Epidemiology of Oestrus ovis infection of sheep in northeast Spain (mid-Ebro Valley).

Slaughterhouse surveys to determine the prevalence and intensity of larval Oestrus ovis Linnaeus (Diptera: Oestridae) in sheep, were conducted monthly for 1 year in northeastern Spain. The prevalence of O. ovis in 120 sheep in northeast Spain was 84.2%. The monthly prevalence ranged from 62.5% in January to 100% in June and October. Of the 3,831 larvae collected, 3,005 were first instar larvae (78.4%), 744 second instar larvae (19.4%), and 82 third instar larvae (2.1%). The mean larval burden per infected sheep was 37.9, throughout the year although infection was higher in October. The high number of first stage larvae in winter (especially October, November, and December) may be due to a period of slower larval maturation. Third-stage larvae were always present but sometimes in very low numbers compared to the total. According to the results, oestrosis appears to be a serious problem in the region.