Brief overview
- What is malaria? A tropical-subtropical infectious disease caused by unicellular parasites (plasmodia). Depending on the type of pathogen, different forms of malaria develop (malaria tropica, malaria tertiana, malaria quartana, knowlesi malaria), whereby mixed infections are also possible.
- Occurrence: mainly in tropical-subtropical regions worldwide (except Australia). Africa is particularly affected. In 2020, an estimated 241 million people worldwide contracted malaria and 627,000 died from the disease, mainly children (significant increase compared to 2019, which is mainly due to interruptions in malaria programs as a result of the COVID-19 pandemic).
- Infection: Usually through the bite of blood-sucking anopheles mosquitoes infected with malaria pathogens.
- Symptoms: Typical are fever attacks (hence the name intermittent fever), the rhythm of which depends on the form of malaria. Other possible symptoms include a general feeling of illness, headaches and aching limbs, diarrhea, nausea, vomiting and dizziness.
- Prognosis: In principle, all malaria is curable. However, especially in the case of malaria tropica, the prognosis depends on whether the patient is treated early and correctly.
Where does malaria occur?
Malaria occurs in tropical and many subtropical regions worldwide, with the exception of Australia. However, the various malaria regions differ to some extent in the type of malaria pathogen that is prevalent there. In addition, the number of new cases per year (incidence) varies from one malaria region to another. The higher this incidence is in a region, the more likely it is that not only the local population but also a traveler can become infected with malaria.
A distinction is made with regard to the risk of infection with malaria:
- Areas without malaria risk: e.g. Europe, North America, Australia, China, Sri Lanka
- Areas with a minimal risk of malaria: e.g. certain regions in South Africa, Namibia and Mexico, most of India and Thailand, the main Indonesian islands of Sumatra, Java and Sulawesi, the Dominican Republic
- Areas with a seasonal malaria risk: e.g. the northern half of Botswana (only the northern part of the North-West Province has a high malaria risk all year round), certain regions in the north-east of Namibia, the western half of Zimbabwe, the north-east of South Africa, parts of Pakistan
- Areas with a high malaria risk: e.g. almost the entire tropical-subtropical region of Africa south of the Sahara, the Amazon basin, Papua New Guinea, some areas in the east and northeast of India
In recent years, people in southern Europe (e.g. Spain, Greece) have also been infected with malaria in isolated cases, namely with the mostly harmless variant malaria tertiana.
Below you will find information on the risk of malaria in selected regions worldwide:
Malaria areas in Africa
Other African countries with a high risk of malaria all year round include Malawi, Madagascar, Ghana, Gambia, Liberia, the Republic of Congo, the Democratic Republic of Congo, Nigeria, Sierra Leone, the Comoros and Tanzania.
South Africa has clear regional and sometimes temporal differences in terms of the risk of malaria infection: in the north-east and east of Mpumalanga Province (including Kruger National Park) and in the north and north-east of Limpopo Province, there is a high risk of malaria from November to April and a low risk from May to October. In the rest of the north, the risk of malaria infection is minimal all year round. The rest of South Africa and the cities are considered malaria-free.
In Botswana, there is a high risk of malaria all year round in the north of the North-West Province. The same applies to the rest of the northern half of the country north of Francistown in the months of November to May, while the risk of malaria is low the rest of the year south of Maun. There is a low risk all year round in the central region of the country south of Francistown. In the southern half of the country, the risk of infection is largely minimal; the capital Gabarone is even considered malaria-free.
There is currently no risk of malaria in Egypt. No one there has been infected with the disease since 2014.
Malaria regions in Asia
In Asia, the risk of malaria infection varies greatly depending on the region.
Plasmodium falciparum, the causative agent of the dangerous malaria tropica, accounts for around 13 percent of all malaria pathogens in Thailand. P. vivax, the causative agent of malaria tertiana, is far more common (approx. 86 percent). P. knowlesi is found in certain areas (such as on the island of Little Koh Chang).
