Recent advances in hepatitis A vaccine development

Adaptation of primate cell-adapted hepatitis A virus strain HM175 to growth in guinea pig cells is independent of mutations in the 5' nontranslated region

Previous studies of hepatitis A virus (HAV) genotypes after adaptation of wild-type virus to growth in cell cultures of primate origin identified determinants for growth in cell culture in the viral 2B and 2C protein-coding regions of the genome and demonstrated that an increased growth efficiency in a particular cell line was achieved by subsequent mutations in the 5' nontranslated region (5'NTR). The results reported in this study demonstrate that the passage of HAV adapted to primate BS-C-1 cells in guinea pig cells resulted in increased growth efficiency in the rodent cells and decreased growth efficiency in BS-C-1 cells. This adaptation occurred without mutation in the 5'NTR, but the viral 2B and 2C proteins seem to play a role during adaptation to the new environment, as one mutation occurred in each protein. Although the data presented here do not clearly identify which region of the viral genome underwent mutations to improve the interaction of the viruses with guinea pig proteins, they do confirm that the 5'NTR is not the only region responsible for providing host cell-specific information.

Should adolescents be vaccinated against hepatitis A: the Hong Kong experience

Hong Kong is a well developed city in the center of an endemic region for hepatitis A. The age at which hepatitis A occurs has shifted from childhood and adolescence to adults like many western countries. There is a high chance of outbreaks with the introduction of infection from neighbouring countries. Reducing the susceptibility of a population by vaccination can eliminate the diseases but updated sero-epidemiological data is needed to analyse the level of natural immunity, and identify those susceptible to infection for preventive measures. This study conducted amongst secondary school children seeks to identify those who are at risk and to obtain data on the present sero-prevalence of anti-HAV. Overall prevalence of anti-HAV in this age group was 7% increasing with age. Analysed by multiple regression model, those students living in mainland China over 3 years had odds ratio of 31.6 (95% c. i. 17.4-57.3) compared with those born in Hong Kong. Students with a father in a skilled occupation and an education level of secondary school or above, and both parents with secondary education or above, had an odds ratio of 0.22 (95% c.i. 0.07-0.7) and 0.35 (95% c.i. 0. 17-0.72) associated with presence of anti-HAV, respectively. Improved socio-economic state exposes higher proportion of the population at risk. Immunisation is worthwhile to be considered for the adolescents in Hong Kong. Prevaccination screening is cost effective only for those adolescents who are most likely to have natural immunity.

Immune globulin and vaccine therapy to prevent hepatitis A infection

The hepatitis A virus is usually transmitted person-to-person due to fecal-oral exchange of virus. Approximately 30,000 infections are reported each year in the United States, with the actual incidence being much greater. Prophylaxis with immune globulin has had a minimal impact on the overall incidence of hepatitis A. The recent availability and proven efficacy of a hepatitis A vaccine offers the hope that the incidence of infection may be substantially reduced. Pre- and postexposure prophylaxis should be targeted to individuals at increased risk of either acquiring infection, transmitting infection, or developing fulminant hepatitis, or to help control epidemics. This article reviews the current literature and discusses recommendations for pre- and postexposure prophylaxis against hepatitis A virus.

Mutations within the 5' nontranslated RNA of cell culture-adapted hepatitis A virus which enhance cap-independent translation in cultured African green monkey kidney cells

Mutations in the 5' nontranslated RNA (5'NTR) of an attenuated, cell culture-adapted hepatitis A virus (HAV), HM175/P16, enhance growth in cultured African green monkey kidney (BS-C-1) cells but not in fetal rhesus monkey kidney (FRhK-4) cells (S. P. Day, P. Murphy, E. A. Brown, and S. M. Lemon, J. Virol. 66: 6533-6540, 1992). To determine whether these mutations enhance cap-independent translation directed by the HAV internal ribosomal entry site (IRES), we compared the translational activities of the 5'NTRs of wild-type and HM175/P16 viruses in two stably transformed cell lines (BT7-H and FRhK-T7) which constitutively express cytoplasmic bacteriophage T7 RNA polymerase and which are derived from BS-C-1 and FRhK-4 cells, respectively. Translational activity was assessed by monitoring expression of a reporter protein, chloramphenicol acetyltransferase (CAT), following transfection with plasmid DNAs containing bicistronic T7 transcriptional units of the form luciferase-5'NTR-CAT. In both cell types, transcripts containing the 5'NTR of HM175/P16 expressed CAT at levels that were 50- to 100-fold lower than transcripts containing the IRES elements of Sabin type 1 poliovirus or encephalomyocarditis virus, confirming the low activity of the HAV IRES. However, in BT7-H cells, transcripts containing the 5'NTR of wild-type virus. This translational enhancement was due to additive effects of a UU deletion at nucleotides 203 and 204 and a U-to-G substitution at nucleotide 687 of HM175/P16. These mutations did not enhance translation in FRhK-T7 or Huh-T7 cells (a T7 polymerase-expressing cell line derived from human hepatoblastoma cells) or in vitro in rabbit reticulocyte lysates. These results demonstrate that mutations in the 5'NTR of a cell culture-adapted HAV enhance viral replication by facilitating cap-independent translation in a cell-type-specific fashion and support the concept that picornaviral host range is determined in part by differences in cellular translation initiation factors.

