Helminths: The fate of poor people and livestock

Anthelmintics are therapeutic agents used to destroy parasitic worms or remove them from the infected host. Commercially available anthelmintics belong to one of three chemical classes-benzimidazoles, macrocyclic lactones or imidazothiazoles.¹ All the anthelmintics work in a similar fashion; they prevent absorption of sugar from infected hosts, necessary for the worm’s survival.

Helminths: Parasitic worms Common helminths-        Nematodes        Trematode        Cestodes

Tropical people and animals are the worst victims of helminths due to unhygienic food and water. WHO estimates that around 25% of world’s population (1.5 billion people) are infected with helminths; among them, 835 million are children.

Endemic Area: Tropical countries Host: Human and domestic animals Reason: unhygienic food and water

The immune system of the infected people faces significant changes including, eosinophilia, elevated serum IgE, impaired signal transduction and delayed response to recall antigens. Helminth infection adversely affects livestock production, causing a loss around $13.96 billion/year worldwide. Excessive use of anthelmintics in livestock is one of the major reasons for growing anthelmintic drug resistance.²

Benzimidazoles are a large chemical family with a common chemical structure which have variances only in radical groups. Thiabendazole, fenbendazole, oxfendazole, albendazole, mebendazole and oxibendazole are representatives of this group.² They have a broad spectrum of activity against helminths and are being used to treat nematode and trematode infections both in human and animal. They also have limited activity against cestodes.

The advantage of using benzimidazoles is its wide safety margin. The effectiveness of anthelmintics is challenged highly because of the worldwide growth of resistance in livestock.^2,3 If a helminth can tolerate the standard recommended dose of an anthelmintic drug and can pass this ability on to his offspring, then this helminth is said to be resistant to that anthelmintic drug. The problem of anthelmintic resistance can be circumvented either by enhancing the available drugs or inventing new drugs. However, discovery of new drug to fight helminth infection rarely takes place due to the lack of resources of the countries where this disease is more prevalent.

References

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13. Soulsby, E.J.L. Helminths Arthropods and Protozoa of Domesticated Animals. English Language Book Society, Bailliere Tindall, London, 1982.
14. MAFF. Parasitological Laboratory Techniques. Technical Bulletin No. 18. Ministry of Agriculture Fisheries and Food Manual of Veterinary. Her Majesty’s Stationary Office, London, 1979.