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Biomedical subjects

C G Meyer

Publications and source records attributed to C G Meyer.

At least 37 records · Page 2Linked to original sources
PubMed1999

The role of red blood cell polymorphisms in resistance and susceptibility to malaria.

In regions highly endemic for Plasmodium falciparum malaria, red cell polymorphisms that confer resistance to severe disease are widespread. Sickle cell trait, alpha-thalassemia, glucose-6-phosphate dehydrogenase deficiency, and blood groups were determined in 100 children from Gabon with severe malaria who were matched with 100 children with mild malaria and followed up for evaluation of reinfections. The sickle cell trait was significantly associated with mild malaria and blood group A with severe malaria. During follow-up, the original severe cases had significantly higher rates of reinfection than the original mild cases, with higher parasitemia and lower hematocrit values. Incidence rates did not differ in the context of erythrocyte polymorphisms, but patients with sickle cell trait presented with markedly lower levels of parasitemia than those without. Thus, the severity of malaria is partly determined by the presence of blood group A and the sickle cell trait. The different presentation of reinfections in severe versus mild cases probably reflects different susceptibility to malaria.

ABO Blood-Group System↗
PubMed1999

High rate of mixed and subpatent malarial infections in southwest Nigeria.

The rate of malarial parasitemia in children and adults was assessed by microscopy and the polymerase chain reaction in a holoendemic area in Nigeria. A high rate of subpatent Plasmodium falciparum parasitemia (19.6%) was found. Plasmodium malariae and P. ovale infections were common in a rural area (26.1% and 14.8%) but were observed sporadically in individuals from an urban area. Simultaneous infections with P. falciparum, P. malariae, and P. ovale were frequent in the rural area (11.7% triple infections). The rate of triple infections was higher than expected from the prevalences of each species (P < 0.00001). Spleen enlargement was associated with mixed infections of P. falciparum and P. malariae (odds ratio [OR] = 5.9, 95% confidence interval [CI] 3.0-11.7) and less frequently observed in individuals without detectable parasitemia (OR = 0.06, 95% CI = 0.01-0.3). Spleen enlargement and titers of antibodies to schizonts were positively correlated with parasite densities. The results also suggest that in some individuals a long-lasting subpatent parasitemia might occur.

Adolescent↗
PubMed1999

Short report: high prevalence and imbalanced age distribution of the Plasmodium falciparum dihydrofolate reductase gene Asn108 mutation in an area of low pyrimethamine usage in Nigeria.

Resistance of Plasmodium falciparum to pyrimethamine is associated with a non-silent point mutation of the parasite dihydrofolate reductase (DHFR) gene (Ser108 --> Asn108). Wide-scale use of antimalarials is thought to contribute to the emergence of drug resistance. In 131 P. falciparum-infected children in rural Nigeria, the frequency of the resistant Asn108 genotype was assessed by enzymatic restriction digestion of polymerase chain reaction-amplified DHFR sequences and compared with residual pyrimethamine blood levels. The prevalence of the Asn108 variant was 41.2%. In 18.3% of the isolates, both the Asn108 and the wild-type alleles were present. In contrast to the high prevalence of resistant genotypes, residual pyrimethamine blood levels were detected in only 4%. Furthermore, age was found to be a determinant of the parasite genotype since the proportion of Asn108 variants decreased with age (P < 0.05). These findings indicate that additional, unidentified factors, rather than selection by residual drug levels alone, might be responsible for the emergence of pyrimethamine-resistant parasite genotypes.

Age Distribution↗
PubMed1999

Serum transferrin receptor levels are increased in asymptomatic and mild Plasmodium falciparum-infection.

