Inaccuracy of enzyme-linked immunosorbent assay using soluble and recombinant antigens to detect asymptomatic infection by Leishmania infantum.

BACKGROUND: One of the most important drawbacks in visceral leishmaniasis (VL) population studies is the difficulty of diagnosing asymptomatic carriers. The aim of this study, conducted in an urban area in the Southeast of Brazil, was to evaluate the performance of serology to identify asymptomatic VL infection in participants selected from a cohort with a two-year follow-up period. METHODOLOGY: Blood samples were collected in 2001 from 136 cohort participants (97 positive and 39 negatives, PCR/hybridization carried out in 1999). They were clinically evaluated and none had progressed to disease from their asymptomatic state. As controls, blood samples from 22 control individuals and 8 patients with kala-azar were collected. Two molecular biology techniques (reference tests) were performed: PCR with Leishmania-generic primer followed by hybridization using L. infantum probe, and PCR with specific primer to L. donovani complex. Plasma samples were tested by ELISA using three different antigens: L. infantum and L. amazonensis crude antigens, and rK39 recombinant protein. Accuracy of the serological tests was evaluated using sensitivity, specificity, likelihood ratio and ROC curve. FINDINGS: The presence of Leishmania was confirmed, by molecular techniques, in all kala-azar patients and in 117 (86%) of the 136 cohort participants. Kala-azar patients showed high reactivity in ELISAs, whereas asymptomatic individuals presented low reactivity against the antigens tested. When compared to molecular techniques, the L. amazonensis and L. infantum antigens showed higher sensitivity (49.6% and 41.0%, respectively) than rK39 (26.5%); however, the specificity of rK39 was higher (73.7%) than L. amazonensis (52.6%) and L. infantum antigens (36.8%). Moreover, there was low agreement among the different antigens used (kappa<0.10). CONCLUSIONS: Serological tests were inaccurate for diagnosing asymptomatic infections compared to molecular methods; this could lead to misclassification bias in population studies. Therefore, studies which have used serological assays to estimate prevalence, to evaluate intervention programs or to identify risk factors for Leishmania infection, may have had their results compromised.

Hepatitis C, HCV genotypes and hepatic siderosis in patients with chronic renal failure on haemodialysis in Brazil.

BACKGROUND: The aim of this study was to investigate the HCV genotypes, hepatic siderosis, inflammatory activity and fibrosis of the liver in patients with chronic renal failure (CRF) on haemodialysis in Brazil. METHODS: A cohort of 72 CRF patients was compared with a group of 65 candidates for blood donation (CBD). For the subjects selected, who tested positive for anti-HCV antibodies and were HCV-PCR positive, a protocol with epidemiological, clinical and laboratory information was completed. An ultrasound-guided liver biopsy was performed and histological analysis of liver fragments was carried out. The presence of HCV-RNA in plasma was established by nested-RT-PCR. The genotype was determined by Restriction Fragment Length Polymorphism (RFLP) analysis of the PCR product. RESULTS: HCV genotype 1 was predominant in both groups, but genotype 2 was the second most common amongst CRF patients, and there was a significant difference when compared with the CBD group (P=0.016). Regarding inflammation and fibrosis, no significant difference was observed in the histology of the liver between the study groups. Siderosis of the liver was more prevalent in the CRF group (P=0.000). Severe complications of liver biopsies were reported in 10 CRF patients (13.2%). CONCLUSIONS: Genotype 2 was observed more frequently in the haemodialysis group. No statistically significant difference was detected between the CRF and CBD groups with regard to both inflammatory response and liver fibrosis. Hepatic siderosis has been attributed to excessive iron administration. As percutaneous liver biopsy resulted in severe complications, we suggest that other procedures of evaluating liver damage in CRF patients should be looked at thoughtfully.