Hepatitis B virus found in bats from Panama and Gabon.

Hepatitis B virus (HBV) is a substantial human pathogen. WHO estimates
that there are now 240 000 000 individuals chronically infected with
HBV worldwide, of which 25 percent percent will die from chronic liver
disease or hepatocellular carcinoma. The hepatitis B virus vaccine is
highly effective at preventing infection. Because there are no known
animal reservoirs of the virus, it is believed that HBV could be
globally eradicated. The recent finding of HBV in bats raises the
possibility of zoonotic introduction of the virus.

Serum and liver biopsies from 3080 bats from Panama, Brazil, Gabon,
Ghana, Germany, Papua New Guinea, and Australia were screened for
HBV-like sequences by polymerase chain reaction (PCR). 10 positive
specimens were found from 3 bat species: _Uroderma bilobatum_ from
Panama, and _Hipposideros cf. ruber_, and _Rhinolophus alcyone_ from
Gabon. The complete viral genome sequence was determined for 9 of the
positive specimens. Phylogenetic analysis revealed that the bat
viruses form 3 different lineages, and that each virus differs by at
least 35 percent from known hepadnaviruses. The virus from _H. cf.
ruber_ has been named roundleaf bat HBV, while those from
_Rhinolophus_ and _Uroderma_ have been named horseshoe bat HBV, and
tent-making bat HBV.

Viral DNA in the liver of _Hipposideros_ bats was found to be higher
than in other organs or serum. Some lymphocyte infiltration was
observed in the liver of these animals, as well as deposits of viral
DNA within hepatocytes. These observations indicate that the bat HBV
viruses likely replicate in the bat liver and cause hepatitis.

Serological studies revealed that hepadnaviruses are widespread in Old
World bats: antibodies against bat hepadnaviruses were detected in 18
percent of hipposiderid bats and 6.3 percent of rhinolophid bats. An
important question is whether these 3 bat hepadnaviruses can infect
human cells. Only tent-making bat HBV could infect primary human
hepatocytes, which occurred via the human HBV cell receptor, sodium
taurocholate cotransporting polypeptide. However serum from humans
that had been immunized with HBV vaccine did not block infection of
human hepatocytes with this virus.

These observations show that viruses related to human HBV are
replicating in the liver of bats. Earlier this year (2013) another
hepadnavirus was identified in long-fingered bats (_Miniopterus
fuliginosus_) in Myanmar. The complete genome sequence was obtained
and virus particles were observed in bat liver tissues. The finding of
hepadnaviruses in bats raise many interesting questions. The 1st is
whether human HBV originated by infection with bat HBV, either by
consumption of bat meat or another mode of transmission. How long ago
this occurred is not known. It has been suggested that HBV has been in
humans for at least 15 000 years. Some avian species contain
avihepadnaviral sequences integrated into their genome, indicating
that these viruses originated at least 19 million years ago. These
findings also raise many questions about the pathogenesis of
hepadnaviral infection in bats, including the mode of transmission (in
humans, the virus is transmitted by exposure to blood, for example, by
injection or during childbirth), and whether chronic infections can
occur as they do in humans.

Finally it is interesting to consider the zoonotic potential of
tent-making bat HBV, which can infect human cells. Because bat
hepadnaviruses are genetically distinct from HBV, current serological
and nucleic acid screening programs would not detect human infections.
The authors suggest that human and non-human primate sera from areas
in which these bat viruses were isolated should be screened using
assays that detect the bat hepadnaviruses. Without such information we
do not know if these viruses currently infect humans.
Fuente: promed. 20.102013