Morphological and molecular characterization of a Sarcocystis bovifelis-like sarcocyst in American beef

Parasites in the apicomplexan genus Sarcocystis infect cattle worldwide. Assessing the economic importance of each such parasite species requires proper diagnosis. Sarcocystis cruzi, a thin-walled species, infects virtually all cattle. The prevalence of the other thin-walled parasite, Sarcocystis heydorni, remains less well established. The remaining six species all have thick (> 3 µm) cyst walls (Sarcocystis hirsuta, S. hominis, S. bovifelis, S. bovini, S. sigmoideus, and S. rommeli). Thick-walled sarcocysts often induce inflammation in striated muscles (causing bovine eosinophilic myositis), leading to condemnation of carcasses at slaughter. One of these, S. hirsuta, can be seen macroscopically and lead to condemnation of beef. Two Sarcocystis species, S. hominis and S. heydorni, are zoonotic. Although S. hominis has been reported as prevalent in Europe, the occurrence of thick-walled species in the US remains poorly known. Here, for the first time to our knowldge, we characterize a thick-walled Sarcocystis species from a sample of beef from a local grocery store in Maryland. By morphological and genetic criteria, it closely, but not perfectly, resembles parasites previously ascribed to S. bovifelis.

Beef samples were examined for Sarcocystis infection, using acid-pepsin digestion to search for bradyzoites, microscopically by compression between a glass slide and coverslip, by histology of paraffin embedded sections stained with hematoxylin and eosin, and by transmission electron microscopy (TEM). Molecular characterization was attempted employing genetic markers: 18S rRNA, 28S rRNA, cox1, ITS1, gapdh1, ron3, and rpoB.

Molecular evaluation revealed 100% identity with S. bovifelis-like sarcocysts from naturally infected cattle from Germany and Argentina; although the condition of the frozen material precludes complete characterization by TEM, we noted morphological features which differed from the S. bovifelis originally described from experimentally infected cattle from Germany.

A novel Sarcocystis species is described from beef from the USA but not named until further evaluation.