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Biomedical subjects

S E Meredith

Publications and source records attributed to S E Meredith.

At least 19 recordsLinked to original sources
PubMed2002

The effect of 5 years of annual treatment with ivermectin (Mectizan) on the prevalence and morbidity of onchocerciasis in the village of Gami in the Central African Republic.

To assess the impact of 5 years of annual community treatment with ivermectin (Mectizan) on the prevalence of onchocerciasis and onchocerciasis-associated morbidity, data collected, before and after such treatment, in the village of Gami, in a hyper-endemic area of the Central African Republic, were analysed. Skin snips from all the villagers treated in 1990 and/or 1995 were used to assess the prevalence and intensity of infection with Onchocerca volvulus. Ocular and dermatological morbidity was assessed by ophthalmological and clinical examinations of the same subjects. Following the five annual treatments, there was a reduction in the prevalence of infection and a dramatic decrease in the microfilarial load of the community. The prevalences of pruritus, onchocercal nodules and impaired vision were all significantly reduced. The results emphasise the long-term benefits of the mass-treatment programmes, particularly for children aged <10 years.

Adolescent↗
PubMed2000

DNA in situ hybridization on polytene chromosomes of Simulium sanctipauli at loci relevant to insecticide resistance.

A DNA technique for in situ hybridization developed by Kumar & Collins (1994) for use on polytene chromosomes of adult Anopheles mosquitoes (Diptera: Culicidae) was modified for use with Simulium larval salivary gland chromosomes (Diptera: Simuliidae). Cloned fragments of several Simulium genes (coding for aspartate amino transferase, cytochrome P450 and DNA polymerase) were successfully mapped physically by assigning specific band locations in Simulim sanctipauli V. & D. This represents the first attempt at locating genes beyond the resolution of linkage to inversions in any blackfly species.

Animals↗
PubMed1998

The Mectizan Donation Programme--a 10-year report.

In the 10 years since 1987 when Merck & Co. announced a plan to donate its safe and effective microfilaricide, Mectizan (ivermectin, MSD), to treat onchocerciasis wherever and for as long as needed, more than 96 million treatments have been enabled in community-based treatment programmes in all 34 countries, in Africa, the Middle East, and Latin America, where the disease is endemic. It is expected that donations enabling some 33 million treatments will be approved in 1997. Since the beginning of the donation programme, it is estimated that some 19-20 million people have received at least one dose of the drug and that many have received their sixth, seventh, eighth, or even ninth annual dose.

Filaricides↗
PubMed1996

Sensitivity of a polymerase chain reaction-based assay to detect Onchocerca volvulus DNA in skin biopsies.

A polymerase chain reaction (PCR) of a 150-bp tandem repeat of Onchocerca volvulus (O-150) combined with Southern-blot hybridization to species-specific DNA probes was employed for DNA detection. O-150 was amplified from parasites originating from Uganda, Benin, Cameroon, Liberia, Ghana, Burkina Faso, Mali, and Zaire and was successfully hybridized to digoxigenin-labeled oligonucleotides. To investigate the sensitivity of the PCR, 2 skin biopsies were taken from each of 227 persons from Uganda with proven O. volvulus infections but with low microfilaria (mf) densities due to ivermectin treatment. One biopsy was tested by PCR and the other was digested using collagenase to assess the total number of mf. The PCR revealed 76.2% of the samples to be positive, and the collagenase method showed that 78.9% were positive, indicating similar sensitivity for the two methods. It is probable that for both techniques the biopsy must contain at least one live mf or fragments of a dead mf. In this study, no free or circulating O. volvulus DNA could be detected in skin biopsies by PCR.

Animals↗
PubMed1995

Leish-KIT, a stable direct agglutination test based on freeze-dried antigen for serodiagnosis of visceral leishmaniasis.

In order to increase the application potential of the direct agglutination test (DAT) for the detection of anti-Leishmania antibodies in human serum samples, we developed an antigen based on stained and freeze-dried Leishmania donovani promastigotes. We describe here the evaluation of the performance of the DAT based on this freeze-dried antigen. It was shown that the freeze-dried antigen remains fully active, even after storage at 56 degrees C for 18 months. With a cutoff value of 1:1,600, the sensitivity of the DAT was shown to be 92% and the specificity of the test was 99.7%, which were comparable with the results found for the DAT based on liquid antigen. The major advantages of the freeze-dried antigen are that the production of a large batch of this antigen allows reproducible results in the DAT over a long period of time and that the freeze-dried antigen can be stored at ambient temperature, which, as was shown, makes the test a valuable diagnostic tool for use in the field.

Agglutination Tests↗
PubMed1994

Genomic fingerprinting of Onchocerca species using random amplified polymorphic DNA.

A method based on amplification of genomic DNA by decamer primers of random nucleotide sequence was used to obtain DNA fingerprints from different species of the genus Onchocerca. Each of the 20 primers tested allowed a clear distinction between the different species of the genus on an agarose gel. The technique offers the potential to construct species or strain specific probes and oligonucleotides PCR primers from the species specific fragments. A combination of these primers or others could be useful as population markers.

