OUTLINE

Viral hepatitis is still one of the most common causes of acute and chronic liver disease worldwide. The subject of viral hepatitis results in about 10,000 new papers each year, from molecular structure to newest treatments. Major new advances have been made in our knowledge of these diseases, many during the past two years.

Five hepatotropic viruses A to E are now recognised and all are important public health issues, although more so in some countries than others. Three additional viruses, Hepatitis G, TT virus, and SEN-V have been discovered recently, but have to be proved to be hepatotropic and pathogenic to liver.

It is evident that these viruses, although similar in some respects, have a number of intriguing differences. Most are RNA viruses but Hepatitis B and TT virus are DNA viruses. Each belongs to a different virus family and, with the exception of Hepatitis D virus, has unique features that have resulted in being classified in a new genus within family. Two viruses (Hepatitis B and C) are enveloped and two (Hepatitis A and E) are not, whereas the Hepatitis D virus requires an envelope provided by the surface-coat material of Hepatitis B virus for it to propagate. Only Hepatitis B virus integrates into the host DNA. Two viruses (Hepatitis A and E) are spread enterically and cause acute illness, whereas three (Hepatitis B, C, D, G, TTV and SEN-V) are spread parenterally and Hepatitis B, C and D cause chronic disease. Hepatitis G, TTV and SEN-V are also thought to cause mild acute and chronic disease. Although viral factor may contribute to the nature of the disease they cause, the host's immunologic reaction to the presence of virus in hepatocytes emerges as the dominant mechanism of liver-cell damage and inflammation (Mondel MJ 2000). Newer medications in the form of interferon alfa and nucleoside analogues have been added to the armamentarium of chronic viral hepatitis. Liver transplantation has been established as an effective therapy for patients with end-stage liver disease (Bzowej NH 1999). This review discusses the recent advances in our knowledge of viral hepatitis A to E and viral hepatitis Non-A-to Non-E, focussing on the literature of the past two years.

Non-A -To-Non-E Viral Hepatitis

The list of potential hepatotropic viruses continues to grow, with the recent discovery of the GB virus-C, the TT virus, and the SEN virus. Prevalence rates of the GB virus-C have ranged from 1.2% to 13% among healthy blood donors from all over the world. Higher prevalence rates have been reported among intravenous drug users. Similarly, the TT virus has a global distribution. However, in spite of numerous reports of the presence of both of these viruses in various kinds of liver diseases, definite evidence linking them to a specific disease, or illness is lacking. The SEN virus is thought to be a novel viral agent that may be linked to cryptogenic chronic hepatitis, but data are awaited.

The Hepatitis G virus (HGV) is a single-stranded DNA virus that is included in the Flaviviridae family and shares a 27% homology with HCV. The name HGV actually denotes 2 independent viruses, HGV and GBV-C. The HGV has not yet been isolated.

Hepatitis G virus, was first isolated in 1995. Two lines of investigations led its discovery: 1) an agent termed GBV-C was recovered from a human following the identification of similar viral isolate, GBV-A and GBV-B, isolated from tamarinds infected with serum from a surgeon (G.B.) with hepatitis, and 2) a blood-borne virus was isolated from a plasma from a patient with chronic hepatitis and designated Hepatitis G virus (HGV). These two human isolates (GBV-C and HGV) are now considered strains of the same virus and have amino acid sequence homology of 95%.

Although Hepatitis G virus (HGV) can cause chronic infection and viraemia, it is a rare cause of hepatic inflammation and most infected persons are asymptomatic. Histologic evidence of HGV infection is rare, and serum aminotransferase concentrations usually are normal (Patric CC 1999). Currently no conclusive evidence indicates that HGV causes fulminant - or chronic disease and co-infection does not seem to worsen the course of infection with Hepatitis B virus (HBV) or Hepatitis C virus (HCV).

The HGV has been reported in adults and children throughout the world. Infection has been reported in 10% to 20% of adults with chronic HBV or HCV infection, indicating that co-infection is a common occurrence. The primary route of spread is through blood transfusions, but HGV also can be transmitted by organ transplantation. Other important risk factors include injection drug use, haemodialysis, and homosexual and bisexual relationships, indicating that sexual transmission may occur. Transplantation transmission seems to be rare and has been associated with high-titer maternal viraemia; when it occurs, infection usually becomes persistent in infants.

