Serologic Diagnosis of Encephalomyocarditis Virus Infection in Swine by the Microtiter Serum Neutralization Test

Abstract

ophilic cytoplasmic and sometimes intranuclear inclusions characteristic of canine distemper infection. No viral inclusions were seen in the brain and lungs. However, in lung there was moderately severe patchy interstitial alveolar thickening. Other incidental findings included moderate numbers of Sarcocystis in striated muscles (heart, tongue, diaphragm, esophagus, masseter, and extraorbital muscles), a few Capillaria sp. in the mucosa of the esophagus and urinary bladder, large numbers of Cryptosporidium sp. in the intestines, and a few unidentified helminthic eosinophilic granulomas in the lung and mesenteric lymph nodes. The eosinophilic meningitis observed in the present case appears to be an incidental finding not related to the protozoa1 infection. Based on these findings, the primary disease in the raccoon was distemper. The neurologic signs were attributed to the extensive multifocal lesions produced by the unidentified protozoa. Based on morphologic and antigenic differences, the organism was neither T. gondii nor N. caninum. Both N. caninum and T. gondii divide into two progeny by endodyogeny, whereas the present organism divided into numerous progeny by schizogony. The low T. gondii antibody titer (10) in the raccoon serum is considered nondiagnostic in the agglutination test. The organism causing encephalitis in the raccoon is morphologically similar to the organism associated with equine protozoa1 myeloencephalitis (EPM). The organism in the raccoon and that causing EPM resemble Sarcocystis in structure, react with Sarcocystis immunologically, are located free in the host cell cytoplasm, divide by schizogony, have no rhoptries, multiply in neurons, and cause malacia of the central nervous system. Acknowledgements. This research was supported in part by grants from the Pennsylvania Department of Agriculture. The authors thank Eva Kovacs, M. Coicou, S. Hindman, B. Lehmann, and J. Dieter for technical assistance, Charlie Brown for transmission electron microscopy, and Dr. D. E. GranStrom for providing Sarcocystis cruzi serum.