The most dangerous mosquito-borne diseases Science In-depth reporting on science and technology DW


You can hardly see sandflies with the naked eye. These mosquitoes are dangerous because they transmit the leishmaniasis of the infectious disease. They are at home in southern countries such as the Mediterranean or the tropics. But they are also seen in Germany. Only fertilized females suck blood. Non-fertilized females and male sand flies are no risk. There are 30 different Leishmania species. Animals, such as dogs, are usually infected by the parasitic protozoa, but ten Leishmania species can also infect humans.

First symptoms sometimes only appear after weeks or months. It starts with fever and headache. The lymph nodes swell. The infected person feels tired and weak and can lose a lot of weight.

Leishmaniasis affects different parts of the body. The mucocutaneous form of the disease affects the nose and throat. A skin ulcer usually develops in the beginning. If the disease is not treated, it spreads to cartilage and connective tissue and destroys it. This can for example lead to holes in the nasal septum. But it can also get worse: you could develop intestinal leishmaniasis. It attacks important internal organs such as liver and spleen.

Every year about 12 million people contract leishmaniasis worldwide. The disease can be cured, but people with the symptoms described should consult a doctor as soon as possible. Leishmaniasis can lead to death without proper treatment. There is no effective vaccine.

Read more: No longer a joke – our blood is the fault of mosquito bites

Hausmücke Gemeine Stechmücke Culex spec. Stechrüssel Rüssel (Imago)

Mosquitoes have nice tools to penetrate the skin

Sindbis virus

The night-time mosquitoes of the genus Culex transmit the so-called Sindbis virus. It is most common in African regions, but scientists have also found it in mosquitoes and people in European countries.

In the beginning, the affected person has flu-like symptoms and fever. In some cases the body temperature can reach more than 40 degrees Celsius (104 degrees Fahrenheit). Brain inflammation can develop. After the first stage, the joints are inflamed. The inflammations become stronger during the course of the disease. They mainly occur at the wrists, finger joints and ankles and are later accompanied by skin rashes.

If the disease is not treated properly, it can become chronic. This results in constant joint pain. But that only happens in the most extreme cases. Usually the human immune system is able to deal with the virus. The symptoms of the disease disappear after a few weeks without any after-effects. There is no vaccine.

Yellow fever

The tiger mosquito, as well as some other mosquitoes of the genus Aedes, are responsible for yellow fever, a so-called flavivirus. The danger of being stabbed by the mosquito and getting yellow fever exists in 34 countries in Africa and 13 countries in South and Central America.

Scientists distinguish three different transmission paths: in the so-called sylvatic cycle, mosquitoes normally transmit the virus between monkeys in the rainforest. If the odd person becomes infected, he or she can take the virus to the city.

A primate in Brazil (Reuters / P. Whitaker)

Yellow fever spreads among primates that live in the rainforest

This leads to the second transmission, known as urban cycle. In dense urban settlements, mosquitoes carry the virus from one person to another. That is how yellow fever in cities becomes endemic.

The third yellow fever cycle affects people in peripheral areas between forests and savannah, where mosquitoes, monkeys and people live close together. There, infections from animals to humans and back again and again take place.

Fever and flu-like symptoms occur first. Those affected are ill and have to surrender. If yellow fever is not treated, it can lead to meningitis and even to vital organs that are severely damaged or do not function at all.

The good news: there is a vaccine against yellow fever! Some affected countries call a yellow fever vaccination as one of the admission requirements for travelers, for example Uganda and Sierra Leone. The immunization lasts a lifetime.

Dengue fever

Aedes aegypti are also the vectors that transmit dengue fever. Popular holiday destination Thailand, for example, is home to the tiger mosquito, which distributes dengue. In fact, the virus is found in large parts of Southeast Asia – from Afghanistan to North Australia, but also in Sub-Saharan Africa, Central and South America and some southern states of the US.

