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Biomedical subjects

R J Post

Publications and source records attributed to R J Post.

48 records · Page 3Linked to original sources
PubMed1986

Gametogenesis and fertilization in Dirofilaria immitis (Nematoda: Filarioidea).

Gametogenesis in Dirofilaria immitis has been studied principally by means of the aceto-orcein chromosomal squash technique, but with additional ultrastructural observations. A terminal germinative zone, in which a continuous and rapid division of germ cells occurs, has been identified in the gonoduct of both male and female worms. Approximately 20% of cells within these germinative zones were in arrested mitotic division following the incubation in vitro of excised gonads in 0.01% colchicine for 4 h. All primary spermatocytes within a 1-2 cm length of the testis proximal to the germinative zone were at the prophase of the 1st meiotic division. In the corresponding region of the ovary, the primary oocytes were similarly at the prophase of the 1st meiotic division in 75% of female worms examined but in the remaining 25% all primary oocytes possessed markedly less condensed, probably interphase nuclei. A possible hormonal control of the cyclical development of primary oocytes, but not primary spermatocytes in D. immitis is suggested. In most of the remaining length of the gonoducts beyond this region of cells at meiotic prophase, the chromatin material of both primary spermatocytes and oocytes is decondensed. Recondensation of chromosomes in the spermatocytes is observed just prior to entry into the seminal vesicle, where meiosis I is completed and meiosis II takes place. In the primary oocyte, completion of meiosis only occurs after fertilization within the seminal receptacle by an entire male gamete. Following the 2 meiotic divisions in the oocyte and subsequent extrusion of the 2 polar bodies, the haploid chromosome complement of the female unites with that of the male, re-establishing the diploid number of the zygote (2n = 10). Male chromosomes within the oocyte remain visible throughout late oogenesis and fusion occurs without the formation of pronuclei.

Animals↗
PubMed1986

Development of a method for the cytological identification of man-biting sibling species within the Simulium damnosum complex.

A method is described for the preparation of adult Malpighian tubule polytene chromosomes from members of the Simulium damnosum complex. This method was used to show that the banding pattern is conserved between adult and larval tissues, and consequently it has been possible to demonstrate that within the S. sanctipauli subcomplex both S. soubrense 'B' and S. sanctipauli bite humans. The degree tubule development is correlated with the gonotrophic cycle and appears to be dependent on food source. This suggests that there is a physiological stage which is optimum for obtaining maximum polyteny for cytotaxonomy.

Animals↗
PubMed1985

The distribution of the Simulium damnosum complex in Sierra Leone and its relation to onchocerciasis.

Because of the paucity of literature concerning onchocerciasis and its vectors in Sierra Leone, new information of the geographical distribution of the Simulium damnosum complex is presented in the context of a comprehensive review of what is known generally about S. damnosum s.l. in Sierra Leone, and how the data relate to the transmission of onchocerciasis. Neither biting adults nor breeding sites have been found on the coastal plain and Freetown peninsula, and these area seem to be free from infestation. Throughout the rest of the country S. damnosum s.l. breeds extensively in all the major river systems. The close proximity of the major rivers to one another facilitates inter-river migration, and ensures that most villages are well within the fly's dispersal range. In accordance with this, onchocerciasis is widespread throughout Sierra Leone and vector biting has been recorded away from riverine breeding sites. Seven cytospecies have been recorded in Sierra Leone but of these S. sirbanum and S. damnosum s.str. are rare outside the far north, in the narrow savanna belt. Simulium squamosum and S. yahense are widely distributed, although S. squamosum is somewhat less common than S. yahense which unexpectedly occurs in large rivers of the forest and savanna as well as small forest streams. Simulium sanctipauli has been found in the south-east of the country, where the forest is most dense, whereas S. soubrense occurs farther north. A new species referred to as S. soubrense 'B' is restricted to the south and west of the country. Over most of Sierra Leone onchocerciasis shows a 'forest' epidemiology and is transmitted by 'forest' vector cytospecies. However, data from the narrow savanna belt in the extreme north are sparse.

Animals↗
PubMed1984

Natural interspecific hybridisation of simulium sanctipauli s.l. with Simulium squamosum and Simulium yahense (Diptera: Simuliidae).

