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Biomedical subjects

F Davidson

Publications and source records attributed to F Davidson.

At least 37 records · Page 2Linked to original sources
PubMed1996

Relevance of RIBA-3 supplementary test to HCV PCR positivity and genotypes for HCV confirmation of blood donors.

HCV antibody screening of 624,910 blood donations resulted in 3,832 samples being referred for confirmation. All were tested by RIBA-3 with 2,710 negative, 945 indeterminate and 177 positive results. HCV RNA was detected by PCR in an average of 69.5% of RIBA-3 positives (4 bands 84.1%; 3 bands 74.1%; 2 bands 34.1%) and only 0.53% of RIBA-3 indeterminates. Eighty-four percent of samples with a total RIBA-3 band intensity score (maximum 16) of > or = 8 were PCR positive compared with only 22% of those with a score of < 8. Total mean band intensities for HCV genotype 1 samples (n = 65) were 13.2, genotype 2 (n = 17) 11.4 and genotype 3 (n = 65) 11.2 with type 1 samples showing greater reactivity with c100 and c33 antibodies. No PCR positive type 1 samples were found with RIBA-3 total band scores less than 8, no PCR positive type 2 samples less than 6, whilst PCR positive type 3 samples were found with scores as low as 2. NS5 indeterminates were the most common (40.2%) single band pattern but yielded no PCR positive samples, followed by c33 (23.3%) with one PCR positive and c100 (20.2%) with one PCR positive whilst c22 indeterminates were least common (16.3%) but included three PCR positive donors. All five RIBA-3 indeterminate PCR positive donors were type 3.

Blood Donors↗
PubMed1996

Lymphocyte responses to human cytomegalovirus in different groups of patients in Britain and in adults from west Africa and the Middle East.

Antibody prevalence and lymphocyte proliferation responses to cytomegalovirus (CMV) and herpes simplex virus (HSV) were compared in several different groups of patients: genitourinary medical (GUM) patients, hemophiliacs, men with clinical acquired immunodeficiency syndrome (AIDS) and cases of primary CMV mononucleosis, and also in adults in the general population (control subjects) comprising separate groups native to Britain, West Africa, and the Middle East. Among the British control subjects who were positive for CMV IgG, all were also positive against CMV antigen by the lymphocyte transformation test (LTT). However, among those who were CMV IgG-positive in the various groups of patients, 20-86.9% gave positive responses to CMV antigen by the LTT; moreover, 75.7% and 55.5% of the CMV IgG-positive healthy control subjects from West Africa and the Middle East, respectively, gave positive LTT responses to CMV antigen. When the same groups of patients were tested for responsiveness to HSV antigen by the LTT, there was good agreement between a positive result by this test and by serology in all except those with primary CMV mononucleosis (42.8%). Overall, lymphocyte responses to CMV were significantly impaired in healthy, CMV antibody-positive subjects from West Africa and the Middle East compared to similar subjects from Britain.

Adult↗
PubMed1996

Third-generation recombinant immunoblot assay: comparison of reactivities according to hepatitis C virus genotype.

BACKGROUND: Recombinant immunoblot assay (RIBA) is widely used as a supplemental test in hepatitis C virus (HCV) confirmatory algorithms. As this assay is based on HCV type 1, its performance was examined with the common European HCV genotypes (1, 2, and 3). STUDY DESIGN AND METHODS: A study was performed to retest in third-generation RIBA (RIBA-3) all 146 second-generation RIBA (RIBA-2)-positive polymerase chain reaction-positive samples detected by second-generation enzyme-linked immunosorbent assays and having known HCV genotypes (74 HCV type 1, 21 type 2, 51 type 3). RIBA band intensities were examined according to HCV genotype. An additional 90 RIBA-3-confirmed PCR-positive samples (47 HCV type 1, 5 type 2, 38 type 3) detected by third-generation enzyme-linked immunosorbent assays were also examined. RESULTS: In the first group of 146 samples, the RIBA-3 NS4 (c100p) band showed a marked improvement in sensitivity for the detection of HCV types 2 and 3 over that of the c100 antigen of RIBA-2, but the mean band intensities of HCV types 2 and 3 remained significantly lower than those of type 1. Improved sensitivity of the NS3 band of RIBA-3 to HCV type 3 was also apparent, but, again, the mean band intensity measured was lower for type 3 than for either type 1 or type 2. The c22 band of RIBA-2 and RIBA-3 exhibited equal sensitivity for all HCV genotypes. These differences were also apparent when RIBA-3 was used in conjunction with third-generation enzyme-linked immunosorbent assays. CONCLUSION: The current RIBA-3 lacks sensitivity to the NS4 antibody for HCV types 2 and 3. The incorporation of type-specific components to other genotypes for NS4 (and NS3) antigens should be considered by the manufacturers.

