Malaria Prevention

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QUESTION

what is the prevention of malaria?

ANSWER

There are many ways in which to prevent malaria. I’ll break them down into three categories: 1) medical prevention, 2) protection from getting mosquito bites and 3) vector control.

1) Medical prevention

Malaria can be prevented using certain medications. Taking drugs to prevent a disease is known as “chemoprophylaxis”, and so these drugs are often referred to as “malaria prophylactics”. There are several different types of malaria prophylactic: the most common ones are chloroquine, a mix of atovaquone and proguanil (marketed as Malarone), mefloquine (marketed as Lariam) and doxycycline. The mode of taking these medications vary (Lariam is taken once a week, for example, whereas the others are usually taken once every day), and they also have different restrictions and side effects. Chloroquine is not effective in areas where local forms of malaria have become resistant, for example, and Lariam is not recommended for people with a history of mental instability, as it is known to cause hallucinations and otherwise impair consciousness. Here on Malaria.com, we are actually currently running a survey on side effects of malaria prophylactic drugs, so if you have ever taken medication to prevent malaria, please take the survey: Malaria Medication Side-effects Survey: Treatment and Prophylaxis

It is worth noting that these drugs have not been tested for long term use, plus they can be expensive if taken for an extended period of time. As such, they may not be appropriate for people living in endemic areas for malaria. However, medication can be useful for preventing malaria in high risk groups, even when they are living in a malaria endemic area. One example is the use of intermittent preventive treatment (IPT) for preventing malaria infection in pregnant women, infants and young children. For more information on this, please see the review article written by Dr Felicia Lester for this website: http://www.malaria.com/research/malaria-pregnancy-preventive-treatment

2) Protection from getting mosquito bites

This section links in with the more general vector control strategies, which will be discussed below. Since malaria is transmitted through the bite of infected mosquitoes, preventing mosquito bites is a very effective way of reducing malaria incidence. One of the most popular methods for personal protection, especially in areas where malaria is endemic, is through sleeping under a mosquito bednet. The mesh prevents mosquitoes from being able to fly close to the person sleeping; however, if there are holes in the net, or the person skin is pressed directly against the mesh, the mosquito may still be able to bite them. This is where insecticide-treated bednets come in – they are impregnated with mosquito repellents to stop mosquitoes from biting through the mesh or passing through holes. Newly developed long-lasting insecticide treated bednets (LLINs) are even more effective, in that they don’t require “re-dipping” to maintain the level of repellent in the fibres, and so can protect a person for several years without losing efficacy. These LLINs have been instrumental in reducing cases of severe and fatal malaria, especially among pregnant women and young children, who are often targeted by bednet distributors.

Other methods for preventing mosquito bites include wearing long-sleeved clothing and personal application of mosquito repellent, particular those containing a percentage of DEET, which is a very effective insecticide. These measures should be especially taken in the evening, early morning and at night, which is when the Anopheles mosquitoes that carry malaria are most active.

3) Vector control

Finally, malaria can be prevented from reducing numbers of mosquitoes directly. Some methods target the adult mosquitoes; one such initiative is indoor residual spraying (IRS), whereby the inside of a house is sprayed with an insecticide to kill mosquitoes. Twelve different insecticides are approved by the World Health Organisation for this purpose, though pyrethroids are among the most popular, as they can be used on a variety of surfaces, do not leave a visible stain and can also protect against other insect pests, such as bedbugs.

Other methods for vector control focus on other parts of the mosquito lifecycle. Mosquito larvae require stagnant freshwater for their development, so some projects have worked to eliminate standing water sources, such as unnecessary ditches and puddles, which reduces the amount of habitat available for mosquitoes to lay their eggs and sustain larvae. Other programmes have spread insecticides directly in stagnant water to kill the larvae, or sought to introduce fish or other aquatic organisms, such as copepods, which consume mosquito eggs and larvae. This latter biological control approach is popular because it can also supply an area with fish for local consumption, and doesn’t contaminate water sources with chemicals.

Safety of Bed Net Insecticides

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QUESTION:

Are the insecticides used on the bed nets safe? What are the brand names and chemical names of those insecticides, and can you point me to any studies that have been done to determine their safety?

ANSWER:

The short answer is yes, the insecticides used in bednets are safe under the conditions in which people are exposed to them through using bednets.

Most standard bednets are treated with a chemical known as a pyrethroid, and usually permethrin or deltramethrin. Both of these chemicals have low toxicity to most mammals and are poorly absorbed by the skin, making them safe for treating bednets. There are some studies on mice which suggest that pyrethroids such as permethrin can be carcinogens when ingested, though once bound to the fibre of a bednet the chemical is not ingested by the person sleeping under the net so this is not a danger.

The World Health Organisation maintains a comprehensive set of specifications (PDF) for maintaining quality and safety in insecticide treated bednets.

There is another WHO report on the safety of pyrethroids (PDF) for public health use, which gives more details about conditions under which these compounds are considered toxic and the risk of exposure through bednet use.

Insecticide-Treated Mosquito Nets (ITMNs) Helps Prevent Japanese Encephalitis

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A new study reveals that using treated mosquito nets could drastically reduce the transmission of Japanese Encephalitis (JE) to humans.

The study, conducted by the Regional Medical Research Centre (RMRC), Dibrugarh, North East Region (NE), Indian Council of Medical Research and released in the March issue of the American Journal of Tropical Medicine and Hygiene, showed that the use of insecticide-treated mosquito nets (ITMNs) on humans and pigs reduced transmission of JE 72 percent in humans.

The study looked at the effectiveness of using ITMNs to protect both pig and human populations. It evaluated the efficacy of reducing the transmission of JE in areas where high virus activity has been reported. The JE virus multiplies rapidly in pigs, considered by experts to be a key element in the natural cycle of the virus and its transmission to humans.

Sharp drops in infection rates were found in three locations following the use of ITMNs. In one location, the nets were used to protect both humans and pigs which resulted in the greatest drop in infection rates (72 percent), compared with areas where treated mosquito nets protected only humans (67 percent) or pigs (56 percent).

“We are pleased that the results of this study show that ITMNs are extremely effective against JE,” said Prafulla Dutta, Scientist, RMRC, NE, “Educating people in JE-prone areas that using ITMNs will help reduce the transmission of the disease without disturbing social customs in these communities. We believe that this will, in turn, reduce mortality associated with JE while keeping communities healthy and productive, further improving the global economy.”

JE is a viral disease transmitted by mosquitoes that infects both animals and humans. It is the leading cause of viral encephalitis (infection of the brain) in Asia and is estimated to be fatal in 30 percent of cases. Death as a result of JE is particularly high among children, killing approximately 8,000 children yearly.

“Increasingly, ITMNs have been shown to be an easy-to-use and effective tool in preventing mosquito-borne diseases such as JE, lymphatic filariasis and malaria,” said Peter J. Hotez, MD, PhD, President, American Society of Tropical Medicine and Hygiene. “This simplicity of action, combined with its low cost, drives the absolute necessity for distribution of these life-saving devices on a much larger scale.”

The researchers note that insecticide components, particularly pyrethroids, are gaining importance in mosquito control because of their low toxicity towards mammals and the strong repellant impact on mosquitoes.

Source: American Society of Tropical Medicine and Hygiene (ASTMH)