B型肝炎ウイルス
"Hepatitis B virus" is classified in the genus "Orthohepadnavirus", which contains 11 other species. The genus is classified as part of the "Hepadnaviridae" family, which contains four other genera, "Avihepadnavirus", "Herpetohepadnavirus", "Metahepadnavirus" and "Parahepadnavirus". This family of viruses is the only member of the viral order "Blubervirales". Viruses similar to hepatitis B have been found in all apes (orangutans, gibbons, gorillas and chimpanzees), in Old World monkeys, and in New World woolly monkeys (the woolly monkey hepatitis B virus), suggesting an ancient origin for this virus in primates.