Temperature-sensitive hepatitis A virus mutants with deletions downstream of the first pyrimidine-rich tract of the 5' nontranslated RNA are impaired in RNA synthesis

Hepatitis A virus (HAV) mutants containing large deletions within the first pyrimidine-rich tract (pY1; nucleotides [nt] 99 to 138) of the 5' nontranslated RNA (5'NTR) replicate well in cultured cells, while those with pY1 deletions which extend in a 3' direction to include nt 140 to 144 (CUUGU) have a temperature-sensitive (ts) replication phenotype (D.R. Shaffer, E.A. Brown, and S.M. Lemon, J. Virol. 68:5568-5578, 1994). To characterize this replication defect, the ts mutant delta 131-144 was grown under one-step conditions at the nonpermissive temperature (37 degrees C). A shift to the permissive temperature (31 degrees C) for the first 18 h of the viral replication cycle did not enhance virus yields, indicating that temperature sensitivity is not due to a defect in viral entry or uncoating. Similarly, absence of increased yield with a late shift to 31 degrees C between 54 and 72 h suggested that the ts defect does not involve viral assembly. Although monocistronic RNA transcripts containing the delta 99-144 deletion directed translation 22 to 58% less efficiently than the standard 5'NTR in transfected BS-C-1 cells, this difference was present at both 31 and 37 degrees C. In addition, there were no temperature-dependent differences in the abilities of bicistronic transcripts containing either ts or non-ts 5'NTR sequences within the intercistronic space to direct translation of a downstream reporter gene. Thus, ts mutations do not confer a demonstrable temperature-related defect in cap-independent translation. In contrast, an RNase protection assay showed that synthesis of viral plus-strand RNA was markedly delayed in BS-C-1 cells infected with ts virus at 37 degrees C. Analysis of the nucleotide sequence surrounding the deletion in a non-ts revertant derived from delta 116-144 virus revealed that a single U-to-G transversion at nt 114 (CUUUU-->CUUGU) had restored the sequence normally present between nt 140 and 144. These results indicate that ts mutants of HAV with deletions extending downstream from the pY1 domain to nt 140 to 144 are defective in RNA synthesis and that the single-stranded RNA segment containing nt 140 to 144 plays a critical role in replication of HAV RNA.

Age-specific antibody prevalence to hepatitis A in England: implications for disease control

Sera from an age-stratified sample of 7196 individuals, submitted for diagnostic purposes to four public health laboratories in England in 1986/7, were tested for hepatitis A antibody. The serological profiles, which showed marked regional differences, were consistent with declining incidence in the past. The decline in the incidence of hepatitis A has resulted in an increase in susceptibility in adults. This has three main consequences: an increase in the average age of infection may be leading to an increase in morbidity; normal immunoglobulin may become less protective against hepatitis A; the risk of transmission through blood products contaminated by viraemic blood donors may rise. Current average annual incidence in 5-14-year olds was estimated to vary between regions from 0.5-1.9%. This supports the view that, in the absence of a vaccination programme, hepatitis A will remain endemic unless there are further improvements in living conditions and standards of hygiene. A vaccine giving long-lasting protection could eliminate hepatitis A transmission with modest coverage at a young age. Targeting childhood vaccination on economically deprived areas or using vaccine to control outbreaks might be more effective policies.

