Catching the malaria mosquito

Researchers’ sweaty socks have been harnessed for science: they helped lure malaria-transmitting mosquitoes into traps at the Haartman Institute. The goal is to develop the best possible mosquito net and new mosquito-control methods.

Imagine a hospital in a crisis region in Africa, in the midst of a bloody civil war. Severely injured patients keep being brought in. The facilities are basic at best, and there are not enough resources to help everyone.

These are the kinds of places where Finnish surgeon Mikko Aalto has been working for more than three decades. The desire to help the poor and make a difference which awoke in Aalto at age 16 has taken him to the most crisis-ravaged areas in Africa, including Mozambique, the Democratic Republic of the Congo, the Republic of the Congo and the Central African Republic. He currently works in Somalia.

Aalto has seen a lot of death. Still, the greatest killer has been the smallest – the mosquito.


Just over ten years ago, Aalto was working in a hospital in Kindu, in the Democratic Republic of the Congo. Malaria was the most common cause of death in the area. In the evenings, Aalto would watch mosquitoes swarm against the nets protecting the hospital’s windows. In the mornings they were gone.

 “Each night we missed a chance to eliminate the mosquitoes on the outside of the nets,” says Aalto.

Aalto thought that a system could be developed for the windows which would trap the mosquitoes between two nets. It took time, however, to get others excited about the idea.

Five years ago, malaria researchers at the University of Helsinki’s Haartman Institute and the textile and fibre researchers at the Tampere University of Technology got to work on the project. Their goal was to create a semi-permeable net that would allow mosquitoes to fly through in one direction but not the other.

When such a special net is fixed on top of a regular mosquito net in a window, a handy trap is created: the mosquitoes cannot enter the building, but neither can they escape.


A plastic tunnel was built in the basement of the Haartman Institute, and a variety of net models were tested using malaria mosquitoes farmed at the Institute. The mosquitoes used in the experiments were harmless, as they had not been exposed to the human malaria parasite.

Researchers at the Tampere University of Technology constructed the experimental nets, conducting approximately thirty tests before arriving at a successful prototype. At first, the researchers took air cushions out of sneakers, cut them in half and studied them to see if they could be used as the structure for the net.

“We thought that if there were prickly hairs sticking out of the net, the mosquitoes wouldn’t dare to fly into it. But that didn't work at all. We tried to think like mosquitoes and failed,” recounts Seppo Meri, head of the research group and professor of immunology.

Neither was having the mosquitoes fly through the tunnel entirely without its problems. Mosquitoes need something to entice them to fly. The researchers first tried to lure them in with a carbon dioxide spray. But the most effective method turned out to be the lowly dirty sock.

“We started harvesting our socks and bringing them to the laboratory. The mosquitoes couldn’t get to the socks fast enough once they were attached to the opposite end of the tunnel,” Meri says.

In the tunnel experiment, the researchers calculated how many mosquitoes flew through the net and how many flew back in the other direction. Ultimately they developed a net that allowed 97% of the mosquitoes to pass through but not a single one to get back.


As many as 200 million people contract malaria each year, and nearly 500,000 die. Many of them are children. When child mortality is high, people tend to have more babies. A large family is a guarantee that at least one of the offspring will survive.

“If we want to stop the population explosion, we need to bring down child mortality. One way is to fight malaria,” Aalto points out.

The good news is that the malaria mortality rate has decreased by half in a decade. At the moment, the best protection against the disease is sleeping under a mosquito net treated with an insecticide.

“Even then, some mosquitoes can get through. The risk with using an insecticide is that the mosquitoes may develop a resistance to it. Our method is non-toxic and environmentally friendly, but it kills the mosquitoes effectively," says Meri.

The malaria mosquitoes only fly by night, so protecting homes will already make a significant difference.


Currently, most mosquito traps use electricity or gas, neither of which may be available for people in developing countries. They are also used outdoors, so changes in the wind can impact the effectiveness of the traps. One benefit of the Finnish innovation is that the people sleeping inside constitute a natural bait that lures in the mosquitoes.

