In warm climates people are more likely to sleep unprotected outdoors, thereby increasing exposure to night-biting Anopheles mosquitoes. Thus, malaria transmission is much more intense in warm and humid areas, with transmission possible in temperate areas only during summer months. falciparum), development cannot be completed and malaria cannot be transmitted. If temperatures are too cool (15☌ or 59☏ for Plasmodium vivax, 20☌ or 68☏ for P. This process takes a minimum of nine days when temperatures are warm (30☌ or 86☏) and will take much longer at cooler temperatures. Only older females can transmit malaria, as they must live long enough for sporozoites to develop and move to the salivary glands. Life is usually short for adult mosquitoes as well, with temperature and humidity affecting longevity. Life is precarious for mosquito larvae, with most perishing before becoming adults. If larval habitats dry up before the process is completed, the larvae die if rains are excessive, they may be flushed and destroyed. Eggs hatch within a few days, with resulting larvae spending 9-12 days to develop into adults in tropical areas. Without sufficient rainfall, mosquitoes cannot survive, and if not sufficiently warm, parasites cannot survive in the mosquito.Īnopheles lay their eggs in a variety of fresh or brackish bodies of water, with different species having different preferences. In rare cases malaria parasites can be transmitted from one person to another without requiring passage through a mosquito (from mother to child in "congenital malaria" or through transfusion, organ transplantation, or shared needles.)Ĭlimate is a key determinant of both the geographic distribution and the seasonality of malaria. More on: Malaria Parasites Human Factors And Malariaīiologic characteristics and behavioral traits can influence an individual’s risk of developing malaria and, on a larger scale, the intensity of transmission in a population. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle. The oocysts grow, rupture, and release sporozoites, which make their way to the mosquito’s salivary glands. The zygotes in turn become motile and elongated (ookinetes) which invade the midgut wall of the mosquito where they develop into oocysts. While in the mosquito’s stomach, the microgametes penetrate the macrogametes generating zygotes. The parasites’ multiplication in the mosquito is known as the sporogonic cycle. The gametocytes, male (microgametocytes) and female (macrogametocytes), are ingested by an Anopheles mosquito during a blood meal. Blood stage parasites are responsible for the clinical manifestations of the disease. Some parasites differentiate into sexual erythrocytic stages (gametocytes). The ring stage trophozoites mature into schizonts, which rupture releasing merozoites. ovale a dormant stage can persist in the liver (if untreated) and cause relapses by invading the bloodstream weeks, or even years later.) After this initial replication in the liver (exo-erythrocytic schizogony ), the parasites undergo asexual multiplication in the erythrocytes (erythrocytic schizogony ). Sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites. During a blood meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host. The malaria parasite life cycle involves two hosts. Thus the infected mosquito carries the disease from one human to another (acting as a “vector”), while infected humans transmit the parasite to the mosquito, In contrast to the human host, the mosquito vector does not suffer from the presence of the parasites. When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected together with the sporozoites, which migrate to the liver, thereby beginning a new cycle. After 10-18 days, a form of the parasite called a sporozoite migrates to the mosquito’s salivary glands. When certain forms of blood stage parasites (gametocytes, which occur in male and female forms) are ingested during blood feeding by a female Anopheles mosquito, they mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito. The blood stage parasites are those that cause the symptoms of malaria. In the blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter parasites (“merozoites”) that continue the cycle by invading other red cells. In humans, the parasites grow and multiply first in the liver cells and then in the red cells of the blood. The natural history of malaria involves cyclical infection of humans and female Anopheles mosquitoes.
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