Epidemiology and control of sheep helminthiasis in Itaqui county, Rio Grande do Sul State, Brazil

Abstract

An epidemiological study of ovine helminthiasis was carried out in Itaqui county, Rio Grande do Sul, Brazil, from 1966 to 1972. The mean monthly incidence of worms was correlated with the animal age the biology of the parasite, the season and climatic data. A high prevalence of Haemonchus contortus, Trichostrongylus sp. and Oesophagostomum columbianum was verified showing that these species are the principal agents that cause economic losses to sheep production in this region. Pathogenic levels of H. contortus, Trichostrongylus sp. and O. columbianum were found respectively during the following periods: summer and autumn, from mid-autumn to the end of winter, and mid-autumn to the end of spring Ostertagia, Cooperia and Dictyocaulus genera were not of epidemiological importance due to the low incidence of infestation. The genus Moniezia was similar because it did not cause a homogenous infestation and the worms were expelled spontaneously from the sheep's gut; the epidemiological importance of the genus Nematodirus has still to be determined in this region. From the basis of the epidemiological data, a minimum of six anti-helminthic drenches are theoretically needed each year to maintain a sub-clinical level of parasitism in the flocks of Itaqui.