Epidemiology of Oestrus ovis infection of sheep in Morocco.

The epidemiology of Oestrus ovis was studied by two methods, slaughterhouse survey and tracer lambs study. The prevalence of infection varied from 10 to 100%, the highest being between June and September and the lowest in March. The mean annual larval burden was 6.7. The maximum number of larvae recovered from a single head was 35 in the month of September. Two larval peaks were observed, the first in May and June and the second in September and October. The flies are absent from December to March. The first generation flies appear in April and up to four generations may occur during the year. During the hottest month of the year (August) flies are either absent or in negligible numbers. During winter the perpetuation of species is ensured by the overwintering larvae in the heads of sheep and the pupae on the ground.