The Epidemiology and Control of some Nematode Infections in Grazing Animals

Abstract

This chapter discusses the epidemiology and control of some nematode infections in grazing animals. The epidemiological effects of differences in the reaction of different hosts to a common parasite are given. The connection between arrested development and the increase in worm egg output seen in many host–nematode systems at or following parturition, and which has come to be called the postparturient, periparturient, or lactation rise, is largely incidental. The chapter discusses the parasitic gastro-enteritis in sheep. The central issue appeared to be whether disease-producing infections were built up by exponential population growth through several generations. As the grazing season progresses, the relative numbers of worms of different species present in lambs change. The worm eggs passed by ewes in the course of the postparturient rise were the source of nearly all the worms that were the cause of disease in their lambs. Strategies for the control of parasitic gastro-enteritis in lambs are presented. Cattle exposed to regular infection gradually acquire a resistance to the establishment of Ostertagia ostertagi (O.ostertagi). The chapter discusses the methods for controling the parasitic gastro-enteritis in cattle and the parasitic bronchitis in cattle and the methods for controling it.