The incubation period is not yet known. Currently, HGV infection can be diagnosed only by identifying viral genomes by using polymerase chain reaction (PCR) assay. No serologic test is available. In United States 1% to 2 % blood donors are viraemic as defined by the presence of viral nucleic acid in their blood.

A group in Japan, in December 1997, reported yet another transfusion-transmissible virus discovered via the use of cloning and DNA sequence analysis. This novel, single-stranded linear DNA virus has been designated TT-virus or TTV after the initials of the first patient (TT) from whom the virus was isolated. The virus is unenveloped and has been associated with biopsy proven, post-transfusion hepatitis of unknown aetiology. TTV has a significant prevalence in the United States, United Kingdom, Japan, Thailand and Germany.

Transaminase activity or liver histological score is not significantly increased among TTV positive patients (Zein NN 2000). The Hepatitis B infection (HBV) and Mediterranean origin are the risk factors associated with TTV infection. TTV is a widely spread infectious agent with a weak pathogenesity. TTV infection does not impact on liver damage with HCV infection. TTV infection also does not affect the development and progression of hepatocellular carcinoma. Cryptogenic cirrhosis (one in which the cause of cirrhosis is not evident) accounts for 5% to 15% patients with chronic liver diseases in the United States, supporting that unidentified viral agents are associated with liver disease (Tuveri R et al 2000).

TTV DNA is detected by PCR and by phylogenetic analysis. (Phylogenesis is the evolutionary development of a species, as distinguished from ontogeny, development of the individual.) TTV strains can be divided into 6 genotypes using phylogenetc analysis. The majority of TTV-DNA sequences are related to genotypes 1 and 2 as described in Europe.

In July 1999, the recent data from the Diasorin Research Centre in Bresica, Italy document that a novel virus, provisionally named SEN-V, most likely causes acute and chronic hepatitis, probably accounting for many cases of Non A-to-G hepatitis. This virus is parenterally transmitted, and therefore, appropriate screening of blood and blood products could control its spread. In addition, this virus appears capable of co-infecting patients who have other types of viral disease raising the possibility that it may aggravate their clinical course and/or their response to treatment (Menon KV, Zein NN 2000).

In 1994, French researchers reported the isolation of an enteric agent responsible for sporadic cases of Non-A-E hepatitis and named the virus Hepatitis F (HFV), for hepatitis French virus. However, their findings have not been confirmed by others and the term HFV is currently unclaimed.

Hepatitis A virus (HAV) is an enterovirus in the family of Picornaviridae. It has one serotype. The genome is a single strand of positive-sense RNA. Hepatitis A is still the most frequently reported vaccine preventable disease. The risk of Hepatitis A in patients with chronic liver disease has been confirmed and the efficacy of Hepatitis A vaccine in these patients has been proved (Olive G et al 2000). The reduction in the incidence of Hepatitis A will only be achieved by routine childhood vaccination rather than by targeted vaccination of high-risk group. Unlike Hepatitis B virus (HBV) transmission by blood via parental routes can occur but is unusual in Hepatitis A infection.

The advances in molecular biology techniques in the past decade have led to the clarification of Hepatitis B viral DNA sequences. However, much remains to be established regarding the emerging Hepatitis B mutants. Several putative forms of Hepatitis B virus have been isolated, but their epidemiology, natural course of infection and clinical significance remain sketchy. Compounding these problems are factors created by human interventions, such as HBsAg mass immunization, chemotherapy of chronic HBV patients and HBIg prophylaxis of orthoptic liver transplant (OLT) patients, which tend to encourage new mutants to emerge.

