Lungworm infection in small ruminants in Ethiopia: Systematic review and meta-analysis

Lungworms are important parasitic nematodes of small ruminants that colonize the lower respiratory tract and cause high morbidity and economic loss throughout the world. This systematic review was conducted with the aim of estimating the pooled prevalence of lungworm infection in small ruminants in Ethiopia. Besides, it examines the predictors thought to be responsible for heterogeneity noted between the reports. The search databases used were PubMed, CAB direct, AJOL and Web of science. Eligible studies were selected based on predefined inclusion and exclusion criteria. Thirty two studies published between 2000 and 2016 were found eligible and data were generated on 14,257 small ruminants (12,310 sheep and 1947 goats). Predictors including the study area, type of small ruminants affected, parasitic species involved, a diagnostic test used, study design, management systems, breed, agroecology, and year article published were used as milestone of data extraction. The statistical tool employed were meta-analysis, univariable and multivariable meta-regression and Egger's and begg's statistics for sensitivity analysis. Accordingly, the estimated pooled prevalence of lung worm infection in small ruminants was 40.8% (95% CI: 36.1, 45.6) with a very high heterogeneity between the study reports (I² = 96.5%). However, diagnostic test used and administrative States were the only two predictors identified to explain 15.5% of the explainable heterogeneity (R² = 0.1545, tau² unexplained = 0.6032, tau² total = 0.7135) noted between studies. The reviewed studies showed that three genera of lungworms, namely Dictyocaulus filaria, Mullerius capillaris and Protostrogylus rufescens were prevalent both in sheep and goats in Ethiopia. Mixed infection with two or three species was reported in 4.4 to 48.6% of the total infected animals. Indeed this review is informative and provides a better picture on lungworm infection in Ethiopia; however, it is not exhaustively detailed as there was lack of clear data on the role of some important factors like age, flock size, management system and seasonal variation on lungworm infection. Thus, thorough epidemiological studies including all seasons are required for formulation of meaning full control strategies.