BACKGROUND AND OBJECTIVE: The serum transferrin receptor (sTfR) concentration in an individual reflects the extent of erythropoietic activity and is considered a useful marker of iron deficiency independent of concurrent inflammation or infection. However, data on the impact of malaria on this parameter are ambiguous. We have examined potential associations of asymptomatic and mild Plasmodium falciparum-infections and of several erythrocyte variants with sTfR values in South West Nigeria. DESIGN AND METHODS: In a cross-sectional study among 161 non-hospitalized children, sTfR concentrations and P. falciparum parasitemia were assessed. In addition, hemoglobin (Hb) and serum ferritin values, Hb-types, glucose-6-phosphate dehydrogenase (G6PD)deficiency and a-globin genotypes were determined and the effects of these factors on sTfR levels were analyzed by univariate and multivariate statistical methods. RESULTS: P. falciparum-infection was present in 77% of the children. Mean sTfR levels were higher in infected than in non-infected children (geometric mean, 3.68, 95% confidence interval [3.5-3.9] vs. 2.99 [2.7-3.3] mg/L; p = 0.0009). There was a significant trend for higher sTfR values with increasing parasite density. sTfR values decreased continuously with age. Hb-types, G6PD-, and a-globin genotypes did not correlate with sTfR levels. In the multivariate analysis, age, Hb and log ferritin values, and parasite density of P. falciparum were independently associated with log sTfR values. INTERPRETATION AND CONCLUSIONS: sTfR concentrations are increased in asymptomatic and mild P. falciparum-infections suggesting adequate bone marrow response in this condition. The diagnostic value of sTfR levels for iron deficiency may be impaired in areas where stable malaria occurs.

Age Factors↗
PubMed1998

Human leukocyte antigens in tuberculosis and leprosy.

Human mycobacterial infections are characterized by a spectrum of clinical and immunological manifestations. Specific human leukocyte antigen (HLA) factors are associated with the subtypes of leprosy that develop and the course of tuberculosis after infection. The identification of protective mycobacterial antigens presented by a broad variety of HLA molecules will have important implications for the design of vaccines.

Animals↗
PubMed1998

HLA DPA1/DPB1 genotype and haplotype frequencies, and linkage disequilibria in Nigeria, Liberia, and Gabon.

The frequencies of DPA1 and DPB1 alleles and their occurrence in haplotypic linkage were assessed and compared in Nigerian, Liberian, and Gabonese individuals. Differences were seen in the distribution patterns; these differences were more pronounced between the Gabonese and the other two populations than between Liberians and Nigerians. Several haplotypic DPA1-DPB1 combinations could be verified by homozygosity. Linkage disequilibria of DPA1-DPB1 combinations, indicating further probable haplotypes, were estimated. Although different allele and haplotype frequencies were recognized in the three subgroups, the linkage disequilibria were mostly either positive or negative in all populations.

Ethnicity↗
PubMed1998

Blinded, externally controlled multicenter evaluation of light microscopy and PCR for detection of microsporidia in stool specimens. The Diagnostic Multicenter Study Group on Microsporidia.

The quality parameters for the detection of microsporidia in identical sets of 50 stool samples were determined for six laboratories where technicians used light microscopy and for six laboratories where technicians used PCR. The average overall sensitivities were 67% (89% for patient samples only) for the PCR laboratories and 54% (80% for patient samples only) for the light microscopy laboratories. Specificities were 98 and 95%, respectively. Differences in results were most apparent between the individual laboratories rather than between the two major methods used.

Animals↗
PubMed1998

HLA-DP control of human Schistosoma haematobium infection.

The DPA1 and DPB1 alleles of the major histocompatibility complex (MHC) class II were determined in 110 patients and 120 healthy controls of a Gabonese population from an area endemic for Schistosoma haematobium infection. The MHC-DP alleles of the variable second exons and their human leukocyte antigen (HLA) epitopes were correlated with egg excretion, interleukin-4 and interferon-gamma patterns, and bladder abnormalities, as detected by ultrasonography. A methionine at position 11 of the DP alpha molecule (Met-11) and DPA1*0301 were associated with schistosomiasis when compared with controls (phenotypic gene frequencies = 0.791 versus 0.583 and 0.555 versus 0.375, respectively). Met-11 homozygosity occurred more often in patients, whereas healthy controls were more frequently homozygous for an alanine at position 11 (Ala-11). The combination of the DPB1-epitope DEAV (positions 84-87 of the DP beta molecule) and Met-11 positive DPA1 alleles was more frequent in patients than in controls (0.573 versus 0.316). Two years after antischistosomal treatment, the rate of reinfection as examined in 55 of the 110 former patients was higher in DPA1*0301-positive individuals than in those not possessing this allele (P < 0.001). Ala-11 positive individuals showed less frequently ultrasonographic signs of bladder pathology than Ala-11 negative individuals (P < 0.05). Our results suggest a role of MHC-DP elements in the manifestation of disease in S. haematobium infection.

