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Biomedical subjects

S E Meredith

Publications and source records attributed to S E Meredith.

31 records · Page 2Linked to original sources
PubMed1988

Simulium (Edwardsellum) rasyani n.sp., the Yemen species of the Simulium damnosum complex.

The examination of the polytene chromosomes of the Yemen representative of the Simulium damnosum complex revealed hitherto unknown arrangements distinct enough to justify the description of this form as the new species Simulium (Edwardsellum) rasyani. The newly recognized inversion II L-60.65 was always present and found to be homozygous in 62% and heterozygous in 38% of the 106 larvae which were examined. A short description is given of the morphology of the females, males, larvae and pupae. Populations from the five permanent Wadis Kabir, Rasyan, Al Barh, Zabid, and Surdud were genetically and morphologically very uniform.

Animals↗
PubMed1987

Experimental hybridization between members of the Simulium damnosum complex.

Males of the Beffa form of Simulium soubrense Vajime and Dunbar were successfully crossed with female S.squamosum V. & D. and S.sanctipauli V. & D. Fertile eggs from both crosses were reared to larvae and, in the case of the Beffa x squamosum cross, to adults. Larval chromosomes from the Beffa x sanctipauli cross had normally paired homologues but those of the Beffa x squamosum cross showed extensive asynapsis and large heterozygous loops. The morphology of the larval and adult hybrids from the Beffa x squamosum cross were more characteristic of squamosum, but the adult males had scutal patterns typical of the Beffa form and retained this form's laboratory-mating propensity.

Animals↗
PubMed1986

Following movements of resistant populations of Simulium soubrense/sanctipauli (Diptera: Simuliidae) by means of chromosome inversions.

Following larval insecticide treatment, resistance to the organophosphates temephos and chlorphorxim appeared in a population of the Simulium soubrense/sanctipauli group of the S. damnosum complex on the Bandama Rivers, Ivory Coast. Resistant populations were subsequently identified from other river basins in the north of Ivory Coast. A small chromosomal rearrangement, IIL-A, was found to be associated with resistant populations. Monitoring the presence of this inversion was used to detect the spread or resistance eastwards into untreated areas.

Animals↗
PubMed1983

Identification of a laboratory mating form of the Simulium damnosum Theobald complex in West Africa.

Larvae and pupae of Simulium damnosum s.l. were collected from the Begba rapids on the Mono river. Emerging adults were induced to mate, blood feed and oviposit. Six out of 13 discrete egg batches counted were fertile. The F1 females did not blood feed and thus no F2 eggs were obtained. Larvae from the breeding site and the F1 generation were identified as being the Beffa form of the S. sanctipauli/S. soubrense group. This form appears to be the only member of the S. damnosum complex in West Africa which mates in the laboratory and is almost certainly the same form as that colonized by Simmons and Edman (1982). The mating behaviour of West African S. damnosum s.l. described by several authors is similar to that observed in the Beffa form, and the possibility that earlier reports referred to the Beffa form is discussed.

Africa, Western↗
PubMed1983

Variation and distribution of forms of Simulium soubrense and S. sanctipauli in West Africa.

Examination of specimens from savanna areas of Togo and Benin attributable to Simulium soubrense and S. sanctipauli according to the criteria of Vajime and Dunbar (1975) revealed hitherto undescribed features. Cytological examination showed many larvae with the arrangement IIL- 4.6/4.6.7, heterozygous for the 'diagnostic' inversion and 86% of the males possessed a previously undescribed inversion IIS-6b. The occurrence of such larvae in Togo and Benin was associated in adult males with records of a type of scutal pattern which is described and termed Type IV. This pattern is one extreme of a range of scutal pattern variation in the males of the S. soubrense/S. sanctipauli sub-group, which was separated into four arbitrary classes and specimens were scored as Type I, II, III or IV. The distribution of these different types of male scutal pattern, based on collections made in West Africa between 1963 and 1981, is presented. Type I and II patterns predominated in forest areas and Type IV in savanna. Many female flies which occurred together with the latter possessed pale wing tufts. In the light of the above and additional evidence, derived from the progeny of individual females, and because the 'diagnostic' inversion for S. soubrense and S. sanctipauli together with a previously undescribed sequence IIL-6 occurred in Hardy-Weinberg equilibrium, it was concluded that the populations in Togo and Benin are a single interbreeding group. This group is described as a new form, named the Beffa form, of the S. soubrense/S. sanctipauli subgroup of the S. damnosum s.l. complex and its possible taxonomic status is discussed.

Africa, Western↗
PubMed1981

Enzymes for species identification in the Simulium damnosum complex form West Africa.

An electrophoretic survey of 44 enzyme systems of the Simulium damnosum complex has revealed only two that are of value in species diagnosis, namely PGM and trehalase. S. yahense has a unique PGM variant, and S. yahense and S. squamosum have a different trehalase variant from S. sirbanum, S. damnosum s.s., S. sanctipauli and S. soubrense. Examination of S. damnosum s.l. from Mali, Ivory Coast and Ghana has shown that PGM and trehalase can be used to distinguish accurately adult S. yahense from S. squamosum and these two from S. sirbanum, S. damnosm s.s., S. sanctipauli and S. soubrense.

Africa, Western↗
PubMedDate not supplied

Visceral leishmaniasis: use of the polymerase chain reaction in an epidemiological study in Baringo District, Kenya.

