30th Annual Meeting of the German Society for Parasitology

Prof. Dr.

Interactions of Trypanosoma cruzi and triatomines and intestinal bacteria: open questions

Abstract text Trypanosoma cruzi is the etiologic agent of Chagas disease, a neglected disease endemic in Latin America. If infected people are emigrating, it is also relevant to other countries. Analyses of the interactions of T. cruzi with the triatomines and the microbiota of the latter aim to interrupt the transmission cycle. Investigations of the initial development of different strains of T. cruzi in the stomach differ whether or not all ingested blood trypomastigotes are killed there and allowing a development only those parasites which &quot;escaped&quot; into the small intestine. Investigating in vitro the interactions of T. cruzi with components of the small intestine, the fragility of the parasites should be considered to avoid damages of the surface by high centrifugation forces and protein-free buffers. Focussing on the development of epimastigotes in the rectum, the compounds at the hydrophobic attachment zone of the flagellum remain to be identified. Investigations of in vitro metacyclogenesis use conditions which are not occurring in the rectum of the vector. Therefore, concentrations of oxygen, monosaccharides, free amino acids, proteins and lipids should be determined. T. cruzi induces the synthesis of intestinal antibacterial compounds, and after a knockout of these compounds more bacteria and less T. cruzi develop. However, the strong diversity of the bacteria in the gut requires very detailed analyses. Mutualistic symbionts are only known for four species triatomines. The factors enabling a strong development of mutualistic symbionts in the stomach possessing a high level of antibacterial activity and the reduction of the population of these symbionts in the small intestine possessing a low antibacterial activity are important open questions. Also the vitamin B hypothesis requires attention. So far all mutualistic symbionts are Actinomycetales, and perhaps their unique compounds, mycolic acids, are important for the triatomines. Effects of T. cruzi on triatomines seem to occur in some parasite vector systems, but in experimental infections the supply with the mutualistic symbiont should be guaranteed, and feeding triatomines on living hosts gives an impression of the relevance of observed effects in populations at the field. The proteomic map of T. cruzi, the transcriptome and genome of the triatomine Rhodnius prolixus and the genome sequence of the symbiont Rhodococcus rhodnii should be evaluated for compounds relevant for the interactions in these systems.

Molecular Parasitology

Vectors and Entomology

Talk

Abundance of Ixodes ricinus and influencing factors in northern Germany during 2021-2022

Abstract text Ixodes ricinus is the main vector of tick-borne pathogens in Europe. Although there have been many studies on this tick species, the driving factors of its local abundance are not yet fully understood. In northern Germany, tick abundance has been little studied, as compared to southern parts of the country. In this ongoing study, we aim to assess questing tick abundance and ecological correlates across northern Germany. From April to July of 2021 and 2022, i.e. during the main I. ricinus activity period, 43 sites in 13 areas were sampled monthly by the flagging method. Associations with habitat characteristics and climate data were analysed via mixed modelling. Approximately 25,000 I. ricinus/inopinatus specimens were collected. The average density of questing nymphs ranged from 0.9/100 m² to 227.4/100 m² depending on the studied site, with a mean number of adult ticks from 0.4 to 29.5/100 m². Altogether, higher questing tick densities were observed in 2021 (ø 1.0-359.0 nymphs/100 m²) than in 2022 (ø 0.8-149.3 nymphs/100 m²), but there were differences among areas and sites. Significant correlations of nymph density with forest type, temperature and precipitation were observed. The number of frost days in the preceding winter was significantly associated with nymph density in broadleaved and coniferous, but not in mixed and inner-urban forests. Monitoring of these comparatively high questing tick densities will be continued in this so far neglected geographic area in 2023.

Prof.

