Recent developments in the molecular cloning and characterization of hepatitis C and E viruses

Health risks of enteric viral infections in children

Children are at a greater risk of infections from serious enteric viral illness than adults for a number of reasons. Most important is the immune system, which is needed to control the infection processes. This difference can lead to more serious infections than in adults, who have fully developed immune systems. There are a number of significant physiological and behavioral differences between adults and children that place children at a greater risk of exposure and a greater risk of serious infection from enteric viruses. Although most enteric viruses cause mild or asymptomatic infections, they can cause a wide range of serious and life-threatening illnesses in children. The peak incidence of most enteric viral illnesses is in children <2yr of age, although all age groups of children are affected. Most of these infections are more serious and result in higher mortality in children than adults. The fetus is also affected by enterovirus and infectious hepatitis resulting in significant risk of fetal death or serious illness. In addition to the poliovirus vaccine, the only vaccine available is for hepatitis A virus (HAV). A vaccine for rotavirus has currently been withdrawn, pending review because of potential adverse effects in infants. No specific treatment is available for the other enteric viruses. Enteric viral infections are very common in childhood. Most children are infected with rotavirus during the first 2yr of life. The incidence of enteroviruses and the viral enteric viruses ranges from 10% to 40% in children and is largely dependent on age. On average, half or more of the infections are asymptomatic. The incidence of hepatitis A virus is much lower than the enteric diarrheal viruses. There is no current evidence for hepatitis E virus (HEV) acquisition in children in the U.S. Enteric viral diseases have a major impact on direct and indirect health care costs (i.e., lost wages) and amount to several billion dollars a year in the U.S. Total direct and indirect costs for nonhospitalized cases may run from $88/case for Norwalk virus to $1,193/case for enterovirus aseptic meningitis. Direct costs of hospitalization ran from $887/case for Norwalk virus to $86,899/case for hepatitis A. These costs are based on 1997-1999 data. Generally, attack rates during drinking water outbreaks are greater for children than adults. The exception appears to be hepatitis E virus where young adults are more affected. However, pregnant women suffer a high mortality, resulting in concurrent fetal death. Also, secondary attack rates are much higher among children, probably because of fewer sanitary habits among this age group. Overall, waterborne outbreaks of viral disease have a greater impact among children than adults. To better quantify the impact on children, the literature hould be further reviewed for case studies of waterborne outbreaks where data are available on the resulting illness by age group. The EPA and/or Centers for Disease Control should attempt to collect these data as future outbreaks are documented.

Virology of hepatitis C virus

Advances in molecular biology techniques have allowed the cloning of HCV and the characterization of this virus. This article provides a short summary of our current knowledge on the genomic organization of HCV, the implications of its genetic heterogeneous nature, and the probable replication strategy of this virus.

Problem hepatitis viruses: the mutants

Genetic variations in the known human hepatitis viruses are probably the result (a) of high viral replication rates and poor or absent proofreading ability intrinsic to RNA viruses (HAV, HCV, HDV, HEV) and (b) to a DNA virus (HBV) that uses a reverse-transcription mechanism for genomic replication. Nucleotide substitutions, deletions, duplications, insertions, and rearrangements resulting in amino acid changes may have no consequences, may impair replication, change host susceptibility, or may lead to escape from immune attack. Genetic diversity has been identified in each of the known hepatitis viruses. The importance of mutant viruses in pathogenicity, immunity, natural history, clinical outcomes, vaccine production, and responsiveness to treatment has emerged as an area for intensive study.