Feline Toxoplasmosis from Acutely Infected Mice and the Development of Toxoplasma Cysts*

Abstract

The development of Toxoplasma cysts was studied in mice inoculated with tachyzoites by several routes. After 1-30 days of infection, murine tissues were examined microscopically and portions or whole carcasses were fed to mice and cats. The feces of the cats were examined for oocyst shedding. Cyst-like structures containing distinct PAS-positive granules were first seen after 3 days of infection with tachyzoites, and became numerous by 6 days. Argyrophilic walls were first seen after 6 days, and became numerous by 16 days of infection with tachyzoites. Prepatent periods to oocyst shedding (PPO) were either "short" (3-10 days) or "long" (19-48 days). The "short" PPO was found only in cats that had ingested mice infected for 3 days or longer, and was related to the development of PAS-positive granules in T. gondii, and to high, 60-100%, oral infectivity rates for cats. The "long" PPO followed the ingestion of mice infected for only 1-2 days, and was related to tachyzoites without distinct PAS-positive granules and low, 32% or less, infectivity for cats. The "long" PPO followed also the ingestion of oocysts and the parenteral inoculation of tachyzoites, bradyzoites, or sporozoites. Using the "short" PPO as a criterion for detecting cysts in tissues, it was shown that (a) numerous cysts developed in mice 5 days after inoculation with tachyzoites, 7-9 days after inoculation with cysts, and 9-10 days after inoculation with oocysts, and (b) cysts developed faster and more frequently in the brain and muscle than in lungs, liver, spleen, and kidneys of mice inoculated with tachyzoites.

Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts

“…The evidence for this was that milk treated with HCl for 60 min at room temperature produced T. gondii infection in bioassayed mice. This result disagrees with the conclusion reached by Dubey and Frenkel (48), who found that bradyzoites were not formed in any tissue of mice until 7 days after bradyzoite inoculation.…”

“…The 15 h needed to convert bradyzoites to tachyzoites in cell culture agrees with the data obtained with mice, where functional tachyzoites were not found 18 h after bradyzoites were fed to mice (42). The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48).…”

“…The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48). Unlike in vitro studies, all bradyzoites had converted to biologically defined tachyzoites by 18 h p.i.…”

Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts

“…The evidence for this was that milk treated with HCl for 60 min at room temperature produced T. gondii infection in bioassayed mice. This result disagrees with the conclusion reached by Dubey and Frenkel (48), who found that bradyzoites were not formed in any tissue of mice until 7 days after bradyzoite inoculation.…”

“…The 15 h needed to convert bradyzoites to tachyzoites in cell culture agrees with the data obtained with mice, where functional tachyzoites were not found 18 h after bradyzoites were fed to mice (42). The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48).…”

“…The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48). Unlike in vitro studies, all bradyzoites had converted to biologically defined tachyzoites by 18 h p.i.…”

Toxoplasma GondiiBradyzoites Form Spontaneously during Sporozoite-Initiated Development

“…2), indicating that these events are most likely genetically controlled rather than host induced. A delay in VEG tachyzoite in vitro differentiation is consistent with the reported time lag (7 to 10 days) between T. gondii oocyst infection and the appearance of functional bradyzoites in various mouse tissues (M-7741 and VEG strains) (8, 10). Thus, the VEG strain used here is developmentally competent, although we have not tested in vitro-produced VEG bradyzoites in the feline bioassay (10).…”

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

“…Organisms were most commonly intracytoplasmic within macrophage multinucleate cells and neutrophils and less commonly within type II alveolar pneumocytes or the bronchiolar epithelium. Lesions were similar to those described previously in cats with both experimental and naturally occurring generalized toxoplasmosis (14,28,44). The one control animal that died following anesthesia and fluorescein angiography on p.i.…”

Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts

“…The evidence for this was that milk treated with HCl for 60 min at room temperature produced T. gondii infection in bioassayed mice. This result disagrees with the conclusion reached by Dubey and Frenkel (48), who found that bradyzoites were not formed in any tissue of mice until 7 days after bradyzoite inoculation.…”

“…The 15 h needed to convert bradyzoites to tachyzoites in cell culture agrees with the data obtained with mice, where functional tachyzoites were not found 18 h after bradyzoites were fed to mice (42). The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48).…”

“…The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48). Unlike in vitro studies, all bradyzoites had converted to biologically defined tachyzoites by 18 h p.i.…”

Toxoplasma GondiiBradyzoites Form Spontaneously during Sporozoite-Initiated Development

“…2), indicating that these events are most likely genetically controlled rather than host induced. A delay in VEG tachyzoite in vitro differentiation is consistent with the reported time lag (7 to 10 days) between T. gondii oocyst infection and the appearance of functional bradyzoites in various mouse tissues (M-7741 and VEG strains) (8, 10). Thus, the VEG strain used here is developmentally competent, although we have not tested in vitro-produced VEG bradyzoites in the feline bioassay (10).…”

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

“…Organisms were most commonly intracytoplasmic within macrophage multinucleate cells and neutrophils and less commonly within type II alveolar pneumocytes or the bronchiolar epithelium. Lesions were similar to those described previously in cats with both experimental and naturally occurring generalized toxoplasmosis (14,28,44). The one control animal that died following anesthesia and fluorescein angiography on p.i.…”

Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts

“…The evidence for this was that milk treated with HCl for 60 min at room temperature produced T. gondii infection in bioassayed mice. This result disagrees with the conclusion reached by Dubey and Frenkel (48), who found that bradyzoites were not formed in any tissue of mice until 7 days after bradyzoite inoculation.…”

“…The 15 h needed to convert bradyzoites to tachyzoites in cell culture agrees with the data obtained with mice, where functional tachyzoites were not found 18 h after bradyzoites were fed to mice (42). The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48).…”

“…The 72 h needed for tachyzoites to completely lose their tachyzoite-specific markers also agrees with the 3 days needed to form biologically functional tissue cysts after inoculation of tachyzoites into mice (48). However, when bradyzoites were inoculated into mice by any route, the minimum period needed to form biologically functional tissue cysts was 6 days (48). Unlike in vitro studies, all bradyzoites had converted to biologically defined tachyzoites by 18 h p.i.…”

Toxoplasma GondiiBradyzoites Form Spontaneously during Sporozoite-Initiated Development

“…2), indicating that these events are most likely genetically controlled rather than host induced. A delay in VEG tachyzoite in vitro differentiation is consistent with the reported time lag (7 to 10 days) between T. gondii oocyst infection and the appearance of functional bradyzoites in various mouse tissues (M-7741 and VEG strains) (8, 10). Thus, the VEG strain used here is developmentally competent, although we have not tested in vitro-produced VEG bradyzoites in the feline bioassay (10).…”

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

“…Organisms were most commonly intracytoplasmic within macrophage multinucleate cells and neutrophils and less commonly within type II alveolar pneumocytes or the bronchiolar epithelium. Lesions were similar to those described previously in cats with both experimental and naturally occurring generalized toxoplasmosis (14,28,44). The one control animal that died following anesthesia and fluorescein angiography on p.i.…”