Equine Protozoal Myeloencephalitis (EPM) is a serious neurologic disease of horses in the United States. The primary etiologic agent is Sarcocystis neurona (S. neurona). Currently, there is limited knowledge regarding the protective or pathologic immune response to infection to the intracellular protozoa S. neurona. The objective of these studies was to determine the effects of S. neurona infection on the immune response of horses that had EPM due to natural infection (experiment 1) and experimental infection (experiment 2). In experiment 1, twenty-two horses with naturally occurring cases of EPM, which were confirmed positive based on detection of antibodies in the serum and/or CSF and clinical signs, and 20 clinically normal horses were included to determine whether S. neurona altered the immune responses, as measured by immune cell subsets (CD4, CD8, B-cell, monocytes, and neutrophils) and leukocyte proliferation (antigen specific and non-specific mitogens). Our results demonstrated that naturally infected horses had significantly higher percentages of CD4 and neutrophils (PMN) in peripheral blood mononuclear cells (PBMCs) than clinically normal horses. Leukocytes from naturally infected EPM horses had a significantly lower proliferation response, as measured by thymidine incorporation, to a non-antigen specific mitogen phorbol 12-myristate 13-acetate (PMA) / ionomycin (I) than did clinically normal horses (p=0.04). The implications of these findings will be discussed. In experiment 2, 13 horses were randomly divided into two groups. Baseline neurologic examinations were performed and all horses were confirmed negative for S. neurona antibodies in the CSF and serum. Then, one group with 8 clinically normal seronegative horses was inoculated intravenously with approximately 6000 S. neurona infected autologous leukocytes daily for 14 days. All the challenged horses showed neurologic signs consistent with EPM. PBMCs were isolated from the control and infected horses to determine how S. neurona alters the immune responses based on changes in immune cell subsets and immune function. There were no significant differences in the percentage of CD4 cells in peripheral blood lymphocytes or IFN-γ production by CD4 and/or CD8 cells. PMA/I stimulated proliferation responses in PBMCs appeared suppressed compared to that of uninfected controls. Additional studies are necessary to determine the role of CD4 and CD8 cells in disease and protection to S. neurona in horses, as well as to determine the mechanism associated with suppressed in vitro proliferation responses. This project was funded by Patricia Stuart Equine grants and paramutual racing funds from Virginia Tech. / Master of Science

Equine Protozoal Myeloencephalitis is the most frequently diagnosed neurologic disorder of horses in the united states, which is caused by the protozoan organism Sarcocystis neurona. The disease has a profound impact on the American Horse Industry. This impact includes prolonged and expensive treatment without a guaranteed return to a previous level of use for the individual horse. Poor respponse to and prolonged duration of treatment may suggest an immune mediated impariement of host response. There is limited information about the direct interaction between the pathogen and the host. In two in vitro experiments we investigated a) whether the presence of the protozoan organism can influence mitogen-stimulated peripheral blood mononuclear cells (PBMCs), suggesting a direct influence of the protozoan organism on cells of the immune system, and b) if cerebrospinal fluid (CSF) from horses with EPM has an effect on mitogen-stimulated PBMCs, suggesting that the microenvironment of the site of infection influences the course of disease. Experiment 1: Mitogen simulated PBMCs from EPM affected and control horses were co-cultured with fragments of freeze thawed bovine turbinate cells that were infected with S. neurona merozoites. Compared to controls PBMCs co-cultured with S. neurona fragments were the only cells that showed a decreased proliferation (p<0.05). A difference between EPM affected and control horses could not be detected (p>0.05). These results may imply that the persistence of S. neurona infection in the horses CNS is, in part, due to a pathogen-derived mechanism that attentuates the hosts immune