the Copernicus global land cover layers were extracted from each sampling site to analyze its influence on the mosquito-host interaction. Results In total, we collected 4,827 blood-fed specimens of 48 different mosquito taxa. The molecular biological analysis revealed 82 host taxa, including 3 amphibia, 42 bird, 36 mammal and 1 reptile species. The five dominant host species were domestic cattle (34%), human (18%), pig (13%), horse (9%) and roe deer (6%). C-scores indicated a random structure in the host-feeding patterns, i.e. mosquitoes use a broad range of different host species. Nevertheless, most mosquito species preferred certain host groups. Species from the genus Aedes predominantly fed on mammals, while we detected a balanced proportion of mammal and bird blood in Culex specimens. The analyses showed that the mosquito-host interaction is significantly affected by land use factors, e.g. at forest sites, human blood was predominantly detected in Aedes mosquitoes, while at unforested sites, particularly in urban areas or in shrublands, humans are more likely to be bitten by Culex mosquitoes. Conclusion Land use changes can influence the abundance and species composition of mosquitoes and vertebrates affecting vector-host dynamics. This large data with a standardized molecular screening method gives a unique insight in the spatial-temporal host-feeding patterns of mosquitoes and the relevance for mosquito-host interaction on the epidemiology of mosquito-borne diseases.

Veterinary Parasitology

Developing a hybrid model for early-warning against mosquito-borne diseases in Germany

Abstract text Driven by globalisation and climate change, mosquito-borne viruses have emerged in the last decades, with Usutu virus (USUV) transmission first detected in Germany in 2010, and West Nile virus (WNV) in 2018. Mechanistic (e.g., epidemiological R0-models) and correlative (e.g., environmental niche models, ENMs) modelling approaches are commonly used to evaluate the risk of transmission, but there is a gap in literature that integrates both streams for more informative results. Most studies also employ static data instead of regularly updated data, limiting their ability to make near-real time predictions and guide mosquito control measures. In this study, a "hybrid" model was developed in which estimates of the spatial-temporal abundance of mosquito populations generated from ENMs were used to refine a mechanistic R0 model based on temperature-dependent and taxa-specific transmission parameters. Real-time mosquito surveillance data collected from traps across Germany provided an accurate estimate of vector abundance, and allowed deriving the vector-to-host ratio parameter fed into the model. Nation-wide climate data updated on an hourly basis also served as model input to yield short-term forecasts presented as risk maps, which can be easily interpreted and used as a tool for risk assessment. Results so far suggest that the role of Culex torrentium in WNV transmission may have been grossly underestimated, as its high vector competence for this virus generated high R0 values. Integrative models that take advantage of regularly updated climate and mosquito surveillance data could be of great value to better guide decision-making by public health authorities regarding surveillance plans and preventive measures.

Geographic Distribution of Dermatobia hominis and Cochliomyia hominivorax: A Gateway to Myasis Prevention in Colombia

Abstract text Background: Myasis, a vector-transmitted disease, is a persistent public health problem in South America, where it is most commonly transmitted to humans by the fly larvae Dermatobia hominis (Dh) and Cochliomyia hominivorax (Coh) of the order Diptera. In Colombia, the geographic distribution of Dh and Coh is little known, and clinical reports of myasis are scarce. Results: Based on an exhaustive review of the biological-medical literature, biological collections, and clinical case records, the geographic distributions of Dh and Coh in Colombia were determined by province; the history of the myasis literature in Colombia was sketched; and the typical clinical presentation of myasis in Colombia was summarized. Conclusions: Myasis is endemic in Colombia and is concentrated in the cities and provinces of the country´s Andean Mountain ranges, where the majority of its population and primary medical care services are also found. Key Words Myasis, fly larvae, geographic distribution, Andes, Colombia.

Session XVII
Vectors and Entomology 1

Appointment

Chairs

Programme

Session XVIIVectors and Entomology 1

Appointment

Chairs

Programme

Session XVII
Vectors and Entomology 1