Browsing by Author "Mitchell, S. M."

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    Cystoisospora canis Nemeseri, 1959 (Syn. Isospora canis), infections in dogs: Clinical signs, pathogenesis, and reproducible clinical disease in beagle dogs fed oocysts
    Mitchell, S. M.; Zajac, Anne M.; Charles, S.; Duncan, R. B.; Lindsay, David S. (American Society of Parasitology, 2007-04)
    Canine intestinal coccidiosis is a cause of diarrhea in young dogs and dogs that are immunocompromised. Reports in the literature indicate that experimental reproduction of clinical coccidiosis with Cystoisospora canis (syn. Isospora canis) is difficult, and few studies have been done with C canis. Experimental oral infections were attempted in 22, 6- to 8-wk-old female beagles with 5 x 10(4) (n = 2) or 1 x 10(5) (n = 20) sporulated C. canis oocysts. Diarrhea was observed in all inoculated dogs. Diarrhea began 2-3 days before oocyst excretion. Five of the 22 dogs were given an anticoccidial (sulfadimethoxine) because of their clinical signs. The mean prepatent period was 9.8 days (range, 9-11 days, n = 22 dogs), and the patent period was 8.9 days (range, 7-18 days, n = 20 dogs). Two dogs exhibiting clinical coccidiosis were examined at necropsy 10 days after infection. Developmental stages of C canis were present in cells in the lamina propria throughout the entire small intestine in both dogs. Microscopic lesions observed in both of these dogs were villous atrophy, dilation of lacteals, and hyperplasia of lymph nodes in Peyer's patches. Results of bacterial and viral examinations of these 2 dogs were negative, indicating that intestinal coccidiosis was the cause of the diarrhea. Our study indicates that C. canis can be a primary cause of diarrhea in young dogs.
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    Development and ultrastructure of cystoisospora canis nemeseri, 1959 (syn. isospora canis) monozoic cysts in two noncanine cell lines
    Mitchell, S. M.; Zajac, Anne M.; Lindsay, David S. (American Society of Parasitology, 2009-08)
    Cystoisospora canis is a coccidial parasite of the intestinal tract that can cause severe disease in dogs. Clinical Signs include watery diarrhea, vomiting, fever, and weight loss. Extraintestinal stages of Cystoisospora spp. have been demonstrated in the mesenteric lymph nodes of paratenic hosts. information on the biology of extraintestinal stages of canine Cystoisospora species is limited. The Current study examined the development of C canis in 2 noncanine cell lines and the ultrastructure of the monozoic cysts that formed. Monolayers of bovine turbinate cells and African green monkey kidney cells were grown on coverslips and inoculated with excysted C canis sporozoites. Coverslips were collected oil various days and fixed and stained for light microscopy (LM) or transmission electron microscopy (TEM). A single, centrally located, slightly crescent-shaped sporozoite Surrounded by a thick cyst wall within a parasitophorous vacuole was observed with the use of LM and TEM. No division and no multinucleated stages were observed with either LM or TEM. With TEM, typical organelles of sporozoites were observed, such as rhoptries, dense granules, a crystalloid body, polysaccharide granules, and a conoid. The structure and ultrastructure of C. canis monozoic cysts produced in vitro are similar to extraintestinal cysts of other Cystoisospora species in experimentally infected animals and those of Cystoisospora belli observed in immunocompromised humans. This is the first Study that fully demonstrates in vitro the development of what structurally resemble extraintestinal cysts or a Cystoisospora spp.
