Detection of antibodies to HAV 3C proteinase in experimentally infected chimpanzees and in naturally infected children

Evaluation of hepatitis A virus recombinant proteins for detecting anti-HAV IgM and IgG antibodies

Hepatitis A virus (HAV) is a major causative agent of self-limiting liver infections. India was highly endemic for HAV in the past; children were exposed to the virus at an early age without any disease symptoms and developed lifelong immunity. With improvements in living conditions, an epidemiological transition is occurring. There is a significant increase in hepatitis A outbreaks involving adolescents and young adults. The gold standard for hepatitis A diagnosis is anti-HAV IgM antibodies. Although antibody responses are primarily targeted against HAV structural proteins (capsid proteins), non-structural proteins are also immunogenic. In the present study, we expressed HAV capsid proteins VP1-2A, VP0 (VP4 + VP2), VP3, and non-structural protein 3CPro in the bacterial system and explored the possible use of these as antigens to detect anti-HAV IgM and IgG antibodies using a well-defined serum sample panel. The capsid protein-based assays showed overall less sensitivity for detection of both anti-HAV IgM and IgG antibodies as compared to whole virus antigen-based commercial assays. Among capsid proteins, rVP1-2A showed the highest sensitivity (86.3%) and specificity (84.2%) in detecting anti-HAV IgG, while rVP0 (VP2 + VP4) exhibited the highest sensitivity (79.5%) and specificity (80.2%) for IgM antibodies. Interestingly, r3CPro exhibited higher sensitivity (96.9%) and specificity (93.2%) in IgM detection and 93.94% sensitivity and 88% specificity for IgG, indicating its usefulness in detecting both anti-HAV IgM and IgG antibodies during the acute phase of the disease. Though 3CPro appeared to be useful in differentiating antibody responses due to infection and vaccination, our analysis revealed that the anti-3CPro antibody response is short-lived after natural infection, and hence, it cannot be used as a marker to differentiate between infection and vaccination. However, 3CPro would be useful for developing a hepatitis A diagnostic assay.

IMPORTANCE

Hepatitis A was highly endemic in India earlier. With recent developments, there is a shift in the endemicity to intermediate levels. This has resulted in the occurrence of hepatitis outbreaks with symptomatic infections in adolescents and adults. Occasionally, the disease manifestations are serious, leading to acute liver failure. In such a situation, there is a need for a timely diagnosis of the infection.

Hepatitis A virus infection

Hepatitis A is a vaccine-preventable infection caused by the hepatitis A virus (HAV). Over 150 million new infections of hepatitis A occur annually. HAV causes an acute inflammatory reaction in the liver that usually resolves spontaneously without chronic sequelae. However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure. Host factors, such as immunological status, age, pregnancy and underlying hepatic diseases, can affect the severity of disease. Anti-HAV IgG antibodies produced in response to HAV infection persist for life and protect against re-infection; vaccine-induced antibodies against hepatitis A confer long-term protection. The WHO recommends vaccination for individuals at higher risk of infection and/or severe disease in countries with very low and low hepatitis A virus endemicity, and universal childhood vaccination in intermediate endemicity countries. To date, >25 countries worldwide have implemented such programmes, resulting in a reduction in the incidence of HAV infection. Improving hygiene and sanitation, rapid identification of outbreaks and fast and accurate intervention in outbreak control are essential to reducing HAV transmission.

Hepatitis A vaccination and its immunological and epidemiological long-term effects - a review of the evidence

Hepatitis A virus (HAV) infections continue to represent a significant disease burden causing approximately 200 million infections, 30 million symptomatic illnesses and 30,000 deaths each year. Effective and safe hepatitis A vaccines have been available since the early 1990s. Initially developed for individual prophylaxis, HAV vaccines are now increasingly used to control hepatitis A in endemic areas. The human enteral HAV is eradicable in principle, however, HAV eradication is currently not being pursued. Inactivated HAV vaccines are safe and, after two doses, elicit seroprotection in healthy children, adolescents, and young adults for an estimated 30-40 years, if not lifelong, with no need for a later second booster. The long-term effects of the single-dose live-attenuated HAV vaccines are less well documented but available data suggest they are safe and provide long-lasting immunity and protection. A universal mass vaccination strategy (UMV) based on two doses of inactivated vaccine is commonly implemented in endemic countries and eliminates clinical hepatitis A disease in toddlers within a few years. Consequently, older age groups also benefit due to the herd protection effects. Single-dose UMV programs have shown promising outcomes but need to be monitored for many more years in order to document an effective immune memory persistence. In non-endemic countries, prevention efforts need to focus on 'new' risk groups, such as men having sex with men, prisoners, the homeless, and families visiting friends and relatives in endemic countries. This narrative review presents the current evidence regarding the immunological and epidemiological long-term effects of the hepatitis A vaccination and finally discusses emerging issues and areas for research.

