Hepatitis B virus epidemiology, disease burden, treatment, and current and emerging prevention and control measures

Sexual transmission of hepatitis B

PURPOSE OF REVIEW

Hepatitis B virus infection is prevalent worldwide and is a significant cause of morbidity and mortality particularly in Asia. Adults chronically infected with hepatitis B virus remain a significant potential source of sexually transmitted hepatitis B. The purpose of this article is to review the recent literature relating to hepatitis B virus transmission with particular emphasis on sexual transmission and efforts to prevent spread.

RECENT FINDINGS

The introduction of hepatitis B virus vaccine and the implementation of universal childhood vaccination for hepatitis B in some countries have led to a dramatic reduction in the number of children with chronic hepatitis B. However, recent reports suggest that we are not as successful in preventing infection by sexual transmission. It is clear that sexual transmission of hepatitis B virus is still widespread and is a major problem in certain high-risk groups such as men who have sex with men, intravenous drug users, prisoners and sex workers. Significant problems remain with respect to education and vaccination within these groups.

SUMMARY

Hepatitis B virus remains a major health burden but it is preventable by education and vaccination. Greater resources are required to expand vaccination to the at-risk, sexually active adult populations if the World Health Organization ideal of hepatitis B virus eradication is to be realized and the burden of hepatitis B virus-related morbidity and mortality contained.

Epidemiology and Prevention of Hepatitis B Virus Infection

Hepatitis B is one of the most common infectious diseases globally. It has been estimated that there are 350 million chronic hepatitis B virus (HBV) carriers worldwide. The prevalence of chronic HBV infection varies geographically, from high (>8%), intermediate (2-7%) to low (<2%) prevalence. HBeAg-negative chronic hepatitis B (e-CHB) and occult HBV infection are two special clinical entities, and the prevalence and clinical implications remain to be explored. The predominant routes of transmission vary according to the endemicity of the HBV infection. In areas with high HBV endemicity, perinatal transmission is the main route of transmission, whereas in areas with low HBV endemicity, sexual contact amongst high-risk adults is the predominant route. HBV has been classified into 7 genotypes, i.e. A to G, based on the divergence of entire genome sequence and HBV genotypes have distinct geographical distributions. Three main strategies have been approved to be effective in preventing HBV infection. They are behavior modification, passive immunoprophylaxis, and active immunization. The implement of mass HBV immunization program is recommended by the WHO since 1991, and has dramatically decreased the prevalence of HBV infection and HCC in many countries.

Screening of binding protein of hepatitis B virus pre-pre-s promoter by phage display technique

AIM: To screen the binding protein gene of hepatitis B virus pre-pre-s promoter using phage display technique.

METHODS: Taking HBV pre-pre-S promoter as a solidified selective molecule, the phage-human liver cDNA library was biopanned and the positive clones were selected. The positive plaques were amplified and then cloned into pGEM-Teasy vector. The selected positive plaques were analyzed using bioinformatics and DNA sequencing.

RESULTS: Twenty positive clones were obtained, which included 17 clones with known function and 3 with unknown function.

CONCLUSION: The binding protein genes of HBV pre-pre-s promoter can be obtained by phage display technique, which may be helpful for further study of the pathogenesis of HBV infection.

Is vaccine therapy the future in cancer prevention?

One vaccine designed to prevent cancer by preventing a precursor infection is already in common use, and at least one more is in the latter stages of clinical development. These vaccines are part of a new era of cancer immunoprophylaxis. Several further vaccines are in preclinical and clinical development, targeted at preventing cancer precursor infections, and these should add to our ability to prevent this common human disorder. However, vaccines to prevent cancers not triggered by infection are a more remote prospect, for a variety of reasons.

Association of TNF-α gene promoter polymorphisms with outcome of hepatitis B virus infection

AIM: To investigate the polymorphism of tumor necrosis factor-a(TNF-α) gene promoters in Chinese Han people, and to clarify whether such polymorphism was associated with the outcome of hepatitis B virus infection.

METHODS: After the process of extracting genomic DNA from blood in 165 subjects who spontaneously recovered(SR) and 131 patients with chronic hepatitis B (CHB), four single nucleotide polymorphism (SNP) sites in TNF-α gene promoter marked as -238G/A, -308G/A, -857C/T and -863C/A were determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis.

