The resurrection of a species: Sarcocystis bovifelis Heydorn et al., 1975 is distinct from the current Sarcocystis hirsuta in cattle and morphologically indistinguishable from Sarcocystis sinensis in water buffaloes

Abstract

In the mid-1970s, it was established through transmission experiments and ultrastructural studies of sarcocysts by transmission electron microscopy (TEM) that cattle was the intermediate host of three Sarcocystis spp. using dogs, cats and humans, respectively, as definitive hosts. The cat-transmitted species with microscopic sarcocysts was initially named Sarcocystis bovifelis, but it was soon renamed Sarcocystis hirsuta, since it was considered to be identical with a previously named species. In recent years, an apparently new species has been detected in cattle in several countries by molecular methods and TEM and found by both methods to be indistinguishable from Sarcocystis sinensis in water buffaloes. This species was recently named Sarcocystis rommeli. Beginning in August 2014, a thorough review of papers comprising TEM micrographs of thick-walled sarcocysts in cattle was made in order to determine whether S. sinensis-like sarcocysts had been reported previously under other designations. Surprisingly, the review showed that the species S. bovifelis Heydorn et al., 1975 as described from cattle in Germany was S. sinensis-like and that indistinguishable sarcocysts had also been found in cattle in New Zealand and Canada in the 1980s. However, in the New Zealand study, these small sarcocysts were erroneously thought to represent developmental stages of a species with ultrastructurally similar but macroscopic sarcocysts, since the macroscopic cysts were found to be infective for cats. Thus, in the late 1980s, the cat-transmitted S. bovifelis, after having been renamed S. hirsuta, was erroneously synonymised with a second cat-transmitted species in cattle and then slid into obscurity until recently being rediscovered as a S. sinensis-like species in cattle and then named S. rommeli. Following the erroneous synonymisation, the name S. hirsuta has consistently been used for a taxon with macroscopic sarcocysts, and this usage should be continued. The name S. bovifelis should again be used not only for the species originally described from cattle in Germany but also for morphologically indistinguishable taxa recently reported from cattle under the names S. sinensis and S. rommeli. Because of the morphological similarity between S. bovifelis and S. sinensis, it is likely that cats also act as definitive hosts for S. sinensis. The present paper also gives a thorough review of all research in the 1970s pertaining to S. bovifelis, including its development in cats and cattle; a review of reports of S. bovifelis-like sarcocysts in cattle, water buffaloes and other hosts; and a review of reports of the taxon currently named S. hirsuta in cattle. The usage of the name S. sinensis versus Sarcocystis dubeyi for the S. bovifelis-like taxon in water buffaloes is discussed, and the latter name is found to represent a nomen dubium since the original description concerned a mixture of a S. sinensis- and a Sarcocystis hominis-like species. Based on available transmission (TEM) and scanning electron microscopy (SEM) images, the three-dimensional configuration of the cyst wall protrusions of S. bovifelis/S. sinensis and the current S. hirsuta has been inferred and is described. The protrusions of S. bovifelis/S. sinensis are shaped like soft plastic tubes, having a cylindrical basal portion and a flattened distal portion, making them prone to fold over. The protrusions of the current S. hirsuta are thin, flattened and flexible rectangular structures (like a soft cover note book), which are attached to the cyst surface with a narrow stalk. The appearance of both types of protrusions in ultrathin sections viewed by TEM is highly dependent on how the sarcocysts and the protrusions themselves have been sectioned.

Keywords: Cats; Cattle; Life cycle; Sarcocyst morphology; Sarcocystis bovifelis; Sarcocystis hirsuta; Sarcocystis sinensis; Transmission electron microscopy; Water buffalo.