Trichinella spiralis. Light micrograph of a section though pork muscle, showing the encysted worm Trichinella spiralis. The cyst (at centre) is enclosed in a blue stained capsule formed by muscle cells. Inside, coiled larvae are visible. Muscle tissue (red) surrounds the cyst. T.spiralis is a parasitic nematode worm that infects various mammals including pigs, dogs and humans. Human infection, caused by eating contami- nated or undercooked pork, causes Trichinosis. Worms infect the body, causing fever and pains and forming cysts in the muscles, such as the one pictured. Magnification: x85 at 35mm size.