: A cross-sectional study was conducted on 381 sheep randomly sampled with the objective to
determine prevalence of lungworm infestation and identifying the species of respiratory helminthes circulating
in and around Assela. Modified Baermann technique was used to detect first stage larvae (L1). Dictyocaulus
filaria (D. filaria) was the dominant lungworm species with prevalence of 27.80% (95% CI=49.1-61.1%),
followed by Protostrongylus rufescens (P. rufescens), 13.9% (95% CI=10.4-17.4%), Mulliries capillaries
(M. capillaries), 6.6% (95% CI=4.1-9.1%) and Mixed infection, with two or more of the common sheep
lungworm infection, 6.8%. There was statistical significant difference in susceptibility between young and old
age groups (Chi square = 28.9, 1df, P<0.05), the young being more affected. Significant differences (P< 0.05)
were found among areas of different altitude with an infection rate of 46.4%, 52.7% and 66.1% at low, medium
and higher altitude areas, respectively. The overall results obtained during this investigation showed that
D. filaria is the most common lungworm species in its not only high prevalence rate, but also high degree of
association with occurrence of clinical respiratory signs. Due to its impact on sheep production of the area, due
emphasis should be given for the control and prevention of lungworm infestation.