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Whoriskey ST, Duignan PJ, McClain AM, Seguel M, Gulland FMD, Johnson SP, Field CL. Clinical signs, treatment, and outcome for California sea lions (Zalophus californianus) with Sarcocystis-associated polyphasic rhabdomyositis. J Am Vet Med Assoc 2021; 259:1196-1205. [PMID: 34727074 DOI: 10.2460/javma.20.06.0348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To describe clinical signs, treatment, and outcome for California sea lions (Zalophus californianus) with Sarcocystis-associated polyphasic rhabdomyositis. ANIMALS 38 free-ranging juvenile to adult California sea lions examined at a rehabilitation center in California between September 2015 and December 2017. PROCEDURES Medical records at The Marine Mammal Center were reviewed to identify sea lions in which sarcocystosis had been diagnosed. RESULTS Clinical signs were highly variable and associated with polyphasic rhabdomyositis attributed to Sarcocystis neurona infection. Generalized severe muscle wasting, respiratory compromise, and regurgitation secondary to megaesophagus were the most profound clinical findings. Respiratory compromise and megaesophagus were associated with a poor prognosis. Eight of the 38 sea lions were treated and released to the wild, and 2 subsequently restranded and were euthanized. Two additional animals received no targeted treatment and were released. The remaining 28 animals were either euthanized or died during treatment. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that unlike other marine mammals, which typically develop encephalitis, California sea lions with sarcocystosis often have polyphasic rhabdomyositis with highly variable clinical signs and that extensive diagnostic testing may be required to confirm the diagnosis. Treatment with an antiprotozoal drug in combination with corticosteroids may resolve clinical disease, but the prognosis is guarded.
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2
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Rosenthal BM. Zoonotic Sarcocystis. Res Vet Sci 2021; 136:151-157. [PMID: 33626441 DOI: 10.1016/j.rvsc.2021.02.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 01/25/2021] [Accepted: 02/04/2021] [Indexed: 10/22/2022]
Abstract
Apicomplexan species in the genus Sarcocystis form tissue cysts, in their intermediate hosts, similar to those established in chronic toxoplasmosis. More than 200 species are known, but just a few are known to threaten human health owing to infection in livestock species. Intestinal sarcocystosis occurs when people consume raw or undercooked beef contaminated with Sarcocystis hominis or S. heydorni or undercooked pork contaminated with S. suihominis. Those infections may cause mild enteritis, but most infections are thought to be asymptomatic. People also become dead-end (intermediate) hosts for non-human Sarcocystis spp. after accidentally ingesting sporocysts, leading to extraintestinal sarcocystosis. The clinical spectrum may range from asymptomatic muscle cysts to a severe, acute, eosinophilic myositis associated with systemic symptoms with peripheral eosinophilia. Most human cases have been described from Southeast Asia, but Sarcocystis parasites have a worldwide distribution, especially where livestock is raised, and human infections in other areas have been described but may be underrecognized.
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Affiliation(s)
- Benjamin M Rosenthal
- Animal Parasitic Disease Laboratory, United States Department of Agriculture- Agricultural Research Service, 10300, Baltimore Avenue, Beltsville, MD 20705, United States of America.
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Burgess TL, Tinker MT, Miller MA, Smith WA, Bodkin JL, Murray MJ, Nichol LM, Saarinen JA, Larson S, Tomoleoni JA, Conrad PA, Johnson CK. Spatial epidemiological patterns suggest mechanisms of land-sea transmission for Sarcocystis neurona in a coastal marine mammal. Sci Rep 2020; 10:3683. [PMID: 32111856 PMCID: PMC7048795 DOI: 10.1038/s41598-020-60254-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Accepted: 01/27/2020] [Indexed: 01/07/2023] Open
Abstract
Sarcocystis neurona was recognised as an important cause of mortality in southern sea otters (Enhydra lutris nereis) after an outbreak in April 2004 and has since been detected in many marine mammal species in the Northeast Pacific Ocean. Risk of S. neurona exposure in sea otters is associated with consumption of clams and soft-sediment prey and is temporally associated with runoff events. We examined the spatial distribution of S. neurona exposure risk based on serum antibody testing and assessed risk factors for exposure in animals from California, Washington, British Columbia and Alaska. Significant spatial clustering of seropositive animals was observed in California and Washington, compared with British Columbia and Alaska. Adult males were at greatest risk for exposure to S. neurona, and there were strong associations with terrestrial features (wetlands, cropland, high human housing-unit density). In California, habitats containing soft sediment exhibited greater risk than hard substrate or kelp beds. Consuming a diet rich in clams was also associated with increased exposure risk. These findings suggest a transmission pathway analogous to that described for Toxoplasma gondii, with infectious stages traveling in freshwater runoff and being concentrated in particular locations by marine habitat features, ocean physical processes, and invertebrate bioconcentration.
