The reason behind the recent outbreak of acute hepatitis in children has been identified, according to a team of researchers.
UK scientists believe they have identified the reason for the rise of liver illness globally, after investigations by research teams in London and Glasgow suggested the hepatitis cases are the result of two common viruses.
But what is the cause behind the rise in hepatitis cases and what have scientists said?
Here’s what you need to know.
What was the cause of hepatitis cases in children?
More than 1,000 children in 35 countries are thought to have recently developed hepatitis, with some needing liver transplants, including 12 in the UK.
In the UK, most of the 268 children affected by sudden-onset hepatitis have been aged under five, with nearly 40% taken to hospital needing intensive care.
The two teams of researchers found that the rise in hepatitis cases is connected to the common adeno-associated virus 2, also known as AAV2.
AAV2 is not known to normally cause disease on its own and often accompanies infection with adenoviruses to cause cold or flu-like illness.
Although experts said they could not completely exclude the likelihood that affected children had somehow developed increased susceptibility to getting sick, they said this was extremely unlikely to be caused by Covid.
The studies are published by the University of Glasgow and Great Ormond Street Hospital (GOSH) in London, but have yet to be peer-reviewed.
They found that AAV2, which cannot replicate without a “helper” virus such as an adenovirus, was present in all nine cases in the Glasgow study and 16 of 17 of the cases in the GOSH study.
This is significantly higher than the 16% normally found in the general population.
The Scottish study also examined the genetics of affected children to find out whether any of them may be more susceptible to acute hepatitis.
Researchers identified differences in the Human Leukocyte Antigen gene that were not commonly found in the control groups of healthy children, or in the genes of children with other forms of hepatitis.
The team said these genetic sequences may offer another part of the answer as to why some children have become seriously unwell.
‘Larger studies are urgently needed’
Professor Judy Breuer, honorary consultant virologist at GOSH, said: “While we still have some unanswered questions about exactly what led to this spike in acute hepatitis, we hope these results can reassure parents concerned about Covid-19 as neither teams have found any direct link with SARS-CoV-2 infection.
“Our data does, however, point to AAV2 in the liver and/or blood of cases as the strongest biomarker for the hepatitis. Additionally, the presence of HHV6 and adenovirus in the damaged livers, removed from the five children who needed liver transplants, raises questions as to the role of co-infections with these three viruses in the most severe cases.”
Professor Emma Thomson, senior author of the Scottish study and an expert in infectious diseases, said: “There are many unanswered questions and larger studies are urgently needed to investigate the role of AAV2 in paediatric hepatitis cases.
"We also need to understand more about seasonal circulation of AAV2, a virus that is not routinely monitored - it may be that a peak of adenovirus infection has coincided with a peak in AAV2 exposure, leading to an unusual manifestation of hepatitis in susceptible young children.”