When they are bitten and infected, the symptoms of muscle and joint pains vary to headache and fever. Even people who have survived an infection with dengue are not safe. A second infection is much worse than the first infection.

96 million people get dengue fever every year. This makes it the disease that is most often transmitted by mosquitoes. There is now a vaccine. However, this is subject to certain limitations, because even a vaccination can cause lethal reactions in the body.

For example, in endemic areas with a high transmission rate only children of nine years and older, as well as HIV-positive individuals, i.e. those who have already been infected once, should be vaccinated. The World Health Organization recommends that the vaccine should only be used in countries where more than 70 percent of the population has developed antibodies to dengue.

Zika infection

Aedes aegypti, the yellow fever mosquito and Aedes albopictus, the Asian tiger mosquito, transmit the Zika virus. It occurs in the tropical regions of Africa, in South and Central America, but also in Florida and Texas. Areas in Southeast Asia are also being affected. These include Thailand, Vietnam and the Philippines.

Brasilien Zika Virus - Mikrozephalie - Mother with Baby (picture-alliance / dpa / A. Lacerda)

Microcephaly: When the mother of this baby was pregnant, she became infected with the Zika virus.

In 2015, many babies with severe disabilities were born in Brazil. The children have a skull reduction, called microcephaly. In the first trimester of pregnancy, women run the risk of contracting the virus and passing it on to their babies, especially as the transmission often goes unnoticed.

In adults only about one in five infected people develop symptoms: rash, conjunctivitis, joint pain and fever. Unlike in newborns, there are usually no long-term consequences for adults. The symptoms simply disappear after a while. Researchers are still working on an effective vaccine.

West Nile Fever

This virus can be dangerous for the elderly or for people with a weakened immune system. It can cause meningitis and myocarditis.

The virus is originally from African and Asian countries, but scientists have also found it in the South of France, the US and Canada. It is currently spreading to Italy, Greece and various Southeast European countries and has already claimed several lives.

Signs of infection in humans are similar to many other mosquito-borne diseases: shaking, chills, fever, headache and dizziness, followed by skin rashes. Not every infected person exhibits these symptoms. They only appear in about one in five. There is no vaccine and to date there are no prophylactic drugs.


The Chikungunya virus is widespread in South and East Africa, but also on the Indian subcontinent, on the islands in the Indian Ocean and in Southeast Asia. Like many diseases transmitted by mosquitoes, it causes fever.

But this usually only lasts for about three days. It is followed by a period of severe joint pain that lasts one to two weeks before it falls again. Some of the infected patients get itchy, pointed skin bleeding and mucous membrane problems, for example from the nose. There is no permanent damage. Once the disease is overcome, the patient is immune for the rest of their lives. There is no vaccine.


Malaria is probably the most famous tropical disease. The Anopheles mosquito transmits the parasite, a single-cell organism called a plasmodium. Approximately forty percent of all people around the world live in areas with increased malaria risk.

The disease progresses in fever episodes. There is a combination of symptoms: headaches and pains in the limbs, sweating and chills, but also diarrhea.

Serious damage to the nervous system can occur during the course of the disease. About half a million people die of malaria every year, most of them children. The Anopheles mosquito feels very comfortable in warm areas. It needs heat to transmit the disease. Only women are active – they are the dangerous leeches. Although the study is in full swing, there is still no reliable vaccine, but you can take prohpylactic medicines to reduce the risk of contracting the disease.

Kampf gegen Malaria in Burkina Faso (Cécilia Conan)

Mosquito nets provide effective protection against nocturnal mosquitoes

Protection against mosquitoes

The general recommendation: use mosquito repellent sprays. In warm areas, mosquito nets are also a good measure, just like light-colored clothes that cover the entire body.

But there is no such thing as a fail-safe protection unless there is a vaccine against the relevant pathogen. Unfortunately, this is not the case for all diseases that are transmitted by mosquitoes – until now.

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