Control of Gastrointestinal Nematode Infections in the Arid and Semi-Arid Areas of Kenya

Abstract

A background to epidemiological aspects of gastrointestinal nematode infections in the arid and semi-arid areas is essential. The rainfall distribution in these areas is uneven during the year. This means that there are times when grazing is in short supply and animals suffer from nutritional stress. Chronic helminth conditions are common in these areas due a slow build-up of worm burdens coupled with poor feeding. Tichostrongylus, Haemonchus, and Oesophagostomum can all be present resulting in a generalized parasitic gastroenteritis. During the dry season, the invading larvae (L3) may enter a period of delayed development in the animals. This phenomenon, called hybobiosis, is an adaptive characteristic that facilitates the survival of H. contortus and subsequent transmission in semi-arid areas of Kenya. Essentially, this phenomenon allows the persistence of larval stages in the host in a physiologically inert form that resumes development when conditions become conducive for transmission. The stocking rates in most areas are low although this may not be the case in areas around the watering places and the bomas. Toxocara may be encountered in young suckling calves.