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Rising above the rat trap

Recent surveys conducted with farmers in Mozambique by World Vision have shown that rats are having a serious impact on the livelihoods and welfare of farmers and their families. Rural households in Zambezia Province have consistently identified that rats are one of the primary post-harvest problems, consuming and contaminating stored food such as rice, groundnuts and maize. Rats are a constant problem because they affect crops, both in store and in the field. They also cause damage to buildings, eating and contaminating livestock feed, killing poultry and eating their eggs.

3 of the species of rat caught in trapping trials
Credit: Dr S.R.Belmain

Rats also pose considerable health risks and are most commonly associated in history with the spread of Bubonic Plague (Black Death). Even today Plague is still a problem throughout the world and outbreaks of the Plague occur every year in endemic areas of the Zambezi Valley, often killing hundreds of people. Because rodents are closely associated with other diseases such as Leptospirosis and can rapidly spread other gastroenteric diseases such as Cholera and Salmonella, contamination of water and food inside houses by rodents is a serious health risk to rural farmers. In addition, approximately 10% of people are regularly bitten by rats whilst sleeping at night, leading to secondary infections and rat bite fevers from bacteria entering the wounds. Households, in these areas, traditionally store harvested food on shelves within the living quarters, exposing people to high levels of rat urine and faeces which increases the likelihood of contracting rat borne diseases. Spread of these diseases is currently of particular concern in flooded areas of Southern Mozambique. It is unknown what impact rodents may be having upon human health because the symptoms of many gastroenteric and viral diseases are similar to Malaria and, without testing, it is difficult to determine which disease may be the real cause of an illness assumed to be Malaria.

Collaborative research* has been trying to develop rodent control strategies, which can be sustainably managed by rural householders, by first assessing the impact which rodents are currently having upon rural livelihoods. Farmers estimate that up to 100 rats can live in roof thatch at any one time. With intensive daily trapping, farmers have, on average, caught more than 1000 rats in a 12-month period, which implies that rats may have eaten excess of 400kg per year of stored food. The impact of rodents on food security and human health is, therefore, severe. Existing knowledge and technology on rodent control is, in most cases, inappropriate for the control of rats in rural villages. Rodenticides are not an option as such toxicants are usually too expensive, not readily available, and likely to be used incorrectly. Discussions with farmers also reveal that rats are the main source of protein for many villagers in the region so use of chemicals would be inappropriate. The importance of rat protein as a nutritional source has been an important element to consider when developing effective strategies for rodent control.

Trapping is not usually a reliable technique for control because it is labour intensive, fails to eliminate the population and can sometimes lead to the development of trap shy animals. However, most farmers surveyed in the region were familiar with trapping, and initial research using this technique has shown that households can reduce the rat population inside their huts by 50-70% in comparison to those who have not been trapping over an annual agricultural cycle. The average size of rodents caught is also reduced by 50%. Farmers involved in trapping have commented that more food is available and their families have not fallen ill so frequently. In addition, householders are particularly happy with their success as trapped rodents are eaten.

Up to 100 rats may live in the roof thatching of one building
Credit: Dr S.R.Belmain

The majority of farmers replace their thatching annually because of associated rat problems. Collected data has already confirmed that the estimated number of nests in a roof was correlated to the frequency of roof replacement, i.e. farmers who replace their thatch more frequently find fewer nests. Comparing rodent populations in households with thatch or metal roofs should establish the impact of nesting areas in the roof on the severity of rodent problems. Better management of areas in and surrounding houses should also help to reduce rodent problems. For instance, covering drinking water vessels limits water resources available to rodents, as well as reducing disease transmission. Placing waste and rubbish away from households and clearing vegetation to a distance of 10 metres or more should also help to reduce numbers of rodents.

However, rodent control relies not only upon proven technology but upon provision of farmer support networks, advice, education and supervision. Uptake of control strategies by farmers must be supported through agricultural extension agents and farmer field schools. The control strategies identified are also likely to have relevance in other countries and could be easily adapted to similar conditions where rodents have an impact on food security and/or health.

* NRI, Acheta Partnership consultants, World Vision rural extensionists
For further information: Dr S.R.Belmain, Natural Resources Institute, UK

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