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Eye to eye: diagnosing internal parasites

Looking into a sheep's eyes does not appear to offer much to a veterinary surgeon or a farmer. So why are more and more farmers, vets and animal health workers doing precisely this? Surprisingly, the answer is that the eyes are a good way of revealing the presence of stomach worms. By examining the colour of the inside of the lower eyelid of a sheep or goat, you can tell how badly the animal is suffering from bloodsucking stomach-worms. Parasitic stomach-worms result in heavy losses in flocks: they make the host animal anaemic, and the paler the colour of the lower eyelid, the more serious is the infestation and the more urgent the need to treat the animal.

A bright red colour of the eyelid indicates either that the animal has few or no worms, or that the sheep or goat has the capacity to tolerate its worms. An almost white eyelid colour is the warning sign of very severe anaemia, as the worms present in the FAMACHA, the simple test for wormsstomach are in such numbers that they are draining the animal of its blood. If left untreated, such an animal will soon die.

Test by colour

A very simple test or "assay", known as the FAMACHA anaemia guide, has been developed by African scientists in South Africa and is being used increasingly widely. Most importantly, the FAMACHA test not only indicates which animals in a flock need treatment, it also shows which animals don't need to be treated. And, says Armando Nari, a parasitologist with the UN Food and Agriculture Organisation (FAO), this is having many different benefits. FAO has been supporting the field validation (testing the effectiveness on-farm) of this diagnostic technology and is very pleased with the benefits for farmers. By indicating animals in urgent need of treatment, farmers can be sure to treat them and ensure that they survive. And, by indicating those animals not needing treatment, farmers are saved the cost of unnecessary treatment. But, even more important, the FAMACHA test can also help to prevent the development of drug resistance in the worms, prolonging the effectiveness of useful chemicals.

So far, the FAMACHA system has been developed for one species of stomach parasite, which infects sheep and goats, but it is by far the most important species: the wireworm or Haemonchus contortus. Hopefully, equally low-cost and simple to use systems will be developed for use for other worm parasites.

Prolonging drug effectiveness

Drug resistance to internal and external parasites is a widespread and serious problem. As farmers use drugs to protect their livestock they unintentionally store up problems for the future. This happens because no drug is so effective that it kills every pathogen or parasite, and even if only one wireworm individual in thousands survives, and it does so because it alone is resistant to that chemical, it goes on to replicate, and its drug-resistant progeny soon replace the original drug-susceptible population. Then, as farmers see their chemicals giving poorer control, they may use the chemical more often or at higher doses, increasing the level of resistance.

For further information emal: Professor G F Bath, South Africa or Armando Nari, FAO

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