Histopathological, morphological, and molecular characterization of Sarcocystis species in elk (Cervus elaphus) from Pennsylvania, USA

Authors: CEZAR-CERQUEIRA, CAMILA - Non ARS Employee; THOMPSON, PETER - Non ARS Employee; MURATA, FERNANDO - Non ARS Employee; Mowery, Joseph; BROWN, JUSTINE - Pennsylvania Game Commission, Bureau Of Wildlife Management; BANFIELD, JEREMY - Pennsylvania Game Commission, Bureau Of Wildlife Management; Rosenthal, Benjamin; Dubey, Jitender

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2018
Publication Date: 8/17/2018
Citation: Cezar-Cerqueira, C., Thompson, P., Murata, F., Mowery, J.D., Brown, J., Banfield, J., Rosenthal, B.M., Dubey, J.P. 2018. Histopathological, morphological, and molecular characterization of Sarcocystis species in elk (Cervus elaphus) from Pennsylvania, USA. Parasitology Research. 117:3245-3255. https://doi.org/10.1007/s00436-018-6024-2.
DOI: https://doi.org/10.1007/s00436-018-6024-2

Interpretive Summary: Toxoplasma and Sarcocystis are related single celled parasites of livestock and humans. While Toxoplasma has long been recognized to cause neurologic disease in many warm blooded hosts, several species of Sarcocystis also cause a variety of disorders in livestock, pets, and wild animals and some of them are zoonotic. The American elk is a popular game and hunters become concerned about pparasites that might be zoonotic. In the present study the authors found Sarcocystis in muscles of 83 of 91 hinted elk in Pennsylvania. They morphologically characterized Sarcocystis species for helping diagnosis. The results will be of interest to biologists, zoo veterinarians, and parasitologists, and help diagnosis of sarcocystosis.

Technical Abstract: Sarcocystis sarcocysts are common in many species of domestic and wild animals. Here we report sarcocystosis in muscles from 91 free range elk (Cervus canadensis) from Pennsylvania, USA tested by histopathology, transmission electron microscopy (TEM) and molecularly. Sarcocysts were detected in hematoxylin and eosin (HE)-stained sections in 83 of 91 (91.2%) elk, including 83/91 (91.2%) tongues and 15/17 (88.2%) hearts. With respect to age, sarcocysts were found in 8/9 (88.8%) yearlings, 75/77 (97.4%) adults and 0/5 calves. Sarcocysts were detected in 62/69 (89.4%) females and 21/22 (91.2%) males. Associated lesions were mild and consisted of inflammatory foci around degenerate sarcocysts. There were 2 morphologically-distinct sarcocysts based on wall thickness, thin (<0.5 µm) and thick-walled (>4.0 µm). The thin-walled sarcocysts had a TEM “type 2” and villar protrusions (vp), identical to Sarcocystis wapiti previously described from elk in western USA. This species was present both in tongue and heart samples and was detected in all 83 infected elk. The thick-walled sarcocysts consisted of three morphologic variants, referred to herein as sub-kinds A, B, C. Subkind A sarcocysts were rare; only 4 sarcocysts were found in 3 elk. They had a 5-8 µm thick wall with tufted vp, the tips of vp stained darker with HE stain. By TEM, the sarcocyst wall was “type 12” appeared similar to Sarcocystis sybillensis sarcocysts previously described from elk in USA. The subkind B was also rare; it was found in only 1 elk. Its sarcocysts had up to 7 µm thick wall with TEM “type 15b” vp. This species was not named because it was found only in 1 elk. The subkind C sarcocysts were more common (22/91). Morphologically, its wall had “type 10b” villar protrusions. A new name, Sarcocystis elaphusi is proposed for the subkind C. In HE-stained sections the sarcocysts were up to 950.0 µm long; and up to 144.0 µm wide. The parasitophorous vacuolar membrane was highly folded all along the vp, except base. The vp were up to 5.3 µm long, 1.0 µm wide cylindrical to rectangular shape, and contained few microfilaments that were denser at the base than at the tips. Fine granules were distributed throughout the vp. The ground substance (gs) layer was up to 1.2 µm thick, without microtubules but had few granules. The total thickness of the wall with vp and gs was up to 6.5 µm. The bradyzoites were 7.2-10.8 µm long with a prominent mitochondria. Comparisons of ribosomal DNA loci with published sequences showed that all cysts were very similar to other Sarcocystis parasites isolated from cervid hosts across the northern hemisphere. Phylogenetic analysis placed the thin-walled S. wapiti within a strongly supported clade with S. linearis and S. taeniata, while the thick-walled cysts were very closely related to S. truncata, S. elongata, S. silva, and S. tarandi. Further sequencing is needed to produce molecular diagnostics to distinguish among these species. North American elks are hosts to multiple Sarcocystis species with diverse morphology, deriving from two separate evolutionary lineages.