Hepatitis B (HBV) is a Hepadnavirus .It is a small enveloped DNA virus containing 3.2 kb. The Hepatitis B virion consists of a surface and a core. The core contains a DNA polymerase and the e antigen. The DNA structure is double stranded and circular. There are four major polypeptide reading frames (genes): the S (surface), the C (core), the P (polymerase) and the X (transcriptional transactivating). The S gene consists of two regions, the pre-S1, pre-S2 and encodes the surface proteins (HBsAg). Very rarely a mutation may occur in the S gene and may abort the HBsAg with the result that a person may be HbsAg negative but still have virus present as determined by HBV DNA. The C gene is divided into two regions, the pre-core and the core, and codes two different proteins, the Core antigen (HBcAg) and the E antigen (HBeAg)

Because HBV uses a reverse transcription mechanism, mutations are fairly common. It is now known that HBV mutates far more frequently than the usual DNA virus but less than rotaviruses. During the last 7 years a series of HBV mutants have been recognized. The most important of these is the so-called pre-core mutation, in which there is a defect in the pre-core region of HBV DNA. This mutation results in the failure to express HBeAg. The pro-core may stop production of HBeAg and these persons will be HBsAg positive, HBV DNA positive, but HBeAg negative. The pre-core mutation has been implicated in the pathogenesis of fulminant hepatitis and may be responsible for severe exacerbations of chronic hepatitis associated with HBV infection. In general, patients with this mutant are more likely to progress to cirrhosis and hepatic insufficiency, compared to infection with wild strains.

A wide geographical variation seems to emerge from pre-core mutants. A high as 25% of chronic HBV infections in patients in Delhi were found to be caused by pre-core and surface mutants. If pre-core mutants become a clinically important problem, it will be important to incorporate them into the next generation of Hepatitis B vaccine (Gupta et al 1996). Although the efficacy of HBV immunization is well proven, cases of vaccine failure leading to chronicity, acute self-limited symptomatic hepatitis and in some cases, fulminant hepatitis has been reported. In some of these cases, anti-HBsAg neutralization-resistant mutants or/naturally occurring escape mutants have been identified. Vaccine escape mutants have also been identified in newborns from infected mothers who had been vaccinated at birth. Clearance of HBV infection results from complex immune mechanisms including TH1 cytokines significantly associated with HLA class II alleles. Escape HBV mutants, especially pre-core mutants influence the outcome.

To make it even more complex, the HBsAg particles are antigenically complex and these antigenic determinants have been identified. There is a single common determinant designated a, and four sub-determinants designated d, y, w, and r. Thus, the four major determinants are: adr, ayw and ayr.

Although uncommon, a number of conditions associated with Hepatitis B antigen-antibody complexes have been recognised. These include: polyarteritis, glomerulonephritis, polymyalgia rheumatica, Guillian-Barre syndrome, myocarditis and essential mixed cryoglobulinaemia - sometimes only a test tube finding (Amarapurkar DN et al 2000).

Lamivudine is a major advance in the therapy of chronic Hepatitis B. Although drug resistant mutants may be selected during therapy, additional nucleoside analogues including adefovir are promising. Aggressive combination therapy has emerged as a promising strategy from chronic Hepatitis B and C. Liver transplantation has become routine for end stage Hepatitis B virus liver disease (Ramarakhiani S, Bacon BR 2000). The spontaneous risk for viral recurrence after transplantation is high, but has been decreased effectively in Hepatitis B-positive recipients with the use of HBIG and lamivudine (Rosenberg W 1999).

Concerns have been raised by reports of multiple sclerosis (MS) or other demyelinating diseases occurring in adults who had recently received Hepatitis B vaccine. There are three hypotheses that could explain the observed cases of demyelinating diseases following HB vaccine: (1) coincidence, because of the large number of HB vaccine doses administered, many of them in age groups where symptoms of MS first occur. (2)"triggering": an increased risk of symptomatic demyelination following HB vaccine, which would act as "trigger" in individuals predisposed to develop MS or CNS demyelinating diseases - these individuals would have developed demyelination with or without an altered natural history after some immunologic or other precipitating factor and (3) a true causal relationship between HB vaccination and MS or other CNS demyelinating disease.

Evidence to support the first hypothesis includes the fact that no statistically significant association was found between HB vaccine and MS in the limited studies conducted to date. Further the age and sex distributions of MS cases reported through spontaneous reporting of MS reporting systems match the recognised age and sex distribution of MS cases that preceded the use of the vaccine and are not correlated with vaccine administration.

