A Review of the Epidemiology and Control of Gastrointestinal Nematode Infections of Small Ruminants

Abstract

Small ruminants are the host to different species of gastrointestinal nematodes and their epidemiology depends on the aspects of host–parasite relationship and the prevailing agro-climatic conditions. Haemonchus, Trichostrongylus, Bunostomum are highly prevalent in small ruminants of warmer climates, whereas Teladorsagia (Ostertagia), Nematodirus and Cooperia are responsible for severe diseases in small ruminants of temperate areas. This is, because of the fact that the free-living stages of these parasites are strongly affected by moisture conditions of the soil and the climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperature generally accelerates the development. Although nematodes of small ruminants are ubiquitous in all agro-climatic zones, their presence does not necessarily result in diseases. Various categories of anthelmintics decrease the level of infection and reduce the egg output of these parasites, whereas grazing management lowers the level of larval exposure to host. Usually the treatment regimes of gastrointestinal nematodes are based on extrapolation of epidemiological studies carried out elsewhere, although the control strategies designed for one geo-climatic region and farming system may not necessarily be appropriate for all agro-ecological zones and farming systems. This paper reviews the current epidemiology, control of gastrointestinal nematode infections of small ruminants and the current alternatives to conventional anthelmintics to control gastrointestinal nematode infections with an emphasis on the inevitable rise of anthelmintic resistance and the suggestions that need to be considered for the future integrated control of these nematode infections in small ruminants.