ROME, 10 May 2002 -- Nearly 10 million square kilometres of Africa are infested by tsetse fly. Part of this large area is composed of fertile land that is left uncultivated -- a so-called green desert abandoned by humans and cattle. Eradicating the tsetse -- and with it trypanosomiasis, the disease it carries -- would allow rural Africans to reclaim areas of their continent and greatly increase food production.

The biting tsetse fly transmits a deadly parasite, trypanosome, that attacks the blood and nervous system of its victims. It causes trypanosomiasis, known as nagana in livestock and sleeping sickness in humans.

Trypanosomiasis is one of the most devastating diseases in sub-Saharan Africa, killing 80 percent of infected victims. It affects an estimated total of 500 000 people. The disease kills 3 million livestock animals each year and reduces the productivity of sick animals. About 50 million animals are at risk from nagana, and sleeping sickness threatens around 60 million people, mainly in rural areas.

At the root of poverty

Of the 37 countries infested with tsetse, 32 are among the poorest in the world. Further compounding these countries' economic burden, between US$600 million and US$1.2 billion are lost each year in attempts to control the disease and in direct losses in meat and milk production.

"Tsetse is a poverty fly," says Jorge Hendrichs, an FAO expert in insect and pest control. "It keeps people poor by preventing them from producing the food they need to survive." In fact, tsetse and trypanosomiasis are major impediments to the development of sustainable agricultural systems in the region, hitting the poorest of the poor -- rural people in the most indebted countries in Africa.

Of 165 million cattle in sub-Saharan Africa, 155 million are in tsetse-free areas, such as the highlands or the semi-arid Sahel zone, leading to overgrazing by animals and overuse of land by people for food production.

Breaking the cycle of poverty and hunger must therefore incorporate decisive action against trypanosomiasis, according to Mr Hendrichs. "If we want to achieve the World Food Summit goal of halving hunger by 2015, addressing this unique African problem is an important precondition."

Tsetse and trypanosomiasis are often forgotten because their victims, rural Africans, have no voice at the international level, points out Mr Hendrichs. But that is changing. In October 2001, at the request of African Heads of State, the Organization of African Unity launched the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC) to tackle the problem. FAO, the World Health Organization and the International Atomic Energy Agency have agreed to actively support this initiative. National authorities, in collaboration with PATTEC, will begin work soon to develop tsetse-free zones in three areas of sub-Saharan Africa - the cotton belt in West Africa, the Southern Rift Valley of Ethiopia and Botswana.

Stopping the spread with sterile insects

One method that has proved successful in combating the tsetse is the sterile insect technique. Male flies are sterilized through radiation and then released into the tsetse-infested area, where they mate. But while the sterile males transfer sperm, the eggs in the wild female do not develop. With continuous release of sterile males, the reproductive rate of the whole population rapidly declines, leading to extinction. The technique, used in combination with traditional methods, such as traps and insecticide, was successful in ridding the Tanzanian island of Zanzibar of the tsetse in 1997.

According to Mr Hendrichs, these efforts to eliminate tsetse have no persistent side effects on the ecosystem. "The only thing that really depends on the tsetse is the disease," he says. "Parasite transmission cannot be sustained without the tsetse vector."

Raffaele Mattioli, an FAO animal health specialist, points out that the presence oftsetse flies and the diseases they transmit influence where people decide to live, how they manage their livestock and the intensity of crop agriculture. The combined effects result in changes in land use and exploitation of natural resources and environment, affect human welfare and increase the vulnerability of agricultural activity. All of these factors must be considered when designing tsetse intervention strategies, including eradication programmes, in order to generate sustainable agricultural development. FAO's strategy to combat tsetse and trypanosomiasis includes considerations of human well-being, poverty reduction, food security and improved public health.

Optimizing the costs

The integrated approach -- the application of the sterile insect technique along with other methods -- seems costly, considering the poverty of sub-Saharan Africa, the large surfaces to be eventually covered and therefore the large number of sterile flies needed.

"The question is not how much this integrated approach costs to eliminate the tsetse," says Mr Hendrichs, "but rather how much living with the tsetse costs." And living with the tsetse fly is very expensive. Traditional control methods have to be repeated regularly and never achieve total elimination of the pest in an environmentally friendly way.

The advantage of the sterile insect technique is that, unlike traditional methods, it is most effective at low population levels in dealing with the last remaining flies. When applied in broad areas against larger populations, the integrated approach is the most cost-effective due to the resulting economies of scale. The sterile insect technique package (sterile males released once a week over a period of 18 months) requires an investment similar to the cost of applying conventional methods over two to eight years.

However, appropriate target areas have to be identified before any large-scale eradication operation is undertaken to ensure cost-effectiveness and sustainability. Infested regions unsuitable for agriculture or cattle should not be given high priority. FAO promotes action in selected areas where the disease constrains mixed farming systems, involving cattle and food production, and where there is potential for raising agricultural productivity. The sterile insect technique, like any other, has to be used in a way that maximizes its impact while minimizing its cost.

For a successful campaign to establish tsetse-free areas, communities, governments and the private sector should all contribute to the effort, according to Mr Hendrichs. Without strong commitment and sustained financial support over decades, a regional initiative such as PATTEC cannot succeed.