A seroepidemiological survey of toxoplasmosis in Scotland and England.

The Sabin-Feldman dye test was used to detect the presence of Toxoplasma antibodies in two groups of blood donors in central Scotland, one group from a rural area and one from an urban area, and in patients attending a medical outpatients clinic and females attending an antenatal clinic serving a mixed urban and rural area in the midlands of England. Results obtained from these four groups showed that 7.6, 7.8, 35.7 and 14.9% respectively had antibody titres of 1: greater than or equal to 10. A group of travelling people, defined in the Local Government and Planning (Scotland) Act, 1982, as '...persons of nomadic habit of life, whatever their race or origin...', from Scotland were also surveyed and 28% of this group had antibodies of 1: greater than or equal to 10. Individuals in this latter group were reported to have minimal contact with cats because of their lifestyles. The prevalences of the travelling people were analysed by age group and showed no correlation with age, but other groups did show an increasing prevalence with age. The significance of these results is discussed.

Meningo-encephalitis accompanying retinochoroiditis in a murine model of congenital toxoplasmosis.

A histopathological study of the brains of adult mice infected in utero with Toxoplasma gondii and presenting manifestations of ocular toxoplasmosis is reported. All brains contained Toxoplasma tissue cysts. A sub-acute/chronic meningo-encephalitis was the main feature of the inflammatory response in the brain. Microscopical features suggest that autoimmune processes may play a part in the disease. We suggest that our mouse model will provide a simple and inexpensive tool for the investigation of histopathological processes in the CNS resulting from congenital Toxoplasma infection.

Encephalitis in mice with congenital ocular toxoplasmosis.

The brains of mice with congenital ocular toxoplasmosis were examined histologically. Toxoplasma tissue cysts and a subacute/chronic meningo-encephalitis were present in the brains of all infected mice. The findings were very similar to those seen in human congenital toxoplasmosis. The murine model of congenital toxoplasmic encephalitis described in this paper will be valuable in the study of the pathogenesis, natural history and treatment of this condition.

Congenital toxoplasmic retinochoroiditis in a mouse model.

A study of the eyes of adult mice infected in utero with Toxoplasma gondii is reported. The histopathological features of the ocular inflammatory response in the infected mice ranged from minimal damage to complete destruction of the retinal tissue. Notable features such as retinal vasculitis and an almost uniform and highly selective destruction of the photoreceptor layer of the retina suggest a similarity between experimental autoimmune retinitis and the disease process in the retinas of our Toxoplasma-infected mice. We suggest that our mouse model could provide a simple and inexpensive tool for the investigation of immuno-pathological processes in the retina resulting from congenital Toxoplasma infection. The model has the advantage of low post-natal mortality coupled with high ocular morbidity. Furthermore, its aetiology is probably analogous to that of human ocular toxoplasmosis, in that the foetus becomes infected in utero via a mother whose primary infection is acquired during gestation.

A murine model of congenital toxoplasmic retinochoroiditis.

A histopathological study of toxoplasmic retinochoroiditis in 39 eyes of mice infected in utero with Toxoplasma gondii and sacrificed at 16 weeks post-partum showed a wide variation in the pattern of tissue destruction. The changes in individual eyes were graded from mild to severe; Toxoplasma cysts were present in the retina and optic nerve in each grade. In the least affected eyes, Toxoplasma cysts were rarely seen and the disease was limited to a low grade uveitis and retinal lymphocytic perivasculitis. In the more severely affected eyes, there was focal, sectorial or total retinal destruction with secondary degeneration in the lens. In some eyes inflammatory destruction of the outer retina was associated either with a paucity of cells, or with lymphocytic infiltration or with plasma cell infiltration; giant cell granulomatous reactions were rare. In the most severely affected eyes the retina was necrotic and calcified. The findings illustrate the complexity of toxoplasmic retinochoroiditis and suggest that autoimmunity may play a part in the disease process.

Scanning electron microscopy of the oocyst and sporocyst of Toxoplasma gondii.

Oocysts and sporocysts of T. gondii were examined with the scanning electron microscope. The oocysts were slightly ellipsoidal in shape with a smooth outline. The sporocysts were also ellipsoidal with a smooth surface on which there were a number of raised ridges. The ridges represent the junctions between the four plates comprising the sporocyst wall. From the distribution of the ridges it was concluded that the wall consisted of two upper and two lower plates which were at an angle to each other and which interlocked along the mid-line suture. The specific orientation of the plates would provide a structure extremely resistant to mechanical disruption. During excystation, an infolding of the surface was observed along the suture lines between the plates of the sporocyst wall.

Ultrastructural observations on microgametogenesis and the structure of the microgamete of Isospora felis.

