10 Facts about Hepadnaviridae:

1. Retroviridae is not the only family that has reverse transciptase. Hepadnavirus utilizes reverse transcriptase in their replication as well.

2. Hepadnaviridae is NOT the only DNA family that utilizes reverse transcriptase It is the only human DNA family, but there are Caulimoviruses which make up a truly double stranded DNA virus family that also use RT. The caulilower mosaic virus (CaMV), the representative virus of this plant family, has shown that it is a reverse-transcribing virus with properties in between Retroviruses and Hepadnaviruses.

3. Hepadnaviridae consists of only one human virus – Hepatitis B. There are other hepatitises as well. Hepatitis A (Picornaviridae), Hepatitis C (Flaviviridae), Hepatitis D (No family), Hepatitis E (Hepeviridae), Hepatitis G (Flaviviridae).

4. Hepadnaviridae’s Hepatitis B genome is 3,182 base pairs long. Out of all the DNA viruses that are replication competent, Hepatitis B has the smallest genome.

5. This family is the only human viral family with a partially double stranded DNA organization.

6. The name “Hepadnaviridae” comes from “Hepatotropic DNA virus."

7. There are two genera: Orthohepadnaviruses and Avihepadnaviruses, and classification is based on DNA sequence similarities.

8. Hepatitis B not only causes acute and chronic disease, it also causes Hepatocellular Carcinoma or liver cancer.

9. Hepatitis B is associated with Hepatitis D (even though Hepatitis D is not a Hepadnavirus) because Hepatitis D steals envelope proteins in order to replicate in the host.

10. There have been 3 vaccines to treat Hepatitis B.The first was Heptavax which is not used today. Two types, Recombivax and Engerix, are still used today.

References:
Dimmock, Easton, and Leppard. Introduction to Modern Virology. Carlton, Victoria: Blackwell, 2007. 126

Richman, Douglas D., Richard J. Whitley, and Frederick G. Hayden, eds. Clinical Virology. 2nd ed. Washington, DC: ASm P, 2002. 623-634