J.R. Baker

Electron microscope studies on motile stages of malaria parasites VI. The oöknete of Plasmodium berghei yoelii and its transformation into the early oocyst

Abstract The ookinete and early oocysts of Plasmodium berghei yoelii in Anopheles stephensi have been studied by electron microscopy. The ookinete resembles that previously described for other species of the genus. It contains a single nucleus, one or more crystalloids, mitochondria, a number of anterior elongated, convoluted rods or tubules, and it is bound by a pellicle of 2 unit membranes and a layer of subpellicular microtubules. The structure of the anterior end of the ookinete was revealed in more detail than hitherto. There is an annular thickening of the pellicle, the polar ring, from which the subpellicular microtubules appear to arise. In some specimens, the polar ring was on a narrow anterior protuberance; in others, it was retracted and, behind it, there was a cavity between the tubules and the pellicle apparently formed by a split in the plasmalemma.

Electron microscope studies of motile stages of malaria parasites V. Exflagellation in Plasmodium, Hepatocystis and Leucocytozoon

Exflagellating microgametocytes and microgametes of Plasmodium berghei, P. cynomolgi, Hepatocystis kochi and Leucocytozoon marchouxi were examined in the electron microscope. The morphology was similar in all species. Sections through the exflagellating gametocytes revealed 3 zones: (a) a light outermost envelope (not always present) representing the degenerating erythrocyte; (b) a dense region corresponding to the cytoplasm of the parasite and containing Golgi apparatus, endoplasmic reticulum, mitochondria, pigment and developing flagella; and (c) the nucleus undergoing endomitotic division, the 8 daughter nuclei eventually moving to the point of emergence of the gametes. Shadow-cast replicas of microgametes showed elongated bodies without free flagella. Sections of microgametes revealed the presence of an internal flagellar axial filament complex extending throughout their length, an elongated nucleus and a pellicle. The complex was made up of the typical 9 + 2 filaments with 9 radial spokes. The fundamental difference between the (short) microgamete of the Eimeriidea with 2 free flagella and the (long) microgamete of malaria parasites with no free flagellum is pointed out. A diagrammatic scheme of development of the latter is given.

Electron microscope studies on the motile stages of malaria parasites VII. The fine structure of the merozoites of exoerythrocytic schizonts of Plasmodium berghei yoelii

Maturing and mature exoerythrocytic schizonts of Plasmodium berghei yoelii in the livers of laboratory-bred mice have been studied by electron microscopy. Merozoites are produced by budding from pseudocytomeres. At the tip of each bud, a thickened region of pellicle appears to give rise to the apical rings and conoid; below these structures the paired organelle is formed. As development proceeds, the nucleus enters the base of the bud. Alongside the nucleus is an aggregation of smooth membranes. As no typical mitochondrion was seen, we suggest that this membranous structure may be its analogue. In the pear-shaped free merozoites, there is, in addition to the above structures, a cytostome (“micropyle”), probably non-functional at this stage. The cytoplasm contains large, closely packed ribosomes; in the nucleoplasm are both fine and coarse granular elements. Subpellicular microtubules were not seen. The development and structure of the exoerythrocytic merozoite resemble those described by other writers for avian malaria parasites, apart from the apparent absence of mitochondria and subpellicular microtubules. After penetrating erythrocytes, the parasites lose one of their membranes, the apical rings, conoid and paired organelle; phagotropy commences and smooth and granular endoplasmic reticulum becomes prominent. In many of these parasites the nucleus is lobulated as if dividing.

Human trypanosomiasis in Ethiopia. Ecology of Illubabor Province and epidemiology in the Baro River area.

Abstract African human trypanosomiasis was first seen in Ethiopia in March 1967. Between March 1967 and March 1968, 4 cases were recorded; in the following 12 months the total had risen to 95. The disease occurs mainly in an area of southwestern Ethiopia bounded to the north by the Baro River, to the south by the Akobo River and to the east by the escarpment leading up to the central Ethiopian plateau: its western limits are uncertain. Within this area there are centres of infection, associated mainly with the Gilo River and a low-lying moist region north of it. The disease is of the acute type, caused by Trypanosoma brucei rhodesiense . The present paper introduces the subject and describes the situation in the northern part of the affected area along the Baro River. Two men probably acquired the infection in that region in 1967 and one in 1968. A blood film survey of 430 people in 1968 failed to reveal any further infections, and it is probable that here the disease is a zoonosis, transmitted to man sporadically by Glossina morsitans and, perhaps, G. pallidipes and G. fuscipes .

Human trypanosomiasis in Ethiopia: the Gilo River area.

Abstract The current outbreak of Rhodesian sleeping sickness in Ethiopia is centred on the Gilo River region of Illubabor Province. Up to the end of March 1970 there have been 232 confirmed cases—4 in 1967, 28 in 1968, 173 in 1969, and 27 in the first three months of 1970. Of the total, 210 were from the villages in relation to the Gilo River and 15 from those close to the Akobo River and the Sudan-Ethiopian border. High IgM values were observed in 153 of 364 inhabitants of the Gilo River area examined during blood surveys conducted in June 1968 and February 1969; of these, 86 also gave strongly positive IFAT results. No parasite was found in blood films from any of these individuals. 4 species of Glossina have been collected in the area, G. morsitans, G. pallidipes, G. fuscipes and G. tachinoides . Whereas G. morsitans is almost certainly the main vector for the sporadic zoonotic infections which have occurred between the Baro River and the Akobo River, circumstantial evidence suggests that G. tachinoides and probably G. pallidipes are important vectors in the Gilo River area, accounting for the focal epidemics at village level which have been a feature of the present outbreak.