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    Efficacy of ponazuril in vitro and in preventing and treating Toxoplasma gondii infections in mice
    Mitchell, S. M.; Zajac, Anne M.; Davis, W. L.; Lindsay, David S. (American Society of Parasitology, 2004-06)
    Toxoplasma gondii is an important apicomplexan parasite of humans and other warm-blooded animals. Ponazuril is a triazine anticoccidial recently approved for use in horses in the United States. We determined that ponazuril significantly inhibited T gondii tachyzoite production (P < 0.05) at 5.0, 1.0, or 0.1 mug/ml in African green monkey kidney cells. We used outbred female CD-1 mice to determine the efficacy of ponazuril in preventing and treating acute toxoplasmosis. Each mouse was subcutaneously infected with 1,000 tachyzoites of the RH strain of T. gondii. Mice were weighed daily, and ponazuril was administered orally in a suspension. Mice given 10 or 20 mg/kg body weight ponazuril I day before infection and then daily for 10 days were completely protected against acute toxoplasmosis. Relapse did not occur after prophylactic treatments were stopped. Toxoplasma gondii DNA could not be detected in the brains of these mice using polymerase chain reaction (PCR). One hundred percent of mice treated with 10 or 20 mg/kg ponazuril at 3 days after infection and then daily for 10 days were protected from fatal toxoplasmosis. Sixty percent of mice treated with 10 mg/kg ponazuril at 6 days after infection and 100% of mice treated with 20 mg/kg or 50 mg ponazuril 6 days after infection and then daily for 10 days were protected from fatal toxoplasmosis. Relapse did not occur after treatments were stopped. Toxoplasma gondii DNA was detected in the brains of some, but not all, of these mice using PCR. The results demonstrate that ponazuril is effective in preventing and treating toxoplasmosis in mice. It should be further investigated as a safe and effective treatment for this disease in animals.
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    Evaluation of the mood-stabilizing agent valproic acid as a preventative for toxoplasmosis in mice and activity against tissue cysts in mice
    Goodwin, David G.; Strobl, J. S.; Mitchell, S. M.; Zajac, Anne M.; Lindsay, David S. (American Society of Parasitology, 2008-04)
    Toxoplasma gondii is a common intracellular protozoan infection of humans worldwide. Severe disease can occur in immunocompromised individuals and the in the fetuses of nonimmune pregnant women. Chronic infection is associated with vision and hearing problems, and functional mental alterations, including schizophrenia. The mood-stabilizing agent valproic acid has been shown to inhibit the development of T. gondii in vitro at dosages that are normally achieved in the serum and cerebral spinal fluid of human patients and to have positive effects on the behavior of rats chronically infected with T. gondii. The present study was done to examine the in vivo activity of valproic acid against acute toxoplasmosis in mice. Two studies were done with valproic acid given in the drinking water at concentrations of 1.5 mg/ml (Experiment 1) or 3.0 mg/ml (Experiment 2). In a third experiment (Experiment 3), valproic acid was injected intraperitoneally (i.p.) at doses of 200 or 300 mg/kg every 12 hr. Valproic acid was not effective in preventing acute toxoplasmosis. All mice treated with valproic acid died or were killed and did not (P > 0.05) live significantly longer than the controls. Tachyzoites were demonstrated in the tissues of infected valproic-acid-treated mice. A fourth study was done to determine if valproic acid has activity against T. gondii tissue cysts in chronically infected mice. Mice were chronically infected with the ME-49 strain of T. gondii for 8 wk and then treated orally with valproic acid at approximately 6.6 mg/ml (800 mg/kg/day) in the drinking water for 10 wk (amount was varied due to increasing mouse weights). No significant differences (P > 0.05) were present in tissue cyst numbers in valproic-acid-treated T. gondii chronically infected mice and in mice chronically infected with T. gondii but not given valproic acid. Our results indicate that valproic acid, although effective in vitro against T. gondii tachyzoites, is not effective as a preventative in mice inoculated with T. gondii tachyzoites. Additionally, no activity against tissue cysts was observed in chronically T. gondii-infected valproic-acid-treated mice.
