LONDON, May 12 (Xinhua) -- There are some leads for the cause of an outbreak of hepatitis among children, but none of them is convincing enough yet to define what exactly causes the illness, a British virologist has said.
World experts remained baffled by the cause of the mysterious outbreak, with teams battling to seek the reason, Will Irving, a professor of virology at the University of Nottingham, told Xinhua recently in an exclusive interview.
"I think when we get to the bottom of it, we will find there are two or three or four different factors which will all coalesce to produce what is really quite an extraordinary event," said Irving.
The World Health Organization (WHO) said Tuesday that there are now 348 probable cases of acute hepatitis among children across five regions globally.
As of May 3, there have been 163 cases of acute non-A-E hepatitis identified in children aged under 16 years old in Britain since January 1, 2022, eleven of which have received a liver transplant. No cases resident in the country have died, according to the UK Health Security Agency (UKHSA).
Irving explained that the number of cases is higher than it should be, with clinicians usually seeing rare cases of severe hepatitis in young children, maybe one or two cases every couple of months in Britain.
"So the fact that we've seen 160-plus cases in three months is a considerable increase on what we've seen in years gone by. So there is something unusual happening," he noted.
The investigation suggests an association with adenovirus. According to the UKHSA, adenovirus is the most frequently detected virus in samples tested. However, it is not common to see hepatitis following adenovirus infection in healthy children.
Irving said the adenovirus has been found in about three quarters of the reported children, but it is a very common infection in young children. "Up until 2022, it's not a virus that has been associated with any form of hepatitis, never mind very severe hepatitis," he added.
"That is the leading contender that there is something about this adenovirus that may be causing it, but it's not going to be the whole explanation because these adenoviruses have been around for hundreds of years, and they don't usually cause hepatitis," said Irving. "We need a lot of other forms of experimentation to sort out whether or not this adenovirus is incidental or whether it's the cause, and we really can't say at the moment."
Irving mentioned that these cases have occurred geographically right across Britain and no links were found between them apart from two cases in Scotland.
In Britain, investigations are continuing into other possible contributing factors, including previous SARS-CoV-2 or another infection, a change in susceptibility possibly due to reduced exposure during the pandemic, and a change in the adenovirus genome itself.
"In some way, either the virus itself or the consequences of our response to the pandemic have initiated whatever it is that's causing this hepatitis," said Irving.
Irving said there are several different hypotheses at the moment, stating the most obvious one is that during the pandemic, young children under the age of five were largely shielded and not exposed to the normally trivial virus infections that young children are usually exposed to.
Now with all the restrictions such as social distancing lifted, these children are being exposed to a whole range of viruses which are increased in circulation, he continued. "Their immune system is simply not handling either a multitude of infections or the specific infection with this adenovirus," he said.
In Britain, the UKHSA is coordinating the investigation of the cases, issuing guidance to clinicians who are seeing individual cases, asking them to take a whole series of biological samples, throat swabs and faeces and blood samples. Laboratories in London and Glasgow are doing genetics work on the adenoviruses.
Toxicologists are looking at whether any of the children have been exposed to some kind of toxin. Epidemiologists are also interviewing parents to see if there is any common feature in their diet or their behavior or their environmental exposure.
"So there is a huge amount of work going on trying to sort it all out; it is possible that whatever's causing it will decline, and the number of cases will decline before we work out what it is," said Irving.
Speaking of a possible outbreak getting out of hand, Irving responded that there has to be a theoretical possibility if it is a truly new agent or a toxin that has not been recognized before.
"This has been going on since early January and we haven't seen that kind of curve, so I'd be reasonably hopeful it's not going to take off and explode, but given that I don't know what the cause is, I can't say that for certain," he said. ■