response. Experiment 2: Mitogen stimulated PBMCs from a horse affected with EPM and a control were co-cultured n the presence of CSF from EPM affected and uninfected controls. Prior to co-culture the CSF was fractionated by a filtration process over two microfilter units. An identical volume of NaCl (0.9%) served as a control for the volume of CSF that was added. The proliferation assay revealed a deviation of the response depending on cell donor and CSF fraction used. The effect was independant of the protein concentration of the CSF fraction, and a decrease in lymphocyte proliferation was not caused by increased cellular death. This suggests the presence of subsets within the CSF which have a stimulatory of suppressive influence on the cells in culture. The effect was cell donor dependant which implies a difference in lymphocyte subsets between the two horses that were used. / Master of Science

Horses that are exposed to Sarcocystis neurona, a causative agent of equine protozoal myeloencephalitis, produce antibodies that are detectable in serum by western blot (WB). A positive test is indicative of exposure to the organism. Positive tests in young horses can be complicated by the presence of maternal antibodies. Passive transfer of maternal antibodies to S. neurona from seropositive mares to their foals was evaluated. Foals were sampled at birth (presuckle), at 24 hours of age (postsuckle), and at monthly intervals. All foals sampled before suckling were seronegative. Thirty-three foals from 33 seropositive mares became seropositive with colostrum ingestion at 24 hours of age, confirming that passive transfer of S. neurona maternal antibodies occurs. Thirty-one of the 33 foals became seronegative by 9 months of age, with a mean seronegative conversion time of 4.2 months. These results indicate that evaluation of exposure to S. neurona by WB analysis of serum may be misleading in young horses. Cerebrospinal fluid (CSF) samples from 15 neonatal (2-8 day) foals were examined for the presence of antibodies to S. neurona by WB analysis. Twelve of 13 foals that were seropositive were also CSF positive, suggesting that maternal antibodies to S. neurona cross the blood-CSF barrier in neonatal foals resulting in a positive CSF WB. Repeat taps were performed on 5 of the foals which showed that the immunoreactivity of the western blot decreases over time. Two of the 5 foals were CSF negative at 83 and 84 days of age, with 1 foal still positive at 90 days, and 2 foals positive at 62 days. These results indicate that maternal antibodies to S. neurona in the CSF can confound WB results in neonatal foals up to several months of age. / Master of Science

Previous studies have demonstrated differences in CD4+, CD8+ and B-cell populations between EPM affected and normal horses. The overall goal of our project was to further define the immune deficiencies associated with S. neurona infection. We hypothesized that PMA/I stimulated suppression in EPM horses is due to decreased proliferation of monocytes, CD4+ and CD8+ cells. Our objectives were 1) to determine whether S. neurona infection causes an increase in apoptosis of a particular immune subset, and 2) to determine whether S. neurona causes a decrease in the number of cellular divisions (proliferation) of a particular immune cell subset. For this study, nine S. neurona antibody negative, immunocompetent horses were obtained. Baseline neurologic examinations, SnSAG1 (S. neurona Surface Antigen 1) ELISAs on cerebrospinal fluid (CSF) and serum, and baseline immune function assays were performed. Horses were randomly divided into groups. Five horses were challenged for ten days via intravenous injection of autologous lymphocytes infected with S. neurona. Neurologic parameters of all horses were assessed for 70 days following infection. Immune function was based on proliferation responses to mitogens, as assessed through thymidine incorporation. Enumeration of cellular subsets, degree of apoptosis and number of cellular divisions were assessed through flow cytometry. SnSAG1 ELISA of serum and CSF samples performed post-infection confirmed infection and disease. All infected horses displayed moderate neurologic signs on clinical examination. Some significant differences in cellular activities were noted. Additionally, this is the first time the method using S. neurona infected lymphocytes has been reproduced successfully by different investigators. / Master of Science

