Popular Science: Is there a danger from arctic mosquitoes?
Mosquitoes can transmit a whole spectrum of viruses called arboviruses (i.e. Arthropod-borne viruses) according to their method of transmission. Transmission by arthropods plays a decisive role in the fight against diseases caused by these viruses. Their distribution is relatively well known in tropical areas, however noticeably less towards the poles. A rarer occurrence of these diseases, mainly due to more developed health care and a lower human population density, plays its role in this lack of knowledge. From the viruses recorded in the past, we can mention e.g. the Bunyaviridae family, recorded in Alaska, Canada and the polar regions of Eurasia. Antibodies against the St. Louis Encephalitis Virus and West Nile Virus were also recorded in animals in Alaska and Canada, proving that the animals had to come into contact with these viruses. Nevertheless, all these few records are known from the continents, there are no records of viruses from polar islands. Looking closer at these data, it is also worth to note that all of them are from areas south of 70° N. In other words, they are from areas just slightly north of the Arctic Circle, not from the Arctic itself. On the other side of the world, the Antarctic, there is no information about mosquitoes at all.
The authors took up the challenge that this gap in human knowledge presents. Their research took place in the summer seasons in Greenland and on Svalbard. During the period of 2012 - 2016 they collected over 11 thousand mosquitoes Aedes nigripes. This is the most common mosquito species in the Arctic and the only one occurring in both locations where the research was done. The authors split the collected mosquitoes into groups of 30 individuals and tried to detect the presence of five species of viruses in these groups. They did not manage to prove any of these viruses in any of the samples, though e.g. in Greenland they expected it. This result corresponds with the previous research by the same authors, in which they tried to detect viruses in ticks on Svalbard. They did not record any viruses In ticks, either. There are several possible explanations for the absence of viruses in ticks and mosquitoes in the Arctic.
Probably the simplest explanation could be the harsh arctic climate, not very suitable for the replication and dispersion of viruses. It is generally known that the reproduction of viruses is very sensitive to temperature. On the other hand, the replication of Northway Virus has already been proven in 4°C. The next possible explanation could be the different habitat in which the mosquitoes live. In the past, the viruses were recorded in mosquitoes inhabiting boreal coniferous forests. Compared to them, this research was carried out entirely in the tundra. We also do not know much about the host preferences of both viruses and mosquitoes. Just like the Classical swine fever virus cannot infect humans, for example, it is possible that the tested viruses can only replicate in some animal species. If these species do not occur in the concerned locations, the viruses cannot be present either. Also, the common idea that mosquitoes suck the blood of all living beings may not necessarly be true. Some of the known mosquito species can be very choosy. In case the mosquito does not feed on animal infected with the virus, it cannot be infected either. Though the Arctic hare, a species in which the viruses were proved in the past, lives in Greenland, we know nothing about ability of the mosquitoes to feed on it. Last but not least, it is possible that the viruses infect the mosquitoes, but only very rarely. Research in other regions has shown that for some viruses, only one of 24 thousand mosquitoes can be infected, for example. That would mean that it can only be proven in one of 24 thousand. Thus, when we “only” collect 11 thousands of them, we have more than a 50% chance that we miss the infected one. Even in the case of luck, we still might not be able to prove the existence of the virus. The amount of the virus might be so small that we were not able to detect it.
So, it seems that the arctic mosquitoes do not represent any danger and they cannot transmit any viruses. However, we should not forget the word “yet”. Global warming is causing the largest changes right in the polar areas. Thus we can expect that the virus transmission in mosquitoes will not be an exception. Currently is has already been proven that, due to the warming, the mosquitoes are overwintering in higher numbers each year. Also, their life cycle and reproduction is faster than ever before. In the future, we will also see if these changes will not bring the consequent appearance of some virus. Furthermore, every year the polar areas are visited by higher and higher numbers of tourists. If some of the tourists are infected by the virus, the mosquito could get infected from the tourist and then spread the virus farther. In addition, the tourist does not even need to notice the infection, it can pass over without any apparent signs. It can also happen that the tourists unintentionally introduce a new mosquito species, which is able to transmit the viruses. This may already be an important intervention into the environment; therefore it is also necessary to pay attention to the research of viruses and mosquitoes in the future.
Müllerová, J., Elsterová, J., Černý, J., Ditrich, O., Žárský, J., Culler, L. E., ... & Grubhoffer, L. (2018). No indication of arthropod-vectored viruses in mosquitoes (Diptera: Culicidae) collected on Greenland and Svalbard. Polar Biology, 1-6.
Author of the text (c) Roman Figura
Popular Science editor