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    Inhibition of toxoplasma gondii and plasmodium falciparum infections in vitro by nsc3852, a redox active anti proliferative and tumor cell differentiation agent
    Strobl, J. S.; Seibert, C. W.; Li, Y. B.; Nagarkatti, R.; Mitchell, S. M.; Rosypal, A. C.; Rathore, D.; Lindsay, David S. (American Society of Parasitology, 2009-02)
    We searched the National Cancer Institute (NCI) compound library for structures related to the antitumor quinoline NSC3852 (5-nitroso-8-quinolinol) and used a computer algorithm to predict the antiprotozoan activity for each of 13 structures. Half of these compounds inhibited Toroplastna gondii tachyzoite propagation in human fibroblasts at <= 1 mu M. The active compounds comprise a series of low-molecular-weight quinolines bearing nitrogen substituents in the ring-5 position. NSC3852 (EC(50) 80 nM) and NSC74949 (EC(50) 646 nM) were the most potent. NSC3852 also inhibited Plasmodium falciparum growth in human red blood cells (EC(50) 1.3 mu M). To investigate the mechanism for NSC3852's anti-T. gondii activity, we used chemiluminescence assays to detect reactive oxygen species (ROS) formation in freshly isolated tachyzoites and in infected host cells; the absence of ROS generation by NSC3852 in these assays indicated NSC3852 does not redox cycle in T. gondii. Inhibitors of enzyme sources of free radicals such as superoxide anion, nitric oxide (NO), and their reaction product peroxynitrite did not interfere with the anti-T. gondii activity of NSC3852. However, inhibition of T. gondii tachyzoite propagation by NSC3852 involved redox reactions because tachyzoites were protected from NSC3852 by inclusion of the cell permeant superoxide dismutase mimetic, MnTMPyP or N-acetylcysteine in the culture medium. We conclude that the Prediction of Activity Spectra for Substances (PASS) computer program is useful in finding new compounds that inhibit T. gondii tachyzoites in vitro and that NSC3852 is a potent T. gondii inhibitor that: acts by indirect generation of oxidative stress in T. gondii.
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    Prevalence of agglutinating antibodies to Sarcocystis neurona in skunks (Mephitis mephitis), raccoons (Procyon lotor), and opossums (Didelphis virginiana) from Connecticut
    Mitchell, S. M.; Richardson, D. J.; Cheadle, M. A.; Zajac, Anne M.; Lindsay, David S. (American Society of Parasitology, 2002-10)
    Equine protozoal myeloencephalitis is the most important protozoan disc a 6 of horses in North America and is usually caused by Sarcocystis neuronal Natural cases of encephalitis caused by S. neurona have been reported in skunks (Mephitis mephitis) and raccoons (Procyon lotor). Opossums (Didelphis spp.) are the only known definitive host. Sera from 24 striped skunks, 12 raccoons, and 7 opossums (D. virginiana) from Connecticut were., examined for agglutinating antibodies to S. neurona using the S. neurona agglutination test (SAT) employing formalin-fixed merozoites as antigen. The SAT was validated for skunk sera using pre- and postinfection serum samples from 2 experimentally infected skunks. Of the 24 (46%) skunks 11 were positive, and all 12 raccoons were positive for S. neurona antibodies. None of the 7 opossums was positive for antibodies to S. neurona. These results suggest that exposure to sporocysts of S. neurona by intermediate hosts is high in Connecticut. The absence of antibodies in opossums collected from the same areas is most likely because of the absence of systemic infection in the definitive host.
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    Prevalence of agglutinating antibodies to Toxoplasma gondii in adult and fetal mule deer (Odocoileus hemionus) from Nebraska
    Lindsay, David S.; McKown, R. D.; DiCristina, J. A.; Jordan, C. N.; Mitchell, S. M.; Oates, D. W.; Sterner, M. C. (American Society of Parasitology, 2005-12)
    Toxoplasma gondii is an apicomplexan parasite of mammals and birds. Herbivores acquire postnatal infection by ingesting oocysts from contaminated food or water. Toxoplasma gondii infection is common in white-tailed deer, Odocoileus virginianus, but little is known about the prevalence of infection in mule deer, O. hemionus. We examined sera from 89 mule deer from Nebraska for agglutinating antibodies to T. gondii using the modified direct agglutination test (MAT) with formalin-fixed tachyzoites as antigen. Thirty-one (35%) of the samples were positive at dilutions of >= 1:25. Samples were examined from 29 fetuses from these mule deer and none were positive in the MAT. Sera from 14 white-tailed deer from Nebraska were also examined and 6 (43%) were positive for T. gondii. Samples were examined from 5 fetuses from these white-tailed deer and none was positive in the MAT. Our results in both deer species from Nebraska are similar to studies conducted in white-tailed deer from other regions of the United States. Our findings indicate that mule deer are frequently infected with T. gondii and that mule-deer meat may be a source of human infection.
