The team has also developed highly sophisticated means of marking or measuring the level of parasite infestation in individual sheep. The gene works by identifying certain protein molecules in the parasite and then directs the sheep's immune system to inhibit the growth of the worm. The gene exists in 20 naturally occurring forms but one version is exceedingly efficient in identifying these proteins and triggering a response. The worms in the resistant sheep produce fewer eggs and this also reduces the level of infection among less resistant sheep in the flock. The presence of the gene can be identified from a blood sample.
Parasitic worms damage the intestine and stomach, inhibit growth and can cause death.
In the third world sheep farmers, often among the poorest of the population, are particularly vulnerable. Normal treatment involves anthelmentic drugs but these can be expensive, time-consuming to administer and the parasites eventually develop resistance. Further research by Dr Stear and his colleagues at the Kenyan Agricultural Research Institute has confirmed earlier observations which showed that the Red Masai breed in East Africa, which was introduced to that continent several thousand years ago, has a much higher resistance to parasites than other sheep breeds imported from Arabia and Europe in historical times. Their research has shown for the first time that the Red Masais are more productive in Kenyan conditions. The scientists believe that natural selection has produced sheep with the ability to respond more effectively to the conditions.