Biomedical subjects

D J Conway

Publications and source records attributed to D J Conway.

44 records · Page 3Linked to original sources

PubMed1988

Atherosclerotic carotid artery disease in patients with retinal ischemic syndromes.

The extracranial carotid systems of 105 patients with retinal ischemia were examined using B-mode ultrasonography with integrated pulsed Doppler. Sixty-four patients had amaurosis fugax (AF), 17 central retinal artery occlusions (CRAO), and 21 branch retinal artery occlusions (BRAO). The prevalence of carotid stenosis (greater than or equal to 60%) ipsilateral to the symptomatic eye was low (16%). Eighty-six percent of AF patients had either no plaque causing less than a 60% stenosis. A significant proportion of subjects with normal duplex scans had alternative explanations for their retinal ischemia (eg, migraine, cardiac embolus). Patients with Hollenhorst plaques were more likely to have stenotic or ulcerated plaque (p = 0.04). The degree of carotid stenosis correlated significantly with the number of vascular risk factors identified in individual patients (p = 0.02). The presence of risk factors was more common in CRAO and BRAO patients compared with the AF group. Combined ultrasound-Doppler investigations of the carotid bifurcation are valuable noninvasive tools for the screening of patients with retinal ischemia.

Arteriosclerosis↗

PubMedDate not supplied

Genetic evidence for the importance of interrupted feeding by mosquitoes in the transmission of malaria.

Plasmodium falciparum isolates were obtained from 17 pairs of Gambian children, each pair living in the same house and presenting with malaria at the same time. Frequencies of allelic serotypes of 3 polymorphic blood stage proteins (MSP1, MSP2, and Exp-1) were previously determined from a large number of isolates from patients in the local area, and the probability of a random pair of isolates containing an identical genotype was calculated to be less than 0.01. However, 3 of 8 household pairs in one year, and 6 of 9 in the next year, contained identical P. falciparum genotypes, a much higher frequency than expected randomly (P less than 0.00005, for each year). This finding is discussed in terms of the probable contribution of single mosquitoes infecting more than one person.

Adolescent↗

PubMedDate not supplied

Immunodiagnosis of Strongyloides stercoralis infection: a method for increasing the specificity of the indirect ELISA.

Indirect enzyme-linked immunosorbent assay (ELISA) allows sensitive detection of serum immunoglobulin (Ig) G against a soluble extract of Strongyloides stercoralis infective larvae. In this study, 40/40 (100%) human strongyloidiasis sera had high levels of anti-S. stercoralis IgG, but 30/40 (75%) filariasis sera, and 12/40 (30%) necatoriasis sera also had higher levels than control sera from UK residents. In attempts to increase the assay specificity by absorption of cross-reactive IgG, the effectiveness of pre-incubation of sera with extracts of different parasitic nematodes was investigated. One hour of incubation with 20 micrograms/ml aqueous extract of Onchocerca gutturosa absorbed cross-reactive IgG in most filariasis and necatoriasis sera, reducing the proportion with IgG levels above the positivity threshold by more than one-half. Preliminary results suggest that absorption with extracts of other filarial nematodes is equally effective, and that some of the cross-reactive IgG is directed against phosphorylcholine. Cross-reactive IgG in most necatoriasis sera was effectively absorbed with 20 micrograms/ml extract of Necator americanus. Cross-reactive IgG was not effectively absorbed with an extract of Ascaris lumbricoides. Absorption of cross-reactive IgG is an effective means of increasing the specificity of the indirect ELISA, for use in the immunodiagnosis and immuno-epidemiology of S. stercoralis infection.

Absorption↗

PubMedDate not supplied

Strongyloides stercoralis in an urban slum community in Bangladesh: factors independently associated with infection.

Stool samples from 880 residents in an urban slum in Dhaka, Bangladesh, were collected on 3 occasions over one year, and examined for intestinal parasites. Information on many potential risk factors for infection was obtained by questionnaire from a respondent in each household studied. In a crude univariate analysis of the data, several of the factors were found to be significantly associated with Strongyloides stercoralis infection. Most of these factors were co-variate with one another, and with poverty generally. Using Mantel-Haenszel chi 2 tests to control for confounding effects of each variable individually, the following 4 factors remained independently associated with S. stercoralis infection: respondent's use of a community latrine rather than a private latrine, living in a house with an earth floor rather than a cement floor, being of Bihari ethnicity, and being 7-10 years of age. Implications of these results for the epidemiology and control of strongyloidiasis are briefly discussed.