Synthetic peptides in the determination of hepatitis A virus T-cell epitopes

Computer search for probable T-epitopes of hepatitis A virus capsid proteins was performed using an integrated set of programs. Eight segments of the VP1, VP2, VP3 and VP4 proteins were chosen and synthesised. Five peptides previously examined as probable B-epitopes were used as well. All the peptides were tested for their ability to stimulate proliferation of lymph node T-cells primed with synthetic peptides. Almost all predicted T-epitopes affected the T-cell proliferation. None of the peptides had mitogenic activity. We demonstrated that regions 17-33 and 276-298 of VP1 are possible immunodominant promiscuous sites activating lymphocytes of all mouse haplotypes.

Cell type-specific proteins which interact with the 5' nontranslated region of hepatitis A virus RNA

The 5' nontranslated region (5'NTR) of hepatitis A virus (HAV) RNA contains structural elements which facilitate 5' cap-independent initiation of virus translation and are likely to interact with cellular proteins functioning as translation initiation factors. To define these interactions, we characterized the binding of ribosome-associated proteins from several cell types to synthetic RNAs representing segments of the 5'NTR by using a UV cross-linking/label transfer assay. Four major proteins (p30, p39, p57, and p110) were identified. p30 and p39 were present in ribosomal salt washes prepared only from HAV-permissive BS-C-1 and FRhK-4 cells, while p57 was found only in HeLa cells and rabbit reticulocyte lysates. p110 was present in all cell types. Both p30 and p39 bound to multiple sites within the 5'NTR. Efficient transfer of label to p30 occurred with minimal RNA probes representing nucleotides (nt) 96 to 155, 151 to 354, and, to a much lesser extent, 634 to 744, while label transfer to p39 occurred with probes representing nt 96 to 155 and 634 to 744. All of these probes represent regions of the 5'NTR which are rich in pyrimidines. Competitive inhibition studies indicated that both p30 and p39 bound with greater affinity to sites in the 5' half of the NTR (a probe representing nt 1 to 354) than to the more 3' site (nt 634 to 744). Binding of p39 to the probe representing nt 96 to 155 was inhibited in the presence of an equal amount of proteins derived from HeLa cells, suggesting that p39 shares binding site specificity with one or more HeLa cell proteins. A 57-kDa protein in HeLa cell protein extracts reacted with antibody to polypyrimidine tract-binding protein in immunoblots, but no immunoreactive protein was identified in a similar BS-C-1 protein fraction. These results demonstrate that ribosome-associated proteins which bind to the 5'NTR of HAV vary substantially among different mammalian cell types, possibly accounting for differences in the extent to which individual cell types support growth of the virus. Mutations in the 5'NTR which enhance the growth of HAV in certain cell types may reflect specific adaptive responses to these or other proteins.

Safety and immunogenicity of hepatitis A vaccine in healthy adult volunteers

The immunogenicity and adverse reaction of an inactivated hepatitis A (HA) vaccine were investigated. Sixty healthy adult volunteers who lacked antibody to HA virus (anti-HAV) received three doses of vaccine containing 720 enzyme-linked immunosorbent assay (ELISA) units (EL.U) according to a 0, 1 and 6 month schedule. Blood tests for serum liver enzymes and anti-HAV were performed at screening 7 days prior to, and 1, 6 and 7 months after the first dose. Anti-HAV was tested by radio immunoassay and ELISA for titre determination. The seroconversion rates measured by ELISA were 98.3% (59/60) at months 1 and 6 and 100% at month 7. Sixty-one per cent (109/180) of the documented injections were followed by local symptoms, essentially mild soreness at the site of injection; and 22.2% (40/180) by minor general symptoms including malaise, fatigue and lethargy. It is concluded that HA vaccine is highly immunogenic and safe. It may replace immunoglobulin as an effective method of preventing HA virus infection in adults.

Antigenic and immunogenic properties of recombinant hepatitis A virus 14S and 70S subviral particles

Hepatitis A virus (HAV) has an immunodominant neutralization antigenic site. By using a panel of monoclonal antibodies targeted against the HAV neutralization antigenic site, it was shown that three epitopes within this site are present on 14S subunits (pentamers of the structural unit). In contrast, two other epitopes within this site are formed upon assembly of 14S subunits into capsids. Thus, the epitopes recognized by these two monoclonal antibodies are formed either by a conformational change in the antigenic site or by the juxtaposition of epitope fragments present on different 14S subunits during assembly of 14S into 70S particles. Both 14S and 70S particles elicited HAV-neutralizing antibodies in mice; thus, these particles may be useful for HAV vaccine development.

