Sarcocystis neurona infection in gamma interferon gene knockout (KO) mice: comparative infectivity of sporocysts in two strains of KO mice, effect of trypsin digestion on merozoite viability, and infectivity of bradyzoites to KO mice and cell culture

Interferon gamma protective against Sarcocystis neurona encephalitis in susceptible murine model

Sarcocystis neurona is the predominant etiological agent of the infectious equine neurologic disease, equine protozoal myeloencephalitis (EPM), which is prevalent in the United States. A wealth of knowledge about S. neurona biology and its life cycle has accumulated over the last several decades. However, much remains unknown about the aberrant equine host's immune response to S. neurona and the relatively high prevalence of exposure to the protozoa but relatively infrequent occurrence of clinical neurologic disease. Mouse models simulating EPM are commonly used to study the disease due to numerous challenges associated with studying the disease in horses. The critical role of the cytokine, interferon gamma (IFNγ), in protection against S. neurona encephalitis has been well established as Ifnγ^-/- mice are highly susceptible to S. neurona encephalitis. However, there are discrepancies in the literature regarding S. neurona disease susceptibility in lymphocyte deficient mice, lacking T-lymphocytes and their associated Ifnγ production. In the current study, we investigated S. neurona encephalitis susceptibility in 2 genetically different strains of lymphocyte null mice, C57Bl/6 (B6).scid and Balb/c.scid. The B6.scid mouse was determined to be susceptible to S. neurona encephalitis as 100 % of infected mice developed neurologic disease within 60 days post infection (DPI). The Balb/c.scid mouse was nearly disease resistant as only 10 % of mice developed neurologic disease 60 DPI. Encephalitis was histologically demonstrable and S. neurona was identified in cerebellar samples collected from B6.scid but absent in Balb/c.scid mice. To further investigate the importance of T-lymphocyte derived Ifnγ, T- lymphocytes were adoptively transferred into B6.scid mice. The adoptive transfer of Ifnγ competent T- lymphocytes offered complete protection against S. neurona encephalitis but transfer of Ifnγ deficient T- lymphocytes did not with 100 % of these recipient mice succumbing to S. neruona encephalitis. Histological analysis of collected cerebellar samples confirmed the presences of S. neurona and encephalitis in recipient mice that developed neurologic disease. These studies show that the background strain is critical in studying SCID susceptibility to S. neurona disease and suggest a protective role of Ifnγ producing T- lymphocytes in S. neurona encephalitis susceptible mice.

High-throughput screen of drug repurposing library identifies inhibitors of Sarcocystis neurona growth

The apicomplexan parasite Sarcocystis neurona is the primary etiologic agent of equine protozoal myeloencephalitis (EPM), a serious neurologic disease of horses. Many horses in the U.S. are at risk of developing EPM; approximately 50% of all horses in the U.S. have been exposed to S. neurona and treatments for EPM are 60-70% effective. Advancement of treatment requires new technology to identify new drugs for EPM. To address this critical need, we developed, validated, and implemented a high-throughput screen to test 725 FDA-approved compounds from the NIH clinical collections library for anti-S. neurona activity. Our screen identified 18 compounds with confirmed inhibitory activity against S. neurona growth, including compounds active in the nM concentration range. Many identified inhibitory compounds have well-defined mechanisms of action, making them useful tools to study parasite biology in addition to being potential therapeutic agents. In comparing the activity of inhibitory compounds identified by our screen to that of other screens against other apicomplexan parasites, we found that most compounds (15/18; 83%) have activity against one or more related apicomplexans. Interestingly, nearly half (44%; 8/18) of the inhibitory compounds have reported activity against dopamine receptors. We also found that dantrolene, a compound already formulated for horses with a peak plasma concentration of 37.8 ± 12.8 ng/ml after 500 mg dose, inhibits S. neurona parasites at low concentrations (0.065 μM [0.036-0.12; 95% CI] or 21.9 ng/ml [12.1-40.3; 95% CI]). These studies demonstrate the use of a new tool for discovering new chemotherapeutic agents for EPM and potentially providing new reagents to elucidate biologic pathways required for successful S. neurona infection.

Isolation, Culture and Cryopreservation of Sarcocystis species

More than 200 valid Sarcocystis species have been described in the parasitological literature. The developmental life cycle in the intermediate host and definitive host has only been described for a few species. Sarcocystis parasites are common pathogens infecting a wide range of animals, including humans, and this unit reviews the methods used for isolating infective stages of the parasite from both definitive and intermediate host(s), as well as methods used to initiate cultures from sporocysts and merozoites and for cryopreservation of various Sarcocystis spp. These methods are based on published reports and our experience with Sarcocystis species in cell culture over many years. The information presented is suitable for the efficient culture of many Sarcocystis species; however, some minor modifications may be needed based on the unique developmental patterns of some species. © 2017 by John Wiley & Sons, Inc.

Detection and characterization of diverse coccidian protozoa shed by California sea lions

Tissue-cyst forming coccidia in the family Sarcocystidae are etiologic agents of protozoal encephalitis in marine mammals including the federally listed Southern sea otter (Enhydra lutris). California sea lions (Zalophus californianus), whose coastal habitat overlaps with sea otters, are definitive hosts for coccidian protozoa provisionally named Coccidia A, B and C. While Coccidia A and B have unknown clinical effects on aquatic wildlife hosts, Coccidia C is associated with severe protozoal disease in harbor seals (Phoca vitulina). In this study, we conducted surveillance for protozoal infection and fecal shedding in hospitalized and free-ranging California sea lions on the Pacific Coast and examined oocyst morphology and phenotypic characteristics of isolates via mouse bioassay and cell culture. Coccidia A and B were shed in similar frequency, particularly by yearlings. Oocysts shed by one free-ranging sea lion sampled at Año Nuevo State Park in California were previously unidentified in sea lions and were most similar to coccidia infecting Guadalupe fur seals (Arctocephalus townsendi) diagnosed with protozoal disease in Oregon (USA). Sporulated Coccidia A and B oocysts did not replicate in three strains of mice or in African green monkey kidney cells. However, cultivation experiments revealed that the inoculum of fecally-derived Coccidia A and B oocysts additionally contained organisms with genetic and antigenic similarity to Sarcocystis neurona; despite the absence of detectable free sporocysts in fecal samples by microscopic examination. In addition to the further characterization of Coccidia A and B in free-ranging and hospitalized sea lions, these results provide evidence of a new role for sea lions as putative mechanical vectors of S. neurona, or S. neurona-like species. Future work is needed to clarify the distribution, taxonomical status, and pathogenesis of these parasites in sea lions and other marine mammals that share their the near-shore marine environment.

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Diverse coccidian protozoa shed by California sea lions (CSL) were characterized.

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Oocyst shedding patterns, taxonomy, morphology and pathogenicity were examined.

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Mice and cell cultures were not susceptible to Coccidia A or B of CSL origin.

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Sarcocystis neurona-like zoites grew in cells inoculated with CSL fecal samples.

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California sea lions may serve as mechanical vectors of an S. neurona-like organism.

An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious disease of horses, and its management continues to be a challenge for veterinarians. The protozoan Sarcocystis neurona is most commonly associated with EPM. S. neurona has emerged as a common cause of mortality in marine mammals, especially sea otters (Enhydra lutris). EPM-like illness has also been recorded in several other mammals, including domestic dogs and cats. This paper updates S. neurona and EPM information from the last 15 years on the advances regarding life cycle, molecular biology, epidemiology, clinical signs, diagnosis, treatment and control.