🕒 6 min
On the 25th of April, the World Malaria Day 2022 took place. This year’s theme was “Harness innovation to reduce the malaria disease burden and save lives“, since the main goal of the World Health Organization (WHO) was to highlight the necessity of research and development for new therapeutic strategies to eradicate the disease. Today, malaria is entirely preventable and curable disease if the symptoms are recognized in earlier stages, but in some cases, it is unfortunately not possible. Therefore, the estimated number of new cases in 2020 was 241 million, and within that number there were 627 thousand malaria-related deaths in 85 countries. The region at highest risk is the sub-Saharan Africa, where more than two thirds of deaths were reported among the children under the age of 5. Despite the promising and steady advances in controlling the disease between 2000 and 2015, in recent years there was an evident set-back especially in the number of preventable deaths. What are the causes of this stagnation and what can be done to prevent the spread of this highly contagious disease?
Malaria is one of the deadliest parasitic diseases caused by species of the genus Plasmodium. There are 5 parasites that can cause malaria in humans, of which the two- Plasmodium falciparum and Plasmodium vivax pose the greatest threat. P. falciparum is the deadliest malaria parasite due to the fast development of fatal complications in infected patients and the most resistant one when it comes to drug therapy. The parasites are spread to humans through the bites of infected female Anopheles mosquitoes whose natural habitat are tropical and subtropical areas. Signs and symptoms of malaria usually begin within a few weeks after being bitten by an infected mosquito, yet some types of parasites can persist in a dormant state in the body for up to a year. Malaria often presents in the form of an attack that starts with unpleasant shivering and chills as primary signs of high fever, which are then followed by sweating and a return to the normal body temperature. Other symptoms also include headache, abdominal pain, nausea and vomiting, diarrhoea, muscle or joint pain, coughing, rapid breathing and rapid heart rate and the general feeling of discomfort. The greatest risk factors for developing malaria are living in or visiting the areas where the disease is common. Malaria can be fatal, particularly when it is caused by P. falciparum and P. vivax species. The main reason for this is the fact that symptoms are not very specific, so the disease is recognized in later stages, when patients develop complications such as brain swelling, breathing problems and organ failure. Groups at a higher risk of serious disease are young children and infants, older people, pregnant women and their unborn children and travellers coming from areas with no malaria.
The spread of malaria is very problematic because of its transmission cycle. A mosquito becomes infected with Plasmodium parasites by feeding on a blood of the person who has malaria. As the infected mosquito bites other people, it transmits malaria parasites to a big number of healthy individuals living in the same area. Once the parasite enters the body, it travels from the bloodstream to the liver, where it matures. Some Plasmodium species can lie dormant in the liver for up to a year. When parasites are mature, they leave the liver and travel back into the bloodstream to infect the red blood cells. In this stage of the transmission cycle infected patients often develop first symptoms. If the uninfected mosquito bites an infected patient in this point of the cycle, it becomes infected with parasites and the cycle repeats itself as the mosquito bites other people. Since parasites affect red blood cells, malaria can also be spread from mothers to unborn children, through blood transfusions and by sharing needles. Residents of the areas at high risk of malaria can, by exposition to the parasite for some extent, acquire partial immunity, but this immunity can wane if they move to a place where they are no longer frequently exposed to the parasite.
As in any other infectious disease, preventive measures are of great importance. Travellers are advised to cover their skin entirely, to apply insect repellent on any exposed skin as to also apply it on clothes. A very effective preventive measure is to sleep under a net, as bed nets that are treated with insecticides prevent mosquito bites during sleep. Also, a few months prior travelling to locations where malaria is common, it is advised to consult a doctor about whether there is a need to take the drugs before, during or after the trip. Generally speaking, drugs used for prevention are the same ones used to treat malaria. The length of treatment and types of drugs used depend on the parasite species that caused the infection, severity of the present symptoms, patients age and pregnancy. The most common antimalarial drugs belong to the class of antiparasitic drugs and include chloroquine phosphate, mefloquine, artemisinin, atovaquone, proguanil, quinine sulphate and primaquine phosphate. Chloroquine was the first antiparasitic drug used for prevention and treatment of malaria and it is the first line treatment for any Plasmodium parasite sensitive to the drug. Unfortunately, parasites became resistant to this therapy which makes it no longer effective when used on its own. Due to the growing resistance to antimalarial drugs, combinations of drugs with different mechanism of action are often used to treat malaria. Artemisinin-based combination therapies (ACT), for example artemeter-lumefantrine and artesunate-mefloquine are effective for chloroquine-resistant malaria. As there is new information emerging about increasing resistance to artemisinin as well, scientists are putting great efforts into designing and synthesizing new molecules as potential antimalarial drugs that could be used in the future.
Since October 2021, WHO recommends broad use of malaria vaccine “Mosquirix” among children aged 6 weeks to 17 months living in regions where malaria is predominantly caused by parasite Plasmodium falciparum. The active substances in this vaccine are proteins found on the surface of the parasite and the hepatitis B virus, but it should not be used just to treat hepatitis infection. When a child is vaccinated, the child’s immune system recognizes the proteins of the parasite and the virus as “foreign” and produces antibodies to destroy them. This first immune reaction to foreign proteins is necessary so that the following reactions to the infection could be quicker. Mosquirix induces production of antibodies against the parasites in the blood, so they are not able to reach the liver, thus limits their ability to mature or cause any symptoms of the disease. The vaccine provides short-term protection that could potentially save lives of the children that are at most risk of severe malaria.
It has also been shown that malaria is a climate sensitive disease, highly influenced by temperature changes, humidity and rainfall. Efficient vectors of malaria, female Anopheles mosquitoes, require only small amounts of water to survive and can reproduce in large numbers. Anopheles are present worldwide except Antarctica, as vectors they are active only in hot seasons, while malaria is also present in temperate regions. The biting adult females are short-lived, with only a small proportion of those that can survive up to 10 days in tropical regions, but these limitations are not enough to restrict malaria diffusion everywhere. There is a growing concern that climate changes might alter the malaria’s transmission into areas of the world where the disease is currently under control or into non-endemic areas.
To conclude, emerging drug resistance and rapid transmission of malaria hinder the eradication of the disease the most. Therefore, it is very important to encourage research and development of new therapeutic strategies such as new drug molecules with completely different mechanisms of action than the existing ones. In the end, the responsibility of implementing certain preventive measures lies on every individual, since malaria is no longer a problem of the third world, it is indeed a growing global problem.