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Affiliation(s)
- Tristan L Burgess
- EpiCenter for Disease Dynamics, Karen C Drayer Wildlife Health Center, One Health Institute, University of California Davis, 1089 Veterinary Medicine Drive, Davis, CA, 95616, USA.,Acadia Wildlife Services, P.O. Box 56, South Freeport, ME, 04078, USA
| | - M Tim Tinker
- U.S. Geological Survey, Western Ecological Research Center, Santa Cruz Field Station, 115 McAllister Way, Santa Cruz, CA, 95060, USA.,Nhydra Ecological Consulting, 11 Parklea Dr Head of St, Margarets Bay, NS, B3Z2G6, Canada
| | - Melissa A Miller
- Marine Wildlife Veterinary Care and Research Center, California Department of Fish and Wildlife, 151 McAllister Way, Santa Cruz, CA, 95060, USA
| | - Woutrina A Smith
- Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, 1089 Veterinary Medicine Drive, Davis, CA, 95616, USA
| | - James L Bodkin
- U.S. Geological Survey, Alaska Science Center, 4201 University Dr., Anchorage, AK, 99503, USA
| | - Michael J Murray
- Monterey Bay Aquarium, 886 Cannery Row, Monterey, CA, 93940, USA
| | - Linda M Nichol
- Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, BC, V9T 6N7, Canada
| | - Justin A Saarinen
- New College of Florida 5800 Bay Shore Road, Sarasota, FL, 34243, USA
| | - Shawn Larson
- The Seattle Aquarium, 1483 Alaskan Way, Pier 59, Seattle, WA, 98101, USA
| | - Joseph A Tomoleoni
- U.S. Geological Survey, Western Ecological Research Center, Santa Cruz Field Station, 115 McAllister Way, Santa Cruz, CA, 95060, USA
| | - Patricia A Conrad
- Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California Davis, 1089 Veterinary Medicine Drive, Davis, CA, 95616, USA
| | - Christine K Johnson
- EpiCenter for Disease Dynamics, Karen C Drayer Wildlife Health Center, One Health Institute, University of California Davis, 1089 Veterinary Medicine Drive, Davis, CA, 95616, USA.
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Honda M, Sawaya M, Taira K, Yamazaki A, Kamata Y, Shimizu H, Kobayashi N, Sakata R, Asakura H, Sugita-Konishi Y. Effects of temperature, pH and curing on the viability of Sarcocystis, a Japanese sika deer (Cervus Nippon centralis) parasite, and the inactivation of their diarrheal toxin. J Vet Med Sci 2018; 80:1337-1344. [PMID: 29973481 PMCID: PMC6115274 DOI: 10.1292/jvms.18-0123] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Recently, the Sarcocystis parasite in horse and deer meat has been
reported to be a causative agent of acute food poisoning, inducing nausea, vomiting and
diarrhea. Compared with other causative agents, such as bacteria, viruses and other
parasites, in deer meat, the Sarcocystis species parasite, including its
stability under various conditions, is poorly understood. In this study, we assessed the
viability of Sarcocystis spp. and the activity of their diarrhea toxin (a
15-kDa protein) in deer meat under conditions of freezing, cold storage, pH change and
curing. In addition, the heat tolerance was assayed using purified bradyzoites. The
results showed that the species lost viability by freezing at −20, −30 and −80°C for <1
hr, heating at 70°C for 1 min, alkaline treatment (pH 10.0) for 4 days and addition of
salt at 2.0% for <1 day. Immunoblot assays showed that the diarrhea toxin disappeared
together with the loss of viability. However, the parasite survived cooling at 0 and 4°C
and acidification (pH 3.0 and 5.0) for more than 7 days with the diarrhea toxin intact.
