London: Like HIV and Ebola, the hepatitis A virus is of likely animal origin, finds a large-scale study looking into the evolutionary origins of the global pathogen.
The virus, which is found worldwide, has previously been considered to be a purely human pathogen which at most is found in isolated cases in non-human primates.
An infection with the hepatitis A virus can trigger acute inflammation of the liver which generally does not cause any symptoms in children and resolves without major complications.
"In tropical regions, nearly all young children are infected with the hepatitis A virus and from that time on, they are immune to this disease," explained one of the researchers Jan Felix Drexler from University of Bonn Medical Centre in Germany.
By contrast, if adults become infected with the hepatitis A virus, the symptoms can be more serious, and the disease can even have a fatal outcome.
Virologists from University of Bonn Hospital, together with their colleagues from several German and international research institutes worldwide, searched for viruses related to the hepatitis A virus.
They investigated a total of 15,987 specimens from 209 different species of small mammals -- from rodents to shrews and bats to hedgehogs.
Viruses from these mammals are very similar to the human hepatitis A virus with regard to their genetic properties, protein structures, immune response and patterns of infection.
"The seemingly purely human virus is thus most likely of animal origin," Drexler pointed out.
"The study enables new perspectives for risk assessments of emerging viruses by investigating functional, ecologic and pathogenic patterns," Drexler explained.
The scientists' evolutionary investigations may even hint at distant ancestry of the hepatitis A virus in primordial insect viruses.
"It is possible that insect viruses infected insect-eating small mammals millions of years ago and that these viruses then developed into the precursors of the hepatitis A virus," Drexler noted.
The findings appeared in the journal Proceedings of the National Academy of Sciences (PNAS).