Plasmodium vivax life cycle


In the past, the focus on falciparum made sense. Money was tight. Falciparum kills 1m people a year, most of them children. Vivax often debilitates, but rarely kills. Now, though, health has moved up the international agenda, and the supply of money to deal with it has increased over the past decade as politicians and aid agencies have come to understand that infectious diseases are not merely causes of suffering and death—though that is bad enough—but are significant barriers to economic development, too. In this context a more sophisticated approach is needed, in the view of those who study vivax .

Numbers are hard to come by, but Ric Price, of Oxford University, reckons that between 80m and 390m people suffer the effects of vivax every year. The cost, to the sufferers alone, is between $1.4 billion and $4 billion a year—and that does not take account of consequential damage to the economies of the countries they live in. These include places like Central Asia and the Caucasus, where falciparum is unknown—for, unlike falciparum , which is genuinely a tropical disease, vivax can thrive in temperate climes. Indeed, in the first half of the 20th century it was found as far north as Archangel, in Russia.

The two parasites also piggyback from host to host on different species of Anopheles . Distributing bednets and spraying insecticide on the walls of houses—strategies that have worked against falciparum —are much less use against vivax because the 40-odd mosquito species which transmit it do much of their biting outdoors.

The intermittent fevers often associated with malaria are due to the synchronous rupture of infected erythrocytes and release of merozoites (see malarial paroxysm ). Trophozoite- and schizont-infected erythrocytes are rarely found in the peripheral circulation during P. falciparum infections. Erythrocytes infected with these stages adhere to endothelial cells and sequester in the microvasculature of vital organs, especially brain, heart and lungs. Sequestration in the brain is a contributing factor in cerebral malaria .

The zygote develops into a motile ookinete (16) which penetrates the gut epithelial cells and develops into an oocyst (17). The oocyst undergoes multiple rounds of asexual replication (18) resulting in the production of sporozoites (19). Rupture of the mature oocyst releases the sporozoites into the hemocoel (body cavity) of the mosquito (20). The sporozoites migrate to and invade the salivary glands (not shown), thus completing the life cycle. (Return to sporogony in main document.)

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In the past, the focus on falciparum made sense. Money was tight. Falciparum kills 1m people a year, most of them children. Vivax often debilitates, but rarely kills. Now, though, health has moved up the international agenda, and the supply of money to deal with it has increased over the past decade as politicians and aid agencies have come to understand that infectious diseases are not merely causes of suffering and death—though that is bad enough—but are significant barriers to economic development, too. In this context a more sophisticated approach is needed, in the view of those who study vivax .

Numbers are hard to come by, but Ric Price, of Oxford University, reckons that between 80m and 390m people suffer the effects of vivax every year. The cost, to the sufferers alone, is between $1.4 billion and $4 billion a year—and that does not take account of consequential damage to the economies of the countries they live in. These include places like Central Asia and the Caucasus, where falciparum is unknown—for, unlike falciparum , which is genuinely a tropical disease, vivax can thrive in temperate climes. Indeed, in the first half of the 20th century it was found as far north as Archangel, in Russia.

The two parasites also piggyback from host to host on different species of Anopheles . Distributing bednets and spraying insecticide on the walls of houses—strategies that have worked against falciparum —are much less use against vivax because the 40-odd mosquito species which transmit it do much of their biting outdoors.

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Plasmodium vivax life cycle
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