Type A viral hepatitis: A summary and update on the molecular virology, epidemiology, pathogenesis and prevention

Although epidemic jaundice was well known to physicians of antiquity, it is only in recent years that medical science has begun to unravel the origins of hepatitis A virus (HAV) and the unique pathobiology underlying acute hepatitis A in humans. Improvements in sanitation and the successful development of highly efficacious vaccines have markedly reduced the worldwide prevalence and incidence of this enterically-transmitted infection over the past quarter century, yet the virus persists in vulnerable populations and remains a common cause of food-borne disease outbreaks in economically-advantaged societies. Reductions in the prevalence of HAV have led to increases in the median age at which infection occurs, often resulting in more severe disease in affected persons and paradoxical increases in disease burden in some developing nations. Here, we summarize recent advances in the molecular virology of HAV, an atypical member of the Picornaviridae family, survey what is known of the pathogenesis of hepatitis A in humans and the host-pathogen interactions that typify the infection, and review medical and public health aspects of immunisation and disease prevention.

Saliviruses-the first knowledge about a newly discovered human picornavirus

The salivirus, first discovered in the year 2009, is a member of the large and growing family Picornaviridae. At present, the genus Salivirus contains 1 species Salivirus A and 2 genotypes, Salivirus A1 and Salivirus A2. Salivirus has been identified in humans and chimpanzees and may cause acute gastroenteritis in humans, having been detected in 0% to 8.7% of fecal samples collected from gastroenteritis in different human populations. Salivirus is ubiquitous in wastewater of human origin and river water specimens worldwide and represents a potential indicator human RNA virus for monitoring of environmental samples. This review summarizes the current knowledge on saliviruses including discovery, taxonomy, genome structure, and genetic diversity; covers all aspects of infection including epidemiology, molecular epidemiology, clinical feature, host species, environmental characteristics, and laboratory diagnosis; and gives a summary of possible future perspectives.

Prevalence and genetic diversity of klassevirus in wastewater in Japan

Klassevirus is a novel virus belonging to the family Picornaviridae. This study examined the prevalence and genetic diversity of klassevirus in wastewater. Raw sewage (100 ml) and secondary-treated sewage (2 l) were collected monthly for 14 months between January 2011 and February 2012 from a wastewater treatment plant in Japan. Klassevirus in the sample was concentrated by the electronegative membrane-vortex method, followed by qualitative detection by means of three types of reverse transcription (RT)-nested polymerase chain reactions (PCRs). Klassevirus was detected in seven of the 14 raw sewage (50 %) and four of the 14 secondary-treated sewage (29 %) samples by the RT-nested PCRs targeting the 2C and/or 3D regions. In contrast, none of the samples tested positive for the virus by the RT-nested PCR targeting the VP0/VP3 region. Based on direct nucleotide sequence analysis of the klassevirus-positive nested PCR fragments, the tested samples showed high nucleotide sequence similarities of 94.7-100.0 % and 93.2-100.0 % in the 2C and 3D regions, respectively, indicating the presence of a single klassevirus strain. To our knowledge, this is the first study evaluating seasonal prevalence and genetic diversity of klassevirus in environmental waters.

Antibody responses to norovirus genogroup GI.1 and GII.4 proteases in volunteers administered Norwalk virus

An assay was developed to detect antibodies against two norovirus proteases among participants in a Norwalk virus (GI.1) challenge study. Prechallenge seroprevalence was lower against the protease from the homologous GI.1 virus than against protease from a heterologous GII.4 strain. Seroresponses were detected for 14 of 19 (74%) infected persons.

