Quantification of complex precore mutations of hepatitis B virus by SimpleProbe real time PCR and dual melting analysis

The Rare, the Best: Spread of Antimalarial-Resistant Plasmodium falciparum Parasites by Anopheles Mosquito Vectors

The emergence of resistance to antimalarials has prompted the steady switch to novel therapies for decades. Withdrawal of antimalarials, such as chloroquine in sub-Saharan Africa in the late 1990s, led to rapid declines in the prevalence of resistance markers after a few years, raising the possibility of reintroducing them for malaria treatment. Here, we provide evidence that the mosquito vector plays a crucial role in maintaining parasite genetic diversity. We followed the transmission dynamics of Plasmodium falciparum parasites through its vector in natural infections from gametocytes contained in the blood of asymptomatic volunteers until sporozoites subsequently developed in the mosquito salivary glands. We did not find any selection of the mutant or wild-type pfcrt 76 allele during development in the Anopheles mosquito vector. However, microsatellite genotyping indicated that minority genotypes were favored during transmission through the mosquito. The analysis of changes in the proportions of mutant and wild-type pfcrt 76 alleles showed that, regardless of the genotype, the less-represented allele in the gametocyte population was more abundant in mosquito salivary glands, indicating a selective advantage of the minority allele in the vector. Selection of minority genotypes in the vector would explain the persistence of drug-resistant alleles in the absence of drug pressure in areas with high malaria endemicity and high genetic diversity. Our results may have important epidemiological implications, as they predict the rapid re-emergence and spread of resistant genotypes if antimalarials that had previously selected resistant parasites are reintroduced for malaria prevention or treatment.

IMPORTANCE Drug selection pressure in malaria patients is the cause of the emergence of resistant parasites. Resistance imposes a fitness cost for parasites in untreated infections, so withdrawal of the drug leads to the return of susceptible parasites. Little is known about the role of the malaria vector in this phenomenon. In an experimental study conducted in Cameroon, an area of high malaria transmission, we showed that the vector did not favor the parasites based on sensitivity or resistance criteria, but it did favor the selection of minority clones. This finding shows that the vector increases the diversity of plasmodial populations and could play an important role in falciparum malaria epidemiology by maintaining resistant clones despite the absence of therapeutic pressure.

Accurate Detection of Hepatitis B Virus G1896A Mutant by Developed Taqman-ARMS Followed a Strict Control System

BACKGROUND

Hepatitis B virus (HBV) G1896A mutation was associated with HBeAg seronegativity and hepatitis B related acute-on-chronic liver failure. In this study, we developed Taqman amplification refractory mutation system (Taqman-ARMS) and established a strict control system to detect HBV G1896A mutant.

METHODS

HBV viral DNA was isolated from 60 patient serum samples, and full-length HBV genome was cloned. Then, Taqman-ARMS was used to detect HBV G1896A mutant.

RESULTS

The assay has the sensitivity of 1E+3 IU/ml G1896A template, and 0.1% weak population virus with G1896A could be found in mixtures. Total of all 60 clinical samples random collected were detected by Taqman-ARMS, the results were consistent with those by DNA sequencing.

CONCLUSION

The proposed Taqman-ARMS real-time PCR method for the detection of G1896A mutation of HBV was rapid, simple, sensitive, specific, and applicable in the clinical setting.

Hepatitis B virus preS1 deletion is related to viral replication increase and disease progression

AIM: To investigate the clinical implications of hepatitis B virus (HBV) preS1 deletion.

METHODS: We developed a fluorescence resonance energy transfer-based real-time polymerase chain reaction (RT-PCR) that can detect four genotypes (wild type, 15-bp, 18-bp and 21-bp deletion). The PCR method was used in two cohorts of Korean chronic HBV subjects with genotype C infections. Cohort I  included 292 chronic HBV subjects randomly selected from Cheju National University Hospital (Jeju, South Korea) or Seoul National University Hospital (Seoul, South Korea), and cohort II included 90 consecutive chronic HBV carriers recruited from Konkuk University Hospital (Seoul, South Korea); the cohort II patients did not have hepatocellular carcinoma or liver cirrhosis.

RESULTS: The method proposed in this study identified 341 of 382 samples (89.3%). Deletion variants were identified in 100 (29.3%) of the 341 detected samples. In both cohorts, the subjects with deletions had a significantly higher Hepatitis B virus e antigen (HBeAg)-positive seroprevalence [cohort I, wild (51.0%) vs deletion (75.0%), P < 0.001; cohort II, wild (69.2%) vs deletion (92.9%), P = 0.002] and higher HBV DNA levels [cohort I, wild (797.7 pg/mL) vs deletion (1678.9 pg/mL), P = 0.013; cohort II, wild (8.3 × 10⁸ copies/mL) vs deletion (2.2 × 10⁹ copies/mL), P = 0.049], compared to subjects with wild type HBV.

CONCLUSION: HBV genotype C preS1 deletion may affect disease progression in chronic HBV subjects through an extended duration of HBeAg seropositive status and increased HBV replications.

Quantitative dynamics of hepatitis B basal core promoter and precore mutants before and after HBeAg seroconversion

BACKGROUND & AIMS

Hepatitis B e antigen (HBeAg) seroconversion is an important clinical and virological "landmark" during chronic hepatitis B virus (HBV) infection. Mutant viruses carrying the precore G1896A and/or the basal core promoter (BCP) A1762T/G1764A mutations are associated with HBeAg seroconversion. However, the exact role of these mutants in HBeAg seroconversion remains unclear, partly because the evolution of these mutant viruses before and after seroconversion has not been well studied.

METHODS

Using our novel mutant quantification methods, the percentage of the mutant viruses was analyzed both cross-sectionally and longitudinally, before and after seroconversion.

RESULTS

Cross-sectional analysis showed that the percentage of both precore and BCP mutants gradually increased with age in the HBeAg-positive population. Follow-up of 18 HBeAg-positive patients revealed that the mutant percentage may stay low and stable for many years, followed by a steady increase in the percentage of G1896A and/or A1762T/G1764A mutants, from <10% to 50-100%, within about 3 years prior to seroconversion. In all cases, increase of mutant percentage was preceded or accompanied by elevated serum alanine aminotransferase. After the seroconversion, the mutant percentage could remain high or decrease significantly, sometimes to below 20%.

CONCLUSIONS

Levels of G1896A and A1762T/G1764A mutants (of genotypes B and C) in the HBeAg-positive patients may predict the time of HBeAg seroconversion. The dominance of these mutants in the HBeAg-positive phase is more likely the result of immune selection rather than the enhanced replication capability of the mutants. However, anti-HBe antibody may not be a major selection force for these mutants.