Undramatic loss?

Throughout the last century, the pharmaceutical industry was able to develop increasingly effective new compounds to control a large number of different, economically important parasites and their associated diseases. An inevitable consequence has been widespread parasite resistance. Today, most of the economically important parasite species of sheep and goats, and some of cattle, have developed resistance to drugs. What will happen now that the pharmaceutical industry has other priorities? The effects upon the animals themselves may not be so dramatic because, for obvious reasons, parasites do not usually kill their hosts although they weaken them and lower their productivity. But what will be the effect upon the livestock industry?

The relentless increase in parasite resistance comes at a bad time, especially for developing countries. It is here that great efforts are needed to boost livestock productivity, in order to meet rapidly increasing demand from an ever more urban-based population. And yet it is here too, at least in those countries in the tropics and sub-tropics, where parasites pose a particular problem. Mixed farming and extensive grazing systems in a hot and humid climate provide an environment very suitable for parasite development, and the variety and prevalence of parasitic diseases are also much greater than in temperate regions.

The debilitating effects of parasites on the animals themselves and upon their profitability are well recognized. Indeed, the market for parasiticides is enormous. So why are we not seeing a continuing supply of alternative, new compounds from the profit-driven pharmaceutical industry? The answer again lies in profitability. The cost of developing a new product is between 100 and 230 million dollars, for a process that can take more than ten years from discovery of a potential candidate to placing it on the market. Antiparasitic compounds have to compete for funding with products for the benefit of other more profitable patients - humans.

The inevitable conclusion is that farmers, veterinarians and the livestock industry generally will have to make the best use of the drugs currently available, and prolong their efficacy by wise use. There are further complications. One is that when a parasite has developed resistance to one chemical or drug from a certain group, it will usually also be resistant to other products from the same group. Another is that many countries lack the capability to diagnose parasite resistance, especially acaricide resistance in ticks, and hence obtain the information necessary to manage the problem wisely.

In response to this, a set of guidelines is being produced by the FAO in collaboration with other international institutions and the pharmaceutical industry. Each of the five economically important groups of parasites (ticks, helminths, flies, mites and lice) will be covered by a separate guide to the diagnosis of resistance and as a decision support system for selecting the 'best bet' options for integrated control and management of resistance to parasiticides.

It will take a combination of wise use of chemicals, and non-chemical husbandry methods, to manage parasite resistance and control. And the stakes are being raised: more opportunity for trade in a growing, globalized market place; greater restrictions on residues and environmental contamination, and the trade restricting fear of introducing parasite resistance through the import of live animals. Losses in productivity could indeed be undramatic when compared to losses in opportunity.

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