Malaria
Malaria on the rebound...
Malaria is an ancient disease caused by a blood-borne
parasite that infects and then destroys red blood cells. Malaria victims
can suffer repeated episodes of fever, or anemia or death.
A female Anopheles gambiae mosquito feeding on a person. Anopheles transmit the malaria parasite.
After years of decline, malaria is on the move with victims in the millions: the disease infects about 400 million people each year, according to the World Health Organization.
About 1,200 Americans are infected with malaria each year; most while traveling abroad. The 1995 Michigan case was not the only recent infection in temperate parts of the United States: in 1993, two people in New York City, which is at least 1,000 miles north of malaria country, caught the ancient illness from mosquitoes that had fed on infected people in the area. Since the outbreak limited itself, mosquito-control efforts were not needed.
Countries with high risk of Malaria risk in parts
of them.
But since anopheles mosquitoes live in the summer all over the United States, there's a possibility that the disease could reestablish itself here. From colonial times until well after the Civil War, malaria was endemic in parts of the Mississippi Valley and Chesapeake Bay.
Still, malaria remains a tropical disease, and it's most severe in Africa, where, it kills 2 million people each year, either directly or with some help from acute respiratory infections. Most of the dead are children.
Mosquito feeds on infected person, thus ingesting
the gametocytes. Once the growth cycle of the parasite is complete within
the mosquito, the mosquito becomes a carrier of the disease. The next meal
she takes will transmit the malaria parasite into that host.
The malaria parasite infects and kills red blood cells, which carry oxygen from the lungs throughout the body. Here's how the anopheles mosquito and the malaria parasite work together to cause malaria:
As a female anopheles mosquito with the parasite drinks blood, it transmits many threadlike structures (called sporozoites) into the new host.
These sporozoites travel to the liver, where they multiply and form another kind of spore, called a merozoite.
The merozoites enter the bloodstream and penetrate red blood cells, where they devour hemoglobin, the chemical that transports oxygen.
When the blood cell disintegrates, the merozoites (now multiplied 16-fold) escape and infect other blood cells.
A few merozoites form a sexual stage, which can be sucked up by another mosquito taking a blood meal.
Two sexually active merozoites meet in the mosquito's gut and produce a new generation of parasites.
This mosquito can transmit the infection only if she sucks more blood from an uninfected person before she dies.
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