The first evidence of hepatitis A virus subgenotype IIIA in the Eastern Brazilian Amazon, 1982-1983.

Hepatitis A virus (HAV) is a major causative agent of acute hepatitis worldwide. Although discovered in 1973, due to limitations of applicable serological and/or molecular methods, HAV remained under limited diagnosis until the late 1980s. This study aimed to retrospectively evaluate the serological and molecular prevalence of the HAV infection among 421 (n = 421) patients with a clinical and laboratory suspicion of acute hepatitis who were admitted in a reference laboratory in the Brazilian Eastern Amazon during 1982 and 1983. The 421 serum samples were screened for anti-HAV IgM antibodies by enzymatic immunoassays. Positive samples were submitted to total RNA purification and tested by Nested reverse-transcription polymerase chain reaction to amplify the HAV-RNA VP1-2A (522 bp) region. Anti-HAV IgM antibodies were detected in 66% (278/421) of the patients. The highest prevalence was observed among males (57.9%, 161/278), and most often among children under 10 years old (63.3%, 176/278). HAV-RNA was detected in 74.4% (207/278) of anti-HAV IgM positive samples. HAV genotyping was performed in 71 samples, and 69 were classified into subgenotype IA. Two samples belonged to the HAV subgenotype IIIA. In this sense, retrospective studies can help in understanding the evolution and determination of wild genotypes and subtypes of HAV.