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Clinical and Diagnostic Laboratory Immunology, November 2004, p. 1134-1139, Vol. 11, No. 6
1071-412X/04/$08.00+0     DOI: 10.1128/CDLI.11.6.1134-1139.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Infection of Immunodeficient Horses with Sarcocystis neurona Does Not Result in Neurologic Disease

Debra C. Sellon,1* Donald P. Knowles,2,3 Ellis C. Greiner,4 Maureen T. Long,5 Melissa T. Hines,1 Tressa Hochstatter,1 Ahmed Tibary,1 and John B. Dame4

Department of Veterinary Clinical Sciences,1 Department of Veterinary Microbiology and Pathology, Washington State University,2 Animal Disease Research Unit, ARS-USDA-PWA, Pullman, Washington,3 Department of Pathobiology,4 Department of Large Animal Clinical Sciences, University of Florida, Gainesville, Florida5

Received 21 April 2004/ Returned for modification 29 June 2004/ Accepted 3 August 2004

Equine protozoal myeloencephalitis is a progressive neurologic disease of horses most commonly caused by infection with the apicomplexan parasite Sarcocystis neurona. Factors affecting neuroinvasion and neurovirulence have not been determined. We investigated the pathogenesis of infection with S. neurona in horses with severe combined immune deficiency (SCID). Two immunocompetent (IC) Arabian horses and two Arabian horses with SCID were infected orally with 5 x 105 sporocysts of S. neurona. Four IC horses and one SCID horse were infected intravenously (i.v.) with 5 x 108 merozoites of the WSU-1 isolate of S. neurona. Despite prolonged parasitemia and persistent infection of visceral tissues (skeletal muscle, cardiac muscle, lung, liver, and spleen) as demonstrated by PCR and culture, SCID horses did not develop neurologic signs after oral or i.v. infection. S. neurona was undetectable in the neuronal tissues of SCID horses by either PCR, immunohistochemistry, or culture. In contrast, although parasitemia was undetectable in orally infected IC horses and of only short duration in i.v. infected IC horses, four of six IC horses developed neurologic signs. S. neurona was detectable by PCR and/or culture of neural tissue but not visceral tissue of IC horses with neurologic disease. Infected SCID horses are unable to clear S. neurona from visceral tissues, but the infection does not result in neurologic signs; in contrast, IC horses rapidly control parasitemia and infection of visceral tissues but frequently experience neuroinvasion and exhibit clinical signs of neurologic disease.

* Corresponding author. Mailing address: Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA 99163. Phone: (509) 335-0733. Fax: (509) 335-0880. E-mail: dsellon{at}vetmed.wsu.edu.

Clinical and Diagnostic Laboratory Immunology, November 2004, p. 1134-1139, Vol. 11, No. 6
1071-412X/04/$08.00+0     DOI: 10.1128/CDLI.11.6.1134-1139.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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