In Indonesia, the big cities are free of malaria. In other regions, the risk of contracting malaria is minimal (e.g. Sumatra, Bali, Java), low (e.g. the Moluccas archipelago) or high (e.g. West Papua and the island of Sumba). Plasmodium falciparum (the causative agent of malaria tropica) is the most common malaria pathogen, accounting for around 61 percent of cases.
In Malaysia, only a few people have been infected with malaria since 2018, with P. vivax responsible for more cases than P. falciparum and other Plasmodium species (although the data is ambiguous). The risk of malaria is low in East Malaysia (on Borneo) and largely minimal in rural areas of the rest of the country. Georgetown and the capital Kuala Lumpur are considered malaria-free.
China was certified “malaria-free” by the World Health Organization (WHO) in 2021.
Vietnam has a high risk of malaria all year round in parts of the border regions with Cambodia and a minimal risk of malaria in the rest of the country. The large urban centers are not malaria areas. The majority of cases (67 percent) are due to P. falciparum, the rest to P. vivax and rarely P. knowlesi.
Sri Lanka has not been considered a malaria area since 2016.
Malaria regions in the Caribbean, Central and South America
Here are some selected examples of these regions:
In the Dominican Republic, almost all malaria cases are also caused by this pathogen. However, there is only a minimal risk of infection here all year round, although it could possibly be higher in areas bordering Haiti.
In Mexico, you can only become infected with Plasmodium vivax, the causative agent of malaria tertiana. This risk is minimal in some regions (e.g. provinces of Campeche, Cancún, Durango, Sonora) and low in others (south of the province of Chihuahua, north of the province of Chiapas). The remaining parts of the country are free of malaria.
In Guatemala, the risk of malaria infection is high all year round in the province of Escuintla on the Pacific coast and in the north in parts of Petén. In most other regions of the country, the risk of infection is minimal (altitudes below 1,500 meters) to low (e.g. northern regions of the province of Alta Verapaz, regions around Lake Izabal). The cities of Guatemala City (capital) and Antigua, Lake Atitlán and altitudes above 1,500 meters are considered malaria-free.
El Salvador was declared malaria-free by the WHO in 2021.
In Costa Rica, there is a minimal risk of malaria in the regions of Heredia, Alajuela, Puntarenas and Limón. The capital San José and the rest of the country are considered malaria-free.
In Brazil, the Amazon basin has a high risk of malaria all year round. In other regions of the country, the risk of infection is low (e.g. city of Manaus, northwest of Mato Grosso) to minimal (e.g. rest of Mato Grosso). The cities of Brasilia, Rio de Janeiro, São Paulo, Recife, Fortaleza and Salvador, the Iguaçu Falls and some regions in the east and south-east of the country are malaria-free. By far the most common malaria pathogen in Brazil is P. vivax. The more dangerous type P. falciparum only accounts for around 10 percent.
In Ecuador, more than three quarters of all malaria cases are caused by P. vivax. There is a high risk of infection all year round in parts of the Amazon basin (including Yasuni National Park). In most other parts of the country, the risk of malaria is low to minimal. The highlands including Quito, Guayaquil and the Galapagos are free of malaria.
Malaria areas in the Middle East
In Iran, malaria cases acquired in the country were last recorded in 2017. Most were caused by P. vivax. There is currently a minimal seasonal malaria risk in rural areas of Hormozgan province, in the south of Sistan-Baluchestan and Kerman provinces (tropical part) and in parts of Fars and Busher provinces. The rest of the country is free of malaria.
In Iraq, malaria cases acquired in the country were last reported in 2009.
In Yemen, the risk of malaria infection is high all year round and throughout the country (possibly lower risk in Socotra). Almost all cases are caused by the dangerous pathogen P. falciparum.
Malaria prophylaxis
For example, in such areas you should wear light-colored clothing that covers the body as much as possible (long sleeves, long pants, socks). If necessary, you can impregnate your clothing with a mosquito repellent beforehand. It also makes sense to have a mosquito-proof sleeping area, for example with a fly screen in front of the window and a mosquito net over the bed.
