Epidemiology of Oestrus ovis L. (Diptera: Oestridae) larvae in sheep and goats in Greece

Oestrosis is a worldwide myiasis caused by larvae of the fly Oestrus ovis, which are obligate parasites of the nasal and sinus cavities of sheep and goats, especially in Mediterranean countries. The aim of this study was to compare the infection levels and seasonal patterns of oestrosis in sheep and goats from areas of similar climate and to explore some potential risk factors associated with this disease in Greece. Of 450 sheep and goat heads examined, 246 (54%) were infected with O. ovis larvae. Goats (76%, 95% CI 68–82) were more commonly infected than sheep (38%, 95% CI 37–49). Larval stages were recovered during all months of the year from both host species, with an overall mean infection intensity of 8.7±13.1 (mean±SD). Host species, month, area and age, but not nose colour, affected the chance of being infected. Parasite intensity varied but was not affected by these factors except for age and season. Seasonal variation in prevalence was much more pronounced for larval stage 1, than for total larvae. In sheep, infection was generally more common and intense in early spring and in autumn, whereas prevalence peaked in goats in winter. Both prevalence and larval intensity increased with age above 3–4 years in sheep, but not in goats. Patterns of aggregation were consistent with density-dependent constraints to development in the host, and suggested lower susceptibility to larval establishment in goats in spite of higher overall prevalence.