Developing better mosquito nets is among the WHO’s top three malaria objectives. However, the organisation requires comprehensive testing before it can officially recommend the net. This means the new trap nets must also be tested in the field.

“Only by testing the nets in practice can we find out whether the net can keep the mosquitoes trapped until they die. The idea is that the trapped mosquitoes dry to death as the sun heats them. Mortal danger is a much more compelling motivator for escape than getting to an old sock,” Aalto muses.

Aalto has connections in Tanzania, and he has negotiated a partnership with the Tanzanian Ministry of Health and Social Welfare, which has offered its study village as a testing site.


The field tests began in April. Ayman Khattab, who designed the test arrangements, flew in to launch the testing, along with doctoral student Subam Kathayat Chhetri, who stayed to supervise the testing for the full 2.5 months.

Originally hailing from Egypt, Khattab heads the Haartman Institute’s malaria laboratory at the University of Helsinki. He is quite happy with the results: the mosquitoes did indeed fly into the trap and remained there. The best catch was 28 mosquitoes in a single dwelling during 24 hours.

“Based on our research, we can say that the window traps are as effective at eliminating mosquitoes as insecticides.”

The study village is located in a rural area, with the closest city being Tanga, approximately 50 kilometres away. The village has five identical huts where a variety of test settings were tried for a week at a time, both with and without the nets. People from a nearby village were hired as bait – to sleep safely under mosquito nets.

The best results were gained with a trap where two of the special nets were affixed on top of each other, with their permeable sides facing outwards. This trap caught not only mosquitoes trying to fly in from the outside, but also the ones flying out of the building in the morning. It is impossible to completely mosquito-proof a home. If the trap can catch the mosquitoes that may have already bitten people inside, they will not be able to fly and spread malaria further.

Chhetri is Nepalese and was visiting Tanzania for the first time.

“The people were very nice. They were also very interested to see whether the nets would work.”


Locals favour buildings with open eaves to improve ventilation and avoid trapping humidity inside. This means mosquitoes can also fly in. The trap nets are still useful, as they can catch mosquitoes from both the outside and inside.

The idea is that the trap can be used in a variety of windows and building types. The material must be heat and dryness resistant, and it must be possible to open the trap so that the dead mosquitoes can be cleaned out. Cultural factors must also be considered. Researchers from Aalto University and the Hanken School of Economics have conducted a cooperation project where they studied how the nets should look in order to be accepted.

The next step is to compare the number of people contracting malaria in two villages, one of which uses the trap nets and one of which doesn't. Early last May, Tekes granted further funding for the research. The researchers will return to the field during a coming rainy season. If the last research stage is successful, the net may finally receive the WHO stamp of approval.


Mikko Aalto believes that malaria can be beaten, perhaps even completely eradicated, in time. All available tools must be used: exterminating mosquitoes, treating patients and symptom-free carriers, protecting people with nets. Mosquito nets around beds will still be necessary even if the window traps are used.

Aalto is interested in finding out whether the same principle could be used to combat sand flies, which spread visceral leishmaniosis, a parasitic infection prevalent in Somalia and particularly lethal to children.

Meanwhile, Seppo Meri and Ayman Khattab are also working on another, even more radical project to battle mosquitoes. Meri calls it the mosquito vaccine, but it is not really a vaccine in the traditional sense. The intention is that blood from the inoculated person would kill the mosquito who makes the mistake of biting him or her.

Such a vaccine would work on both malaria and other mosquito-borne illnesses, such as dengue fever and zika. Ideally, it could remove humans from the mosquito’s menu.

For the moment, however, people must content themselves with other forms of protection. Could the trap nets be useful at a Finnish summer cabin?

“I would love to try it!” Meri enthuses.

Finnish mosquitoes are larger than the malaria-carrying Anopheles mosquito, so a looser net would have to be developed for them. But the underlying principle will work on any mosquitoes, whether they represent the threat of deadly disease or just frustration.

This article was published in Finnish in the Y/06/16 issue of Yliopisto magazine.