Control of hepatitis A by inactivated vaccines: unanswered questions and unresolved issues

The recent development of safe and effective inactivated hepatitis A virus vaccines provides for the first time the opportunity to control hepatitis A. However, control will depend upon the intelligent use of the vaccines. How and when hepatitis A vaccines should be used will be determined from the results of studies of the levels and duration of protective antibody, determination of optimum immunization schedules, estimations of the continuing need for normal immune globulin and discussions of how hepatitis A vaccine can be incorporated into national and international vaccination programs. Cost and feasibility will determine whether live attenuated hepatitis A vaccines will become useful adjuncts or replacements for inactivated hepatitis A vaccines.

Partial characterization of hepatitis A viruses from three intermediate passage levels of a series resulting in adaptation to growth in cell culture and attenuation of virulence

Viruses from passages 9/10, 21, and 32 of a serially passaged human isolate of hepatitis A virus, strain HM-175, were partially sequenced and compared for their abilities to grow in cell cultures and to cause disease in primates. Viruses from all passages grew more efficiently in cell culture than did the wild-type virulent virus from which they were derived, and all displayed some degree of attenuation of virulence for primates. Within the 5' noncoding region and the 2B2C region of the HAV genome, passage 9/10 virus differed in sequence from wild-type at a single and novel position in the 2C gene, while the sequence of the passage 32 virus was almost identical to that of a fully attenuated passage 35 virus. Passage 21 viruses were found to consist of a mixture of viruses which included all but two of the 13 mutations present in the sequenced regions of the virus from passage 32.

Single and booster dose responses to an inactivated hepatitis A virus vaccine: comparison with immune serum globulin prophylaxis

Pre- and postexposure prophylaxis against hepatitis A virus (HAV) infection with immune serum globulin (Ig) is only effective for 4-6 months. We compared the safety, tolerability and immunogenicity of a single i.m. injection of Ig with a single and booster dose of an inactivated hepatitis A virus vaccine (iHAV) in adults. Healthy volunteers (18-50 years) received a single Ig i.m. injection (n = 30), or iHAV i.m. (n = 15) at 0 and 24 weeks, or placebo (n = 4) at the same intervals. Anti-HAV seroconversion was measured by radioimmunoassay (RIA) and neutralizing antibodies by an antigen reduction assay. After Ig injection (0.06 ml/kg), anti-HAV seroconversion occurred in 100% of recipients at week 1, declining to 10% at week 12 and 0% by week 20. In contrast, after a single 25 ng dose, RIA seropositivity in iHAV vaccinees was 80% by week 2, reaching 100% by week 5 and persisted up to week 24, at which time anti-HAV geometric mean titres (GMT) were two fold higher than those seen at week 1 after Ig. Postbooster anti-HAV titres in iHAV recipients rose within 4 weeks to 73-fold greater than the peak GMT seen one week after Ig, and 400-fold higher than GMT at 12 weeks after Ig. Neutralizing antibody titres after iHAV followed a similar pattern, as observed for anti-HAV. iHAV was well tolerated; placebo and vaccine tolerability were indistinguishable, with no serious adverse experiences observed. In conclusion, active vaccination with a single iHAV dose may eventually replace Ig for pre-exposure prophylaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutations within the 5' nontranslated region of hepatitis A virus RNA which enhance replication in BS-C-1 cells

Passage of human hepatitis A virus (HAV) in cell culture results in attenuation of the virus as well as progressive increases in the efficiency of virus replication in cell culture. Because the presence of identical mutations within the 5' nontranslated regions (5'NTRs) of several independently isolated cell culture-adapted HAV variants suggests that the 5'NTR may play a role in determining this change in virus host range, we constructed chimeric infectious cDNA clones in which portions of the 5'NTR of cell culture-adapted HM175/p35 virus were replaced with cDNA from either wild-type virus (HM175/wt) or a second independently isolated, but closely related cell culture-adapted virus (HM175/p16). Substitution of the complete 5'NTR of HM175/p35 with the 5'NTR of HM175/wt resulted in virus with very small replication foci in continuous African green monkey kidney (BS-C-1) cells, indicating that 5'NTR mutations in HM175/p35 virus are required for optimal growth in these cells. A chimera with the 5'NTR sequence of HM175/p16 retained the large foci of HM175/p35 virus, while the growth properties of other viruses having chimeric 5'NTR sequences indicated that mutations at bases 152 and/or 203 to 207 enhance replication in BS-C-1 cells. These findings were confirmed in one-step growth experiments, which also indicated that radioimmunofocus size is a valid measure of virus replication competence in cell culture. An additional mutation at base 687 of HM175/p16 had only a minor role in enhancing growth. In contrast to their effect in BS-C-1 cells, these 5'NTR mutations did not enhance replication in continuous fetal rhesus monkey kidney (FRhK-4) cells. Thus, mutations at bases 152 and/or 203 to 207 enhance the replication of HAV in a highly host cell-specific fashion.

