Mosquitoes like warm and humid atmospheres and are attracted by carbon dioxide, the scent of skin and contrasts in light. In the past two years, researchers at the University of Veterinary Medicine Vienna (Vetmeduni Vienna) sampled about 30,000 of these insects which not only annoy humans and animals alike, but may even present a health hazard.
Within the context of an international research project and with the financial support of the Austrian Science Fund FWF, the researchers from Vetmeduni Vienna set out to identify all species of mosquitoes found in Austria and screen them for pathogens. Between March and October, mosquitoes were collected at more than 40 sites in eastern Austria and then subjected to morphological and, for the first time, genetic testing. In a second step, the team of principal investigator Hans-Peter Führer is currently using molecular methods to screen the mosquitoes for pathogens (parasites and viruses) such as filarial worms, avian malaria and flaviviruses (West Nile virus, Zika virus or the tropical Chikungunya virus). "Analyses are still in progress", says Führer but notes that avian malaria and filarial worms have been found relatively often so far.
At present, 46 species of mosquitoes, four of them non-indigenous, are known in Austria, including the Japanese bush mosquito (Ochlerotatus japonicus japonicus), which is endemic to Japan and arrived in Europe as a consequence of international cargo shipping.
In Austria, the insect finds a climate comparable to its original home. While not yet seen here, the Asian tiger mosquito (Aedes albopictus), a known vector for the Dengue virus, is definitely coming closer due to climate change and mild winters and is already established in Italy, France and other European countries. Führer and his team have recently been able to prove that the range of mosquitoes – and, thus, of the pathogens they carry – is widening by screening for two filarial worms which are mainly transmitted to dogs, but can also infect humans: "Dirofilaria immitis" and "Dirofilaria repens". "In the past, most cases were imported", explains Führer. While the parasites had always been known in the Mediterranean region and south-eastern Europe, they are now spreading westwards.
"Until 2000, there were hardly any indigenous cases in Hungary. But five years later Budapest was reached and the Austrian border by 2008/2009,” specifies the expert from the Institute of Parasitology at Vetmeduni Vienna.
The diversity of mosquito species identified has been increasing since 2011, a finding partly attributable to the more intense research in this field, and scientists believe that non-indigenous species may well displace their indigenous counterparts.
"In such cases we speak of invasive species,” observes Führer. The invaders are generalists, meaning they are highly adaptive and quite undemanding. Determining mosquito species requires a great deal of experience. The Viennese researchers analyse at least three genes in order to obtain positive identification. If uncertainties persist, the scientists have to resort to complex molecular biology analysis.
"Many species look similar but have a completely different genetic make-up and vice versa", explains Carina Zittra, a member of the project team. As a matter of fact, even the genetic analysis of the common house mosquito (Culex pipiens) has furnished new insights. Although it is one species, it comes in two different ecological forms with different requirements. One prefers birds, the other mammals; one likes to live in towns, the other in the countryside. "When dealing with the issue of what disease could be transmitted, such knowledge of the behaviour and variety of species is helpful,” notes Zittra. The new insights are published in the journal "Parasites & Vectors".
In the international research project, experts from France, Germany and Austria are collaborating in order to model mosquito populations, their adaptability and the transmission of pathogens regarding current and future ranges of spreading. The project involves both the cataloguing of species and the environmental parameters which affect the spatial and temporal spreading of indigenous and non-indigenous mosquitoes.
"We may expect to see the Japanese bush mosquito and the tiger mosquito spreading into eastern Austria in the coming years,” predicts Hans-Peter Führer.
Publications Zittra, C; Kocziha, Z; Pinnyei, S; Harl, J; Kieser, K; Laciny, A; Eigner, B; Silbermayr, K; Duscher, GG; Fok, É; Fuehrer, HP (2015): Screening blood-fed mosquitoes for the diagnosis of filarioid helminths and avian malaria. Parasite Vectors. 2015; 8:16; doi: 10.1186/s13071-015-0637-4. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4305256/
Werblow, A; Flechl, E; Klimpel, S; Zittra, C; Lebl, K; Kieser, K; Laciny, A; Silbermayr, K; Melaun, C; Fuehrer, HP (2016): Direct PCR of indigenous and invasive mosquito species: a time- and cost-effective technique of mosquito barcoding. Med Vet Entomol. 2016; 30(1):8-13; doi: 10.1111/mve.12154. http://onlinelibrary.wiley.com/doi/10.1111/mve.12154/abstract;jsessionid=948E22650B426160494DA208FB192E41.f02t03
Zittra C, Flechl E, Kothmayer M, Vitecek S, Rossiter H, Zechmeister T, Fuehrer HP: Ecological characterization and molecular differentiation of "Culex pipiens" complex taxa and "Culex torrentium" in eastern Austria. Parasites & Vectors, 2016 Apr 11; 9(1):197; doi: 10.1186/s13071-016-1495-4. (in press).