In support of hypothesis of an increased risk of MS after HB vaccination seen as a precipitating factor is that some studies have shown slightly elevated odds ratios, although these were not statistically significant. Evidence inconsistent with this hypothesis is the observation that no increased risk was found in another study.

The data available to date, although limited do not demonstrate a causal association between HB vaccination and CNS demyelinating diseases, including MS (Halsey NN 1999).

The present studies support the WHO recommendations that all countries should have universal infant and/or adolescent immunization programmes and continue to immunize adults at increased risk of HB infection as appropriate.

Studies have shown that the vaccine is 95% effective in preventing children and adults from developing chronic infection if they have not yet been infected. In many countries where 8% to 15% of children used to become chronically infected with HBV, the rate of chronic infection has been reduced to less than 1% in immunized group of children.

Ten years have elapsed since identification of the viral agent (Hepatitis C virus [HCV]) responsible for hepatitis was first reported. This remarkable achievement occurred after more than 20 years of intense efforts by investigators worldwide following observation that at least one additional viral agent, other than Hepatitis A and Hepatitis B, was the major cause of post-transfusion hepatitis (Arch RD et al 2000).

HCV is an enveloped, positive stranded RNA virus with a genome that consists of 10,000 nucleotides. The virus is a member of flavivirus family, which also includes other parenenterally spread viruses such as yellow fever and dengue. At least 6 genotypes as well as a number of subtypes have been identified. A correlation seems to exist between the genotype and clinical course of infection and its treatment. For example, genotype1, which is common in the United States, seems to be most virulent of the genotypes and more resistant to treatment. Unfortunately HCV is a very mutagenic virus, a characteristic that enables it to survive the immune defence mechanisms of the host. As a result more than 75%of the adults acquiring acute infection go on to develop chronic Hepatitis C with continuing HCV infection (Widdermann BL 1999).

Three per cent of the world population has been infected with Hepatitis C virus (HCV). Epidemiology has shifted from transfusion to non-transfusion settings. Intravenous drug abuse is currently the main risk but nosocomial (hospital) infection is also a concern.

Nosocomial spread is potentially important and in some instances preventable. It has been shown, for example, that in many chronic haemodialysis patients, there is 20% to 30% prevalence of ant-HCV positivity in the absence of any clear parenteral risk factors.

A recent Australian report has raised the possibility of HCV transmission through contaminated anaesthetic equipment intra-operatively. This is the first case report of patient-to-patient transmission of HCV. Transmission of HCV by endoscopy is also possible, as suggested by a French report that highlights the importance of meticulous cleaning of endoscopic instruments, including biopsy channel.

An increasing body of evidence suggest that a large proportion of hepatitis infections in Egypt were caused by unsafe injection practices during the last decades. In particular, improperly sterilized needles appear to have been used to treat schistosomiasis. Approximately 13% of the Egyptian population is infected with Hepatitis C virus leading to a high burden of chronic liver disease, cirrhosis, and liver cancer as well as mortality resulting from these diseases. The tartaric emetic intravenous injections were given twice a week for 7 weeks to treat schistosomiasis. The tartaric emetic is an antimonial compound. The use of injections to treat schistosomiasis stopped about 15 years ago; the current treatment for schistosomiasis is oral administration of praziquintel. Evidently, this practice has resulted in a large reservoir of the virus that has contributed to the spread of infection in the country. This is one the historic events in which the introduction of a new modality or a new technique was considered initially of major credit to the patient but later, unfortunately, turned out to be a virtual catastrophe. Such events are not rare in the history of medicine.

The UK researchers have found that delivering at-risk babies by caesarean section may protect the infants from the Hepatitis C virus.

There is correlation between hepatitis quasi species and the progression of liver disease. The quasi species hypothesis suggests that viruses, particularly RNA viruses, circulate as mixed populations of closely related variants. Changing population dynamics may lead to alterations in the relative dominance of one or more variants, and new variants emerge. Quasi species may have relevance for the capacity of a virus to evade immune control. They have been documented in Hepatitis C virus infection, typically a chronic infection with a varying clinical impact amongst patients.

