Infectious Disease: Evolving Challenges to Human Health

The Malaria Life Cycle

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1. Infecting a Mosquito
Mosquitoes are born uninfected. Females require blood meals before laying a batch of eggs, and when a female Anopheles takes a blood meal from an infected person, a few parasites in the sexual stage of development may be hidden in red blood cells that enter her gut.

In the Infected Mosquito
After she feeds on infected blood, male and female parasites rapidly combine in the mosquito’s gut. Within 1 – 2 weeks they form cysts and release long, thin sporozoites. The parasites spread throughout the mosquito’s body and invade the salivary glands. After one to two weeks, when the mosquito feeds again, she may pass the parasites along to a new human host.

2. Infecting a Person
When an infected mosquito feeds again, a few of the parasites pass into the person’s bloodstream. Although her salivary glands may contain 1,000 parasites, less than 50 of them typically pass to a human host. Only one is required to infect a person and cause malaria disease.

In the Infected Person’s Liver
Within an hour, parasites migrate to the liver where they invade the cells and reproduce. During the next 7 – 10 days, each parasite produces 10,000 – 30,000 descendents.

In the Infected Person’s Red Blood Cells
The parasites burst out of the liver cells into the bloodstream, where they rapidly infect red blood cells. They feed off the cells and reproduce. After 2 – 3 days they burst out of the cell, killing the cell in the process. This process causes sweats and chills that recur every 2 – 3 days, and can lead to severe anemia and damage to the brain and vital organs.

In the Infected Person: Sexual Stage Parasites
Some of the parasites form new sexual stage parasites that do not cause illness. These parasites circulate in the bloodstream and perpetuate the cycle of infection when siphoned by a new female mosquito.

photos of malaria parasites

Stages in the Malaria Life Cycle

The malaria parasite migrates to the liver (left). After 7- 10 days they burst out and enter the blood stream where they infect red blood cells (middle). Some of the parasites form new sexual stage parasites (right). (Images courtesy of the Centers for Disease Control)


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