Epidemiology and control of dictyocauliasis and epidemiology of parasitic gastroenteritis in ruminants

A survey carried out at eleven Regional Laboratories of the National Institute of Agricultural Technology to determine the importance of Dictyocaulus filaria showed that no specific information is available in Argentina. Therefore, studies on grazing lambs were made as well as examinations of lungs obtained from slaughterhouses. These showed that during the pre-lambing period (July through October), adult ewes were positive for D. filaria. These ewes were the principal source of infection of lambs between October and March. A strong immunity in adult cattle grazing in fields with low levels of contamination was noticeable. Experimental production of the disease with L3 obtained by in vitro culture was successful in guinea pigs, mice and sheep. Sheep inoculated with radiation attenuated larvae were more resistant to a challenge infection with normal larvae than control animals. The epidemiology of parasitic gastroenteritis was also examined in sheep and cattle. Faecal egg counts and cultures, larval grass counts and necropsy of 'tracer' animals indicated a high mixed contamination of paddocks, with ewes being the most important source of infection for lambs. Between November and April, a high incidence of Haemonchus contortus was found to cause death of lambs. For cattle, the egg counts and faecal cultures showed a mixed parasitism, with Haemonchus spp. and Cooperia spp. predominating towards the end of spring and summer, and Ostertagia spp. and Trichostrongylus spp. predominating during autumn and winter; infections were normally subclinical. (author). 14 refs, 4 figs, 6 tabs