In some cases, malaria prevention with medication (chemoprophylaxis) is also possible and advisable.
It is best to seek advice from a doctor (preferably a tropical or travel medicine specialist) well in advance of your trip. They can recommend the right malaria prophylaxis for you – depending on the malaria risk in your destination, the duration of your trip and the type of travel (e.g. backpacking or hotel trip).
You can read more about the various ways to prevent malaria in the text Malaria prophylaxis.
Malaria: causes and risk factors
- Plasmodium falciparum: Trigger of malaria tropica, the most dangerous form of malaria. This type is mainly found in tropical regions, such as sub-Saharan Africa, southern and south-eastern Asia and the Amazon basin.
- Plasmodium vivax and Plasmodium ovale: Triggers of malaria tertiana. P. vivax is the predominant pathogen type in most tropical-subtropical regions outside sub-Saharan Africa. P. ovale, on the other hand, is mainly found in West Africa south of the Sahara.
- Plasmodium malariae: Trigger of the rare malaria quartana. Occurs in tropical regions worldwide.
- Plasmodium knowlesi: Only widespread in Southeast Asia. Causes malaria mainly in monkeys (more precisely: macaques) and only occasionally in humans.
Malaria: Transmission routes
There is a simple formula for the risk of infection in a particular region: The more Anopheles mosquitoes in an area carry the pathogen, the more people they infect. If these patients are not treated and are bitten again by an uninfected mosquito, this mosquito can ingest the pathogen and transmit it to another person during the next blood meal.
It is very rare for people outside of malaria-endemic areas to contract the tropical disease. For example, there is so-called airport malaria: infected Anopheles mosquitoes imported by airplane can bite people on the plane, at the airport or in its immediate vicinity and infect them with the malaria pathogen.
Transmission of the malaria pathogen is also possible via a blood transfusion or infected needles (injection needles, infusion needles). However, due to the strict safety regulations, this only happens extremely rarely in this country. However, the risk of infection may be greater with blood transfusions in malaria regions.
Sickle cell anemia offers a certain degree of protection against malaria. Malaria is much rarer and much less pronounced in people with this hereditary disease. In sickle cell anemia, the shape of the red blood cells is altered in such a way that the malaria pathogen cannot infect them or can only infect them to a limited extent in order to multiply. This is probably the reason why sickle cell anemia is particularly common in many malaria regions.
Life cycle of the malaria pathogens
The malaria pathogens are transmitted from mosquitoes to humans as so-called sporozoites. Sporozoites are the infectious developmental stage of the pathogens. The parasites enter the liver via the bloodstream and penetrate liver cells. Inside the cells, they transform into the next stage of development: Schizonts, which fill almost the entire liver cell. Thousands of mature merozoites develop inside them. Their number depends on the type of malaria pathogen – it is highest with Plasmodium falciparum (pathogen of the dangerous malaria tropica).
In malaria tertiana, M. quartana and Knowlesi malaria, the infected erythrocytes burst synchronously to release the merozoites. This results in rhythmically occurring fever attacks. In malaria tropica, the bursting of the erythrocytes is not synchronized, resulting in irregular fever attacks.
In Plasmodium vivax and P. ovale (the causative agent of malaria tertiana), only some of the merozoites in the red blood cells develop into schizonts. The rest go into a resting phase and remain in the erythrocytes for months to years in the form of so-called hypnozoites. At some point, these dormant forms can become active again and transform into schizonts (and further into merozoites). This is why relapses can occur in malaria tertiana even years after infection.
Is malaria contagious?
The malaria pathogen cannot be transmitted directly from person to person – except via blood contact, such as between an infected pregnant woman and her unborn child, or via contaminated blood transfusions. Otherwise, infected people do not pose a risk to other people.
