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Natural immunity only partially protects only a limited number of people. Prevention is the key to wiping out malaria—keeping mosquitoes away from people, either by physically blocking them or by eliminating them from the environment. There are many ways to do this.

Countries affected by malaria use a multifaceted approach to stopping this scourge. First, antimalarial drugs can be given to prevent epidemics, particularly in areas with small outbreaks. The second approach uses mosquito control to prevent outbreaks. The third approach, still under development, will prevent the disease through vaccination.

Drugs for Prevention

The drugs that treat malaria—mefloquine, doxycycline, chloroquine, atovaquone/proguanil, and primaquine—can also be used to prevent malaria. Travelers from countries that have eliminated malaria routinely take antimalarial drugs when they visit countries where malaria occurs. These drugs must be taken exactly as ordered: when, in the prescribed dosage, and for the prescribed time period. The drug used depends on a person’s health, medical history, and location of travel. For example, chloroquine can be taken in areas without resistant parasites, but resistance is widespread.

Some countries routinely use the same approach with pregnant women. At routine checkups, they may receive antimalarial drugs, an approach called intermittent preventive treatment.  These drugs don’t prevent infectious mosquito bites, but they suppress the growth of parasites in the blood.

Mosquito Control

If people reduce the number of mosquito bites they receive, they decrease their chances of getting malaria. A few simple steps go a long way. Putting screens in all windows keeps mosquitoes out of buildings. Sleeping with mosquito netting—without holes in it—around all beds keeps the few that get in away during the night. Using netting treated with mosquito repellent pesticides chases away those that do approach during the night. Spraying the inside walls of a house with pesticides prevents the mosquitoes that do get in from living long enough to bite. Regular use of insect repellent containing chemicals such as DEET prevents mosquitoes from biting.

If everyone in a community takes these steps, they not only reduce mosquito bites, they shorten the overall mosquito life span, reducing the number of mosquitoes. As a side benefit, this approach decreases the number of bites from any kind of insect, decreasing all insect-related illnesses.

The big drawback: insecticides used on netting or for spraying require retreatment. Despite the ease of retreatment, people often forget to do it. Walls require respraying every 6 to 12 months. Until very recently, bed nets also needed to be retreated with insecticide every 6 to 12 months. In the last year, the World Health Organization has backed the use of bed nets treated with insecticides that last for up to 3 years before needed retreatment.

The initial Global Malaria Eradication Campaign of 1955-69 sprayed indoor walls and surfaces with DDT and dieldrin. The program eliminated malaria in some areas and decreased it in others. But mosquitoes built up resistance to the chemicals, and environmentalists worried about the effects of these chemicals on birds and other animals. Eventually the cost of regular spraying fell to local governments, which couldn’t afford the program.  Malaria eradication efforts stopped, and the disease returned.

South Africa started spraying indoor walls with DDT in 2000, and malaria cases decreased. In 2006 the World Health Organization endorsed using DDT for indoor room spraying throughout Africa in epidemics and where malaria is common. Insecticide resistance remains an issue, but careful use and immediate detection of any developing resistance can limit the problem.

Photos courtesy of CDC. Spraying the inside walls of a house with insecticide kills mosquitoes that land on the treated surfaces.

Photos courtesy of CDC. Fogging, or spraying a region with insecticide, is used to stop a malaria outbreak. Fogging is done in the evening, when mosquitoes are most active.

Mosquitoes breed in still waters, so reducing mosquito breeding grounds controls malaria. Containers of standing water can be covered or drained. In swamps, applying biodegradable oil to the edges where the mosquitoes breed suffocates the larvae before they hatch. Biological toxins such as Bacillus thuringiensisvar. israelensis or insect growth regulators such as methroprene wipe out larvae. Fish that eat mosquitoes, among them the mosquito fish, Gambusia affinis, do well in larger waters.

During epidemics, whole regions can be fogged or sprayed with insecticide. This must be done at the mosquitoes’ most active times—early evening or early morning.

Malaria Vaccines

A vaccine against malaria offers the best hope for wiping out this disease. The ideal vaccine would be safe for everyone, easy to make, and easy to administer. Best of all it would give lifelong immunity against this disease. But with four species of parasite at work, is this possible?

The genetically complex Plasmodium parasite makes finding the right vaccine tricky. Researchers have found at least 40 antigens that could work against the parasite. The various life stages of the parasite add another dimension to the vaccine search. Which stage should the vaccine target? How can effective immunity be created for something that changes so often?

A number of factors tilt the scale in favor of developing an effective vaccine. First, people living in areas where malaria regularly occurs develop immunity to the most severe forms of the disease. Second, in a test situation people bitten by mosquitoes carrying irradiated sporozoites—ones that could not develop further—showed immunity when subsequently bitten by malaria-infected mosquitoes. Third, researchers took   immunoglobulin (a substance from the immune system) from people who lived in regions where malaria is common and gave it as treatment against severe malaria. The treatment worked by preventing the Plasmodium parasites from invading new red blood cells and cleared parasites from the spleen. (The spleen destroys old red blood cells and filters out blood cell wastes.) The only thing preventing this approach from becoming a regular treatment for severe malaria is the fear of transmitting other infectious diseases.

Research labs around the world study the many vaccine possibilities, with several in clinical trials on people in Africa and China. Vaccines for P. falciparum, the most severe form of malaria, and P. vivax, the most widespread form, are the top priority. Malaria experts hope to make vaccination against malaria a reality by 2011.

Mosquitoes are known to carry other dangerous diseases, but none seems to be as big a problem as malaria. Why do we hear much less about those illnesses? Have those other scourges been brought under control?