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Electron Microscopy of Infectious AgentsCase 3: Toxoplama EncephalitisPathology A 4 cm craniotomy was performed and biopsies were taken and divided for microbiological cultures, serology, light microscopic and stat examination with transmission electron microcoscopy.. Sera obtained from the patient 6 days before and 11 weeks after transplantation, an 11 week post-transplant CSF specimen, and paraffin sections of the brain tissue were subsequently sent to the CDC for examination. Paraffin sections of brain, liver, and spleen biopsies were also sent to Palo Alto, California for immunoperoxidase staining. Microscopic examination of smears from the brain tissue showed rare neutrophils with inclusions suggestive of microorganisms. All cultures were negative. CMV was isolated from the spleen and varicella-zoster was recovered from the skin vesicles. Light microscopy showed 2-5 micron bodies which were black on GMS staining. Some of the bodies were within macrophages or neutrophils, and were surrounded by a halo. No Toxoplasma cysts, viral inclusions, fungi, bacteria, Pneumocystis, or amoebae were identified Immunofluorescence and Immunohistochemical Stains Immunofluorescence microscopy of paraffin sections of brain tissue were non-diagnostic. However, immunoperoxidase stains for T. gondii were positive in the brain tissue. |
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 Figure 6 Magnify Image |
Transmission electron microscopy revealed tachyzoite forms of Toxoplasma gondii protozoa within neutrophils (Figures 6, 7). | |
 Figure 7 Magnify Image |
The organism has a double-layered pellicle with a space between the outer and inner layers. At the anterior pole micronemes and microtubules can be seen in figure 7. Within the cytoplasm are few mitochondria, dense bodies and vacuoles, and profiles of 3 to 4 mottled rhoptries. The organism is surrounded by a parasitophorus vacuole which corresponds to the halo seen by LM. | |
 Figure 8 Magnify Image |
In figure 8, a cross-section of a tachyzoite shows profiles of at least 6 rhoptries, a mitochondrion, and part of the nuclear material. | |
| Serologic
Studies Analysis of sera was negative for toxoplasma-specific IgM antibody, and titers were elevated but non-diagnostic for IgG. The post-transplant CSF contained no detectable toxoplasma-specific IgM or IgG antibodies, |
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| Discussion | ||
| August 1998 Case-of-the-Month | ||