Adolescent↗

PubMedDate not supplied

Enzyme polymorphisms in Ascaris lumbricoides in Bangladesh.

Fourteen enzymes of Ascaris lumbricoides were analysed electrophoretically on cellulose acetate plates; 8 stained well and 3 were found to be polymorphic. Allelic and genotypic frequencies at the 3 polymorphic enzyme loci, Mpi, Pgi and 6-Pgd, were determined in a sample of 117 worms from 8 children living in different houses in an urban slum in Bangladesh. Allele frequencies in samples of parasites from the different children were compared to test for the possibility of non-random distribution of parasite genotypes between people. No strong evidence of differences was found. Diploid genotype frequencies did not deviate significantly from those expected from the Hardy-Weinberg equilibrium. Significant linkage disequilibrium was observed in one of 3 pairs of enzyme loci tested, which might suggest that some genetic subdivision exists in the local A. lumbricoides population, although no strong interference should be made from this single result. Overall, the results suggest that the worms sampled formed part of a single population which appears to be randomly mating.

Alleles↗

PubMedDate not supplied

Household aggregation of Strongyloides stercoralis infection in Bangladesh.

Strongyloides stercoralis infections were shown to be aggregated in households in an urban slum community in Dhaka, Bangladesh. Parasitological data on 880 residents living in 280 households were analysed statistically using 3 different tests, each of which yielded significant evidence of household aggregation of S. stercoralis infection. One test was applied to the data after stratification for 4 variables were previously shown to be independently associated with infection. Evidence of household aggregation of infection remained after stratification, suggesting that aggregation is due not only to shared risk factors, but also to either familial genetic predisposition to infection or close contact person to person transmission of infection within households.

Adolescent↗

PubMedDate not supplied

Genotyping of Plasmodium falciparum infections by PCR: a comparative multicentre study.

Genetic diversity of malaria parasites represents a major issue in understanding several aspects of malaria infection and disease. Genotyping of Plasmodium falciparum infections with polymerase chain reaction (PCR)-based methods has therefore been introduced in epidemiological studies. Polymorphic regions of the msp1, msp2 and glurp genes are the most frequently used markers for genotyping, but methods may differ. A multicentre study was therefore conducted to evaluate the comparability of results from different laboratories when the same samples were analysed. Analyses of laboratory-cloned lines revealed high specificity but varying sensitivity. Detection of low-density clones was hampered in multiclonal infections. Analyses of isolates from Tanzania and Papua New Guinea revealed similar positivity rates with the same allelic types identified. The number of alleles detected per isolate, however, varied systematically between the laboratories especially at high parasite densities. When the analyses were repeated within the laboratories, high agreement was found in getting positive or negative results but with a random variation in the number of alleles detected. The msp2 locus appeared to be the most informative single marker for analyses of multiplicity of infection. Genotyping by PCR is a powerful tool for studies on genetic diversity of P. falciparum but this study has revealed limitations in comparing results on multiplicity of infection derived from different laboratories and emphasizes the need for highly standardized laboratory protocols.

Analysis of Variance↗

PubMedDate not supplied

Humoral responses in human strongyloidiasis: correlations with infection chronicity.

Strongyloides stercoralis L3-specific antibody isotype responses amongst individuals with known long-standing (28-46 years) infection were compared with those of 'young' (6-29 years of age) and 'old' (30-80 years of age) infected individuals from an endemic Jamaican population. Characterization of age-dependent isotype patterns in the endemic community showed that immunoglobulin (Ig) G1 responses were significantly inversely correlated with age. Additionally, a trend towards lower IgE levels in the older age group was observed. Comparison with responses amongst known chronically infected individuals showed that IgG1 and IgE levels were similar to those of the 'old' endemic group, but were significantly lower than those of the 'young' group. In contrast, IgA levels were similar in both endemic groups, but were elevated in chronically infected individuals. IgG4 levels were similar in all groups studied. These findings suggest that age correlates with infection chronicity in communities endemic for S. stercoralis, and that individuals acquire infection early in their lives and remain infected into adulthood. Early and sustained upregulation of IgG4 may facilitate the establishment of infection and, in combination with developing IgE hyporesponsiveness, may promote chronic asymptomatic strongyloidiasis. Conversely, upregulated IgA may be involved in controlling chronic infection levels which are reflected in reduced IgG1 production.

Adolescent↗