Three independent factors seem associated with fibrosis progression in HCV: age, daily alcohol consumption of 50g or more and male gender. Median duration of progression to cirrhosis is about 30 years. At the cirrhotic stage, about 3-5% of patients per year develop hepatocellular carcinoma. There is little evidence that direct cytopathogenecity plays a significant role in the liver cell injury. The spontaneous Hepatitis C virus clearance is determined by class II antigens (mainly DQB10301) and female sex, while viral genotype plays no role (Alric L 2000). HCV also infects extrahepatic cells which seem critical in the pathogenesis of any extrahepatic manifestations (Amarapurkar DN 2000). The recent identification of CD81 protein as one the HCV receptor candidates may help to understand how chronic HCV infection may trigger a wide spectrum of clinical manifestations, autoimmune or even lymphoproliferative, through potent continuous B cell activation in the context of various host and/or environmental cofactors. Hepatitis C virus infection occurs with increased frequency in patients with non-Hodgkins's lymphoma. Evidence of prior infection with HCV is common in patients with non-Hodgkin's lymphoma (Vallisa D et al 1999).

Infection may cause a mild acute hepatitis but many cases are asymptomatic: fulminant hepatitis is rare. HCV infection persists up to 80% of patients; up to 35% of these develop cirrhosis, liver failure and hepatocellular carcinoma between 10 and 30 years later. This occurs because frequent virus mutation results in immunologically distinct quasi-species, allowing the organism to escape immunological control.

Among patients with chronic Hepatitis C, 48 weeks of treatment with interferon/ ribavirin therapy produced a response rate of 28% among those with genotype 1 and 66% with other genotypes. Similar differences were found in combination therapy among patients who had relapsed following previous interferon (IFN) therapy. Viral load prior to treatment has been clearly shown to be predictive of response to interferon treatment, with increased viral load associated with decreased rate of response. In patients non-responsive to interferon, a second course of interferon alone has non-beneficial effect whereas combination therapy may induce response in 25% of patients. The combination therapy is recommended in all situations. Viral eradication should not be the only objective of the treatment since histological improvement may be obtained despite persisting viral replication with prolonged maintenance of antiviral therapy (Shaffer EA 2000).

The Hepatitis D virus (also called delta virus) is a small circular RNA virus. The Hepatitis D virus is replication defective and therefore cannot propagate in the absence of another virus. In humans, Hepatitis D virus infection only occurs in the presence of Hepatitis B infection.

A patient can acquire Hepatitis D virus infection at the same time as she/he is infected with the Hepatitis B virus. This is called co-infection. A patient with Hepatitis B can be infected with Hepatitis D virus at any time after acute Hepatitis B virus infection. This is called super-infection (Desai et al 1990).

Hepatitis virus super-infection should be suspected in a patient with chronic Hepatitis B whose condition suddenly worsens. There is usually an obvious history of continued exposure to blood or blood products (e.g. an active intravenous drug user). A particularly aggressive acute Hepatitis B infection could suggest Hepatitis D co-infection. Co-infection or super infection with Hepatitis D virus in a patient with Hepatitis B is diagnosed by the presence of antibodies against the Hepatitis D virus. IgM antibodies indicate acute infection.

Interferon-alfa is used to treat patients with chronic Hepatitis B and Hepatitis D infection. Some studies have suggested that a dose higher than that usually used for Hepatitis B infection may beneficial.

Hepatitis E virus consists of small, 32 to 34 nm. diameter, icosahedral, nonenveloped particles with a single-stranded, positive-sense, 7.5-kb RNA. The virus has two main geographically distinct strains, Asian and Mexican; recently, novel isolates from non-endemic areas and a genetically related swine HEV have been described. HEV is responsible for large epidemics of acute hepatitis and a proportion of sporadic hepatitis cases in the Indian subcontinent, Southeast and central Asia, the Middle East, parts of Africa, and Mexico (Khuroo MS et al 1994). Clinical illness is similar to other forms of acute viral hepatitis except for pregnant women, in whom illness is particularly severe with a high mortality rate. Sub-clinical and unapparent infection may occur, however, chronic infection is unknown. No specific treatment is available. Use of clean water and proper sanitation is currently the most effective method of prevention. Passive immunization has not been proved to be effective, and recombinant vaccines for travellers to disease-endemic areas and for pregnant women currently are being developed (Krawczynki K 2000).