Blood Donors↗
PubMed1996

Outbreak of acute hepatitis C following the use of anti-hepatitis C virus--screened intravenous immunoglobulin therapy.

BACKGROUND & AIMS: Hepatitis C virus (HCV) infection has been associated with intravenous (IV) immunoglobulin (Ig), and plasma donations used to prepare IV Ig are now screened to prevent transmission. Thirty-six patients from the United Kingdom received infusions from a batch of anti-HCV antibody-screened intravenous Ig (Gammagard; Baxter Healthcare Ltd., Thetford, Norfolk, England) that was associated with reports of acute hepatitis C outbreak in Europe. The aim of this study was to document the epidemiology of this outbreak. METHODS: Forty-six patients from the United Kingdom treated with Gammagard (34 exposed and 12 unexposed to the batch) returned epidemiological questionnaires. RESULTS: Eighty-two percent of the exposed patients (28 of 34) became positive for HCV RNA. Eighteen percent of the patients (6 of 34) who had infusions with this batch tested negative for HCV RNA, but 2 of the patients had abnormal liver function and subsequently seroconverted to anti-HCV antibody positive. Twenty-seven percent of the patients (9 of 34) developed jaundice, and 79% (27 of 34) had abnormal liver transferase levels. Virus isolates (n=21), including an isolate from the implicated batch, were genotype 1a and virtually identical by sequence analysis of the NS5 region, consistent with transmission from a single source. CONCLUSIONS: Hepatitis C infection can be transmitted by anti-HCV-screened IV Ig. Careful documentation of IV Ig batch numbers and regular biochemical monitoring is recommended for all IV Ig recipients.

Acute Disease↗
PubMed1996

Levels of hepatitis C virus in blood donors infected with different viral genotypes. International HCV Collaborative Study Group.

The level of hepatitis C virus (HCV) in the serum of 337 blood donors infected with different viral genotypes was investigated by branched DNA assay. Viral genotype was deduced by restriction analysis of the virus 5'-noncoding region. Samples included genotypes 1a, 1b, 2a, 2b, 3,4,5, and 6. Multivariate analysis revealed that the ranges of HCV levels were similar for all viral genotypes and subtypes (P=.18), with the possible exception of genotype 4. Virus levels were significantly lower in female than in male subjects (P<.001) but did not correlate with donor age (P=.06) or genotype or with donor age, sex, or country. These results indicate a similar replicative capacity in vivo for different HCV genotypes and clarify the influence of host and virus factors on disease severity and responsiveness to interferon treatment.

Blood Donors↗
PubMed1996

Comparison of culture with the polymerase chain reaction for detection of Ureaplasma urealyticum in endotracheal aspirates of preterm infants.

Polymerase chain reaction (PCR) amplification of the urease genes of Ureaplasma urealyticum was compared with culture for detection of the organism in 100 endotracheal aspirates from 54 ventilated preterm infants. Ninety specimens gave negative results by both culture and PCR and three specimens gave positive results by both culture and PCR. Six specimens were negative by culture but positive by PCR. The one specimen positive by culture and negative by PCR was interpreted as a false-positive culture result. Overall agreement between results obtained by culture and PCR was 93%. PCR is a sensitive and reliable method for the detection of U. urealyticum in neonatal endotracheal secretions. Detection by PCR (1-2 days) is more rapid than culture (2-5 days) and this will be important if early therapeutic intervention is shown to be effective.

Base Sequence↗
PubMed1996

Survey of type 6 group variants of hepatitis C virus in Southeast Asia by using a core-based genotyping assay.

Previous surveys of the prevalences of genotypes of hepatitis C virus (HCV) in different populations have often used genotyping assays based upon analysis of amplified sequences from the 5' noncoding region (5'NCR), such as restriction fragment length polymorphism (RFLP) or hybridization with type-specific probes (e.g., InnoLipa). Although highly conserved, this region contains several type-specific nucleotide polymorphisms that allow major genotypes 1 to 6 to be reliably identified. Recently, however, novel HCV variants found in Vietnam and Thailand that are distantly related to the type 6a genotype (type 6 group) by phylogenetic analysis of coding regions of the genome often have sequences in the 5'NCR that are similar or identical to those of type 1 and could therefore not be identified by an assay of sequences in this region. We developed a new genotyping assay based upon RFLP of sequences amplified from the more variable core region to investigate their distribution elsewhere in southeast (SE) Asia. Among 108 samples from blood donors in seven areas that were identified as type 1 by RFLP in the 5'NCR, type 6 group variants were found in Thailand (7 from 28 samples originally identified as type 1) and Burma (Myanmar) (1 of 3) but were not found in Hong Kong (n = 43), Macau (n = 8), Taiwan (n = 6), Singapore (n = 2), or Malaysia (n = 18). Although this small survey suggests a relatively limited distribution for type 6 group variants in SE Asia, larger studies will be required to explore their distribution in other geographical regions and the extent to which their presence would limit the practical usefulness of 5'NCR-based genotyping assays for clinical or epidemiological purposes.

