Malaria , also known as swamp fever, is an acute infectious disease caused by several species of protozoa of the genus Plasmodium and transmitted by the bite of an Anopheles mosquito. It is widely distributed in warm and humid regions with an average annual temperature of 16C and above, and is also found in more temperate zones. Currently, about 400 million people suffer from it, 130 million new cases of the disease are recorded every year. Tropical malaria causes the death of almost 2 million cases a year; in Africa, one child dies from this disease in 20 seconds.
Malaria in humans is caused mainly by three types of Plasmodium: Plasmodium vivax (the most common pathogen), P. falciparum and P. malariae. The fourth type of Plasmodium that can cause human disease, P. ovale, is distributed only in some parts of Africa. Malaria affects reptiles and birds, as well as monkeys and other mammals. Only female mosquitoes carry the pathogen, since males do not have the necessary piercing and sucking parts of the oral apparatus.
The reproduction phase of the parasite in the human body begins with the bite of an infected mosquito. Mobile microscopic forms of the parasite, called sporozoites, along with the saliva of the mosquito, enter the skin and enter the bloodstream. Then they are introduced into human red blood cells – erythrocytes, where they continue to develop. After that, the parasite proceeds to asexual reproduction – it is divided into many small mononuclear individuals. As a result, the erythrocyte is destroyed, and small individuals – merozoites – enter the bloodstream. Here they penetrate into new red blood cells, and the cycle of development of the malaria parasite in humans is repeated. The massive release of merozoites from erythrocytes, accompanied by the entry into the blood of plasmodium metabolic products, leads to an attack of chills and fever, and the interval between attacks depends on the type of plasmodium. When infected with P.
Three-day malaria (benign three-day malaria) is caused by P. vivax. The first symptoms develop 6–21 days after being bitten by an infected mosquito: severe chills herald an attack of high fever, which lasts up to 8 hours and ends in profuse sweating. Such attacks are repeated every third day, but can be observed more often if, during the period of infection, infected mosquitoes bit the sick person for several days.
Attacks of fever are accompanied by an increase in heart rate and a decrease in blood pressure. At the height of the attack, symptoms of damage to the central nervous system are found: nausea, vomiting, delirium, sometimes a coma develops. Anemia often occurs due to the destruction of red blood cells by plasmodia multiplying in them. Typical symptoms also include loss of appetite, headache, pain throughout the body (arms, legs, back). As a rule, a gradual recovery begins after a few weeks, but repeated attacks of malarial fever can be observed for three or more years.
Malignant three-day malaria (fulminant three-day malaria) is caused by P. falciparum and is the most severe form of malaria. The symptoms in this case are the same as in benign three-day malaria, but they are more pronounced and are accompanied by more severe complications. This form of malaria is characterized by aggregation of red blood cells and their attachment to the wall of small vessels (the so-called parasitic stasis), which leads to blockage of the capillaries. Functional disorders of the nervous system and gastrointestinal tract are often observed. The liver and kidneys are often affected. Blockage of small blood vessels in the brain can be fatal. In the case of recovery, the recurrence of attacks of malaria is not often observed.
Four-day malaria is caused by P. malariae; it tends to be milder than the other forms, but it is more likely to have recurrent attacks of fever. The incubation period is 1–6 weeks; fever develops at four-day intervals.
After examining the sick person and collecting an anamnesis (history of the disease), a blood test is prescribed (microscopy of a blood smear for visual detection of parasites).
For the treatment of malaria, various products are used that can prevent attacks of malaria, quickly stop the symptoms of an attack that has begun, or completely destroy the pathogen. Among them, the best known are chloroquine, quinine, mefloquine, primaquine, and quinacrine hydrochloride, also sold under the names atabrine and quinacrine. Individuals planning to travel or stay long-term in malaria endemic areas are advised to regularly take antimalarial products such as chloroquine.
In persons who have had malaria, a state of relative immunity (immunity) develops, i.e. re-infection with the same pathogen is accompanied by a milder fever with milder clinical manifestations, despite the same number of plasmodia in the blood. Over time, immunity weakens, and parasites remaining in the human body can begin to multiply again, causing a new attack after a few months or even years.
The three main types of Plasmodium that cause malaria in humans exist in nature in several strains. Each of the strains has its own antigenic features and is traditionally distributed only in certain areas. Thus, immunity appears only to the strain that caused the primary infection.
Measures to limit the number of mosquito vectors are aimed at the destruction of their larvae, which live in the subsurface layer of quiet water bodies (the body of the larva is located under water, and the so-called spiracle protrudes outward). For this purpose, wetlands are drained, an oil film is applied to the surface of reservoirs, insecticides are sprayed, and small fish that feed on mosquito larvae are bred.