Hepatitis E virus (HEV) is an important cause of enterically transmitted acute viral hepatitis in several less-developed countries and is transmitted by faecal-oral route. Data on duration of viral excretion and viraemia during HEV infection are limited. An outbreak of Hepatitis E in Lucknow, India provided the authors (Aggarwal et al 2000) with an opportunity to obtain such data. Their data suggest that extended viral excretion and viraemia, particularly those extending beyond the duration of biochemical hepatitis, are distinctly rare. Thus, in disease-endemic areas, individuals who have recovered from acute Hepatitis E are unlikely to serve as a reservoir of HEV infection.

The histological features of viral hepatitis have not been changed and light microscopic examination remains essential for making diagnosis and classification of chronic hepatitis and the provision of objective parameters on grading and staging (Dhillon Amar P 2000). However, new understanding and knowledge of viral pathogenesis, host immune responses, the biological behaviour of the causative viral agents and, in particular, viral interference in multiple hepatotropic viral infections must be taken into consideration in the interpretation of histopathological and immunopathological findings of liver tissues. The study by Huang et al (1997) presents some histopathological analyses on multiple hepatotropic viral infections. The diagnostic histological criteria for acute hepatitis remain applicable in such settings. However, the cause of acute flare up in chronic hepatitis could not be determined without clinical, virological and serological information. Routine histopathology cannot distinguish a new infection from an acute exacerbation due to high level of viral replication or mutant virus. A battery of immunocytochemical stains for viral antigens is helpful, but caution must be exercised in suggesting a specific viral aetiology due the fact that suppression of pre-existing viral antigens can be pronounced when the new or concurrent infection is Hepatitis C virus related. Furthermore even in the presence of normal aminotranserase concentrations, considerable liver pathology can be found in 10% to 20% of HBsAg and anti HBVe positive individuals. Such pathology is not associated with the occurrence of pre-core stop codon mutations (TerBong 2000).

It is especially noteworthy to note the little-appreciated fact that half the patients with hepatocellular carcinoma who test negative for HBsAg have HBV DNA sequences in their tumours.

Cytokines play an important role in the defence against viral infections, both indirectly, through determination of the predominant pattern of host response and directly, through inhibition of viral replication. However, in the context of an inflammatory response against a virus, cytokines may also lead to liver damage. The importance of this is best illustrated in viral Hepatitis B (HBV). In acute HBV infection, a vigorous polyclonal cellular immune response is critical; thus type 1 cytokine release is essential to initiate an effective immune response. The cytokines released by CD4+ and CD8+ cells also play an important role in down regulation of HBV replication, demonstrating that it is possible to control a viral infection without the death of infected cells. However, if there is a defect in the acute response, HBV becomes chronic; in that case, the presence of an ongoing sub-optimal inflammatory can activate the process of hepatic fibrosis. In Hepatitis C infection, the role of cellular immune responses and cytokines is less clear. Hepatitis C may be resistant to inhibition by cytokines, so cytokines may have a more prominent role in liver damage than controlling viral replication. Both Hepatitis B and C may have specific mechanisms to inhibit cytokine production, highlighting the critical role these molecules in recovery from infection (Koziel MJ 1999).

Although they are referred to as "liver function tests," elevation of serum AST, ALT and GGT actually are indicative of hepatocellular damage. Slight elevations of AST and ALT do not always predict mild disease, and both can fall with end-stage liver failure. The most useful indicator of hepatic synthetic function is the prothrombin time (PT) (MacPharsen RA 1994). In some cases of Hepatitis A, a falling aminotransferase level may predict a poor outcome if the decline occurs in conjunction with rising bilirubin level and prolonged PT. This combination of findings indicates that massive hepatic injury has occurred, resulting in few functioning hepatocytes. Acute Hepatitis A is diagnosed by a positive IgM anti-HAV. The additional findings of IgG anti-HAV, in the absence of IgM, indicates a resolved Hepatitis A infection with lasting immunity. Patients who have been immunized against Hepatitis A may have undetectable antibody titers by standard commercially available laboratory assays. Diagnostic antibodies,anti-HAV IgM appear before jaundice develops and persists for three months.