Asia, Southeastern↗
PubMed1996

Production of fruits and vegetables at the homestead is an important source of vitamin A among women in rural Bangladesh.

BACKGROUND: Vitamin A deficiency is considered to be an important public health problem in Bangladesh. A universal biannual distribution of high-dose vitamin A capsules has been in place for over the past two decades. This supplementation has been beneficial for preschool children. Bangladesh has been exploring more sustainable approaches for all segments of the population. To support this initiative, Helen Keller International has implemented a homegardening promotion project since 1993. This project is executed on a large scale and currently reaches an estimated 244,000 families. METHODS: This paper presents data from 7341 women of reproductive age which were collected as part of the baseline census of a community monitoring system whose objective is to track progress and measure the impact of home-gardening activities. RESULTS: Vitamin A intake in this population derived almost entirely from the consumption of fruits and vegetables. Logistic regression analyses showed that maternal vitamin A intake was determined by qualitative indicators of homestead gardens (type of home garden, the total quantity of provitamin A-rich food produced and the number of fruits and vegetables varieties grown in the garden) after adjusting for socio-economic status. CONCLUSIONS: These results indicate that traditional production of provitamin A-rich fruits and vegetables in the homestead may provide a valuable contribution to vitamin A intake in communities where alternative dietary sources of vitamin A are scarce.

Agriculture↗
PubMed1995

Molecular epidemiology of an outbreak of infection with hepatitis C virus in recipients of anti-D immunoglobulin.

In a retrospective investigation of possible transmission of hepatitis C virus (HCV) by anti-rhesus D immunoglobulin (anti-D) in 1977, we compared variants infecting anti-D recipients in Ireland of one of the implicated batches with those of epidemiologically unrelated HCV-infected individuals. All 100 of the recipients of the batch investigated to date were infected with a single genotype (type 1), consistent with a single-source outbreak, whereas a wider range of genotypes (1, 2, and 3) were found in anti-HCV positive individuals from Ireland infected by different routes. Nucleotide sequences from a 222 base fragment from the NS-5 region of the genome amplified from stored aliquots of the implicated batch closely matched those detected in anti-D recipients 17 years after the transmission event. This study shows the value of molecular epidemiological techniques for identifying distant sources of infection, and for the epidemiological investigation of the current distribution and transmission of HCV in different populations.

Antibodies, Anti-Idiotypic↗
PubMed1995

Survey of major genotypes and subtypes of hepatitis C virus using RFLP of sequences amplified from the 5' non-coding region.

A method is described for identifying different genotypes of hepatitis C virus (HCV) by restriction endonuclease cleavage of sequences amplified by PCR from the 5' non-coding region. Using the enzymes HaeIII-RsaI and HinfI-MvaI, followed by cleavage with BstU1 or ScrFI, it was possible to identify and distinguish HCV genotypes 1a, 1b, 2a, 2b, 3a, 3b, 4, 5 and 6. The method was used to investigate the prevalence of these genotypes in 723 blood donors in 15 countries, the largest survey to date, and one which covered a wide range of geographical regions (Europe, America, Africa and Asia). These results, combined with a review of the existing literature, indicate the existence of several distinct regional patterns of HCV genotype distribution, and provide the framework for future detailed epidemiological investigations of HCV transmission.

Blood Donors↗
PubMed1995

Variation of the hepatitis C virus 5' non-coding region: implications for secondary structure, virus detection and typing. The International HCV Collaborative Study Group.

Variation in the 5' non-coding region (5'NCR) of hepatitis C virus (HCV) was investigated in detail by comparing 314 5'NCR sequences of viruses of genotypes 1 to 6. Evidence was obtained for the existence of associations between particular 5'NCR sequence motifs and virus types and subtypes. No recombination was observed between the 5'NCR and coding regions of different genotypes, implying that the sequence of subgenomic regions such as the 5'NCR can be used to deduce virus genotype. The distribution of polymorphic sites within the 5'NCR is used to propose improved oligonucleotide primers for virus detection and quantification that would be equally efficient in detecting RNA of different virus genotypes. The accuracy of two different genotyping methods (RFLP and the line probe assay) based on analysis of sequence polymorphisms in the 5'NCR is predicted from the sequences surveyed to be 97% and 83% respectively for types 1 to 6, with higher accuracies for distinguishing between subtypes 1a/1b, 2a/2b or 3a/3b. Several sites of genotype-specific polymorphism were covariant and maintained the base pairings required for a secondary structure model of the 5'NCR. Other sites of variation suggest minor modifications to this model and have implications for the probable functions of the 5'NCR.

