Comparison of three subspecies of Trichinella spiralis by scanning electron microscopy.

The surface morphology of three subspecies of Trichinella spiralis was examined by SEM in an attempt to find characteristics useful for distinguishing the subspecies. The subspecies studied were T. spiralis spiralis, which had been maintained in swine and laboratory animals for about 50 yr; T. spiralis nativa collected from Ursus maritimus at 58 degrees N latitude and 95 degrees W longitude in 1976; and, T. spiralis pseudospiralis, which was derived from the original isolation of this subspecies from Procyon lotor at 43 degrees N latitude and 47 degrees 30'E longitude in 1972. All three subspecies were passed in CFW mice and adult worms were collected from the small intestine at 4, 5, 6, 7, 8, and 11 days PI. Characteristics examined included labial and cephalic papillae, cuticular ridges and folds, hypodermal gland cell pores, pseudobursal lobes, genital papillae, cloacal aperture, copulatory bell and vulval morphology. Previous reports of subspecies differences within Trichinella spiralis in the number and distribution of hypodermal gland cell pores, position of genital papillae, shape of the cloacal aperture and shape of pseudobursal lobes were not confirmed and are believed to have been in error resulting from artifacts of fixation and a lack of knowledge of variations within the subspecies caused by low numbers of samples. Differences in surface morphology were not found among the three subspecies. The available names of the recognized biological populations of Trichinella were used at the subspecies level rather than species level because this more clearly represents the state of our knowledge of the nematodes. The question of whether the epidemiology of trichinosis is complicated by the presence of more than one species has not been answered, and it is important that our nomenclature reflect this.