These results provide useful information for developing practical applications for the
prevention of food poisoning induced by diarrheal toxin of Sarcocystis
spp. in deer meat during cooking and preservation.
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Affiliation(s)
- Mioko Honda
- Department of Animal Nursing Science, Yamazaki University of Animal Health Technology, 4-7-2 Minami Osawa, Hachioji, Tokyo 192-0364, Japan
| | - Mamoru Sawaya
- Department of Food and Life Science, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
| | - Kensuke Taira
- Faculty of Veterinary Medicine, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
| | - Akiko Yamazaki
- Department of Veterinary Sciences, University of Iwate, 3-18-8, Ueda, Morioka, Iwate 020-8550, Japan
| | - Yoichi Kamata
- Department of Food Design, Faculty of Nutrition, Koshien University, 10-1 Momijigaoka, Takarazuka, Hyogo 665-0006, Japan
| | - Hideki Shimizu
- Kyonan Public Health Department of Yamanashi Prefecture, 771-2 Kajikazawa, Fujikawa, Minamikoma, Yamanashi 400-0601, Japan
| | - Naoki Kobayashi
- Department of Food and Life Science, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
| | - Ryoichi Sakata
- Faculty of Veterinary Medicine, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
| | - Hiroshi Asakura
- Division of Biomedical Food Research, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Yoshiko Sugita-Konishi
- Department of Food and Life Science, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
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Verma SK, Lindsay DS, Grigg ME, Dubey JP. Isolation, Culture and Cryopreservation of Sarcocystis species. ACTA ACUST UNITED AC 2017; 45:20D.1.1-20D.1.27. [PMID: 28510359 DOI: 10.1002/cpmc.32] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
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.
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Affiliation(s)
- S K Verma
- United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Parasitic Diseases Laboratory, Beltsville, Maryland
| | - D S Lindsay
- Department of Biomedical Science and Pathology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia
| | - M E Grigg
- Molecular Parasitology Section, Laboratory of Parasitic Diseases, National Institutes of Health, National Institutes of Allergy, and Infectious Diseases, Bethesda, Maryland
| | - J P Dubey
- United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Parasitic Diseases Laboratory, Beltsville, Maryland
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California mussels (Mytilus californianus) as sentinels for marine contamination with Sarcocystis neurona. Parasitology 2016; 143:762-9. [PMID: 27003262 DOI: 10.1017/s0031182016000354] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Sarcocystis neurona is a terrestrial parasite that can cause fatal encephalitis in the endangered Southern sea otter (Enhydra lutris nereis). To date, neither risk factors associated with marine contamination nor the route of S. neurona infection to marine mammals has been described. This study evaluated coastal S. neurona contamination using California mussels (Mytilus californianus) as sentinels for pathogen pollution. A field investigation was designed to test the hypotheses that (1) mussels can serve as sentinels for S. neurona contamination, and (2) S. neurona contamination in mussels would be highest during the rainy season and in mussels collected near freshwater. Initial validation of molecular assays through sporocyst spiking experiments revealed the ITS-1500 assay to be most sensitive for detection of S. neurona, consistently yielding parasite amplification at concentrations ⩾5 sporocysts/1 mL mussel haemolymph. Assays were then applied on 959 wild-caught mussels, with detection of S. neurona confirmed using sequence analysis in three mussels. Validated molecular assays for S. neurona detection in mussels provide a novel toolset for investigating marine contamination with this parasite, while confirmation of S. neurona in wild mussels suggests that uptake by invertebrates may serve as a route of transmission to susceptible marine animals.
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Abstract
Recurrent outbreaks of muscular sarcocystosis among tourists visiting islands in Malaysia have focused international attention on sarcocystosis, a disease once considered rare in humans. Sarcocystis species require two hosts, definitive and intermediate, to complete their life cycle. Humans can serve as definitive hosts, with intestinal sarcocystosis for two species acquired from eating undercooked meat: Sarcocystis hominis, from beef, and Sarcocystis suihominis, from pork. Symptoms such as nausea, stomachache, and diarrhea vary widely depending on the number of cysts ingested but appear more severe with pork than with beef. Humans serve as intermediate hosts for Sarcocystis nesbitti, a species with a reptilian definitive host, and possibly other unidentified species, acquired by ingesting sporocysts from feces-contaminated food or water and the environment; infections have an early phase of development in vascular endothelium, with illness that is difficult to diagnose; clinical signs include fever, headache, and myalgia. Subsequent development of intramuscular cysts is characterized by myositis. Presumptive diagnosis based on travel history to tropical regions, elevated serum enzyme levels, and eosinophilia is confirmed by finding sarcocysts in muscle biopsy specimens. There is no vaccine or confirmed effective antiparasitic drug for muscular sarcocystosis, but anti-inflammatory drugs may reduce symptoms. Prevention strategies are also discussed.