Poucos estudos quantificam o risco relativo da saúde humana na transmissão spillover de doenças zoonóticas de populações de animais silvestres, estudos cruciais na compreensão da história natural das zoonoses. Coccídios, em particular os da família Sarcocystidae, são importantes agentes transmissíveis na interface homens - animais domésticos e silvestres. O diagnóstico da coccidiose é prejudicado pela limitada disponibilidade de amostras resultantes de populações animais de espécies em risco de extinção. O objetivo deste estudo foi detectar através da amplificação do locus ITS-1, protozoários das subfamílias Sarcocystinae e Toxoplasmatinae em amostras teciduais de Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo e L. pardalis, depositados em coleções biológicas do Rio Grande do Sul, Brasil. Um objetivo adicional foi a obtenção de informações que permitissem avaliar o papel epidemiológico dos protozoários no ciclo silvestre dos parasitas e seu possível impacto sobre as populações de animais silvestres e na saúde pública. Noventa pequenos felídeos neotropicais de vida livre, representando seis espécies, foram amostrados. Destes, 31 felídeos (34,4%), de todas as seis espécies, foram positivos para Toxoplasma gondii e DNA foi detectado em 63 das 433 (14,6%) amostras de tecidos primários coletados a partir de língua (28,6%), cérebro (18,6%), músculo esquelético (17,1%), musculatura ocular (13,6%), globo ocular (13,6%), coração (11,1%), diafragma (5,4%) e humor vítreo (4,5%). Doze amostras primárias positivas ao T. gondii foram genotipadas com os marcadores moleculares SAG1, SAG2, SAG3, BTUB, GRA6, c22- 8, c29-2, L358, PK1, Apico e CS3 e a técnica multilocus PCR-RFLP, a amostra Py#36m foi totalmente caracterizada como do tipo I com alelo II no BTUB e um novo genótipo atípico Py#21M, ambos isolados de Puma yagouaroundi e nunca descrito no Brasil. Nove outras amostras tiveram caracterização parcial. Treze dos 90 felídeos foram positivos para Sarcocystis spp. (14,4%) e outros 18 felídeos, representando cinco espécies albergaram S. felis-like [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) e Lc (#82m, #76m)]. Um único felino de L. pardalis foi negativo. DNA do parasita foi detectado em 11,8% dos tecidos examinados (51/433): musculatura esquelética (26,5%), língua (23,2%), musculatura ocular (13,6%), diafragma (10,7%), cérebro (2,3%), coração (1,6%) e globo ocular (4,5%), nenhuma das 44 amostras de humor vítreo foi positiva. Esta é a primeira detecção e caracterização genética de T. gondii e de S. felislike em felídeos silvestres brasileiros de vida livre, demonstrando a presença destes agentes no ciclo silvestre e, a potencial transmissibilidade ao homem e a outros animais domésticos e silvestres. O uso de amostras de tecidos de animais silvestres depositados em coleções biológicas para estudos epidemiológicos de doenças monstraram serem de grande utilidade. / Few studies have quantified the relative risk of human health from spillover of zoonotic diseases from populations of wild animals; these studies are crucial for understanding the natural history of zoonoses. Coccidia, particularly from the family Sarcocystidae, are important transmissible agents at the interface of man and domestic and wild animals. The diagnosis of Coccidiosis is hampered by the limited availability of samples resulting from protection of natural populations of the species at risk of extinction. The aim of this study was to detected, by amplification of ITS-1 locus, protozoa from the subfamilies Sarcocystinae and Toxoplasmatinae in tissue samples from Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo and L. pardalis, deposited in biological collections of the State of Rio Grande do Sul, Brazil. An additional aim was to obtain information that would enable assessment of the epidemiological role of the protozoa in the sylvatic cycle of the parasite, and its possible impact on wildlife populations and public health. Ninety free-living small wild felines, representing 6 species, were sampled. Of these, 31 felids (34.4%) of all six species were positive for T. gondii and DNA was detected in 63 of 433 (14.6%) primary tissue samples collected from the tongue (28.6%), brain (18.6%), skeletal muscle (17.1%), ocular muscles (13.6%), eye (13.6%), heart (11.1%), diaphragm (5.4%) and vitreous humor (4.5%). Twelve primary samples positive for T. gondii were genotyped with molecular markers SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and apical CS3. Using the multilocus PCR-RFLP technique, sample Py#36m was fully genotyped as Type I with allele II in locus BTUB, and a new atypical Py#21M, both isolates from Puma yagouaroundi and never described in Brazil. Nine other samples had a partial characterization. Thirteen of the 90 felids were positive for Sarcocystis spp. (14.4%) and another 18 felids, representing 5 species, harbored S. felis-like organisms [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) and Lc (#82m, #76m)]. A single felid of L. pardalis was negative. Parasite DNA was detected in 11.8% (51/433) of the tissues examined: muscle skeletal (26.5%), tongue (23.2%), ocular muscles (13.6%), diaphragm (10.7 %), brain (2.3%), heart (1.6%) and eye (4.5%); none of the 44 samples of vitreous humor was positive. This is the first description of the detection and genetic characterization of T. gondii and S. felis-like in free-living Brazilians wild felids, demonstrating the presence of these agents in the sylvatic cycle, and the potential transmition to humans and other domestic and wild animals. The use of tissue samples from wild animals deposited in biological collections for epidemiological studies of diseases demonstrated to be of great utility.

Poucos estudos quantificam o risco relativo da saúde humana na transmissão spillover de doenças zoonóticas de populações de animais silvestres, estudos cruciais na compreensão da história natural das zoonoses. Coccídios, em particular os da família Sarcocystidae, são importantes agentes transmissíveis na interface homens - animais domésticos e silvestres. O diagnóstico da coccidiose é prejudicado pela limitada disponibilidade de amostras resultantes de populações animais de espécies em risco de extinção. O objetivo deste estudo foi detectar através da amplificação do locus ITS-1, protozoários das subfamílias Sarcocystinae e Toxoplasmatinae em amostras teciduais de Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo e L. pardalis, depositados em coleções biológicas do Rio Grande do Sul, Brasil. Um objetivo adicional foi a obtenção de informações que permitissem avaliar o papel epidemiológico dos protozoários no ciclo silvestre dos parasitas e seu possível impacto sobre as populações de animais silvestres e na saúde pública. Noventa pequenos felídeos neotropicais de vida livre, representando seis espécies, foram amostrados. Destes, 31 felídeos (34,4%), de todas as seis espécies, foram positivos para Toxoplasma gondii e DNA foi detectado em 63 das 433 (14,6%) amostras de tecidos primários coletados a partir de língua (28,6%), cérebro (18,6%), músculo esquelético (17,1%), musculatura ocular (13,6%), globo ocular (13,6%), coração (11,1%), diafragma (5,4%) e humor vítreo (4,5%). Doze amostras primárias positivas ao T. gondii foram genotipadas com os marcadores moleculares SAG1, SAG2, SAG3, BTUB, GRA6, c22- 8, c29-2, L358, PK1, Apico e CS3 e a técnica multilocus PCR-RFLP, a amostra Py#36m foi totalmente caracterizada como do tipo I com alelo II no BTUB e um novo genótipo atípico Py#21M, ambos isolados de Puma yagouaroundi e nunca descrito no Brasil. Nove outras amostras tiveram caracterização parcial. Treze dos 90 felídeos foram positivos para Sarcocystis spp. (14,4%) e outros 18 felídeos, representando cinco espécies albergaram S. felis-like [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) e Lc (#82m, #76m)]. Um único felino de L. pardalis foi negativo. DNA do parasita foi detectado em 11,8% dos tecidos examinados (51/433): musculatura esquelética (26,5%), língua (23,2%), musculatura ocular (13,6%), diafragma (10,7%), cérebro (2,3%), coração (1,6%) e globo ocular (4,5%), nenhuma das 44 amostras de humor vítreo foi positiva. Esta é a primeira detecção e caracterização genética de T. gondii e de S. felislike em felídeos silvestres brasileiros de vida livre, demonstrando a presença destes agentes no ciclo silvestre e, a potencial transmissibilidade ao homem e a outros animais domésticos e silvestres. O uso de amostras de tecidos de animais silvestres depositados em coleções biológicas para estudos