The Influence of Syngamus trachea on Pheasant Populations

Abstract

Syngamus trachea is a highly pathogenic parasite affecting managed pheasant populatons within the U.K. Morbidity and mortality rates are high, particularly when birds are managed at high densities, however very little is known about its disease dynamics and direct effects on pheasants. This study sought to determine the spatio-temporal factors influencing disease occurrence on pheasant estates, and to determine what direct effect, if any, S. trachea is having on pheasant populations.

Several factors influenced within and between-year disease transmission; the most important being pen age, average stocking density and soil moisture. Both stocking density and pen age were positively correlated with the number of eggs per gram of soil, whereas soil moisture was best modelled by means of polynomial regression. Larval recovery was both moisture and temperature dependent, with increased movement and abundance of hatched larvae on herbage, which in turn, facilitated transmission. Infection status, i.e. positive faecal egg counts, was associated with larval abundance.

The infectious stages of S. trachea were highly spatially aggregated, with feeders acting as a spatial focus for disease transmission in release pens. This relationship was highly linear, with a steep decline in the number of eggs per gram of soil within the first 2 m's from the feeder.

Syngamus trachea was previously thought to be relatively benign, however it was demonstrated that even sub-clinical infections were sufficient to reduce body condition in managed pheasants. It is clear that S. trachea is pervasive among managed pheasant populations, and the implications for survival and reproduction are likely to be significant in the absence of anthelmintic treatment. The finding of spatial foci upon estates provides a simple, low-cost solution to managing environmental contamination that should be incorporated into gamekeeper's disease management plans.