After 20 Years, Efforts Continue to Improve Mosquito Nets

By Michelle Vachon

Twenty years ago this month, a team of researchers introduced the insecticide-treated bed net for malaria control. This is the first of a three-part series on changes that its use brought to the fight against the disease.

When Yeang Chheang, 18, began working as a malaria-control technician in 1955, the goal of the World Health Organization, which was assisting the launch of Cambodia's program, was to eradicate malaria, he said.

But the disease-carrying mosquitoes' resilience soon caused the WHO to drop that idea and aim for malaria control instead.

At the time, the Ministry of Health was conducting a pilot project in Snoul district, Kratie province, which included studying mosquitoes' 

Those insects transmit the disease by biting people at night. 

"But we discovered that, during the day, they stayed inside houses to reproduce," Yeang Chheang, said. This was why infants and children who spent 
most of their time at home were so affected by malaria, he said. 

As researchers began spraying the insecticide DDT on house walls the usual practice in those days mosquitoes started stationing themselves on the 
vegetation outside houses, waiting to attack, Yeang Chheang said. 

Over the years, mosquitoes would continue changing behavior to cope with insecticides. 

Even today, the National Malaria Center monitors insect response to current products and adjusts the country's strategy accordingly. 

"We have obtained good results [to control the disease], but not malaria eradication," Yeang Chheang said.

Prior to 1951, when the country still was under French administration, Cambodia had no malaria program. Between 1951 and 1953, the WHO and Cambodian health authorities conducted a first study, which expanded into the Snoul pilot project in 1953. 

In those days, people did not use bed nets, Yeang Chheang said. "It was too hot and uncomfortable sleeping under them. They were made of cotton, very thick and heavy," unlike today's polyester nets, he said. 

Even in the 1980s, when malaria took on epidemic proportions in border regions where Cambodians were sent to fight the Khmer Rouge alongside Vietnamese soldiers, people still refused to use those cotton bednets, Yeang Chheang said.

The Snoul project led to a massive spraying campaign in 11 malaria-prone provinces in 1956. Teams of five men were assigned to tour every village on their territory and spray the walls of every house with DDT. 

"We traveled by vehicle, elephant, buffalo carts and sometimes pirogues," said Yeang Chheang, who worked in Siem Reap and Kompong Thom provinces on that campaign, supported by the WHO and US Agency for International Development. 

"It was very effective," he said. 

By 1961, Cambodia's National Malaria Control Program was set up with its own staff, and research continued. During the civil war of the early 1970s, the program could only operate in urban centers; it was virtually eliminated under the Khmer Rouge regime. 

In 1980, Vietnamese forces having ousted Pol Pot, Yeang Chheang was brought back to Phnom Penh to help recreate the malaria program. 

However, hardly any Cambodian experts had survived, he said. One of his first tasks was to train staff with the support of the Hanoi Malaria Institute. 

Using his pre-war contacts, Yeang Chheang managed to get UN funds that had been earmarked for Cambodia in the mid-1970s, but withheld during the Khmer Rouge takeover, he said. 

In 1984, the National Malaria Program was reinstated. When Yeang Chheang retired in 1995, he was the program's deputy director. Since then, he has been working at the National Malaria Center on a series of WHO short-term contracts. 

Around 1996, insecticide-treated bednets became a major part of the Cambodia's malaria-control strategy, Yeang Chheang said. However, comparing it to 
house spraying, he said: "The old method was probably more effective than treated bednets," because mosquitoes start biting before people go to bed. 

"We tell people to get under bednets right after sunset," but they don't go to bed that early, Yeang Chheang said. 

Wall spraying required specialized workers, which made the program costly. The ideal situation would be a bednet insecticide that can kill mosquitoes instantly and can stay on a very long time, since people tend not to re-treat their bednets once the insecticide wears off, he said. 

Manufacturers are working on the development of permanently treated nets.