epidemiológicos de doenças monstraram serem de grande utilidade. / Few studies have quantified the relative risk of human health from spillover of zoonotic diseases from populations of wild animals; these studies are crucial for understanding the natural history of zoonoses. Coccidia, particularly from the family Sarcocystidae, are important transmissible agents at the interface of man and domestic and wild animals. The diagnosis of Coccidiosis is hampered by the limited availability of samples resulting from protection of natural populations of the species at risk of extinction. The aim of this study was to detected, by amplification of ITS-1 locus, protozoa from the subfamilies Sarcocystinae and Toxoplasmatinae in tissue samples from Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo and L. pardalis, deposited in biological collections of the State of Rio Grande do Sul, Brazil. An additional aim was to obtain information that would enable assessment of the epidemiological role of the protozoa in the sylvatic cycle of the parasite, and its possible impact on wildlife populations and public health. Ninety free-living small wild felines, representing 6 species, were sampled. Of these, 31 felids (34.4%) of all six species were positive for T. gondii and DNA was detected in 63 of 433 (14.6%) primary tissue samples collected from the tongue (28.6%), brain (18.6%), skeletal muscle (17.1%), ocular muscles (13.6%), eye (13.6%), heart (11.1%), diaphragm (5.4%) and vitreous humor (4.5%). Twelve primary samples positive for T. gondii were genotyped with molecular markers SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and apical CS3. Using the multilocus PCR-RFLP technique, sample Py#36m was fully genotyped as Type I with allele II in locus BTUB, and a new atypical Py#21M, both isolates from Puma yagouaroundi and never described in Brazil. Nine other samples had a partial characterization. Thirteen of the 90 felids were positive for Sarcocystis spp. (14.4%) and another 18 felids, representing 5 species, harbored S. felis-like organisms [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) and Lc (#82m, #76m)]. A single felid of L. pardalis was negative. Parasite DNA was detected in 11.8% (51/433) of the tissues examined: muscle skeletal (26.5%), tongue (23.2%), ocular muscles (13.6%), diaphragm (10.7 %), brain (2.3%), heart (1.6%) and eye (4.5%); none of the 44 samples of vitreous humor was positive. This is the first description of the detection and genetic characterization of T. gondii and S. felis-like in free-living Brazilians wild felids, demonstrating the presence of these agents in the sylvatic cycle, and the potential transmition to humans and other domestic and wild animals. The use of tissue samples from wild animals deposited in biological collections for epidemiological studies of diseases demonstrated to be of great utility.

Poucos estudos quantificam o risco relativo da saúde humana na transmissão spillover de doenças zoonóticas de populações de animais silvestres, estudos cruciais na compreensão da história natural das zoonoses. Coccídios, em particular os da família Sarcocystidae, são importantes agentes transmissíveis na interface homens - animais domésticos e silvestres. O diagnóstico da coccidiose é prejudicado pela limitada disponibilidade de amostras resultantes de populações animais de espécies em risco de extinção. O objetivo deste estudo foi detectar através da amplificação do locus ITS-1, protozoários das subfamílias Sarcocystinae e Toxoplasmatinae em amostras teciduais de Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo e L. pardalis, depositados em coleções biológicas do Rio Grande do Sul, Brasil. Um objetivo adicional foi a obtenção de informações que permitissem avaliar o papel epidemiológico dos protozoários no ciclo silvestre dos parasitas e seu possível impacto sobre as populações de animais silvestres e na saúde pública. Noventa pequenos felídeos neotropicais de vida livre, representando seis espécies, foram amostrados. Destes, 31 felídeos (34,4%), de todas as seis espécies, foram positivos para Toxoplasma gondii e DNA foi detectado em 63 das 433 (14,6%) amostras de tecidos primários coletados a partir de língua (28,6%), cérebro (18,6%), músculo esquelético (17,1%), musculatura ocular (13,6%), globo ocular (13,6%), coração (11,1%), diafragma (5,4%) e humor vítreo (4,5%). Doze amostras primárias positivas ao T. gondii foram genotipadas com os marcadores moleculares SAG1, SAG2, SAG3, BTUB, GRA6, c22- 8, c29-2, L358, PK1, Apico e CS3 e a técnica multilocus PCR-RFLP, a amostra Py#36m foi totalmente caracterizada como do tipo I com alelo II no BTUB e um novo genótipo atípico Py#21M, ambos isolados de Puma yagouaroundi e nunca descrito no Brasil. Nove outras amostras tiveram caracterização parcial. Treze dos 90 felídeos foram positivos para Sarcocystis spp. (14,4%) e outros 18 felídeos, representando cinco espécies albergaram S. felis-like [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) e Lc (#82m, #76m)]. Um único felino de L. pardalis foi negativo. DNA do parasita foi detectado em 11,8% dos tecidos examinados (51/433): musculatura esquelética (26,5%), língua (23,2%), musculatura ocular (13,6%), diafragma (10,7%), cérebro (2,3%), coração (1,6%) e globo ocular (4,5%), nenhuma das 44 amostras de humor vítreo foi positiva. Esta é a primeira detecção e caracterização genética de T. gondii e de S. felislike em felídeos silvestres brasileiros de vida livre, demonstrando a presença destes agentes no ciclo silvestre e, a potencial transmissibilidade ao homem e a outros animais domésticos e silvestres. O uso de amostras de tecidos de animais silvestres depositados em coleções biológicas para estudos epidemiológicos de doenças monstraram serem de grande utilidade. / Few studies have quantified the relative risk of human health from spillover of zoonotic diseases from populations of wild animals; these studies are crucial for understanding the natural history of zoonoses. Coccidia, particularly from the family Sarcocystidae, are important transmissible agents at the interface of man and domestic and wild animals. The diagnosis of Coccidiosis is hampered by the limited availability of samples resulting from protection of natural populations of the species at risk of extinction. The aim of this study was to detected, by amplification of ITS-1 locus, protozoa from the subfamilies Sarcocystinae and Toxoplasmatinae in tissue samples from Puma yagouaroundi, Leopardus geoffroyi, L. tigrinus, L. wiedii, L. colocolo and L. pardalis, deposited in biological collections of the State of Rio Grande do Sul, Brazil. An additional aim was to obtain information that would enable assessment of the epidemiological role of the protozoa in the sylvatic cycle of the parasite, and its possible impact on wildlife populations and public health. Ninety free-living small wild felines, representing 6 species, were sampled. Of these, 31 felids (34.4%) of all six species were positive for T. gondii and DNA was detected in 63 of 433 (14.6%) primary tissue samples collected from the tongue (28.6%), brain (18.6%), skeletal muscle (17.1%), ocular muscles (13.6%), eye (13.6%), heart (11.1%), diaphragm (5.4%) and vitreous humor (4.5%). Twelve primary samples positive for T. gondii were genotyped with molecular markers SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and apical CS3. Using the multilocus PCR-RFLP technique, sample Py#36m was fully genotyped as Type I with allele II in locus BTUB, and a new atypical Py#21M, both isolates from Puma yagouaroundi and never described in Brazil. Nine other samples had a partial characterization. Thirteen of the 90 felids were positive for Sarcocystis spp. (14.4%) and another 18 felids, representing 5 species, harbored S. felis-like organisms [Py (#75m, #83m, #35m, #20li, #55li), Lg (#80m, #70m, #88m, #71li, #67mOi), Lt (#19m, #48m, #89m, #84m), Lw (#12, #73d) and Lc (#82m, #76m)]. A single felid of L. pardalis was negative. Parasite DNA was detected in 11.8% (51/433) of the tissues examined: muscle skeletal (26.5%), tongue (23.2%), ocular muscles (13.6%), diaphragm (10.7 %), brain (2.3%), heart (1.6%) and eye (4.5%); none of the 44 samples of vitreous humor was positive. This is the first description of the detection and genetic characterization of T. gondii and S. felis-like in free-living Brazilians wild felids, demonstrating the presence of these agents in the sylvatic cycle, and the potential transmition to humans and other domestic and wild animals. The use of tissue samples from wild animals deposited in biological collections for epidemiological studies of diseases demonstrated to be of great utility.

