Characterisation of gastrointestinal helminths and their impact in commercial small-scale chicken flocks in the Mekong Delta of Vietnam

Commercial small-scale chicken farms using all-in-all-out production but operating with low standards of hygiene/biosecurity are increasingly common in Vietnam. These conditions facilitate transmission of gastrointestinal helminths. However there are no published data on these parasites in these systems. The aims were: (1) to determine the prevalence/burden of gastrointestinal helminths in small-scale commercial flocks in commercial small-scale flocks in the Mekong Delta region; and (2) to investigate the association between worm burdens and birds’ weight and disease status. Randomly selected chickens (n=120) (‘normal’ flocks) were investigated at the end of their production cycle (∼18 weeks), as well as 90 chickens with signs of respiratory and/or severe disease. The gastrointestinal tract of chickens was dissected and all visible helminths were identified. 54.2% and 54.4% healthy and diseased chickens contained helminths. Diseased, colonized chickens harboured a higher mass of helminth worms (3.8 ±SD 8.6g) than colonized, healthy chickens (1.9 ±6.3g). Eight species were identified, three nematodes ( Ascaridia galli, Cheilospirura hamulosa and Heterakis gallinarum ), four cestodes ( Hymenolepis, Raillietina cesticillus, Raillietina echinobothrida, Raillietina tetragona ,) and one trematode (Echinostomatidae). Heterakis gallinarum was the most prevalent helminth (43.3% and 42.2% in healthy and sick chickens, respectively), followed by A. galli (26.7% and 41.1%). Colonized chickens weighed 101.5g less than non-colonized birds. Colonisation was significantly higher during the rainy months (May-November) for both H. gallinarum and A. galli . Anthelminthic usage was not associated with reduced helminth burdens. We recommend upgrading cleaning and disinfection and limiting access to ranging areas to control helminth infections in small-scale commercial chicken flocks.