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Dubey JP, Howe DK, Furr M, Saville WJ, Marsh AE, Reed SM, Grigg ME. An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM). Vet Parasitol 2015; 209:1-42. [PMID: 25737052 DOI: 10.1016/j.vetpar.2015.01.026] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 01/27/2015] [Accepted: 01/29/2015] [Indexed: 01/27/2023]
Abstract
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.
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Affiliation(s)
- J P Dubey
- United States Department of Agriculture, Agricultural Research Service, Animal Parasitic Diseases Laboratory, Beltsville Agricultural Research Center, Building 1001, Beltsville, MD 20705-2350, USA.
| | - D K Howe
- M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546-0099, USA
| | - M Furr
- Marion du Pont Scott Equine Medical Center, Virginia Maryland Regional College of Veterinary Medicine, 17690 Old Waterford Road, Leesburg, VA 20176, USA
| | - W J Saville
- Department of Veterinary Preventive Medicine, The Ohio State University, 1920 Coffey Road, Columbus, OH 43210, USA
| | - A E Marsh
- Department of Veterinary Preventive Medicine, The Ohio State University, 1920 Coffey Road, Columbus, OH 43210, USA
| | - S M Reed
- Rood and Riddle Equine Hospital, Lexington, KY 40511, USA
| | - M E Grigg
- Molecular Parasitology Section, Laboratory of Parasitic Diseases, National Institutes of Health, National Institutes of Allergy, and Infectious Diseases, 4 Center Drive, Room B1-06, Bethesda, MD 20892, USA
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9
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Alves Neto AF, Bandini LA, Nishi SM, Soares RM, Driemeier D, Antoniassi NAB, Schares G, Gennari SM. Viability of sporulated oocysts of Neospora caninum after exposure to different physical and chemical treatments. J Parasitol 2010; 97:135-9. [PMID: 21348620 DOI: 10.1645/ge-2571.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The aim of the present study was to evaluate the viability of Neospora caninum sporulated oocysts after various chemical and physical treatments. Bioassays in gerbils and molecular techniques (PCR-RFLP) were used for identification of the oocysts shed by experimentally infected dogs. Sporulated oocysts were purified and divided into 11 treatment groups as follows: absolute ethanol for 1 hr; 20 C for 6 hr; 4 C for 6 hr; 60 C for 1 min; 100 C for 1 min; 10% formaldehyde for 1 hr; 10% ammonia for 1 hr; 2% iodine for 1 hr; 10% sodium hypochlorite for 1 hr; 70% ethanol for 1 hr; and one group was left untreated and kept as a positive control. All chemical treatments were performed at room temperature (37 C). A total of 33 gerbils, or 3 gerbils per treatment, were used for bioassays. After treatment, the oocysts were divided into aliquots of 1,000 oocysts and orally administered to gerbils. After 63 days, the gerbils were anesthetized and killed with 0.2 ml of T61; blood and tissue samples were collected for serological (IFAT and western blotting), molecular (real-time PCR), histopathology, and immunohistochemical tests. Treatments were considered effective only if all 5 detection techniques tested negative. High temperatures at 100 C for 1 min and 10% sodium hypochlorite for 1 hr were the only treatments that met this condition, effectively inactivating all oocysts.
