A mosquito carrying the disease-causing virus is an effective infectious, as the typical lifespan of a mosquito female is a few weeks. During that time, it has time to bleed and lay eggs several times.
Did you get sick in the summer after a mild fever cottage trip? It could also be due to mosquitoes.
Few people know that in Finland, mosquitoes spread three different viruses that can cause disease in humans. The viruses spread by mosquitoes are Inkoo-, Chatanga– Yes Sindbis-virus.
The latter Sindbis virus causes Pogosta disease, which is perhaps best known to us for mosquito-borne diseases. The disease is most prevalent in Eastern Finland, where there are usually a few dozen cases a year. The most recent epidemic peak was in 2012, when there were another hundred cases of the disease.
Mosquito-borne viruses mostly cause very asymptomatic infections, i.e., low-grade fever and other flu symptoms. Postdoctoral Researcher in Virology Essi Korhonen however, viruses can also cause more serious forms of the disease. Korhonen studies mosquitoes at the University of Helsinki.
“Some people who get the virus get neurological symptoms. For example, the Inkoo virus can cause encephalitis, or encephalitis, which requires hospitalization, especially in people under 16 years of age, ”says Korhonen.
According to current knowledge, the Chatanga virus causes more severe symptoms in adults than infections caused by the Inkoo virus.
Pogostan disease raises fever and limbs and the middle body typically develops a very itchy rash. In addition, it may be associated with joint pain and swelling.
“Joint pain can be very troublesome. For others, they leave after-effects for months or even years and can be really detrimental to quality of life. ”
In our country, the viruses spread by mosquitoes only rarely cause serious diseases.
In addition to viruses Causing hare fever in Finland fancisella tularensis The bacterium is mosquito-mediated. Its symptoms include fever and swelling of the lymph nodes and a bite at the mosquito’s injection site. There are 50 to 100 cases of the disease per year.
“The further north we go, the more people can find antibodies to all mosquito-borne diseases,” says Korhonen.
Finnish mosquitoes can therefore spread infectious diseases where their tropical sister species are. However, the viruses spread by mosquitoes that inhabit us cause only very rare serious diseases.
However, the climate is warming and with it the environment is changing. This means that the distribution areas of animal species are changing. Also, the warmer the fall, the longer the mosquitoes are active and at the same time sting people.
“It is probable that new species will be added to the Finnish mosquitoes, because our climate and environment will change so that they can handle us,” says Korhonen.
“The changes are slow, but with the variety, what mosquito-borne pathogens we may have will also change.”
According to some climate change forecasts, we could have some tropical mosquito species in Finland in about 50 years. One such is the Asian tiger mosquito, which can spread zika virus and dengue fever, among others. In addition to Southeast Asia, they also live in South and North America and Africa.
Korhonen is involved in a mosquito species mapping team that collected mosquitoes this summer in the metropolitan area from May to September.
Once a female mosquito sucks blood, it lays eggs, after which it is very soon ready to start a new round.
“The purpose is to map the mosquito species in the Helsinki metropolitan area, to see what pathogens they carry. If we also think that new alien species will be introduced to the country, then it will most likely show up here in southern Finland, ”says Korhonen.
There are also many entry routes in southern Finland, such as the airport and ports and large greenhouses. Temporary populations may be created in them if mosquitoes arrive with consignments of plants as smugglers. The microclimate in greenhouses is good for many more tropical mosquito species.
In addition to mosquito samples, Korhonen examines blood and urine samples received from patients.
With a mosquito the suction tip protrudes through the skin, the route of infection is open immediately, as the virus that infects humans is mosquito in the salivary gland. Thus, the disease can be transmitted as soon as the mosquito carrying the virus has been able to inject.
Mosquito-mediated viruses always have a host animal from which the disease first spreads to the mosquito. The mosquito therefore first draws blood from a bird or mammal from which the mosquito becomes infected.
“Once a female mosquito sucks blood, it lays eggs, after which it is very soon ready to start a new round,” Korhonen says.
The typical lifespan of a mosquito female is a few weeks, during which time it has time to bleed and lay eggs several times.
“That’s why the mosquito is a really effective disease vector,” says Korhonen.
in Finland there is 43 species of mosquitoes, most of which are not currently known to spread pathogens. The research, led by Korhonen, will now map the pathogens carried by mosquitoes in October, and also exactly which mosquito species are able to act as mediators of different pathogens.
Cases of disease are affected by many things, such as what a mosquito year has been like. It is affected, for example, by the type of snow cover in the spring and winter, as it affects the melting waters into which the mosquitoes lay their eggs. In addition, the number of diseases caused by the Sindbis virus, for example, is affected by the number of forest fowl and the variability of the population, as they act as hosts for the virus.
The introduction of a new virus is more likely to occur with the host animal than with a mosquito.
According to Korhonen, last summer was a good mosquito summer, which means that there were many mosquitoes.
“Of course, the amount of disease is also affected by how much people move around in nature,” says Korhonen.
In Korhonen’s opinion, movement in nature should not be reduced for fear of disease, but protective clothing and mosquito repellents are in place when moving in the forest. Just because mosquito bites cause nasty allergic reactions for many.
Mosquito-borne viruses also mapped from bird samples collected by Korkeasaari Wildlife Hospital.
“We have a cooperation project with Korkeasaari. It collects samples of migratory birds coming to us. If found West Nile– or Usutuantibodies to the virus, the birds have at some point encountered this virus, ”says Korhonen.
“We already have suitable species of mediator mosquitoes and the introduction of a new virus is more likely to occur with the host animal than with the mosquito.”
West Nile– and the Usutu viruses, as the name implies, originate in Africa but have climbed into Europe a little quietly. There are already mosquito species in Finland that can transmit them, but we have not yet had any cases of the disease.
Mosquito-borne infections in tourists are already quite well known.
“The West Nile virus is already quite brisk in Southern Europe, but there were already native cases in Germany already in 2018, ie not that the tourist has visited an area where the virus already exists, but that he has been infected in his home country,” Korhonen describes.
These viruses are related to tick-borne tick-borne encephalitis and the symptoms can be very similar, i.e. fever, vague malaise, headache and neck stiffness. Domestic cases of human disease are not expected in Finland in the next few years, but tourists may already experience them.
West Nile virus can be associated with severe neurological symptoms in humans. The Usutu virus lives mainly in birds, but according to Korhonen, some cases of human disease are also known.
Human antibody testing we are done mainly for the Sindbis virus, as the disease is known especially in Eastern Finland. Chatanga and Inkoo viruses, on the other hand, are very few.
According to Korhonen, mosquito-borne infections in tourists are already quite well known and, for example, 50–100 dengue virus infections are diagnosed in tourists every year.
“As a differential diagnosis, antibody tests are important if symptoms persist. With the right diagnosis, useless treatment trials can be avoided, ”says Korhonen.
It may also be important for the prognosis of the disease to know that Sindbis virus, for example, is often associated with joint symptoms that usually improve over time. Proper diagnosis also affects the treatment of neurological symptoms in a hospital.
“Usually, if a person has prolonged or severe symptoms, it is also important to know what it is all about,” says Korhonen.
Mosquito-mediated diseases treat a symptom such as pain, rash, fever, or inflammation. There is no cure for the virus itself.