Equine protozoal myeloencephalitis (EPM), caused by the protozoan parasite Sarcocystis neurona, is one of the most important neurological diseases of horses in the Americas. While seroprevalence of S. neurona in horses is high, clinical manifestation of EPM occurs in less than 1% of infected horses. Factors governing the occurrence and severity of EPM are largely unknown, although horse immunity might play an important role in clinical outcome. We hypothesize that EPM occurs due to an aberrant immune response, which will be discernable in the equine IgG subisotypes a, b, and (T) that recognize S. neurona in infected diseased horses versus infected but clinically healthy horses. Based on previously-established serum antibody concentrations for IgG subisotypes in healthy horses, standard curves were generated and served to establish the concentration of antigen-specific IgG subisotypes in equine serum and CSF in infected diseased and infected normal horses. The subisotype concentrations and ratios between subisotypes were analyzed to assess whether neurological disease is associated with detectable differences in the antibody response elicited by infection. Results indicate a type I biased immune response in infected diseased horses, implicating the role of immunity in the development of EPM.

Sarcocystis neurona is a protozoan parasite that causes the serious neurologic disease equine protozoal myeloencephalitis (EPM). The life cycle of S. neurona progresses through multiple developmental stages that differ morphologically and molecularly. The S. neurona merozoite surface is covered by multiple related proteins, which are orthologous to the surface antigen (SAG) gene family of Toxoplasma gondii. The SAG surface antigens in T. gondii and another related parasite Neospora caninum are life cycle stage-specific and seem necessary for parasite transmission and persistence of infection. The present research was conducted to explore the gene family of SnSAGs in S. neurona. Specifically, the project identified new SnSAGs in the draft genome sequence of S. neurona and examined the stage-specific expression and potential function of these surface antigens. For the first part of the study, expression of the S. neurona merozoite surface antigens was evaluated in the sporozoite and bradyzoite stages. The studies revealed that SnSAG2, SnSAG3 and SnSAG4 are expressed by sporozoites, while SnSAG5 appeared to be downregulated in this life cycle stage. In S. neurona bradyzoites, SnSAG2, SnSAG3, SnSAG4 and SnSAG5 were either absent or expression was greatly reduced. For the second part of the study, the draft sequence of the S. neurona genome was searched for potential new SnSAGs. Multiple searches revealed sixteen potential new SnSAG genes, and bioinformatic analyses of the sequences revealed characteristics consistent with the SAG gene family. Two of the new SnSAGs, designated SnSAG7 and SnSAG8, have been characterized in detail. The studies showed that SnSAG7 is expressed by the merozoite stage, while SnSAG8 is expressed by the bradyzoite stage. The third part of the study assessed the role of SnSAGs in host cell attachment and/or invasion by S. neurona. Serum neutralization assays using polyclonal serum raised against SnSAG1, SnSAG2, SnSAG3, and SnSAG4 suggested that SnSAG1 and SnSAG4 play a role in host cell attachment and/or invasion; treatment with antibodies against SnSAG2 and SnSAG3 were inconclusive. The information acquired about the stage-specific expression of the SnSAGs, identification of new SnSAG paralogues, and their functional characterization will help to understand the importance of the SnSAG proteins for parasite survival and could lead to improved methods for EPM prevention and/or treatment.