A global meta-analysis on mosquito host-feeding patterns

Abstract text Mosquito host-feeding patterns are an important factor shaping the mosquito's vector capacity.As the interaction between vectors and hosts determine transmission cycles and risk of pathogen spill over, the understanding of host selection is important to assess the risk for human and animal health. Host selection can depend on intrinsic (e.g. mosquito genetics) as well as extrinsic factors (e.g. host availability). For example, anthropophagic mosquitoes are potential vectors for pathogens transmitted between humans (e.g. chikungunya virus), while opportunistically feeding mosquitoes can serve as bridge vectors for zoonotic viruses (e.g. West Nile virus). In order to investigate mosquito host-feeding patterns, we collected the data from 339 scientific publications, covering a timeframe of nearly eight decades (1942-2019). We included studies, which sampled engorged mosquito females and screened the bloodmeal for hosts using any serological or molecular biological method. The collected and standardized parameters comprised mosquito species, blood meal hosts, collection method, method for blood meal analysis, time and date, and, if provided, land use and landscape information per study. These data on 544.809 identified blood meals of mosquitoes of 475 taxa allow a wide range of in-depth analysis of the host-feeding ecology of mosquitoes. For example, 285 of the taxa (60%) fed on humans, making them potential vectors of pathogens relevant for public health. Furthermore, the data indicate different host-feeding patterns: while some mosquito species like Culex quinquefasciatus show a broad host range, clear preferences for non-human mammalian species are evident for Culex tritaeniorhynchus. Additionally, the present dataset can be used for standardized classifications of general host-feeding patterns. This comprehensive meta-analysis helps to unterstand the interaction between mosquito and host species to understand global transmission patterns of mosquito-borne pathogens.

Veterinary Parasitology

Novel approaches to repel insect vectors

Abstract text Introduction The use of repellents can reduce the number of insect bites and thereby the risk of pathogen transmission. However, current repellents lack effectiveness as they only work for a limited time and must be applied directly on the skin. Biting midges (Culicoides spp.) are of major significance as vectors of veterinary pathogens. Like mosquitoes, they are attracted to their hosts by carbon dioxide in exhaled air and by their body odours, which are mainly produced by skin bacteria. This opens the possibility to protect animals from biting midges by supplementing the skin microbiome with probiotics that reduce their attractiveness. As another option to this probiotics approach, spatial repellents may be convenient as they eliminate the need to apply repellents directly onto the skin. Objectives Identify skin bacteria from sheep and spatial repellents that reduce biting by midges. Materials &amp; Methods The skin bacterial composition of 89 adult female sheep from different breeds was determined by metabarcoding. Skin bacteria were cultivated on artificial media, and the attractiveness of selected isolates to biting midges determined in laboratory settings using a Y-tube olfactometer and membrane feeding assays. In addition, spatial repellency of different compounds was determined in a high-throughput tube setup and in a cage setup with automated tracking of the biting midges. Results We were able to detect repellent effects and a significant reduction in feeding rate of some of the skin bacteria tested. Next, a repellent bacterial strain will be applied on sheep in an exploratory study. Some of the tested spatial repellents were as effective as the golden standard DEET in the high-throughput tube setup. In addition, spatial repellency was observed in the cage setup and visualized by tracking and heatmaps. These spatial repellents will be tested in large scale semi-field experiments. Conclusion Applying skin probiotics could be a novel solution for long-lasting protection against biting insects, in contrast to the topical application of repellents that evaporate within hours, and spatial repellents could protect from a distance. These studies show that novel approaches to repel insect vectors may help to protect animals and humans against insect bites and thereby reduce pathogen transmission. Funding: Gebert Rüf Stiftung (GRS-089/20); FAN UZH &amp; Gebauer Stiftung; Federal Food Safety and Veterinary Office.