Immunogenicity and antigenicity of chimeric picornaviruses which express hepatitis A virus (HAV) peptide sequences: evidence for a neutralization domain near the amino terminus of VP1 of HAV

We evaluated the antigenic characteristics of chimeric picornaviruses created by inserting peptide sequences from hepatitis A virus (HAV) capsid proteins into the B-C loop of VP1 of Sabin strain type 1 poliovirus (PV-1). Fifteen viable chimeras were generated. Each retained the ability to be neutralized by polyclonal PV-1 antisera. Two chimeras (H15 and H2) stimulated production of low levels of HAV neutralizing antibodies in immunized rabbits or mice, although in both cases only a small fraction of immunized animals produced this response. The H15 chimera, which contains residues 13-24 of HAV VP1, elicited HAV neutralizing antibodies in three of nine rabbits and at least one of seven immunized mice. These results indicate that a neutralization domain exists in this region of VP1. However, human sera with high titers of antibodies to HAV failed to neutralize or immunoprecipitate this chimera, suggesting the absence of a significant antibody response to this neutralization domain following natural infection. Sera from rabbits immunized with H15 that did not develop HAV neutralizing antibodies contained antibodies reactive with the HAV peptide segment expressed by the H15 virus, indicating substantial differences in the specificities of antibodies elicited by this peptide segment among individual immunized rabbits. The H15 peptide insert was an effective antigen, as indicated by a high level of sensitivity of the H15 chimera to neutralization by a related anti-peptide antibody which was itself devoid of HAV neutralizing activity. One of 16 rabbits immunized with the H2 chimera (residues 101-108 of HAV VP1) developed HAV neutralizing antibodies, confirming both the presence and the highly conformational nature of a neutralization antigenic site involving these residues of HAV.

Antigenic structure of human hepatitis A virus defined by analysis of escape mutants selected against murine monoclonal antibodies

We examined the antigenic structure of human hepatitis A virus (HAV) by characterizing a series of 21 murine monoclonal-antibody-resistant neutralization escape mutants derived from the HM175 virus strain. The escape phenotype of each mutant was associated with reduced antibody binding in radioimmunofocus assays. Neutralization escape mutations were identified at the Asp-70 and Gln-74 residues of the capsid protein VP3, as well as at Ser-102, Val-171, Ala-176, and Lys-221 of VP1. With the exception of the Lys-221 mutants, substantial cross-resistance was evident among escape mutants tested against a panel of 22 neutralizing monoclonal antibodies, suggesting that the involved residues contribute to epitopes composing a single antigenic site. As mutations at one or more of these residues conferred resistance to 20 of 22 murine antibodies, this site appears to be immunodominant in the mouse. However, multiple mutants selected independently against any one monoclonal antibody had mutations at only one or, at the most, two amino acid residues within the capsid proteins, confirming that there are multiple epitopes within this antigenic site and suggesting that single-amino-acid residues contributing to these epitopes may play key roles in the binding of individual antibodies. A second, potentially independent antigenic site was identified by three escape mutants with different substitutions at Lys-221 of VP1. These mutants were resistant only to antibody H7C27, while H7C27 effectively neutralized all other escape mutants. These data support the existence of an immunodominant neutralization site in the antigenic structure of hepatitis A virus which involves residues of VP3 and VP1 and a second, potentially independent site involving residue 221 of VP1.

