Experts say West Africa needs to include spraying houses with insecticide in the fight against malaria. Costly and complex to implement, West Africa has been slow to add it to the other strategies it uses to fight the deadly disease. But Naomi Schwarz reports from Dakar, experts say the benefits could be enormous.

A few countries in Africa, especially in southern Africa, have started campaigns to spray pesticides on the insides of houses. Experts say it can be extremely effective in curbing the mosquitoes that spread malaria when used alongside other strategies, including distribution of insecticide-treated bed nets, widespread medical treatment, and preventative drugs for pregnant women.

But the campaigns have been slow to spread among developing countries, and are almost non-existent in West Africa.

Senegalese doctor and Africare health coordinator More Ngom says spraying fills gaps in the protection offered by insecticide-treated bed nets.

People stay outside late, he says, and get bitten. Spraying houses actually kills mosquitoes, which means there are fewer around to spread malaria.

But he says the product is expensive and spraying requires people to leave their homes for a period of hours.

And he says it is ineffective if you spray one house but not next door, so there needs to be enough funding to support a comprehensive campaign.

Indoor spraying works by coating the interior walls of a house with a small amount of insecticide. The insecticide kills any mosquitoes perching on the wall and repels mosquitoes from entering the house. And the effects last for months.

Mary Cobb is USAID's health officer in Senegal, where USAID is funding West Africa's first program to test indoor spraying with a pesticide called lambda cyhalothrin.

"This particular pesticide is estimated to last three to five months on a home, which here in Senegal, in most of the country, one application per year is estimated to be enough to prevent the peak malaria season. If you spray the walls right before the rainy season that should last through the high transmission malarial season," she said.

Cobb says before choosing this pesticide, Senegalese health authorities tested to make sure the mosquitoes there had not developed a resistance to the chemical. They also looked closely at the environment and developed security measures to ensure the potentially harmful chemical was carefully controlled so that it would not harm the community or the environment.

Environmental concerns are another reason spraying campaigns are so costly. And they are the reason that spraying campaigns, which have existed for more than 50 years, almost disappeared.

Decades ago, at the same time indoor spraying was being used against malaria, pesticides were also being sprayed in mass quantities to kill agricultural pests. This led to serious environmental problems.

But recently there has been a movement towards bringing back indoor spraying. In 2006, the U.S. government increased indoor spraying aid to 20-million dollars, up from one-million the year before. And they recently pledged an additional 150-million dollars for spraying campaigns in Africa.

One of the cheapest and most effective insecticides on the market, DDT, is also one of the most controversial. After its harmful environmental consequences were discovered, many countries banned it entirely. But the World Health Organization has recommended DDT be used more widely for indoor spraying campaigns.

Sergio Spinaci is the associate director of WHO's global fight against malaria.

"We are suggesting the use of DDT under controlled situations when it is proved that there is no resistance to the insecticide, and appropriately, sprayed with all protections for the health worker and according to the climate and the malaria epidemic," said Spinaci.

The U.S. government also funds indoor spraying with DDT. It has already paid for DDT to be used in indoor spraying in Zambia, and USAID health officer Cobb says it is prepared to pay for DDT in West Africa as well.

It lasts longer than other pesticides, says Cobb. Plus, it sticks particularly well to the uneven surfaces found in many African homes, such as those made out of mud and grass. 

Some environmental groups say chemical pesticides, and especially ones like the DDT that stick in the environment decades after they are sprayed, should not be encouraged. Henri Diouf is with Senegal's branch of the Pesticide Action Network.

"We still need the support of the international communities and not to focus this support on using not on using chemicals, on DDT, to fight against malaria, but to help us to use the soft strategies that were used in other countries, like Vietnam, like the Philippines, like Mexico," he said.

Mexico was able to significantly reduce malaria cases by carefully studying how and when the disease was most likely to spread. Then they targeted their anti-malaria efforts to those who were most at risk.

But Mexico's malaria fight did include indoor spraying, although they chose a chemical that does not persist in the environment like DDT does.

Health experts say the right pesticide depends on the particular location. USAID's Cobb sayd indoor spraying, with DDT or any pesticide, has proven extremely effective and has never caused problems the way mass agricultural spraying did.

"It is safe to use indoors. You do have to take precautions, but it really has the potential to protect millions and millions of people," said Cobb.

More than 40 percent of the world lives in malaria-affected countries, and the disease kills more than million people every year.