title: Spatial distribution of infectious stages of the nematode Syngamus trachea within pheasant (Phasianus colchicus) release pens on estates in the South West of England: Potential density dependence?
abstract: The spatial distribution of the infectious stages of parasites with a direct life cycle is one of the most important factors influencing infectious disease dynamics, and acquisition rates will generally increase as the contact time between parasite and host increases. For animal species that are constrained by feeding opportunities, one might expect disease patterns to be highly skewed within confined systems. The aim of the present study was to identify to what extent, if any, eggs of avian parasites are aggregated within the release pen, and to evaluate what effect, if any, this aggregation had on the distribution of the adult stages within the host species. The abundance of Syngamus trachea eggs were highly aggregated within pens, with high levels of contamination driven by a combination of feeder placement, soil moisture and host-mediated heterogeneities in immuno-competence. The log mean and log variance of egg abundance was highly linear (R(2)=0.97-0.99), with an estimated slope (b) of between 1.79 and 1.97 for individual sites, and 2.11 when sites were combined, which indicated aggregation relative to an estimated Poisson slope of unity. Although the placement of feeders and environmental moisture could be contributing to parasite aggregation, density-dependent processes appear to be ensuring the population does not become too over or under-dispersed, in order to maintain the transmission-virulence equilibrium. To the best of our knowledge, this is the first paper to explicitly demonstrate the high spatial aggregation of eggs around feeding sites and the first to suggest possible density-dependent regulatory mechanisms stabilising disease dynamics between S. trachea and ring necked Pheasants (Phasianus colchicus).
authors.affiliation: Department of Crop & Environment Sciences, Harper Adams University, Edgmond, Newport TF10 8NB, UK. Electronic address: owengethings@hotmail.co.uk.
authors.forename: O J
authors.initials: OJ
authors.lastname: Gethings
authors.affiliation: Game & Wildlife Conservation Trust, Burgate Manor, Fordingbridge SP6 1EF, UK.
authors.forename: R B
authors.initials: RB
authors.lastname: Sage
authors.affiliation: Department of Crop & Environment Sciences, Harper Adams University, Edgmond, Newport TF10 8NB, UK.
authors.forename: S R
authors.initials: SR
authors.lastname: Leather
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D001715:Bird Diseases / Q000453:epidemiology / Q000469:parasitology*; D004739:England / Q000453:epidemiology; D005243:Feces / Q000469:parasitology; D046094:Galliformes; D010063:Ovum / Q000145:classification; D012307:Risk Factors; D012987:Soil / Q000469:parasitology; D017183:Strongylida / Q000145:classification / Q000302:isolation & purification*; D017206:Strongylida Infections / Q000662:veterinary*; D014132:Trachea / Q000469:parasitology* / Q000473:pathology
chemical_list: D012987:Soil
keywords: Aggregation; Density dependence; Feeding; Helminth; Pheasant; Syngamus trachea