Malaria: incubation period
Malaria does not break out immediately after you have been infected with the pathogen. Instead, some time passes between infection and the appearance of the first symptoms. The duration of this incubation period depends on the type of pathogen. In general, the following incubation periods apply:
- Plasmodium falciparum (trigger of malaria tropica): 6 to 30 days
- Plasmodium vivax and Plasmodium ovale (triggers of M. tertiana): 12 days to over a year*
- Plasmodium malariae (trigger of M. quartana): 12 to 30 days (in individual cases longer*)
- Plasmodium knowlesi (trigger of Knowlesi malaria): over a week
Plasmodium malariae does not produce resting forms (hypnozoites). However, the number of parasites in the blood can be so low that it can take up to 40 years before symptoms appear.
Malaria: Symptoms
In general, symptoms such as fever, headache and aching limbs as well as a general feeling of illness appear first in malaria. Diarrhea, nausea, vomiting and dizziness are also possible. Some patients mistakenly attribute the symptoms to a simple flu-like infection or influenza.
In detail, there are some differences in the symptoms of the various forms of malaria:
Symptoms of malaria tropica
Malaria tropica is the most dangerous form of malaria. Symptoms occur more severely here than with other forms and weaken the organism considerably. The reason for this is that the pathogen (Plasmodium falciparum) attacks both young and older red blood cells (unlimited parasitemia) and thus destroys a particularly large number of erythrocytes as the disease progresses.
Consequences & complications
During the course of the disease, the spleen can enlarge (splenomegaly) because it has to do a lot of hard work in malaria: it has to break down the many red blood cells that are destroyed by the malaria pathogen. If the spleen exceeds a critical size, the spleen capsule surrounding it can rupture (splenic rupture). This leads to severe bleeding (“tropical splenomegaly syndrome”).
Enlargement of the liver (hepatomegaly) as a result of malaria infection is also possible. It can be accompanied by jaundice (icterus).
The simultaneous enlargement of the liver and spleen is called hepatosplenomegaly.
In around one percent of patients, the pathogens penetrate the central nervous system (cerebral malaria). This can lead to paralysis, seizures and loss of consciousness or even coma. Ultimately, those affected can die.
Other possible complications of malaria tropica are impaired kidney function (acute renal failure), circulatory collapse, anemia due to the increased decay of red blood cells (hemolytic anemia) and “disseminated intravascular coagulopathy” (DIC): In this case, blood clotting is activated inside intact blood vessels, causing masses of platelets to be consumed – a lack of platelets (thrombocytopenia) develops with an increased tendency to bleed.
Especially in pregnant women and children, there is also a risk of malaria tropica being accompanied by low blood sugar (hypoglycemia). Possible signs include weakness, dizziness, ravenous appetite and seizures.
Symptoms of malaria tertiana
Patients first get chills in the late afternoon and then very quickly develop a fever of around 40 degrees Celsius. After about three to four hours, the temperature quickly drops back to normal, accompanied by profuse sweating.
Complications and deaths are rare with malaria tertiana. However, relapses can occur years later.
Symptoms of malaria quartana
In this rare form of malaria, fever attacks occur every third day (i.e. every 72 hours). The rise in temperature to up to 40 degrees can be accompanied by severe shivering. The fever subsides after about three hours, accompanied by heavy sweating.
Possible complications include kidney damage and rupture of the spleen. In addition, relapses can occur up to 40 years after infection.
Symptoms of Knowlesi malaria
This form of malaria, which is restricted to South-East Asia, was previously only known to occur in certain monkeys (macaques). Transmitted by Anopheles mosquitoes, however, it can also occur in humans in rare cases.
You can also be infected with different Plasmodium species at the same time (mixed infections), so that the symptoms can be mixed.
Malaria: examinations and diagnosis
If you have been in a malaria risk area in the weeks before the onset of symptoms (or are still there), you should consult a doctor (family doctor, tropical medicine specialist, etc.) at the slightest sign of the onset of illness (especially fever). Starting treatment quickly can be life-saving, especially in the case of the dangerous malaria tropica!
Even months after a trip to a malaria risk area, any unexplained febrile illness should be examined accordingly. This is because malaria sometimes only breaks out after a very long delay.
Doctor-patient consultation
The doctor will first ask you about your medical history (anamnesis). Possible questions include:
- What exactly are your symptoms?
