Mosquito Bytes


1. Mosquito alert
2. Whining in your ear
3. Malaria
4. Illnesses expand (Dengue)
5. Death to mosquitoes
6. Climate change=more disease?
7. Advice for the weary (repellent pictured)
8.Stop already! (Q & A)


Whine with punch
Malaria on the rebound...
Light brown mosquito, near-front view, on a human, gets ready to enjoy a blood meal. 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. Photo courtesy of CDC, viewed at National Institute of Allergy and Infectious Diseases.

After years of decline, malaria is on the move, and despite the recent headlines given to the "catch-me-you're-dead" Ebola virus, it's malaria that counts its 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 (see Mosquito-transmitted malaria...).

red shows areas where malaria exists: Africa, Asia, South and Central America continents are in red.
Countries with high risk of Malaria risk in parts of them. Courtesy CDC.

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.

It's worse
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.

Four parasites, all in the genus Plasmodium, cause various forms of malaria. Malaria expert Clive Shiff of Johns Hopkins University School of Hygiene and Public Health, explains that Plasmodium falciparum is the most severe species since it can infect any red-blood cell. P. falciparum can cause severe anemia and kidney failure, or it can constrict small blood vessels and cause cerebral malaria. Either problem can be deadly.

Although Africa is unlucky enough to be the focus of P. falciparum infection, the species is also found in Southeast Asia and Latin America.

 Adults lay eggs, which become larvae, pupae, and then enter the adult, to lay more eggs.
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. Image adopted from diagram courtesy, BIODIDAC.

How does the malaria parasite do its dirty work?
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 its "wee dram of 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.

why don't mosquitoes get malaria? Because life is not always fair. Photo shows Anopheles taking blood meal on a human arm

Whatever Happened to Malaria Eradication?
Once upon a time, malaria seemed destined for the history books, since it was supposedly caught in a pincer attack. Larvacides and insecticides were used to lambaste mosquitoes before they could carry the parasite between victims. And then a cheap, plant-derived medicine called chloroquine could kill parasites before they gained a foothold in their victims.

From the end of World War II through roughly 1970, malaria was indeed on the decline. And with its status as a global scourge waning, it was not a place to make a big name in medicine.

Then nature took over, with a little help from modern ecological disturbances and tight government budgets:

Most important species of malaria vectors (vectors are organisms that carry pathogens, they don't cause the disease themselves) that evolved resistance to at least one insecticide.

Malaria parasites evolved resistance to chloroquine, and then to several successor drugs.

Increases in travel and international trade moved drug-resistant parasites around the globe.

As mosquito-control efforts expanded, they grew more expensive, forcing some governments to abandon them.

The unfortunate result, says Shiff, was a resurgence of malaria. "There were major programs to control malaria, and they were very successful." But the need to use more expensive insecticides over a broader range meant they were not sustainable."

Want to read about another mosquito-borne menace -- the charmingly named "breakbone fever"?



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