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Population genetic structure of Ascaridia galli re-emerging in non-caged laying hens

Johan Höglund1*, David A Morrison1, Annie Engström1, Peter Nejsum2 and Désirée S Jansson3

Author Affiliations

1 Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, Section for Parasitology, P.O. 7028, Uppsala, SE-750 07, Sweden

2 Department of Veterinary Disease Biology, Danish Centre for Experimental Parasitology, Faculty of Life Sciences, University of Copenhagen, Copenhagen, Denmark

3 Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute (SVA), Uppsala, SE-751 89, Sweden

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Parasites & Vectors 2012, 5:97  doi:10.1186/1756-3305-5-97

Published: 20 May 2012



The poultry roundworm Ascaridia galli has reappeared in hens kept for egg production in Sweden after having been almost absent a decade ago. Today this is a frequent intestinal nematode parasite in non-caged laying hens. The aim of this study was to investigate the genetic diversity (Fst) in A. galli collected from different poultry production sites in southern Sweden, to identify possible common routes of colonization.


Adult parasites (n = 153) from 10 farms, including both broiler breeder parents and laying hens, were investigated by amplified restriction fragment length polymorphism analysis (AFLP). Worms from a Danish laying hen farm were also included for comparison. Most of the farms were represented by worms from a single host, but on two farms multiple samples from different hosts were assessed in order to study flock variation.


A total of 97 fragments (loci) were amplified among which 81% were variable alleles. The average genetic diversity was 0.13 (range = 0.09-0.38), which is comparable to other AFLP studies on nematodes of human and veterinary importance. Within-farm variation showed that worms harboured by a single hen in a flock covered most of the A. galli genetic variation within the same flock (Fst = 0.01 and 0.03 for two farms). Between-farm analysis showed a moderate population genetic structure (Fst = 0.13), along with a low mutational rate but high gene flow between different farms, and absence of strong genetic selection. Network analysis showed repeated genetic patterns among the farms, with most worms on each farm clustering together as supported by high re-allocation rates.


The investigated A. galli populations were not strongly differentiated, indicating that they have undergone a genetic bottlenecking and subsequent drift. This supports the view that the investigated farms have been recently colonized, and that new flocks are reinfected upon arrival with a stationary infection.

AFLP; Ascaridia galli; Nematoda; Parasite infection; Population genetics; Network analysis