Seasonal prevalence of Strongylus vulgaris in the anterior mesenteric artery of the donkey in Morocco

The anterior mesenteric artery and its main branches, collected regularly from donkeys throughout a year, were examined for Strongylus vulgaris larvae. The mean monthly percentage of arteries infected varied from 61.5 to 100, with an overall mean of 90.5. The mean monthly number of larvae varied from 3 in January to 104 in April, with the annual mean of 32.6. A clear seasonal pattern occured in the worm burden and the age structure of larvae. The number of larvae was least in December–January, but rose gradually thereafter to reach a peak in April–May. A steep decline in June–July was followed by a progressive diminution until January. During summer and early autumn, the proportion of fifth-stage larvae was high. These observations indicate that S. vulgaris is an annual species in Morocco, infection occurring in late autumn and winter, development being completed in spring and summer, and sexually mature adults occuring in the gut mainly in summer and autumn.