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Affiliation(s)
- Aldo F Alves Neto
- Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, Av Prof Orlando M de Paiva, 87 Cidade Universitária, CEP 05508-270 São Paulo, Brazil
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10
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Molecular characterization of Sarcocystis neurona strains from opossums (Didelphis virginiana) and intermediate hosts from Central California. Vet Parasitol 2010; 170:20-9. [PMID: 20226596 DOI: 10.1016/j.vetpar.2009.12.045] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 12/15/2009] [Accepted: 12/15/2009] [Indexed: 11/22/2022]
Abstract
Sarcocystis neurona is a significant cause of neurological disease in horses and other animals, including the threatened Southern sea otter (Enhydra lutris nereis). Opossums (Didelphis virginiana), the only known definitive hosts for S. neurona in North America, are an introduced species in California. S. neurona DNA isolated from sporocysts and/or infected tissues of 10 opossums, 6 horses, 1 cat, 23 Southern sea otters, and 1 harbor porpoise (Phocoena phocoena) with natural infections was analyzed based on 15 genetic markers, including the first internal transcribed spacer (ITS-1) region; the 25/396 marker; S. neurona surface antigen genes (snSAGs) 2, 3, and 4; and 10 different microsatellites. Based on phylogenetic analysis, most of the S. neurona strains segregated into three genetically distinct groups. Additionally, fifteen S. neurona samples from opossums and several intermediate hosts, including sea otters and horses, were found to be genetically identical across all 15 genetic markers, indicating that fatal encephalitis in Southern sea otters and equine protozoal myeloencephalitis (EPM) in horses is strongly linked to S. neurona sporocysts shed by opossums.
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Barham M, Stützer H, Karanis P, Latif BM, Neiss WF. Seasonal variation in Sarcocystis species infections in goats in northern Iraq. Parasitology 2004; 130:151-6. [PMID: 15727064 DOI: 10.1017/s0031182004006134] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We investigated the prevalence of sarcocystosis in 826 goats slaughtered in the winter season from November to April in northern Iraq. The prevalence of macrocysts was on average 34%, with only 20% infected animals in November, but 46% in February. The infection rate in 1-, 3- and 6-year-old goats was 4%, 48%, and 83%, respectively. The highest specificity of infection was in the oesophagus (99%) and the lowest in the diaphragm (3%). Grossly, we identified 2 forms of macroscopic sarcocysts, fat and thin, with different morphological characteristics. The prevalence of microcysts was 97% and no effects of age, sex and seasonal variations were observed. Development of microcysts in the small intestine of dogs and cats has also been investigated. The pre-patent period in experimentally infected dogs was 12–14 days and the patent period lasted 64–66 days. A dog shed about 155 million sporocysts, but no sporocysts were shed by cats that had been fed the same infected tissues, thus identifying the microcysts as Sarcocystis capracanis.
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Affiliation(s)
- M Barham
- Institut I für Anatomie, Universität zu Köln, D-50924 Köln, Germany
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12
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Elsheikha HM, Mansfield LS. Assessment of Sarcocystis neurona Sporocyst Viability and Differentiation Between Viable and Nonviable Sporocysts Using Propidium Iodide Stain. J Parasitol 2004; 90:872-5. [PMID: 15357088 DOI: 10.1645/ge-262r] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Sarcocystis neurona has become recognized as the major causative agent of equine protozoal myeloencephalitis (EPM) in the Americas. At least 3 pathogenic species of Sarcocystis, including S. neurona, can be isolated from opossums. Methods are needed to ascertain whether these isolates are viable and capable of causing infections. In this study, the nuclear stain propidium iodide (PI) was used to differentiate between live (viable) and heat-killed (nonviable) S. neurona sporocysts. PI was excluded by live sporocysts but penetrated compromised sporocyst membrane and stained sporozoite nuclei of dead sporocysts. After live and dead sporocysts were mixed at various ratios, the number of unstained sporocysts detected after the staining procedure correlated significantly (r2 = 0.9978) with the expected numbers of live sporocysts. Sporocyst mixtures were also assayed for in vitro excystation and development in tissue cultures. The correlation between the percentage of plaques formed in tissue cultures and the percentage of expected infectious (live) sporocysts in each mixture was r2 = 0.6712. By analysis of variance, no statistically significant difference was measured between the percentage of viable sporocysts and the percentage of infectious sporocysts (P = 0.3902) in each mixture. In addition, there was evidence of a relation between PI impermeability of sporocysts and animal infectivity. These results suggest that the PI dye-exclusion technique can be a useful tool in identifying viability and potential infectivity of S. neurona sporocysts and in differentiating between viable and nonviable sporocysts.
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Affiliation(s)
- Hany M Elsheikha
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824, USA.
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