Both acute and chronic hepatitis B infections are diagnosed by the presence of HBsAg. HBsAg positivity warrants investigation of Hepatitis D co-infection or super infection, as defined by the presence of IgM anti-HDV. Hepatitis D can occur only in the presence of HBsAg positivity. Acute Hepatitis B infection always is associated with the presence of IgM anti-HBc. IgG anti-HBc positivity indicates a resolving infection or chronic Hepatitis B. The presence of HBeAg indicates active viral replication and high infectivity. Anti-HBe appears when viral replication ceases. Resolved hepatitis B and lasting immunity either from infection or immunization are associated with the presence of anti-HBs.

Hepatitis C virus cannot be cultured. Hepatitis C is associated with the detection of anti-HCV by enzyme linked immunosorbent assay, but this test must be followed by supplemental specificity tests to substantiate the diagnosis, including recombinant immunoblot assay (RIBA) or measurement of HCV RNA by polymerase chain reaction (PCR).

PCR assays for HCV infection are used commonly in clinical practise in the early diagnosis of infection, for identifying infection in infant early in life e.g. perinatal transmission when maternal serum antibody interferes with the ability to detect antibody produced by the infant, and for monitoring patients receiving antiviral therapy. A patient with positive PCR result for Hepatitis C is infected with Hepatitis C virus even if serologic markers for Hepatitis C are negative. A negative PCR result for Hepatitis C with positive result for serological markers 1) indicates past Hepatitis C infection, 2) indicates acute HCV infection with transitory negative PCR phases, 3) may indicate a patient who has passively received anti-HCV immunoglobulins during a blood transfusion.

Radioimmuno assay and enzyme immuno assay for anti-HDV (Hepatitis D virus) are available commercially, usually at referral laboratories. Tests for IgM-specific ant-HDV antibody and HDAg are research procedures at present. If markers for HDV infection exist, co-infection with HBV usually can be differentiated from super-infection of an established HBsAg carrier by testing for IgM Hepatitis B core (HBcIgM) antibody; absence of this core antibody suggests that the person is an HBsAg carrier. Methods for detection of HDV RNA are available.

Recombinant DNA technology has resulted in development of antibodies to Hepatitis E virus (HEV) particles, and IgM and IgG assays are available to distinguish between acute and resolved infections. IgM antibody to viral antigen becomes positive after about one week of illness. Viral RNA can be detected in stool and serum by PCR. Diagnosis of Hepatitis E is usually made by detection of specific IgM antibody, which disappears rapidly over a few months; IgG ant-HEV persists for at least a few years.

The only diagnostic tests for Hepatitis G virus infection are PCR assays. They are used to detect HGV RNA

Acute hepatic failure (AHF) in India almost always presents with encephalopathy within four weeks of the onset of acute hepatitis. Viral hepatitis is the cause in approximately 95-100% of patients, who therefore constitute a more homogeneous population than AHF patients in the West. In India, Hepatitis E (HEV) and Hepatitis B (HBV) viruses are the most important causes of AHF; these two viruses cause approximately 60% of cases. Hepatitis B virus core mutants are very important agents in cases of where Hepatitis B results AHF in this country. Half of the patients with AHF are female, one quarter of whom are pregnant. Therefore, pregnant females who contract viral hepatitis constitute a high-risk group for development of AHF. However, the outcome of AHF in this group is similar to that in non-pregnant women and men. In AIIMS, Delhi, approximately one-third of AHF patients survive with aggressive conservative therapy, whereas, two-thirds of deaths occur within 72 hours of hospitalisation (Acharya SK et al 2000).

Hepatitis D is not uncommon in India. In a study reported from Bombay (Banker 1992), out of 331 cases of Hepatitis B, 148 patients had an evidence of Hepatitis D as well. Fulminant hepatitis developed in 39 patients, 32 of whom had Hepatitis B and 20 of these (63%) also had Hepatitis D. These findings indicate the extent of association of Hepatitis D with Hepatitis B and the high-risk of fatal fulminant hepatitis in these patients.