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Today is World Mosquito Day. The Bernhard Nocht Institute for Tropical Medicine (BNITM) dedicates a large part of its research to mosquitoes and the pathogens they transmit. This is because mosquitoes are crucial for the spread of major infectious diseases such as malaria, yellow fever, or dengue fever. The insects are therefore not only annoying, but also a major threat to global health. BNITM supports the fight against tropical infectious diseases. In addition, scientists have been monitoring the mosquito populations in Germany for many years. The latest results provide answers to important questions: Can native mosquitoes transmit tropical viruses? Does the mosquito's immune system influence its ability to transmit pathogens? What influence do environmental changes have?
On 20 August 1897 Sir Ronald Ross was able to prove that the malaria parasite is transmitted by mosquitoes of the genus Anopheles. For this discovery he received the Nobel Prize for Medicine or Physiology in 1902. His findings formed an essential basis for understanding the spread of malaria and for the development of control measures against the tropical disease. Today, BNITM research still addresses the Anopheles mosquito and the parasites it transmits, as well as the clinic, treatment and prophylaxis of malaria. More than 400.000 people still die of malaria every year, especially children in Africa. At the beginning of this year, Tobias Spielmann's research group achieved a milestone in malaria research by identifying the mechanisms of resistance in malaria parasites to the most important drug artemisinin (Science Vol. 367, 2020). This finding will have a direct impact on future development of antimalarial drugs.
However, mosquitoes are not only carriers (vectors) of malaria parasites, but also of many other pathogens such as the dengue or Zika virus. These infections occur most commonly in the tropics, but the BNITM also monitors mosquito-borne diseases in Germany and other European countries. The biosafety laboratory (BSL-3) was established in 2012 and enables experimental studies on the vector competence of mosquitoes right here in Hamburg at BNITM. Even today, mosquito research contributes directly to the control of numerous infectious diseases.
BNITM is involved in various projects monitoring mosquitoes and mosquito-borne diseases in Africa and Europe including Germany. The results of these projects are incorporated into current risk assessments and national recommendations for mosquito surveillance. In cooperation with the Naturschutzbund Deutschland e.V. (NABU) and the Friedrich-Löffler-Institute (FLI), the working group of Jonas Schmidt-Chanasit monitors the spread of Usutu and West Nile viruses. Both virus species were probably introduced to Germany by migratory birds and are transmitted here by mosquitoes to native birds or occasionally to humans. BNITM scientists are working on the development of early warning systems to detect introduced infections.
[Translate to english:] Usutu- und West-Nil-Viren zirkulieren zwischen Stechmücken und Vögeln. Bei einigen Vogelarten können sie schwere, häufig tödlich verlaufende Erkrankungen auslösen. Dies gilt insbesondere für das Usutu-Virus, welches hierzulande seit 2011 regelmäßig zu Massensterben bei Amseln führt. Im Jahr 2018 konnte das West-Nil-Virus erstmals in Vögeln und Pferden in Deutschland nachgewiesen werden, die sich in Deutschland über Stechmückenstiche infiziert hatten (autochthone Infektion). „Insbesondere außergewöhnlich warme Sommer begünstigen die Zirkulation dieser Viren in Deutschland“, erklärt Renke Lühken von der Arbeitsgruppe um Jonas Schmidt-Chanasit.
Both Usutu and West Nile viruses usually cause little or no symptoms in humans. However, infections with the West Nile virus can lead in individual cases to severe disease progression with meningitis. Last year, 2019, the first autochthonous infections of humans with West Nile virus were observed in Germany. In order to better understand the circulation of these viruses, BNITM is participating in a Citizen Science project financed by the Ministry of Agriculture. Every citizen can become a researcher: Please send any dead birds you find to our institute. The BNITM scientists examine the dead birds and thus gain new knowledge about the spread of these human pathogenic viruses. They compare their results to data on the distribution of mosquito species and local climate or land use to better predict future outbreaks.
Vector competence studies in the BSL3 safety insectarium are particularly helpful for risk assessment. Vector competence describes the ability of a mosquito to multiply and transmit a pathogen. BNITM investigates native mosquito species for their ability to transmit tropical viruses, as well as the effects of our temperate climate on the vector competence of Germany mosquito species. For example, some species of the native Culex genus are capable of transmitting the West Nile virus or the Sindbis virus. Vector competence studies in special climate chambers recently showed that the native mosquito species Culex torrentium is a good carrier of West Nile virus at warm average temperatures (from 21 degrees Celsius). However, at lower temperatures it is not. These results clearly show that changed climatic conditions can have a direct influence on the infection process.
It is also possible that the immune response of the mosquito itself has an influence on vector competence. Mosquitoes are often infected with viruses that occur exclusively in insects. Initial results from Esther Schnettler's research group show that such insect-specific viruses activate the mosquito's immune system and thus inhibit the mosquito's vector competence for other viruses, such as West Nile virus. The scientists hope to use such findings to influence the ability of different mosquito species to transmit important infectious agents.