DDT and Africa's war on malaria
One of the most powerful weapons in the war against malaria is the insecticide DDT - effective in curbing the disease-carrying mosquito but also lethal to the environment as a whole. The BBC's Mike Donkin examines South Africa's controversial use of the chemical and the pressures facing neighbouring Mozambique as it struggles to battle malaria without it.
Malaria kills a million people a year in Africa - mainly in the poorest nations south of the Sahara. Most of these victims are children.
Babies and the very young have little resistance to the parasite, which is passed on by the Anopheles funestus mosquito when it pierces the skin to feed on human blood - the parasite that causes malaria is in the mosquito's saliva.
A still wider epidemic is threatened because the malarial parasite has becomes more and more resistant to drugs, like chloraquine, used until now to treat the disease.
No alternative medicine has yet been developed which can be made available soon enough, or in the quantities and at the price that African nations can afford.
So other ways must urgently be found to counter malaria, and one to which some countries are returning is to spray mosquitoes with the chemical long-proven to be the best at killing them - DDT.
It is a chemical, however, known to be lethal to some wildlife and feared to pose a potential risk to humans.
Weighing the risks
In the 1950s and 60s, DDT spraying eradicated malaria across Southern Europe, and it was used commonly in Africa until the late 1970s.
At the same time, DDT was being used across the world as a farming pesticide. But widespread spraying was eventually shown to kill fish and threaten birds.
DDT became a "pariah" chemical. No studies ever proved that it also damaged human health, but it was widely believed to do so and was banned.
Now, however, some African governments judge that the ecological risks posed by DDT do not compare with the danger of malaria getting a deadlier grip.
'A horrible choice'
South Africa is taking the lead, after seeing deaths from the disease rise sharply along its swampy northern coast.
A South African environment minister has called it "a horrible choice we must make for our country".
For the South African health department, malaria "hit-teams" based in the Ubombo region, the spraying season has just started.
The spraymen fan the chemical up and down the hut walls and into the thatch in swathes.
DDT is cheap to buy and its effects are long-lasting; a year's assurance at least against mosquitoes.
But there are drawbacks. As the chemical dries, it leaves a white deposit on the hut walls, and it has been found to make bedbugs more active.
The government entomologist who leads the hit-teams, Keith Hargreaves, says most people accept that as a small price to pay.
"The bedbugs they can tolerate," he says. "But to watch one's children die of malaria - that no man can stand."
Proof of the job that DDT seems to be doing can be found at the Bethseda hospital in Ubombo.
Since DDT was reintroduced two years ago, malaria cases there have plummeted. The malaria ward presently has a calm, almost lonely air, with only the odd patient occupying the ranks of iron beds.
Travel just over the South African border into Mozambique and malaria remains a desperate problem.
It is the country's biggest killer of children, and there is no reason to expect that situation to change.
Melanie Renshaw runs anti-malarial operations there for the United Nation's Children's Fund, and one of the areas in which she works is a coastal shantytown near Mozambique's capital, Maputo.
It is the ideal breeding ground for mosquitoes, she says. That is clear from visiting a state hospital on the edge of Maputo.
Its corridors are crowded with mothers who nurse crying infants, hot and weak with fever from malaria, as they wait for treatment.
The Health Ministry official who has the thankless job of leading Mozambique's day-to-day struggle against malaria is Dr Samuel Mabunda, and he admits that it seems an impossible mission.
"We do not have the money, the manpower or the health facilities to protect people as we would like to do," he says.
Perhaps surprisingly then, DDT is not used in Mozambique and the authorities say they do not want to use it.
Dr Avertino Barreto is Chief of Infectious Disease Control, and he points out that circumstances in a developing country like his would make DDT a big risk. Take the recent disastrous floods for a start, he says.
"You might only use DDT for house spraying, but flood waters could wash it everywhere," he says.
Mosquitoes are no respecters of borders though and because of this, Dr Barreto says, South Africa has been pushing its neighbour hard to change its policy.
"But our two countries are very different. If you use something potentially hazardous like DDT, you have to control this carefully. Mozambique does not have the infrastructure or the organisation to do this."
Mozambique's health ministry resents what it calls South Africa's interference and maintains it should be allowed to find its own ways to deal with malaria prevention.