The endogenous forms of Isospora felis were observed within the epithelial cells of the small intestine of the cat. They were situated within a parasitophorous vacuole which was limited by a multimembranous wall. The ultrastructural features of microgametogenesis were studied at 8 days post-infection. The initial phase of microgamont development consisted of cytoplasmic growth accompanied by a number of nuclear divisions. The gamont was enclosed by a pellicle and its surface area was greatly increased by deep invaginations. In the later stages of development the numerous nuclei were situated close to the pellicle. Each nucleus has peripherally condensed chromatin. Formation of the microgametes occurred as protrusions from the microgamont surface. Two basal bodies, the dense portion of a nucleus and a mitochondrion entered each protrusion. The microgametes matured while still attached to the gamont from which they finally budded off into the parasitophorous vacuole leaving a large residual cytoplasmic mass. The mature microgamete was found to consist of an elogate nucleus which overlaps with a mitochondrion towards the anterior end of the organism. The anterior portion contains a dense perforatorium and two basal bodies with attached flagella. In addition a number of microtubules (5-9) were found to run longitudinally from the basal body region.

Ultrastructural observations on macrogametogenesis and the structure of the macrogamete of Isospora felis.

The ultrastructural changes occurring during macrogametogenes of Isospora felis were studied in the small intestine of the cat at 8 and 9 days post-infection. The parasites were situated in parasitophorous vacuoles within the host epithelial cells. The early macrogamont could be identified by its ellipsoidal shape and by the presence of a large nucleus with a distinct nucleolus. Throughout the development of the macrogamont the organism remained limited by a pellicle. At an early stage of macrogametogenesis the formation of the wall-forming bodies of types I and II (WFB I and WFB II) was initiated simultaneously. The formation of the WFB I appeared to involve the rough endoplasmic reticulum (rER) and the Golgi bodies, whereas the WFB II developed within cisternae of the rER. Early in the developmental process vacuoles were observed which budded off from the nucleus and formed multimembranous vacuoles. During gametogenesis both lipid globules and polysaccharide granules developed within the cytoplasm. The mature macrogamete was spherical in appearance and was limited by a pellicle. It possessed a large nucleus with a nucleolus and the cytoplasm was filled with numerous WFB I, WFB II, lipid globules and polysaccharide granules. A few multimembranous vacuoles were also present together with canaliculi, mitochondria, Golgi bodies and some rER.

Toxoplasma Gondii: scanning electron microscope studies on the small intestine of infected and uninfected cats.

The mucosal surfaces of villi from the small intestine of cats infected with Toxoplasma gondii were studied with the scanning electron microscope and compared with those from uninfected control cats. In uninfected cats villi were predominantly leaf shaped and were lined with ridges; goblet cell openings could be seen. The enterocytes had a hexagonal surface outline and were dome-shaped. Infected cats had both normal and abnormal villi. Injured villi were shortened and attained a broad leaf shape, often with blunt edges. Enterocytes containing oocysts were enlarged, and microvilli were resolvable only on these surfaces. Ruptured cells from which parasite discharge had occurred were seen. Oocysts were observed and possessed a smooth coat.

An ultrastructural study on the excystation of the sporozoites of Toxoplasma gondii.

The ultrastructural changes which occur during the in vitro excystation of the sporozoites of Toxoplasma gondii were examined. The excystation was carried out at 37 degrees C on suspensions of oocysts which had been ground and then treated with an excysting medium containing 0.25% trypsin and 0.75% sodium taurocholate in phosphate buffered saline, pH 7.3. It was found that sporocysts within intact oocysts were unaffected while sporocysts exposed to the medium ruptured. The sporocyst wall consisted of two layers and during excystation the four plates which form the inner layer started to curl inward. At the same time changes were seen at the specialized junctions between these plates. When the junctions finally break, the plates separate. The outer layer of the sporocyst wall is then ruptured at points directly above where the plates were joined. Each of the four portions of the sporocyst wall curled inward to form a tightly wound whorl. The sporozoites can escape through the openings created between the portions of the sporocyst wall.

Ultrastructural studies on the sporulation of oocysts of Toxoplasma gondii. I. Development of the zygote and formation of the sporoblasts.

The initial stages of sporulation in oocysts of Toxoplasma gondii were examined in samples sporulated at 27 degrees C for 0, 6, 12, 16 and 24 hours. The initial zygote was roughly spherical and was limited by a single unit membrane. A few micropores of the inactive type were present on this membrane. The cytoplasm contained a large nucleus with a nucleolus, a number of polysaccharide granules, lipid globules, mitochondria, and Golgi bodies together with a few strands of rough endoplasmic reticulum. After the initiation of sporulation little change was noted in the cytoplasm except for an increase in protein synthesis as evidenced by the augmentation of the amount of rough endoplasmic reticulum and the appearance of polyribosomes. Nuclear division occurred twice giving rise to four nuclei which were situated close to the cell periphery and well separated from each other. At this multinucleate stage a second limiting membrane was formed. The cytoplasmic mass then divided to form the two sporoblasts. This was accomplished by an invagination of the limiting membranes in combination with internally formed membranes. The two binuclear sporoblasts were roughly spherical. They were limited by two unit membranes and contained the same cytoplasmic organelles as described for the zygote.