Sarcocystis strixi, n. sp. from barred owls (Strix varia) definitive hosts and gamma interferon gene knockout mice as experimental intermediate host

Authors: VERMA, SHIV - Non ARS Employee; ROSYPAL, ALEXA - Johnson C Smith University; Mowery, Joseph; SCOTT, DAVID - Non ARS Employee; CERQUEIRA-CEZAR, CAMILA - Non ARS Employee; Dubey, Jitender; LINDSAY, DAVID - Virginia Tech; Rosenthal, Benjamin

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2017
Publication Date: 12/1/2017
Citation: Verma, S.K., Rosypal, A., Mowery, J.D., Scott, D., Cerqueira-Cezar, C., Dubey, J.P., Lindsay, D., Rosenthal, B.M. 2017. Sarcocystis strixi, n. sp. from barred owls (Strix varia) definitive hosts and gamma interferon gene knockout mice as experimental intermediate host. Journal of Parasitology. 103:768-777. https://doi.org/10.1645/16-173.
DOI: https://doi.org/10.1645/16-173

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. Recently, a new species, S. calchasi was identified as killing raptors and other avian species. Identification of Sarcocystis species is difficult. In the present study authors describe a new species of Sarcocystis from the intestine of Barred owl that was found to be infectious to immunosuppressed mice. The results will be of interest to biologists, zoo veterinarians, and parasitologists, and help diagnosis of sarcocystosis.

Technical Abstract: Sarcocystis species have 2-host life cycles with the sexual cycle in the definitive hosts and an asexual cycle in the intermediate hosts. Raptors are definitive hosts for several species of Sarcocystis but intestinal infection with Sarcocystis has not been reported from Barred owls (Strix varia). Here we report a new species of Sarcocystis with Barred owls as the natural definitive host and gamma interferon gene knockout (KO) mice as an experimental intermediate host. A Barred owl submitted to the Carolina Raptor Center, Huntersville, North Carolina, was euthanized because of paralysis. Fully sporulated 12.5 x 9.9 im sized sporocysts were found in intestinal scrapings of the owl’s intestine. Sporocysts from the Barred owl were orally fed to 4 outbred laboratory Swiss Webster (SW) mice (Mus musculus) and 8 KO mice. All mice remained asymptomatic. Microscopic sarcocysts were found in all 5 KO mice euthanized between day 32 and 206 postinoculation (PI). The sarcocysts were not grossly visible and were up to 70 im wide; the length could not be measured accurately because sarcocysts were twisted in myocytes. When viewed with light microscopy, the sarcocyst wall had undulating, flat to conical, protrusions of varying dimensions. The wall varied in width (<1 to 2 im thick), depending on the area. In sections stained with hematoxylin and eosin (HE), numerous sarcocysts were seen in sections of tongue and skeletal muscles from the abdomen, limbs, and eye but not in the heart. In HEstained sections the sarcocyst wall was eosinophilic and often without projections. Live bradyzoites were 7-8 im long at both days PI. By transmission electron microscopy, the sarcocyst wall consisted of a highly undulating parasitophorous vacuolar membrane (pvm) that had undulations which were at irregular distances, up to 2.5 im apart. The pvm was lined by an uneven electron dense layer (edl) that was up to 50 nm thick. The pvm was invaginated into the interior of the sarcocyst and invaginations lacked edl at irregular distances, giving the appearance of pores in the wall. The ground substance layer (gs) was homogenous with very fine granules, and a few vesicles concentrated towards the villar projections. No microtubules were seen in the gs. The gs was up to 2 im thick and continued into the interior of the sarcocyst as septa Longitudinally cut bradyzoites at 206 day PI were 7.8 x 2.2 im in size. Molecular characterization using 18S rRNA, 28S rRNA, and cox1 genes revealed a close phylogenetic relationship with another parasite in this genus those infect birds.