- When did the symptoms first occur?
- When was the last time you were abroad?
- Where were you? How long were you there?
- Did you take malaria prophylaxis medication in the destination country?
Blood tests
If there is the slightest suspicion of malaria (intermittent fever), your blood will be examined microscopically for malaria pathogens. This is done by means of a “blood smear” and a “thick drop”:
In a blood smear, a drop of blood is spread thinly on a slide (small glass plate), air-dried, fixed, stained and viewed under a microscope. The staining serves to make any plasmodia present in the red blood cells visible.
The advantage of this method is that the type of plasmodia can be easily determined. However, if only a few red blood cells are infected with plasmodia, the infection may be overlooked. A thin smear alone is therefore not suitable for detecting malaria.
The disadvantage of the thick drop is that it is not as easy to determine the type of plasmodia as with the thin smear. At best, the pathogens of the life-threatening malaria tropica (Plasmodium falciparum) can be differentiated from other malaria pathogens (such as P. vivax). A thin blood smear is necessary for exact identification.
If no plasmodia can be detected in the blood test, malaria may still be present. In the early stages, the number of parasites in the blood may still be too low for detection (even for the thick drop). Therefore, if malaria is still suspected and the symptoms persist, the blood test for plasmodia should be repeated several times (at intervals of several hours, possibly over several days).
If the test reveals a malaria infection caused by Plasmodium falciparum or P. knowlesi, the level of so-called parasitemia is also determined – i.e. the percentage of infected erythorocytes or parasites per microliter of blood. The extent of the parasitemia influences the treatment planning.
Malaria rapid test
Malaria rapid tests have also been available for some time. They can detect plasmodia-specific proteins in the blood. However, malaria rapid tests are not used as standard to diagnose an infection, but only for initial orientation – especially if a blood test using a thick drop and blood smear is not possible in an appropriate time and quality. The reason for this is the possible disadvantages:
Rapid malaria tests can usually reliably detect a symptomatic infection with P. falciparum (malaria tropica) (high specificity) and hardly miss any cases (high sensitivity). However, in many regions (South America, Africa, South East) mutants of the pathogen have spread in recent years which no longer produce the specific protein that the rapid test detects (HRP-2). An infection with such P. falciparum mutants is therefore not detected by the rapid tests.
On the other hand, false positive results are also possible with such rapid tests. For example, they can falsely diagnose malaria in patients with a positive rheumatoid factor.
Detection of plasmodia genetic material
It is also possible to examine a blood sample for traces of plasmodia genetic material (DNA), to amplify this using the polymerase chain reaction (PCR) and thus detect the exact type of pathogen. However, this takes a relatively long time (several hours) and is very expensive. For these and other reasons, this diagnostic method is only used in special cases, for example with
- very low parasite density in order to identify the exact Plasmodium species
- suspected infection with Plasmodium knowlesi (this type of pathogen can often not be distinguished from P. malariae in microscopic blood tests)
- People who are intended as organ donors in order to rule out a Plasmodium infection with certainty
Detection of antibodies?
Further examinations
The physical examination after a confirmed case of malaria provides the doctor with information about the patient’s general condition and the severity of the infection. For example, the doctor measures body temperature, pulse, respiratory rate and blood pressure. The heart rate can be determined using an ECG. The doctor also checks the patient’s level of consciousness. During a palpation examination, he can also detect any enlargement of the spleen and/or liver.
If the patient is in a poor general condition or has complicated malaria (such as a very high parasite count in the blood, infestation of the brain, kidneys, lungs, etc.), further examinations are necessary: for example, additional blood values are determined (such as calcium, phosphorus, lactate, blood gases, etc.). The amount of urine can also be measured and the chest x-rayed (chest X-ray).
It may also be useful to take blood cultures: Sometimes malaria is accompanied by a bacterial infection (co-infection), which can be detected by culturing the bacteria in a blood sample.