Properties and classification of hepatitis A virus

Hepatitis A virus (HAV) is a member of the picornavirus family. It was first provisionally classified as enterovirus 72, but subsequent determinations of its nucleotide and amino acid sequences showed them to be sufficiently distinct to assign the virus to a new genus. Heparna-virus (Hep-A-RNA-virus) has been suggested as the genus name. HAV shares the key properties of the picornavirus family: an icosahedral particle 28 nm in diameter with cubic symmetry, composed of 30% RNA and 70% protein. The genome is single-stranded 7.48 kb RNA, linear and positive-sense. Like other picornaviruses, HAV possesses four major polypeptides cleaved from a large precursor polyprotein. The surface proteins VP1 and VP3 are major antibody-binding sites. The internal protein VP4 is much smaller than the VP4s of other picornaviruses. As other picornaviruses, HAV has no envelope and replicates in the cytoplasm. HAV is stable to treatment with either and acid, and is much more heat-resistant than other picornaviruses. It withstands 60 degrees C for 1 h. MgCl2 stabilizes the virus to withstand temperatures up to 80 degrees C. The relative resistance of HAV to disinfection indicates a need for extra precautions in dealing with hepatitis patients and their products. Only one serotype is known. There is no antigenic cross-reactivity with other hepatitis viruses. HAV initially was identified in stool and liver preparations by employing immune electron microscopy as the detection system. Chimpanzees and marmoset monkeys are susceptible to HAV. HAV has been cultivated serially in primary explant cultures of adult marmoset livers and in cell lines of primate origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Perspectives on the control of hepatitis A by vaccination

The availability of an inactivated hepatitis A virus (HAV) vaccine, and the development of live attenuated virus vaccines against hepatitis represent great advances in the effort to control an important cause of viral hepatitis. There are a number of ways hepatitis A vaccines could be used, depending on the epidemiology of HAV infection in the country concerned, the cost of the product, the duration of protection that the vaccine affords and its effectiveness for postexposure prophylaxis. Expert groups could recommend vaccine to individuals who are at higher risk of exposure to hepatitis A as a result of behaviour, lifestyle or occupation, or to all infants and/or adolescents. The major public health problem with hepatitis A occurs in developing countries and regions with 'transitional economies' such as Eastern Europe and certain Middle Eastern countries. These countries have high levels of viral circulation, large cohorts of susceptible older children and adults, and high rates of HAV morbidity. Given the experience with hepatitis B vaccine and the economic and political realities of global immunization policy, it is unlikely that the Expanded Programme on Immunization and traditional vaccine donors will take a great interest in HAV vaccine in the near future. Individual countries may, however, decide to use hepatitis A vaccine on a widespread basis. Model cost effectiveness studies are needed for both developing and developed countries to help decide the feasibility of such widespread use. WHO has been involved in activities relevant to hepatitis A vaccine for many years.(ABSTRACT TRUNCATED AT 250 WORDS)

A simplified multiwell plate assay for the measurement of hepatitis A virus infectivity

A standardized multiwell plate assay (MWPA) was developed to provide a simple in situ measurement of hepatitis A virus (HAV) infectivity titers. Following attachment (4 h, 35 degrees C) of serial 10-fold dilutions of HAV strain CR326 F (variant F') to confluent MRC-5 monolayers in 24-well plates, cultures were overlaid with maintenance medium and incubated for 35 days at 35 degrees C with weekly medium replacement. Cells were fixed with 90% acetone and HAV antigen was quantitated by reaction with a radio-iodinated anti-HAV serum. Measurement of virus infectivity was based on the amounts of specifically bound and eluted radiolabelled antibody. Virus titers (50% tissue culture infectious doses/ml, TCID50/ml) were calculated using the method of Reed & Muench (Am J Hyg. 1938; 27: 493-497), with wells producing cpm values greater than 2.1-times that of uninoculated controls considered positive. The use of a virus standard provided an estimate of the test variability (+/- 5% in Log10 TCID50 units). The MWPA offers a significant savings in time and reagents, and is proposed as a standard method for the simple and reliable measurement of the potency of HAV vaccine preparations.

Effect of relative humidity and air temperature on survival of hepatitis A virus on environmental surfaces

Stainless steel disks (diameter, 1 cm) were contaminated with fecally suspended hepatitis A virus (HAV; strain HM-175) and held at low (25% +/- 5%), medium (55% +/- 5%), high (80% +/- 5%), or ultrahigh (95% +/- 5%) relative humidity (RH) at an air temperature of 5,20, or 35 degrees C. HAV survival was inversely proportional to the level of RH and temperature, and the half-lives of the virus ranged from greater than 7 days at the low RH and 5 degrees C to about 2 h at the ultrahigh RH and 35 degrees C. In parallel tests with fecally suspended Sabin poliovirus (PV) type 1 at the low and ultrahigh RH, all PV activity was lost within 4 h at the low RH whereas at the ultrahigh RH it remained detectable up to 12 h. HAV could therefore survive much better than PV on nonporous environmental surfaces. Moreover, the ability of HAV to survive better at low levels of RH is in direct contrast to the behavior of other enteroviruses. These findings should help in understanding the genesis of HAV outbreaks more clearly and in designing better measures for their control and prevention.