Base Composition↗
PubMed1995

The distribution of hepatitis C virus genotypes in Turkish patients.

The distribution of hepatitis C virus (HCV) genotypes was investigated in 89 HCV-infected Turkish patients. Blood samples were collected from haemodialysis patients (n = 45), chronic liver disease (CLD) patients (n = 38), acute non-A, non-B (NANB) hepatitis patients (n = 2) and blood donors (n = 4). HCV RNA sequences were amplified in the 5' non-coding region and were typed by restriction fragment length polymorphism analysis. The predominant genotype was 1b (75.3%), followed by 1a (19.1%), 2 (3.4%) and 4 (2.2%). While there was no significant difference in the distribution of HCV genotypes with respect to age, sex, transfusion history, alanine aminotransferase levels or liver histology (in the CLD group), type 1a-infected patients were younger than type 1b-infected patients (P < 0.05) in the haemodialysis group. Serological reactivity to recombinant HCV proteins was assessed in 58 samples using the Chiron RIBA-2 assay. The reactivity of samples from patients infected with type 1b with 5-1-1 and c100 antigens was significantly lower (P < 0.05) than the reactivity of samples from those infected with type 1a. These results, together with the results of two previous studies, indicate that HCV genotypes 1, 2, 3 and 4 are prevalent in different frequencies in the Turkish population. Determination of the genotype distribution of HCV in a geographical area may provide important clues for studying the epidemiology, transmission and pathogenesis of HCV-related diseases and may also aid in improving serological assays to detect HCV infection.

Adult↗
PubMed1995

Hepatitis C virus variants and the role of genotyping.

Hepatitis C virus demonstrates considerable divergence in nucleotide sequence. This variation may affect virus detection, disease outcome, and the effectiveness of interferon treatment. For example, infection with genotype 1 is associated with a lower response rate to interferon treatment. Hepatitis C virus can be classified into six distinct types, comprising at least 74 different subtypes. Both types and subtypes are subject to geographical differences in distribution, presumably reflecting the epidemiological history of the virus. However, because this history may be blurred by migration and by commerce in blood products between regions, screening and typing assays must recognize both the major indigenous and more exotic virus genotypes. Little information exists about the role of virus sequence variation in screening for hepatitis C virus antibodies, but there is some evidence that the reactivity of current serological screening assays for hepatitis C virus is genotype dependent. In the future, screening assays may need to include antigens specific for different virus types or may need to be designed with regard to the particular types found in a certain area. Antigenic variation may also mean that an effective vaccine needs to be multivalent to protect against all genotypes present in a given region. There are several polymerase chain reaction-based methods of distinguishing between hepatitis C virus variants. These methods must be continually updated, however, as new sequence variants are discovered. Alternative genotyping assays are based on the host's serological response to virus infection, but these cannot distinguish between virus subtypes and are unsuitable for immunocompromised patients. As more countries are sampled, it is likely that more genotypes will be identified and this may help elucidate the origins of hepatitis C virus. Detailed epidemiological studies may delineate past and current routes of transmission.

Enzyme-Linked Immunosorbent Assay↗
PubMed1994

A portable dual energy x-ray absorptiometry technique for the measurement of bone mineral in preterm infants.

A dual energy x-ray absorptiometry technique has been developed for the measurement of bone mineral in preterm infants. Two films are taken of the infant's forearm using a standard mobile x-ray set on the ward at two x-ray energies. Included in the field of view is a double step wedge made of aluminum and Perspex. The images are digitized by viewing them on a light box with a TV camera. The bone mineral content in the forearm can then be mapped by the measurement of light intensity in matching pixels of the two films and comparison with the intensities in the step wedge. The bone mineral concentration in the radius, expressed as bone mineral per unit length (mg/mm), is calculated. The technique has been tested using phantoms of calcium hydroxylapatite set in a tissue equivalent material and in Perspex. It has been shown that the reproducibility of the technique is approximately 7% and that there is a systematic underestimate of bone mineral of about 17%. The technique has been shown to be linear up to a bone mineral concentration of 8 mg.mm-1. Longitudinal studies for 14 infants that show an initial 6-wk period of demineralization after birth with a subsequent mineralization phase are reported.

Absorptiometry, Photon↗