Serological evidence of human klassevirus infection

Klassevirus is a proposed new genus of picornavirus that has been associated with pediatric diarrhea. In this study, we used recombinant klassevirus 3C protease as the capture antigen for an indirect serological enzyme-linked immunosorbent assay (ELISA). Four of six klassevirus reverse transcription (RT)-PCR-positive individuals demonstrated seroconversion against the 3C protease, suggesting that klassevirus infection and replication occur in humans. Additional screening of 353 samples from an age-banded serological cohort from two St. Louis hospitals indicated a seroprevalence of 6.8%.

Immunogenicity of a chimeric hepatitis A virus (HAV) carrying the HIV gp41 epitope 2F5

Its stable particle structure combined with its high immunogenicity makes the hepatitis A virus (HAV) a perfect carrier to expose foreign epitopes to the host immune system. In an earlier report [Beneduce, F., Kusov, Y., Klinger, M., Gauss-Müller, V., Morace, G., 2002. Chimeric hepatitis A virus particles presenting a foreign epitope (HIV gp41) at their surface. Antiviral Res. 55, 369-377] chimeric virus-like particles (HAV-gp41) were described that carried at their surface the dominant gp41 epitope 2F5 (2F5e) of the human immunodeficiency virus HIV-1. Extending this work, we now report that chimeric virus HAV-gp41 replicates in HAV-susceptible cells as well as in non-human primates. Infected marmosets developed both an anti-HAV and anti-2F5 epitope immune response. Furthermore, an HIV-neutralizing antibody response was elicited in guinea pigs immunized with HAV-gp41 chimeric particles. The results demonstrate that the replication-competent chimeric HAV-gp41 can serve as either a live or a subunit vaccine for eliciting of antibodies directed against a foreign antigenic epitope.

Diagnosis of hepatitis a virus infection: a molecular approach

Current serologic tests provide the foundation for diagnosis of hepatitis A and hepatitis A virus (HAV) infection. Recent advances in methods to identify and characterize nucleic acid markers of viral infections have provided the foundation for the field of molecular epidemiology and increased our knowledge of the molecular biology and epidemiology of HAV. Although HAV is primarily shed in feces, there is a strong viremic phase during infection which has allowed easy access to virus isolates and the use of molecular markers to determine their genetic relatedness. Molecular epidemiologic studies have provided new information on the types and extent of HAV infection and transmission in the United States. In addition, these new diagnostic methods have provided tools for the rapid detection of food-borne HAV transmission and identification of the potential source of the food contamination.

Hepatitis vaccines: recent advances

Despite the availability of hepatitis A vaccines that might provide protection for decades, hepatitis B vaccines that provides protection for at least 15 years and the recent introduction of a combined hepatitis A and B vaccine, these infections continue to spread in both the developed and developing world. Hepatitis A vaccine coverage has been limited to high-risk groups: such a selective immunisation policy is unlikely to have a major impact. If adequate immunogenicity in infants is confirmed, dosing schedules can be improved and the costs of vaccination reduced, universal paediatric immunisation with combined hepatitis A and B products is likely to result in the eventual eradication of these infections. In the interim, novel hepatitis A vaccines are being investigated and additional studies on hepatitis A vaccine immunogenicity in infants are in progress. Worldwide use of hepatitis B vaccines for the newborn, young children and high-risk groups should control this infection and obviate the need for a vaccine against hepatitis D. Newer hepatitis B vaccines that may reduce the likelihood of non-responsiveness and have immunotherapeutic value are under study. A recombinant hepatitis E vaccine for use in endemic regions is currently in clinical trials. The development of an effective hepatitis C vaccine has been agonisingly slow and many impediments have been recognised. These include the lack of a susceptible small animal, a high degree of hepatitis C virus (HCV) genomic diversity and failure to produce high quantities of HCV in tissue culture. The development of a novel HCV replicon system may be a major breakthrough. Nonetheless, it may still be exceedingly difficult to produce a vaccine that uniformly provides sterilising immunity; the possibility of developing a hepatitis C vaccine that can prevent chronic infection is an exciting concept that requires further investigation. Advances in recombinant technology, the use of novel genetic (DNA-based) vaccines, expression of hepatitis antigens in plants and improved adjuvants also hold considerable promise.