Malaria: Treatment
- type of malaria (M. tropica, M. tertiana, M. quartana, Knowlesi malaria)
- any concomitant diseases (such as severe heart or kidney disease)
- Presence of pregnancy
- Allergies, intolerances and contraindications to malaria medication
In the case of M. tropica and M. knowlesi, the severity of the disease also influences treatment planning. It also plays a role here whether the patient has previously taken medication for malaria prophylaxis or is currently taking any concomitant medication (for other diseases).
As a rule, the disease is treated with medication. Depending on the pathogen, different antiparasitic agents are used. However, due to the widespread use of drugs in the past, many pathogens are now resistant to certain drugs (such as chloroquine). This is why malaria patients often have to be treated with two or more different drugs.
Malaria tropica: Therapy
- Artemether + lumefantrine
- Dihydroartemisinin + piperaquine (no authorization in Switzerland)
- possibly atovaquone + proguanil
The tablets must usually be taken over three days. Depending on the preparation, possible side effects include nausea and vomiting, abdominal pain, diarrhea, headaches, dizziness, cardiac arrhythmia and coughing.
Complicated malaria tropica requires treatment in intensive care. Doctors speak of “complicated”, for example, when clouding of consciousness, cerebral seizures, respiratory weakness, severe anaemia, shock symptoms, kidney weakness, hypoglycaemia or high parasite density in the blood occur.
In exceptional cases, the administration of artesunate is not possible (e.g. due to a severe intolerance to artesunate and similar compounds). In such cases, complicated malaria tropica can be treated intravenously with quinine dihydrochloride instead. Caution is required here, as severe side effects can occur in some cases. As a rule, treatment is switched to a better therapy as soon as possible.
Malaria tertiana: therapy
Patients with malaria tertiana can usually be treated as outpatients. They usually receive combination tablets with artemether + lumefantrine or dihydroartemisinin + piperaquine (possibly also atovaquone + proguanil), although these preparations are not officially approved for this form of the disease (“off-label use”). The tablets are administered in the same way as for malaria tropica, i.e. over three days.
Malaria quartana: Therapy
Malaria quartana can also usually be treated on an outpatient basis. This usually involves treatment with dihydroartemisinin + piperaquine – as with uncomplicated malaria tropica. Alternatively, the combination of atovaquone + proguanil is sometimes given.
Subsequent treatment with primaquine, as with malaria tertiana, is not necessary here because the causative agent of malaria quartana (Plasmodium malariae) does not develop permanent forms in the liver (hypnozoites).
Knowlesi malaria: Therapy
Knowlesi malaria is treated in the same way as malaria tropica. This means that treatment takes place in hospital, even in the intensive care unit in severe cases. In uncomplicated cases, patients receive a combination preparation of two active substances (such as artemether + lumefantrine) for three days. Complicated Knowlesi malaria (clouding of consciousness, cerebral seizures, severe anemia, etc.) is preferably treated with artesunate.
Supportive treatment
For example, high fever can be treated with physical measures (such as calf compresses) and antipyretics. If malaria patients have developed severe anemia, they receive blood transfusions with red blood cells (erythrocyte concentrates).
If epileptic seizures occur in patients with cerebral malaria (malaria with brain involvement), they are initially treated with benzodiazepines or benzodiazepine derivatives. If the patient falls into a coma, measures are taken that are generally important for coma patients (positioning, possibly ventilation, etc.).
Malaria patients should drink sufficient fluids to ensure adequate blood circulation in the body – but not too much, otherwise pulmonary edema can develop quickly. This is an accumulation of fluid in the lung tissue, which can impair gas exchange. Artificial respiration may then be necessary.
If the kidneys are weak or failing, dialysis may be necessary.
Malaria: course and prognosis
The course and prognosis of malaria depend primarily on the form of the disease and the stage at which it was detected. Malaria tertiana and malaria quartana are usually relatively mild. Sometimes they even heal spontaneously without treatment after a few relapses. Only rarely do severe courses and deaths occur. Knowlesi malaria progresses rapidly due to the short reproductive cycle of the pathogen (P. knowlesi) and can also be severe, but is also rarely fatal.
The mortality rate for untreated malaria tropica is high.