The Anopheles maculipennis complex in the Republic of Moldova: geographical distribution, host feeding preferences and species composition with first record of Anopheles daciae

Abstract text Introduction. The Anopheles maculipennis complex includes the main vectors of malaria parasites in historic Europe. Besides, A. maculipennis s.l. has been found to be naturally infected with Batai virus, West Nile virus, Usutu virus and filarial nematodes. However, data on the spatial distribution of different species are outdated or limited for many European countries. Research on Anopheles species was mainly neglected after malaria eradication in Moldova about 70 years ago and only fragmented data were obtained during the monitoring of other mosquito species. Objectives. The aim of this study was to update the data on the occurrence, distribution and host feeding preferences of the A. maculipennis complex members in Moldova using molecular screening techniques. Materials and methods. The field work was conducted in 2016, 2017 and 2019 in 70 locations in Moldova. A. maculipennis s.l. females were sampled using CO2 - baited CDC traps, CDC light traps and mouth aspirators inside and outside animal stables and natural caves. Species-typing was conducted with PCRs targeting the ITS2-gene. The cytochrome b gene and 16S gene-fragments were sequenced to identify the vertebrate host in mosquito blood meals. Distribution maps were constructed in combination with previous studies and georeferenced records from historic literature. Results. Four taxa of the A. maculipennis complex were identified from 297 specimens: A. atroparvus, A. daciae, A. maculipennis s.s. and A. messeae. Anopheles daciae was recorded for the first time in Moldova. The most widely distributed and abundant species was A. maculipennis s.s. The distribution of A. daciae and A. messeae overlapped in southern Moldova. Overall, 158 DNA sequences of the cytochrome b gene and 16S gene have been obtained from the engorged mosquitoes. Cattle (134 specimens, 84.8 %) and pig (10 specimens, 6.3 %) were the most commonly found hosts, followed by human (4 specimens, 2.5 %) dog (4 specimens, 2.5 %), horse (3 specimens, 1.9 %) and chicken (2 specimens, 1.3 %). Anopheles daciae (72 specimens, 24.3 %) was found to have the highest host diversity including cattle, poultry and humans. Conclusion. The presence and distribution range of A. atroparvus, A. maculipennis s.s. and A. messeae in Moldova was confirmed for the first time by molecular sequencing. Anopheles daciae is a new record for the country. The A. maculipennis complex was found to have a high host diversity with prevalence of non-human mammals.

PD Dr.

Avian Haemosporida in mosquitoes collected in Germany

Abstract text Avian Haemosporida are a diverse group of protozoan blood parasites found worldwide, except at the poles. In Germany, several studies have demonstrated high infection prevalences with the haemosporidian genera Plasmodium, Haemoproteus and Leucocytozoon in birds, but little information exists about their specific native vectors. Mosquitoes are the main vectors of avian Plasmodium-species, which are responsible for the deaths of numerous exotic (= immunologically naïve) birds in zoos, every year, while native birds are adapted to the parasites and largely protected by an effective immune response. In the presented study, mosquitoes were trapped in bird/animal parks and riverine floodplains, and aspirated in gardens from 2020 to 2022. Mosquito females were pooled with up to 10 specimens according to species, location and date. Extracted DNA was screened for avian Haemosporida-specific mitochondrial rDNA using a realtime-PCR. Positive samples were amplified by a Plasmodium/Haemoproteus-specific nested PCR targeting the partial cytochrome b gene for species identification. Of 2,632 pools with 8,841 female mosquitoes, reactions of 47 pools confirmed an infection. The results show the occurrence of H. majoris (n = 1) as well as several Plasmodium species: P. relictum (n = 17), P. matutinum (n = 13), P. vaughani (n = 10), P. circumflexum (n = 3), P. cathemerium (n = 1) and Plasmodium sp. (n = 2). The parasites were detected in three different mosquito species groups: Cx. pipiens s.l. (n = 40), Cs. morsitans/fumipennis (n = 6) and Ae. cinereus/geminus (n = 1). Although the overall pool infection prevalence (1.8 %) appears to be low compared to a study from neighbouring Austria (6.4 %), the minimum infection rate is higher in the present study (5.3 vs. 3.7 in Austria). We not only demonstrated the ongoing circulation of Plasmodium and Haemoproteus parasites in the German mosquito population but show, for the first time, the presence of P. cathemerium in field-collected mosquitoes in Germany.

Session XX
Vector Entomol 2

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Chair

Programme

Session XXVector Entomol 2

Appointment

Chair

Programme

Session XX
Vector Entomol 2