The polymerase chain reaction was applied to capillary blood spots dried on filter paper from 20 parasitologically proved cases of visceral leishmaniasis (VL), 21 subclinical cases, and 11 healthy controls in a longitudinal study of anthroponotic VL in Baringo District, Kenya. Leishmania deoxyribonucleic acid (DNA) was detected 10.5 months before diagnosis and up to 3 years after diagnosis and apparently successful treatment. Subclinical cases can have detectable circulating parasite DNA in their blood. These findings may indicate that subclinical cases can be a reservoir and formerly treated VL patients can remain a reservoir for a long time. Xenodiagnosis should be performed on subclinical cases and former VL patients to establish their role in transmission of VL in Kenya.

Adolescent↗
PubMedDate not supplied

Sudanese mucosal leishmaniasis: epidemiology, clinical features, diagnosis, immune responses and treatment.

The epidemiology, clinical features, pathology, immune responses, diagnosis and treatment of 14 patients with mucosal leishmaniasis in the Sudan are described. The condition occurred mainly in adult males, particularly in certain closely related tribes from the western Sudan. It affected the mucosa of the upper respiratory tract and/or the oral mucosa and sometimes followed treated kala azar. The parasites were sometimes confined to the mucosa, sometimes spread to the lymph nodes, and rarely infected the bone marrow and spleen. One of the 2 patients with both visceral and mucosal leishmaniasis differed from classical kala azar cases; his infection was longer lasting, he was leishmanin positive, and his peripheral mononuclear cells proliferated in response to leishmanial antigens. Mucosal leishmaniasis following treated kala azar is a similar phenomenon to post-kala azar dermal leishmaniasis and post-kala azar uveitis. Post-kala azar mucosal leishmaniasis can therefore be added to the other post-kala azar leishmanial infections. Using the polymerase chain reaction, Southern blot analysis with specific probes, and isoenzyme characterization, the causative parasite was identified as Leishmania donovani in 4 patients and as L. major in one. Unlike American mucocutaneous leishmaniasis, mucosal leishmaniasis in the Sudan was not preceded or accompanied by cutaneous lesions and the response to pentavalent antimony or ketoconazole was good.

Adult↗
PubMedDate not supplied

The direct agglutination test for diagnosis of visceral leishmaniasis under field conditions in Sudan: comparison of aqueous and freeze-dried antigens.

The performance of the direct agglutination test (DAT) was evaluated under field conditions in an endemic area of visceral leishmaniasis in eastern Sudan, using aqueous (Aq) antigen which has to be kept refrigerated and a newly developed freeze-dried (FD) antigen which is stable at ambient temperature. Both antigens compared well, with 92-98% of readings being identical or only with one dilution difference in titre. FD antigen gave titres that were identical with Aq antigen in 73% of samples, higher in 19%, and lower in 8%. Owing to high ambient temperatures and low humidity, microtitre plate wells dried out during the standard procedures for elution and incubation. However, shortening the elution time from 12 to 4 h proved possible for both antigens; incubation could be reduced from 24 to 10 h for Aq antigen, after which the plates could still be read. Incubation with FD antigen required 18 h and the plates needed to be kept cool because of evaporation. Despite the longer procedure with the FD antigen, the DAT can be completed in 24 h and the use of this stable antigen, that does not require refrigeration, is a major improvement in performing the DAT under unfavourable field conditions.

Agglutination Tests↗
PubMedDate not supplied

Biochemical and molecular characterization of Leishmania parasites isolated from an endemic focus in eastern Sudan.

Twelve Leishmania isolates from visceral leishmaniasis patients in eastern Sudan were characterized using isoenzyme analysis, Southern blotting and polymerase chain reaction (PCR) 'fingerprinting'. Isoenzyme analysis revealed the presence of 3 zymodemes: MON-18, MON-30 and MON-82, corresponding to Leishmania donovani sensu stricto, L. infantum and L. archibaldi (still of uncertain taxonomic status), respectively. Southern blotting and PCR 'fingerprinting' revealed identical patterns for all 3 zymodemes, which were indistinguishable from those of L. donovani s.s.

Animals↗
PubMedDate not supplied

Development and application of the polymerase chain reaction for the detection and identification of Leishmania parasites in clinical material.

Detection, diagnosis and identification of Leishmaniasis may be difficult owing to low numbers of parasites present in clinical samples. The PCR has improved the sensitivity and specificity of diagnosis of several infectious diseases. A leishmania specific PCR assay was developed based on the SSUrRNA genes which amplifies DNA of all Leishmania species. Point mutations occurring within the rRNA genes allow differentiation of the Leishmania complexes using primers constructed with the 3/ ends complementary to the specific point mutations present in the SSU rRNA genes of the Leishmania species. Biopsy material, blood, lesion impressions and blood spots on filter paper can be used in the assay. In a longitudinal study on the incidence rates of VL, subclinical cases and PKDL in an endemic region of Sudan, filter paper blood spots from proven and suspected VL patients, PKDL and control samples from an endemic region in Sudan are being taken. The blood spots were analyzed in the DAT and by PCR and results compared with clinical and parasitological data. The first results indicate that the PCR on blood spots is a simple and sensitive means of detecting active VL; in PKDL patients parasites are detectable in the skin.

Animals↗