Four different types of malaria infect humans: Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale. The two most common are Plasmodium falciparum and Plasmodium vivax. Plasmodium falciparum is the deadliest. Some cases in southeast Asia have involved Plasmodium Knowlesi, a type of malaria usually associated with monkeys.
Anopheles mosquitoes transmit malaria, killing almost 1 million people in 2008 alone. This preventable and curable disease afflicts people in 108 countries and territories, but Africa is by far the part of the world most affected. Every 45 seconds, an African child dies of malaria. Children are especially susceptible because they have not yet built up an immunity. Travelers to malaria-infested areas are also at high risk.
Breeding and Biting
The 20 distinct Anopheles species breed in shallow freshwater, such as in hoof prints, puddles and rice fields. They all bite at night. Malaria is a parasitic disease, and the more developed the parasite is at the time of the bite, the worse it is for the victim. So transmission is worst in mosquitoes with longer lifespans, and in places where mosquitoes would rather bite humans than animals. Both are the case in Africa, where more than 85 percent of worldwide malaria deaths occur.
A Parasitic Infection
The life cycle of the malaria parasite requires two hosts. While a malaria-carrying female dines on a human, she releases tiny cells, called sporozoites, into her host. These infect the human's liver cells, where they mature and release organisms called merozoites. These in turn multiply in the red blood cells. The development continues until they mature into cells called gametocytes. At this point, another Anopheles mosquito comes along and bites the host. Inside the second mosquito, male and female gametocytes produce zygotes. These develop, eventually releasing sporozoites, which migrate to the salivary glands of the mosquito. The mosquito bites another human, thus perpetuating the malaria life cycle.
Symptoms appear seven to 15 days after being bitten by an infective mosquito. The person suffers from headache, fevers, vomiting and chills. Symptoms may initially be mild, so the person might not suspect malaria. But if the disease is not diagnosed and treated in the first 24 hours after symptoms occur, it can quickly become severe. More serious symptoms include respiratory distress, anemia and damage to internal organs. Even if the patient receives treatment, the P. vivax and P. ovale forms may stay in the liver. The person might relapse weeks or months later without special treatment to heal the liver.
Control and Eradication
The World Health Organization recommends sleeping under insecticide-treated mosquito nets as the most cost effective way to prevent malaria. Spraying insecticides indoors is also useful, but may be unsafe or cost prohibitive, and mosquitoes rapidly adapt to become immune to them. Travelers visiting infected areas often take medicine to prevent the malaria parasite from developing inside them. But medicine is too costly to protect entire local populations.
- Photo Credit mosquito image by Daniel Wiedemann from Fotolia.com
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