Prevalence of Gastrointestinal Helminths in Free-Range Backyard Poultry

Abstract

Free-range backyard chickens scavenge for much of their feed, and in doing so they meet the eggs and intermediate hosts of the gut helminths that circulate in village and household flocks. Surveys from many countries report that roundworms, caecal worms, capillarids and tapeworms are common in such birds, yet the figures they give are rarely comparable. This narrative review sets out what is known about the main helminth groups of scavenging poultry, how they are transmitted, and how prevalence has been measured, and it reports no new data. The central difficulty is that a prevalence figure folds together the age and season of sampling, the management of the flock, the parasites that were looked for and, above all, the diagnostic method: a faecal egg count and a necropsy answer different questions and miss different infections. Evidence on production losses is real but patchy, and it is hard to separate the effect of worms from poor nutrition and concurrent disease. The review concludes that helminths are widespread in free-range flocks but that their true frequency and cost remain poorly defined, and it proposes a short list of items that future surveys should report so that results can be set side by side.