In addition to exogenous Hepatitis B viruses, a number of endogenous sequences (eHBV), in the form of endogenous viral elements (EVEs), have been identified in animal genomes. Hepatitis B e-viruses have been documented in turtles, crocodiles and snakes. Endogenous viruses are sequences with a viral origin that are included in a genome. About 8 percent of our genome is composed of sequences with viral origin.
In 2016 scientists reported the first amphibian Hepatitis B Virus genome: the Tibetan Frog Hepatitis B Virus (TFHBV)[1]. This indicates that the evolutionary history of the Hepatitis B viruses is more complex than previously realized and combines both virus-host codivergence over millions of years and host species jumping.
The High Himalaya frog (Nanorana parkeri) is also known as Xizang Plateau frog, Parker's slow frog, mountain slow frog or Tibetan frog, is Tibet and in Nepal, although it is expected to be found in neighbouring Bhutan and northern parts of India too.
It is a medium-sized frog. Both males and females grow to a maximum snout–vent length of about five centimeters. This frog is commonly found on high-altitude grasslands, forests, shrubs, lakes, ponds, marshes, streams and rivers in the Tibetan Plateau at elevations between 2,850 and 5,000 meters above sea level. It an explosive breeder in streams and marshes.
As a result of these findings, hepadnaviruses have now been grouped into five genera: Parahepadnavirus, Metahepadnavirus, Herpetohepadnavirus, Avihepadnavirus, and Orthohepadnavirus[2].
[1] Dill et all: Distinct Viral Lineages from Fish and Amphibians Reveal the Complex Evolutionary History of Hepadnaviruses in Journal of Virology - 2016
[2] Magnius et al: ICTV Virus Taxonomy Profile: Hepadnaviridae in Journal of General Virology - 2020. See here.
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