Adult↗
PubMed1997

Hepatitis G virus RNA and hepatitis G virus antibodies in renal transplant recipients: prevalence and risk factors.

BACKGROUND: Hepatitis G virus (HGV/GBV-C) RNA indicating current infection has been frequently isolated from the sera of transplant recipients and other multitransfused individuals. Lifetime exposure to the virus, however, is unknown. We carried out a study to determine the prevalence and risk factors of HGV antibodies and of HGV RNA among renal transplant recipients, and to investigate possible associations between HGV RNA and immunosuppressive treatment. METHODS: HGV RNA was detected by reverse transcriptase-polymerase chain reaction, and HGV antibodies (anti-E2) by a newly developed immunoassay. To assess risk factors for HGV exposure, univariate and multivariate analysis was performed. RESULTS: Of the 221 patients, 14% were HGV RNA positive and 40% had HGV antibodies. Both HGV RNA and anti-HGV were present in only two individuals. Thus, the overall HGV exposure prevalence was 53%. It increased significantly with the number of blood transfusions. In logistic regression, the adjusted HGV exposure prevalence odds ratio was 5.7 (95% confidence interval [CI]: 2.2-15) among patients with > or =10 transfusions (baseline: no transfusions). Other independent risk factors were a longer duration of hemodialysis and a longer time interval since transplantation. HGV viremia was not associated with the type of immunosuppressive treatment. Alanine aminotransferase levels were not significantly increased among HGV RNA-positive patients. CONCLUSIONS: Much higher proportions of renal transplant recipients were exposed to HGV than is suggested by HGV RNA detection alone. The majority of infected individuals apparently eliminate the virus over time. Contaminated blood transfusions have to be regarded as a main risk factor for HGV infection.

Adolescent↗
PubMed1997

HLA DRB1-DQA1-DQB1 haplotype diversity in two African populations.

HLA class II DRB1-DQA1-DQB1 haplotypic polymorphism was determined in 120 Liberian and 230 Gabonese individuals. In our study groups, the number of allelic variants observed for each locus was similar to that found in non-African populations. However, 39 novel haplotypes and several yet unrecognized DRB1-DQA1 and DQA1-DQB1 combinations were identified. The extent of HLA-haplotypic variability in Africans appears to result from the high degree of allele combinations rather than from allelic polymorphism.

Africa↗
PubMed1996

Genetic divergence and speciation in an extremely young species flock in Mexico formed by the genus Cyprinodon (Cyprinodontidae, Teleostei).

The lake Laguna Chichancanab contains one of the evolutionarily youngest species flocks known, composed of five endemic species of the genus Cyprinodon. The presumed sister species Cyprinodon artifrons still exists in marine coastal habitats. Sequences of the mitochondrial control region were obtained for C. artifrons (genes of 17 individuals sequenced) and for all five endemic species (genes of 32 individuals sequenced). While nine different haplotypes were found in C. artifrons, only a single haplotype was shared with the species from the laguna. Four additional haplotypes were found among the endemics. These four were most closely related to that single haplotype shared with C. artifrons. The deprivation in haplotypes among the endemics points to a small founder population or to bottlenecking. The distribution pattern of overlapping haplotypes in four of the five species suggests incomplete lineage sorting or hybridization among them. Complete reproductive isolation is only assumed for one species, C. maya, in which a single and unique haplotype was found.

Animals↗
PubMed1996

Malaria and onchocerciasis: On HLA and related matters.

In recent years, associations of particular factors of the human leukocyte antigen (HLA) system with two major infectious diseases of tropical countries have been recognized: common West African HLA antigens are associated with protection from severe Plasmodium falciparum malaria, and HLA-D alleles are associated with generalized disease, localized disease and putative immunity in Onchocerca volvulus infection. Here, Christian Meyer and Peter Kremsner summarize current information on the involvement of HLA factors in P. falciparum malaria and O. volvulus infection, and briefly report on HLA-related immunological characteristics of various conditions in these infectious diseases.

Journal Article↗
PubMed1996

Autochthonous cutaneous larva migrans in Germany.

Cutaneous larva migrans syndrome is extremely rare in Germany. However, three cases of this syndrome were diagnosed in patients from Berlin, Germany, in the summer of 1994. Exposure to the infective agent in endemic areas and close contact with animals were excluded. It is assumed that the extreme temperatures in summer 1994 favoured the conditions of infection.

Adult↗