Malaria – dangerous tropical disease

Malaria - dangerous tropical disease

Malaria is one of the most important infectious diseases worldwide, killing up to 500 million people and killing up to 3 million people every year. Due to travel to Asian and African countries, malaria also plays a role in Germany, although the malaria pathogen is not native here. Malaria is an infectious disease with typical fever episodes triggered by the malaria pathogen Plasmodium. These Plasmodium are transmitted to humans by a specific species of mosquito, the Anopheles mosquito.

Malaria pathogen: emergence of malaria

Malaria is caused by five different species of Plasmodium – namely Plasmodium falciparum, ovale, vivax, malaria and knowlesi. These five types cause four different types of malaria, which differ in the course of fever and the severity of the disease.

The Plasmodium spends part of its life cycle in the mosquito and the other in humans. Its development in humans is closely related to the fever episodes that occur with malaria. The pathogens enter the human bloodstream through the bite of the mosquito infected with Plasmodium. Depending on the species, they migrate to the liver, where they stay and develop for between 5 and 18 days.

At the end of this stage, the affected liver cells rupture, and the malaria pathogens re-enter the bloodstream. There, they attach themselves to red blood cells (erythrocytes), penetrate them and continue to multiply. When the erythrocytes break down, many pathogens are released, infecting new red blood cells. This mechanism causes recurrent episodes of fever.

 

How can you get infected with malaria?

Most often, malaria is transmitted by the bite of a female Anopheles mosquito infected with Plasmodium. This means that transmission usually takes place from mosquitoes to humans.

If a person is infected, malaria is theoretically contagious. However, the infection from person to person can only take place via blood. However, this happens very rarely, for example, with a blood transfusion or during a pregnancy from mother to unborn child. “Healthy” mosquitoes can also become infected by sucking human blood infected with malaria pathogens and thus become vector mosquitoes – this has also happened before.

incubation period

The incubation period differs depending on the pathogen. After 7 to 40 days, the first uncharacteristic symptoms such as fever, headache, body aches, and a general “feeling of illness” appear. These non-specific symptoms are often misinterpreted as a cold or gastrointestinal flu . The time lag between a stay in the tropics and the occurrence of malaria can favour a misdiagnosis in our latitudes.

 

Malaria: Symptoms and forms

How intense the malaria symptoms are depends on the infected person’s immunity level. People infected multiple times acquire what is known as semi-immunity, which prevents a severe illness. Those who are not immune are most at risk – especially young and older people.

Plasmodium ovale and vivax trigger malaria tertiana. In this form, a regular rhythm of fever attacks sets in after a few days, occurring every 48 hours. There are chills in the late afternoon, and the fever quickly rises to around 40°C. After three to four hours, the fever drops back to normal, accompanied by profuse sweating.

Malaria quartana is the rarest form of malaria and is caused by Plasmodium malariae. The fever attacks occur in a rhythm of 72 hours. Both forms usually heal within eight weeks without treatment.

Malaria tropica is the most dangerous form of malaria. If left untreated, it is fatal in non-immune patients in 20 per cent of cases. In contrast to the other types of malaria, there is no rhythmic intermittent fever, which complicates the diagnosis. More than half of those affected experience a drop in blood platelets, which can lead to clotting disorders, spleen enlargement or liver and diarrhoea. If the nervous system is affected, seizures and clouding of consciousness occur. Complications include acute renal failure and circulatory collapse.

A relatively rare form is Plasmodium knowlesi malaria. It only occurs in Southeast Asia. It is characterized by daily bouts of fever and high levels of parasitemia, i.e. the presence of parasites in the blood.

diagnosis of malaria

The most crucial examination when malaria is suspected is the microscopic examination of the blood. For this purpose, the so-called “thick drop”, an air-dried drop of blood, or sometimes a thin blood smear, is examined for pathogens. An experienced doctor can even distinguish the different malaria pathogens under a microscope based on their appearance. The number of pathogens in the blood drop reflects the disease’s severity. The detection of pathogens in the blood is proof of the presence of malaria.

On the other hand, a negative test result does not rule out malaria – the number of parasites in the blood may still be too low, and the pathogens can only be seen if the test is repeated. There are also rapid malaria tests. as antigen detection. Every traveller on site can use them for self-diagnosis. Unfortunately, they sometimes give false test results when the parasitic values ​​are low or high. In addition, they cannot recognize every pathogen, and their implementation is complex.

If parasites are to be detected in exceptional cases, a malaria PCR test (polymerase chain reaction) can be carried out. However, the results are only available after a few hours. In addition, this test results in high costs.

treatment of malaria

Malaria is treated with medication. The various drugs kill the malaria pathogen. Milder forms can be treated on an outpatient basis, while malaria tropica always has to be treated as an inpatient because of the risk of complications. In addition, the treatment of malaria depends on which pathogen is present, whether it is resistant to a drug, how severe the disease is and whether drugs have already been taken beforehand. In addition to drugs to combat the pathogens, drugs to reduce fever are usually used. In addition, symptoms such as kidney weakness or a drop in blood platelets can be treated.

Malaria is curable. The prognosis depends heavily on how far the disease has progressed. For this reason, medical advice should always be sought immediately if malaria is suspected.

 

Is there a malaria vaccination?

There is currently no vaccination against malaria for adults. The World Health Organization (WHO) issued a corresponding recommendation for children in autumn 2021. The vaccine RTS, S (Mosquirix ® ) is effective against the malaria pathogen Malaria tropica. This is especially dangerous for children.

Possible malaria prophylaxis

To protect themselves against the malaria pathogen, adults can either take measures to avoid being bitten (exposure prevention) or take precautionary medication that kills the pathogen once it is in their body (chemoprophylaxis).

You can take the following measures to prevent exposure:

  • Stay in mosquito-proof rooms that are prepared with fly screens and air conditioning.
  • Sleep under mosquito nets impregnated with insecticidal substances (mosquitoes are nocturnal)!
  • Wear mosquito-proof clothing such as long pants, socks, long-sleeved blouses or shirts.
  • Use insect repellents (mosquito repellent sprays).

Although chemoprophylaxis does not offer absolute protection against infection, it does increase your safety. Which medication you should take depends on the destination, travel time and duration, and your travel style – backpacking for several weeks in the rainy season in northern Thailand is riskier than a short trip to a hotel complex in the south. Talk to your doctor and learn more about prophylactic recommendations for your travel area from the Robert Koch Institute or the Hamburg Tropical Institute.

You can also take a “standby” drug with you on vacation, which is a drug that you take immediately if you have symptoms that suggest malaria – then you should see a doctor as soon as possible. In malaria areas, it is hoped that infected mosquitoes will be displaced by genetically modified forms resistant to malaria.

Where is malaria found?

Malaria is typical of tropical and subtropical areas. It occurs in about 100 countries, particularly Asia, Central and South America, and Africa.

Most of the infections occur in Africa, from sub-Saharan Africa to northern South Africa – WHO estimates that between 300 and 500 million people contract the disease there every year, and hundreds of thousands die from it.

The border region between Thailand and Myanmar, Laos, Cambodia, the Indonesian islands east of Bali, Papua New Guinea and the Solomon Islands are particularly affected in Asia.

In South America, northern countries are particularly affected. These include Brazil, Ecuador, Colombia, Peru, Bolivia and Venezuela.

Most infections occur in West African countries and Kenya. Very rarely, you can get infected if an infected mosquito gets on an aeroplane. Transmission, airport malaria, can occur on the plane or at the airport.

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