Natural hybridisation between Simulium sanctipauli (sensu Quillevéré et al. 1981) and Simulium squamosum/yahense occurs at a rate of around 0.001. A single larva has been found which is unambiguously a backcross between S. sanctipauli s.l. and a S. sanctipauli s.l. X squamosum/yahense hybrid. This discovery indicates the possibility of genetic introgression between these species. Examination of the polytene chromosomes of this backcross progeny and subsequent re-examination of the type specimens has led to the remapping of fixed interspecific inversions in chromosome arm 1L.

Animals↗
PubMed1982

Sex-linked inversions in blackflies (Diptera:Simuliidae).

The family Simuliidae exhibits a diversity of sex-linked inversions which fall into four major classes. Inversions occur which are found only in the X or Y, and these may be fixed or polymorphic. Y-linkage is clearly commoner amongst such inversions. Other inversions are found which phylogenetic evidence suggests cannot have been sex-linked in ancestral species, but have become so in derived forms. Lastly, inversions are found which occur on both sex chromosomes, but at different frequencies.

Animals↗
PubMed1982

The cytotaxonomy of Simulium (Edwardsellum) dieguerense Vajime and Dunbar 1975.

Simulium dieguerense is recorded for only the second time since its description by Vajime and Dunbar (1975). The polytene chromosomes of larvae from the new sample and the type specimens were examined, and consequently the specific idiogram revised. The new specimens confirm the status of S. dieguerense as a species distinct from other members of the S. damnosum complex.

Animals↗
PubMedDate not supplied

Deforestation and the spatio-temporal distribution of savannah and forest members of the Simulium damnosum complex in southern Ghana and south-western Togo.

Spatio-temporal data on cytotaxonomic identifications of larvae of different members of the Simulium damnosum complex collected from rivers in southern Ghana and south-western Togo from 1975 until 1997 were analysed. When the data were combined, the percentages of savannah blackflies (S. damnosum sensu stricto and S. sirbanum) in the samples were shown to have been progressively increasing since 1975. The increases were statistically significant (P < 0.001), but the rates of increase were not linear. Further analyses were conducted according to the collection seasons and locations of the samples, to account for possible biases such as savannah flies occurring further south in the dry season or a preponderance of later samples from northern rivers having more savannah flies. These analyses showed that the increasing trend was statistically significant (P < 0.0001) only during the periods April to June and October to December. The presence of adult savannah flies carrying infective larvae (L3) indistinguishable from those of Onchocerca volvulus in the study zone was confirmed by examinations of captured flies. The percentages of savannah flies amongst the human-biting populations and the percentages with L3s in the head were higher during dry seasons than wet seasons and the savannah species were found furthest south (5 degrees 25'N) in the dry season. Comparisons of satellite images taken in 1973 and 1990 over a study area in south-western Ghana encompassing stretches of the Tano and Bia rivers demonstrated that there have been substantial increases in urban and savannah areas, at the expense of forest. This was so not only for the whole images but also for subsamples of the images taken at 1, 2, 4, 8 and 16 km distant from sites alongside the River Tano. At every distance from the river, the percentages of pixels classified as urban or savannah have increased in 1990 compared with 1973, while those classified as degraded or dense forest have decreased. The possibility that the proportionate increases in savannah forms of the vectors of onchocerciasis, and hence in the likelihood of the transmission of savannah strains of the disease in formerly forested areas, were related to the decreases in forest cover is discussed.

Animals↗
PubMedDate not supplied

Discovery of a new focus of human onchocerciasis in central Brazil.

An autochthonous case of human onchocerciasis was reported 13 years ago in the town of Minaçu, northern Goiás (Brazil), but a subsequent survey of the population using the traditional technique of examining skin biopsies with the light microscope failed to detect other cases. Recent surveys using more sensitive diagnostic techniques (serodiagnosis, DNA probes, Mazzotti test) that are detailed in this paper revealed the presence of other cases of the disease in Minaçu, the nearby town of Formoso and at the Buracão gold mine near Paranã. The data show that transmission of the disease has occurred to local people living in town and on farms and that gold miners (garimpeiros) are a likely source of infection.

Adolescent↗