RESULTS: Twelve different promoter genotypes were detected from all of 296 research subjects, and GG.GG.CC.CC, GG.GG.CC.CA, GG.GG.CT.CC, GG.GA.CC.CC genotypes accounted for about 85% of genotypes in these subjects. By analyzing the four promoter genotypes of TNF-α, the results showed that there were significant differences in the frequencies of GG.GG.CC.CC, GG.GG.CC.CA and GG.GA.CC·CC genotypes in TNF-α gene promoter between CHB and SR, GG.GG.CC.CC genotype carriers were at increased risk of CHB with an odds ratio of 2.15 (95% CI 1.34-3.45); While GG.GG.CC.CA and GG.GA.CC.CC genotypes carriers were at increased risk of CHB with an odds ratio of 0.48(95% CI 0.27-0.86) and 0.35 (95% CI 0.14-0.89), respectively. GG.GG.CC.CA and GG.GA.CC.CC genotypes were strongly associated with the resolution of HBV infection(χ² = 6.14, P = 0.013<0.05; χ² = 5.18, P = 0.023<0.05, respectively). Single site analysis also revealed that TNF-α gene -308G/A and -863C/A SNP sites were associated with persistent HBV infection in Chinese Han people (-308G/A site, χ² = 6.53, P = 0.011<0.05, OR=3.21; -863C/A site, χ² = 4.33, P = 0.037<0.05, OR=1.69, respectively).

CONCLUSION: There is an association between polymorphisms of the promoter region -308G/A and -863C/A of TNF-α and the resolution of HBV infection. The presence of the -308A allele (TNF-α-308GA) and /or -863A allele(TNF-α-863CA or AA) may be resistant to HBV infection, which gives some new clues to the study of pathogenesis of chronic hepatitis B.

Hepatitis B virus reactivation in breast cancer patients receiving cytotoxic chemotherapy: a prospective study

Breast cancer is a rapidly increasing problem in many developing countries, and cytotoxic chemotherapy is now an integral part of its management. In several developing countries, the carriage of hepatitis B virus (HBV) in cancer patients may be as high as 12%, and such patients are at risk of developing fatal HBV reactivation during chemotherapy. HBV reactivation is well recognized in patients with hematological malignancies, but limited data are available on patients with other, more common, cancers, such as breast cancer. Recent data have suggested that increased viral replication, an indication of HBV reactivation, may precede clinical hepatitis. In the absence of serial HBV DNA monitoring, HBV reactivation during chemotherapy may have been underestimated. In this prospective study, breast cancer patients who were hepatitis B surface antigen (HBsAg) seropositive were followed up during chemotherapy. The main objectives were to determine the incidence of HBV reactivation in breast cancer patients undergoing conventional chemotherapy; to investigate whether "serial HBV DNA monitoring" improves the accuracy of diagnosing HBV reactivation when compared with previous schema that only measured HBV DNA at the time of clinical hepatitis ("conventional monitoring"); and to assess the clinical consequences as a result of developing the condition. The secondary objective was to identify risk factors associated with this condition. Over an 18-month period, 41 patients were studied. Ten developed HBV reactivation by conventional monitoring criteria, but with serial HBV DNA monitoring, seven additional patients were diagnosed when increased HBV DNA levels were detected before, but not concomitant with, clinical hepatitis. Thus, a total of 17 patients (41%) developed HBV reactivation. Premature termination of chemotherapy or delay in treatment schedules occurred in 71% of the patients who developed viral reactivation, as compared with 33% in those who did not develop the condition (P = 0.019). No risk factors associated with the development of HBV reactivation could be identified. Serial monitoring of HBV DNA, in addition to liver function, increases the sensitivity of diagnosing of HBV reactivation, and helps explain some cases that would otherwise be labeled as "cryptogenic hepatitis," for which concomitant HBV DNA measured at the time of hepatitis was undetectable. The present study highlights the importance of monitoring HBsAg-seropositive patients who are receiving chemotherapy for common solid tumors such as breast cancer.