Sporocyst size of isolates of Sarcocystis shed by the Virginia opossum (Didelphis virginiana)

The Virginia opossum (Didelphis virginiana) is a definitive host for multip le Sarcocystis species including Sarcocystis neurona, one of the causative agents of equine protozoal myeloencephalitis (EPM), a severe, neuromuscular disease of horses. Size and morphologic characteristics of isolates of Sar cocystis shed by the opossum were examined to determine if differences were useful in discriminating between the isolates and/or species. Collections of sporocysts from 17 opossums were molecularly characterized and measured using an ocular micrometer. The mean sporocyst size of isolates of S. neuro na was 10.7 mum x 7.0 mum, Sarcocystis falcatula 11.0 mum x 7.1 mum, Sarcoc ystis speeri 12.2 mum x 8.8 mum, 1085-like isolate 10.9 mum x 6.8 mum, and 3344-like isolate 19.4 mum X 10.5 mum. The length and width of S. speeri we re statistically different (p < 0.05) from the sporocysts of other types. T he length of S. neurona and S. falcatula sporocysts were statistically diff erent (p < 0.05) from each other and the width of S. falcatula and 1085 dif fered (p < 0.05). The fifth sporocyst type (3344) was observed, but due to pronounced morphological characteristics, statistical analysis was not: per formed. There was no consistent difference between the taxa based on intern al structure of the sporocyst. (C) 2001 Elsevier Science B.V. All rights re served.