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The development of molecular biology techniques has enabled us to clone the genetic sequence of three new hepatitis viruses, namely, hepatitis C virus, hepatitis E virus and hepatitis G, or GBV-C virus in the last decade. Hepatitis C virus (HCV) is now known to account for the majority of the parenterally transmitted non-A, non-B hepatitis and hepatitis E virus (HEV) is the major cause of the epidemics of enterally transmitted non-A, non-B hepatitis in the less developed countries, mainly through contaminated water supplies. While 80% of those who were infected with HCV will become chronic carriers, there is no known chronic carrier state for HEV. To date, 6 major genotypes of HCV were identified, with various variants of genotype 6 described in Southeast Asia. In Singapore, the majority of our chronic hepatitis C patients are infected with genotype 1. The seroprevalence rate of HEV is 10% to 14% in Singapore. This probably reflects our suboptimal sanitary condition in the past rather than a reflection of a currently high HEV infection rate in our population. However, local cases of acute hepatitis E have been reported. As for the most recently cloned hepatitis G virus, its aetiologic role in the remaining cases of non-A, non-B hepatitis is still unclear. Some preliminary evidence suggests that it may be just an innocent bystander with limited pathogenicity and it certainly cannot account for all the remaining cases of non A-E hepatitis. Hence, the search for yet another hepatitis virus continues.

Malignant histiocytosis, as defined by Rappaport, is now known as a manifestation of malignant lymphoma, the majority of which is the T-cell type. However, unlike the typical presentation of most non-Hodgkin lymphomas, this condition presents with atypical features mimicking acute hepatitis or infectious mononucleosis. The latter diagnosis is often made because of the occurrence of atypical mononuclear cells on the peripheral blood films. This is clearly seen in the seven patients we report where the initial diagnoses were that of viral fever or hepatitis. Some characteristics were found in these patients to differentiate the condition from infectious mononucleosis (IMS) and acute hepatitis (AH): paucity of lymph nodes, cholestasis and prolonged prothrombin time (PT) which is atypical IMS; persistent fever, thrombocytopaenia and disproportionately high aspartate aminotransferase which is unusual in AH in the absence of any drug or alcohol history. The PT is the most important prognosis factor. Early diagnosis and treatment led to improved survival in an otherwise aggressive and rapidly fatal condition.