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An international team of virologists, mammalian ecologists and zoologists has uncovered the evolutionary origins of the hepatitis E virus. In their study, in the Proceedings of the National Academy of Sciences, the group analyzed genomic data for multiple viral hosts.

Hepatitis is any condition involving inflammation in the liver. There are a large variety of causes, one of which can be a virus. There are several types of viral hepatitis denoted by the letters A through E, as well as Epstein Barr and cytomegalovirus. Hepatitis C is the most common and is typically chronic. Hepatitis E is most prevalent in Asia and is typically acute—it kills approximately 44,000 people each year out of 20 million infections.

Prior research has shown that the hepatitis E virus has eight genotypes; only types one and two have been detected in human patients—all the others have been found in animals including camels, pigs, rodents and rabbits. In this new effort, the researchers focused their attention and efforts on the evolutionary origins of hepatitis E.

The work involved searching for evidence of hepeviral genes in genome databases for rodents, primates, bats, hooved animals and shrews. The researchers found four that were genetically divergent in bats and rodents. The team then studied 2,565 liver samples collected from 108 rodents and shrews captured in parts of Latin America, Asia and Africa and found hepeviral RNA in 63 of the samples from 14 species.

Combining the data from both their efforts, the research team identified 24 unique hepeviral genomes from bats, shrews and rodents. They noted that the highest diversity was among the rodents.

In conducting an evolutionary analysis of the genomes under study, the researchers found that hepatitis E associated with humans likely got its start in ungulates (hoofed animals) and more remotely, small mammals, mostly likely rodents. They also found evidence that host-switching hepeviruses most likely started with rodents.

The research team suggests their work could contribute to models of hepatitis that could be used to combat the spread of hepatitis E in humans—and more generally, in all hepatitis types as they cross over from animals to humans.

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