These cases are very serious – about 5% of infected children worldwide need a liver transplant, and 22 have died. And the cause of the outbreak is something of a mystery. These children do not have the virus that usually causes the illness.
Initially, the most obvious suspects were SARS-CoV-2, the virus behind covid-19, and adenovirus, a common virus that often causes cold and flu-like symptoms. Adenovirus seems to increase as the lockdown ends and people begin to mingle more, after a period of unusually low transmission.
In an effort to learn more, Ho, along with Emma Thomson, professor of infectious diseases at the University of Glasgow’s MRC Virus Research Center, and their colleagues, carefully studied a number of children with affect. In a recent studyThe team evaluated nine children in Scotland with mysterious hepatitis, and compared them with 58 children without the condition.
The team studied blood, liver and stool samples taken from the children, as well as throat and nose swabs. While they could not find the virus that normally causes hepatitis, they did find the adenovirus in samples of six out of nine children.
The team also found another virus called adeno-associated virus, or AAV-2. The virus was found in samples of all nine children with hepatitis of unknown cause – but not in any children who did not.
This virus is known to infect most people by the time they are 10 years old, and most people begin to develop antibodies to it around the age of three. It has never been directly linked to human disease before, says Thomson.
This virus is unusual in that it relies on other viruses to be able to replicate and make copies of itself. “In this case, we think the helper virus is an adenovirus,” Thomson told journalists at a virtual press conference today. It could be due to adenovirus infection following AAV2 infection, or both viruses attacking at the same time, she added. “We can’t tell you at the moment what virus is causing this,” Thomson said.
But the virus is not the end of the story. In genetic tests, the team found that children with hepatitis of unknown cause were more likely to carry the DRB1*0401 gene—89% of affected children had the gene, which is usually found in 16 % of Scotland’s population. Genes are known to influence how the immune system works. Essentially, the proteins it encodes to help immune cells decide what to kill.