Pathogenesis of acute toxoplasmosis in specific-pathogen-free cats

Systemic toxoplasmosis was produced in specific-pathogen-free cats by intravenous inoculation with Toxoplasma gondii tachyzoites. Infectious organisms were recovered from all tissues studied, but the number of organisms recovered from liver, lungs and spleen was 10-fold to 10,000-fold higher than from heart and brain. The occurrence and severity of Toxoplasma-induced lesions correlated with the number of infectious organisms recovered from the various tissues. In nonlymphoid tissues, the Toxoplasma-associated lesions consisted of multifocal necrosis, usually with demonstrable organisms. Lesions in the spleen and mesenteric lymph nodes consisted of reticuloendothelial and lymphoid hyperplasia, with few demonstrable organisms. Pneumonitis was severe and sometimes fatal in the early stages of systemic toxoplasmosis. Light- and electron-microscopic studies showed that the earliest lung lesions were randomly distributed infiltrates of neutrophils, eosinophils, and mononuclear cells into alveolar walls. Later lesions were diffuse alveolar necrosis, pneumocytic hyperplasia, and extensive fibrinocellular exudates in alveoli. Tachyzoites were present in cytoplasmic vacuoles of fibroblasts, macrophages, type I and II pneumocytes, bronchiolar epithelial cells, bronchiolar smooth muscle cells, endothelial cells, neutrophils, and eosinophils, and circulating monocytes. Replication of organisms was found in all parasitized cell types except neutrophils and eosinophils.     

Abortion and death in goats inoculated with Sarcocystis sporocysts from coyote feces

Ten 75- to 105-day-pregnant does each were inoculated orally within 1 million (2 does), 10,000 (4 does), or 1,000 (4 does) sporocysts of Sarcocystis from coyote feces. Two does not inoculated with sporocysts served as controls. The 2 does inoculated with 1 million sporocysts died from acute sarcocystosis 21 and 22 days after inoculation (DAI), and each had 2 dead fetuses. The 4 does inoculated with 10,000 sporocysts were ill 19 to 33 DAI but survived; 1 aborted at 33 DAI, 1 had a live kid that died within 2 hours of birth 31 DAI, 1 aborted 2 dead fetuses 23 DAI, and 1 had a normal kid 56 DAI. The 4 does inoculated with 1,000 sporocysts and the 2 control does remained clinically normal and had normal kids. Does and their offspring were killed within 24 hours of parturition, and their tissues were examined histologically and microbiologically. Meronts of Sarcocystis were found in the maternal placenta of does inoculated with 1 million sporocysts. Sarcocystis was not found in the placenta, fetuses, or tissues of kids from does inoculated with 10,000 or 1,000 sporocysts, or from control does. Other abortifacient agents were not found in the placenta, fetuses, or kids from any does.     

Direct development of enteroepithelial stages of Toxoplasma in the intestines of cats fed cysts

Four newborn (1- to 2-day-old) and two weaned (55- to 67-day-old) Toxoplasma-free cats were killed between 23 and 120 hours after ingestion of Toxoplasma gondii cysts from the brains of infected mice, and the cats' tissues were examined for the development of Toxoplasma. Intraepithelial Toxoplasma types (B, C, and D) were found in sections of small intestine. Homogenates of mesenteric lymph nodes, spleen, and liver of each cat were injected intraperitoneally into each of six weaned Toxoplasma-free cats to test the hypothesis of extraintestinal pregametogonic stages, as proposed by Overdulve (1978). Of the six cats injected with infected feline tissues, none shed oocysts within 17 days. Thus, the hypothesis of extraintestinal pregametogonic stages was not confirmed.     

Prevalence of Toxoplasma infection in cattle slaughtered at an Ohio abattoir.

Specimens of heart, diaphragm and, in 159 instances, esophagus were taken from 352 cattle slaughtered in an Ohio abattoir. The total weight of the material was 32 kg, and this was fed to 12 specific-pathogen-free cats to test for Toxoplasma infectivity. None of the 12 cats acquired Toxoplasma infection, as evidenced by their failure to excrete oocysts or to develop antibodies, and by failure to isolate Toxoplasma from their tissues by inoculation into mice. In further tests, a 650-g sample of beef from 77 of the 352 cattle was digested in 1% trypsin, then inoculated intraperitoneally into 40 mice. Toxoplasma was not isolated from the mice. Serums from 186 of the 352 cattle were inactivated at 60 C for 1 hour, then examined by the Sabin-Feldman (dye) test for antibodies to Toxoplasma. None had titers of more than 1:8. Of the 186 serums, 77 were also examined for antibodies in the indirect hemagglutination test. One had a titer of 1:64, which was considered nonspecific. Thus, evidence for Toxoplasma infection was not found in 352 cattle.     

A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious neurological disease of horses in the Americas. The protozoan most commonly associated with EPM is Sarcocystis neurona. The complete life cycle of S. neurona is unknown, including its natural intermediate host that harbors its sarcocyst. Opossums (Didelphis virginiana, Didelphis albiventris) are its definitive hosts. Horses are considered its aberrant hosts because only schizonts and merozoites (no sarcocysts) are found in horses. EPM-like disease occurs in a variety of mammals including cats, mink, raccoons, skunks, Pacific harbor seals, ponies, and Southern sea otters. Cats can act as an experimental intermediate host harboring the sarcocyst stage after ingesting sporocysts. This paper reviews information on the history, structure, life cycle, biology, pathogenesis, induction of disease in animals, clinical signs, diagnosis, pathology, epidemiology, and treatment of EPM caused by S. neurona.     