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    Prevalence of agglutinating antibodies to Toxoplasma gondii in striped skunks (Mephitis mephitis), opossums (Didelphis virginiana), and raccoons (Procyon lotor) from Connecticut
    Mitchell, S. M.; Richardson, D. J.; Lindsay, David S. (American Society of Parasitology, 2006-06)
    The prevalence of agglutinating antibodies to Toxoplasma gondii was examined in striped skunks (Mephitis mephitis), opossums (Didelphis virginiana), and raccoons (Procyon lotor) from 8 cities in Connecticut. Ten (42%) of the 24 striped skunks, 2 of 7 (29%) opossums, and 12 of 12 (100%) raccoons were positive at dilutions of 1:50 or greater. These results suggest that T. gondii is prevalent in the environment, or prey items, or both, of these omnivores in Connecticut.
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    Sarcocystis neurona (Protozoa : Apicomplexa): Description of oocysts, sporocysts, sporozoites, excystation, and early development
    Lindsay, David S.; Mitchell, S. M.; Vianna, M. C. B.; Dubey, Jitender P. (American Society of Parasitology, 2004-06)
    Equine protozoal myeloencephalitis is a major cause of neurological disease in horses from the Americas. Horses are considered accidental intermediate hosts. The structure of sporocysts of the causative agent, Sarcocystis neurona, has never been described. Sporocysts of S. neurona were obtained from the intestines of a laboratory-raised opossum fed skeletal muscles from a raccoon that had been fed sporocysts. Sporocysts were 11.3 by 8.2 mum and contained 4 sporozoites. The appearance of the sporocyst residuum was variable. The residuum of some sporocysts was composed of many dispersed granules, whereas some had granules mixed with larger globules. Excystation was by collapse of the sporocyst along plates. The sporocysts wall was composed of 3 layers: a thin electron-dense outer layer, a thin electron-lucent middle layer, and a thick electron-dense inner layer. The sporocyst wall was thickened at the junctions of the plates. Sporozoites were weakly motile and contained a centrally or posteriorly located nucleus. No retractile or crystalloid body was present, but lipidlike globules about I mum in diameter were usually present in the conoidal end of sporozoites. Sporozoites contained 2-4 electron-dense rhoptries and other organelles typical of coccidian zoites. Sporozoites entered host cells in culture and underwent schizogony within 3 days.
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    Survival of Toxoplasma gondii oocysts Eastern oysters (Crassostrea virginica)
    Lindsay, David S.; Collins, Marina V.; Mitchell, S. M.; Wetch, C. N.; Rosypal, A. C.; Flick, George J. Jr.; Zajac, Anne M.; Lindquist, A.; Dubey, Jitender P. (American Society of Parasitology, 2004-10)
    Toxoplasma gondii has recently been recognized to be widely prevalent in the marine environment. It has previously been determined that Eastern oysters (Crassostrea virginica) can remove sporulated T. gondii oocysts from seawater and that oocysts retain their infectivity for mice. This study examined the long-term survival of T gondii oocysts in oysters and examined how efficient oysters were at removing oocysts from seawater. Oysters in 76-L aquaria (15 oysters per aquarium) were exposed to 1 x 10(6) oocysts for 24 hr and examined at intervals up to 85 days postexposure (PE). Ninety percent (9 of 10) of these oysters were positive on day 1 PE using mouse bioassay. Tissue cysts were observed in I of 2 mice fed tissue from oysters exposed 21 days previously. Toxoplasma gondii antibodies were found in 2 of 3 mice fed oysters that had been exposed 85 days previously. In another study, groups of 10 oysters in 76-L aquaria were exposed to 1 x 10(5), 5 x 10(4), or 1 x 10(4) sporulated T. gondii oocysts for 24 hr and then processed for bioassay in mice. All oysters exposed to 1 x 10(5) oocysts were infected, and 60% of oysters exposed to 5 x 10(4) oocysts were positive when fed to mice. The studies with exposure to 1 x 10(4) oocysts were repeated twice, and 10 and 25% of oysters were positive when fed to mice. These studies indicate that T. gondii can survive for several months in oysters and that oysters can readily remove T. gondii oocysts from seawater. Infected filter feeders may serve as a source of T gondii for marine mammals and possibly humans.