Spread of Malaria

Transmission of Malaria 

The malaria parasite typically is transmitted to people by mosquitoes belonging to the genus Anopheles. In rare cases, a person may contract malaria through contaminated blood, or a fetus may become infected by its mother during pregnancy.

Because the malaria parasite is found in RBCs, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria also may be transmitted from a mother to her fetus before or during delivery (“congenital” malaria).

Many biological and environmental factors shape the character of malaria in a given location. Nearly all the people who live in endemic areas are exposed to infection repeatedly. Those who survive malaria in childhood gradually build up some immunity. They may carry the infection, serving as reservoirs for transmission by mosquitoes without developing severe disease. In other areas, where the infection rate is low, people do not develop immunity because they rarely are exposed to the disease. This makes them more susceptible to the ravages of an epidemic. An epidemic can occur when conditions, such as those discussed below, allow the mosquito population to increase suddenly.

mosquitos malaria

Effects of Climate 

Climate affects both parasites and mosquitoes. Mosquitoes cannot survive in low humidity. Rainfall expands breeding grounds, and in many tropical areas, malaria cases increase during the rainy season. Mosquitoes must live long enough for the parasite to complete its development within them. Therefore, environmental factors that affect mosquito survival can influence malaria incidence.

Plasmodium parasites are affected by temperature—their development slows as the temperature drops. P. vivax stops developing altogether when the temperature falls below 60 degrees Fahrenheit. P. falciparum stops at somewhat higher temperatures. This effect explains why parasites can be found in temperate areas.

Effect of Human Intervention

People have worked for centuries to control malaria and were successful in eradicating it from most of North America early in the 20th century. Certain human activities, however, have inadvertently worsened the spread of malaria.

City conditions, for example, can create new places for mosquito larvae to develop. Agricultural practices also can affect mosquito breeding areas. Although the draining and drying of swamps gets rid of larval breeding sites, water-filled irrigation ditches may give mosquitoes another area to breed. In addition, because farmers use the same pesticides on their crops as those used against malaria vector mosquitoes, the problem of insecticide-resistant mosquitoes is growing. Modern transportation also contributes to the spread of the disease, moving travelers and occasionally mosquitoes between malaria-endemic and non-endemic regions.


Malaria is transmitted occasionally through transfusions of blood from infected individuals or sharing of needles to inject intravenous drugs, and can be transmitted from an infected pregnant woman to her unborn child. In the United States, however, transmission rarely occurs through blood transfusions, because blood donors are not allowed to donate for specified periods of time after traveling to or living in a malarious area.

blood drawn

Symptoms of Malaria

Malaria typically produces a string of recurrent attacks, or paroxysms, each of which has three stages— chills, followed by fever, and then sweating. Along with chills, the person is likely to have headache, malaise, fatigue, and muscular pains, and occasionally nausea, vomiting, and diarrhea. Within an hour or two, the body temperature rises, and the skin feels hot and dry. Then, as the body temperature falls, a drenching sweat begins. The person, feeling tired and weak, is likely to fall asleep.

The symptoms first appear some 10 to 16 days after the infectious mosquito bite and coincide with the bursting of infected RBCs. When many RBCs are infected and break at the same time, malaria attacks can recur at regular time periods— every 2 days for P. vivax malaria and P. ovale, and every 3 days for P. malariae.

With P. vivax malaria, the person may feel fine between attacks. Even without treatment, the paroxysms subside in a few weeks. A person with P. falciparum malaria, however, is likely to feel miserable even between attacks and, without treatment, may die. One reason P. falciparum malaria is so virulent is that the parasite can infect RBCs in all stages of development, leading to very high parasite levels in the blood. In contrast, P. vivax parasites infect only young RBCs, which means the number of parasites in the blood does not reach the same high levels as seen in P. falciparum infection. 

(Meyda Azzahra)