Animals↗
PubMed1991

Onchocerca volvulus: application of the polymerase chain reaction to identification and strain differentiation of the parasite.

Previous studies have demonstrated that the genome of Onchocerca volvulus contains a variable tandemly repeated DNA sequence family with a unit length of 150 bp. The variability of the 150-bp family has been exploited to develop O. volvulus strain and species specific DNA probes. Application of these DNA probes to the study of the epidemiologically most significant life cycle stages of the parasite has been confounded by several obstacles. These include the relative insensitivity of some of the DNA probes and the difficulty in releasing genomic DNA from infective larvae and skin microfilariae in a form that may be directly detected by hybridization to the probes. DNA sequence comparison of 18 known examples of the 150-bp repeat has been used to develop two populations of degenerate oligonucleotides. These oligonucleotides have been shown to support the amplification of the 150-bp repeat family from Onchocerca DNA, using the polymerase chain reaction. Both strain and species specific members of the repeat family are faithfully amplified, allowing characterization of a parasite on the basis of hybridization of the PCR amplification products to the previously developed DNA probes. This method is shown to be applicable to all diagnostically important forms of the parasite, including adults, infective larvae, and skin microfilariae. In addition, the method is capable of detecting O. volvulus infective larvae directly in extracts of blackfly vectors.

Animals↗
PubMed1990

Biotechnology as applied to vectors and vector control.

Vector borne diseases remain some of the major public health problems in the developing world. In this review some of the current applications of biotechnology to vectors and vector control and some of the possible future applications are discussed.

Animals↗
PubMed1990

The onchocerciasis focus at Kinsuka/Kinshasa (Republic of Zaire) in 1985. I. Entomological aspect.

The entomological aspect of the onchocerciasis focus at Kinsuka/Kinshasa has not been studied since vector control was carried out in 1948. As in 1940, larvae of Simulium damnosum s.l. are located in the arm of the Zaire River flowing between Mimosa Island and the Zairian bank. They are, however, scarce. Cytotaxonomic studies showed that the S. squamosum group was the only member of the S. damnosum complex present in the region of Kinshasa. Physico-chemical analysis of the water at breeding sites determined that S. squamosum larvae develop in neutral or acid water with a conductivity of less than 50 micronhos cm-1 and a low concentration of dissolved salts. Longitudinal study showed that the 'annual biting rate' (ABR) and the 'annual transmission potential' (ATP) fluctuate from 2406-5999 bites man-1 year-1 and from 120-236 infective larvae man-1 year-1 respectively. The low transmission rate at Kinsuka is mainly due to the low level of the biting population occurring during the main river rising. The increase in Kinsuka's population has reinforced this situation by 'diluting' the parasite in the human reservoir.

Animals↗
PubMed1990

Isolation and characterization of form specific DNA sequences of O. volvulus.

Maintenance of the control of O. volvulus in Africa would be assisted by the development of assays to identify the origin of outbreaks of transmission within the controlled regions. The isolation of pFS-1, a DNA sequence specific for forest form O. volvulus, has suggested that it might be possible to develop such an assay based on form specific DNA probes. The isolation and characterization of pSS-1, a clone which hybridized preferentially to savannah form O. volvulus is described here. DNA sequence analysis demonstrated that pSS-1 was a representative of a highly repeated sequence family of O. volvulus. Comparison of the sequence of pSS-1 to other known examples of this family has identified a region of pSS-1, designated pSS-1BT, which appeared to be specific for savannah form O. volvulus. Tests of isolates from different areas demonstrated that the specificity of pFS-1 and pSS-BT were not confined to a small geographic region. However, the close relationship of pFS-1 and pSS-BT to less specific members of the repeat family means that their specificity and sensitivity are affected by small changes in the conditions under which they are used.

Animals↗
PubMed1989

Cloning and characterization of an Onchocerca volvulus specific DNA sequence.

A cloned sequence, pOvs134, was isolated from a genomic library prepared from Onchocerca volvulus of savanna origin in the plasmid pUC9. pOvs134 hybridizes to all the geographic isolates of O. volvulus tested from both the New and the Old World, but not to the species Onchocerca gibsoni, Onchocerca gutturosa, Onchocerca ochengi, Onchocerca cervicalis, the filarial parasites Brugia malayi, or Dirofilaria immitis, nor to human or simuliid DNA. As little as 250 pg of DNA can be detected on a dot blot hybridization, suggesting that pOvs134 is sensitive enough to detect a single third stage larva. DNA sequence analysis of the inserted DNA of pOvs134 revealed that it consisted of twelve examples of a 149-bp repeat. The sequence of this repeat is strikingly similar to that of two O. volvulus genomic clones previously described, one of which has been reported to be specific for forest form O. volvulus, and one of which hybridizes to genomic DNA of several species of Onchocerca. These results suggest that the 149-bp repeat sequence is highly repeated in the genome of O. volvulus, and that variants of this repeat with different specificities exist.

Animals↗