Prevalence of Sarcocystis neurona sporocysts in opossums (Didelphis virginiana) from rural Mississippi

Sarcocystis species sporocysts were found in intestinal scrapings from 24 of 72 opossums (Didelphis virginiana) from rural Mississippi. The number of sporocysts in each opossum varied from a few ( < 100000) to 187 million. Sporocysts from 24 opossums were bioassayed for Sarcocystis neurona infections by feeding to gamma-interferon knockout (KO) mice. S. neurona was detected in the brains of KO mice fed sporocysts from 19 opossums by immunohistochemical staining with anti-S. neurona specific polyclonal rabbit serum, and by in vitro culture from the brains of KO mice fed sporocysts. The isolates of S. neurona from opossums were designated SN16-OP to SN34-OP. Merozoites from 17 of 19 isolates tested at the 25/396 locus were identical to previously described S. neurona isolates from horses. The high prevalence of S. neurona sparocysts in D. virginiana suggests that this opossum constitutes an ample reservoir of infection in the southern United States.     

Determination of the activity of pyrantel tartrate against Sarcocystis neurona in gamma-interferon gene knockout mice

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in the United States. Some horse owners and equine clinicians believe that horses which are on daily pyrantel tartrate at 2.64mg/kg for helminth prophylaxis are less likely to develop EPM. The present study examined the efficacy of pyrantel tartrate in preventing clinical disease in gamma-interferon gene knockout (BALB/c-Ifng(tm1ts)) mice. No activity was seen against sporocyst-induced Sarcocystis neurona infections in mice treated prophylacticly with 4-5mg pyrantel tartrate per mouse per day in the drinking water.     

Myocarditis and encephalitis associated with Sarcocystis neurona infection in raccoons (Procyon lotor)

Sarcocystis neurona associated granulomatous encephalitis was found in 2 of 84 adult raccoons. Both raccoons also had an extensive nonsuppurative myocarditis and one had S. neurona schizonts and merozoites in the myocardium. Only the asexual stages (schizonts and merozoites) of S. neurona are found in tissues of naturally infected animals (horse, mink, raccoons, cats, skunk, pony, seals, sea otters) and since these have not been reported outside the central nervous system, the presence of concurrent myocarditis in raccoons with the presence of S. neurona in the current study is of interest. Pathologists should consider the possible association of S. neurona with myocardial inflammation in other S. neurona susceptible animals.     

Diclazuril preventive therapy of gamma interferon knockout mice fed Sarcocystis neurona sporocysts

Gamma interferon knockout (KO) mice (n=74) were fed a lethal dose of approximately 1000 sporocysts of the SN15-OP isolate of Sarcocystis neurona. Groups of mice were given pelleted rodent feed containing 50ppm of diclazuril at different times before and after feeding sporocysts. All mice were examined at necropsy and their tissues were examined immunohistochemically for S. neurona infection. Twenty mice were fed sporocysts and given diclazuril starting 5 days before feeding sporocysts and continuing 30-39 days post-infection (p.i.). One mouse died of causes unrelated to S. neurona with no demonstrable parasites; the remaining 19 mice remained clinically normal and S. neurona organisms were not found in their tissues. Sarcocystis neurona organisms were not demonstrable by bioassay of the brains of these 19 mice in uninfected KO mice. Sarcocystis neurona organisms were not found in tissues of five mice treated with diclazuril, starting 7 days after feeding sporocysts and continuing up to 39 days p.i. Therapy was less efficient when diclazuril was given 10 days p.i. Sarcocystis neurona organisms were found in two of 19 mice treated with diclazuril starting 10 days after feeding sporocysts, in two of five mice starting therapy 12 days p.i., and in 10 of 10 mice when treatment was delayed until 15 days p.i. All 15 mice fed S. neurona, but not given diclazuril, developed neural sarcocystosis and were euthanized 22-30 days after feeding sporocysts. Six mice not fed S. neurona, but given diclazuril for 44 days, remained clinically normal. Results indicate that diclazuril can kill the early stages of S. neurona.     

Seroprevalence of Neospora caninum in female water buffaloes (Bubalus bubalis) from the southeastern region of Brazil

Antibodies to Neospora caninum were assayed in sera of 222 female water buffaloes from Ribeira Valley of S?o Paulo State, Brazil, using an indirect fluorescent antibody test (IFAT) and Neospora agglutination test (NAT). IFAT antibodies were found in 64% of buffaloes with titers of 1:25 (42 buffaloes), 1:50 (53 buffaloes), 1:100 (31 buffaloes), 1:200 (10 buffaloes), 1:400 (3 buffaloes), or > or =1:800 (3 buffaloes). NAT antibodies were found in 53% of buffaloes; in titers of 1:40 in 52 buffaloes, 1:80 in 27 buffaloes, 1:160 in 21 buffaloes, and > or =1:320 in 17 buffaloes. Results indicate a high prevalence of N. caninum exposure in water buffaloes in Brazil and warrant an investigation of the role of N. caninum as an abortifacient in water buffaloes.