Archive for the ‘MALARIA PREVENTION’ Category
The prevention of malaria has always been a “hot topic” among travelers to tropical locales. In 1998, the World Health Organization indicated that there were more than 270 million cases of malaria with more than one million deaths due to the disease. In the United States, approximately 1400 cases are reported annually to the Centers for Disease Control and Prevention. The evolving pattern of drug resistance by malaria parasites as well as the changes in the recommendations for chemoprophylaxis present a challenge to physicians who advise travelers on the prevention of this disease. Improving adherence to antimosquito measures and antimalarial medications could prevent many cases of malaria in travelers.
To better appreciate the methods of malaria prevention, it is necessary to understand the parasite’s life cycle. Malaria is transmitted by the bite of an infected female Anopheles mosquito and is caused by infection with one of four species of the protozoa Plasmodium (Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale). When an infected mosquito takes a blood meal during its feeding period between dusk and dawn, it injects sporozoites of Plasmodium from its salivary glands into the bloodstream of the host. The sporozoites circulate to the liver and invade hepatocytes, where they divide to form tissue schizonts and then merozoites, which escape into the bloodstream. Merozoites invade erythrocytes, they differentiate into trophozoites, and the trophozoites then divide to become blood schizonts. These then mature into merozoites, which, when released from red blood cells, can continue the cycle in the blood. A proportion of the sporozoites of P. vivax and P. ovale develop into dormant forms within the liver, called hypnozoites, that can activate months to years later to release more merozoites into the bloodstream, causing a symptomatic relapse. The life cycle is completed when merozoites differentiate into sexual forms called gametocytes. The female Anopheles mosquito ingests gametocytes during a blood meal, and sexual stages result in sporozoites that can be transmitted to the next susceptible human host.
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