Doctors in the UK are investigating whether an adenovirus is behind an unexplained outbreak of liver disease in young children, as case numbers rise in countries including the UK, the US and Israel.
So far, there have been 169 identified cases of hepatitis, or liver inflammation, in 11 countries. Some have been quick to blame the outbreak on either covid-19, its vaccines or lockdowns. But in the UK, which has had the largest number of identified cases, doctors said on 25 April that the cause is still unknown.
Their leading hypothesis is that the culprit is a usually mild adenovirus, a common infection in children, along with a second undetermined factor.
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By 20 April, there had been 111 cases of hepatitis in the UK of unknown cause in under-16s, mostly in children under 5. The covid-19 vaccine can鈥檛 be responsible as it isn鈥檛 offered to this youngest age group in the UK.
The condition has been striking children without underlying health conditions. Most of those affected have recovered, but 10 children in the UK needed a liver transplant and so will have to take drugs that suppress their immune systems for the rest of their lives.
The leading suspect at the moment is an adenovirus called 41F, which usually causes nausea, diarrhoea and fever. Some kind of adenovirus was found in 40 out of 53 cases who were tested for it in England. Out of 11 cases where adenovirus was detected in the blood and could be identified, all were the 41F type.
What could the unknown second factor be? 鈥淚t must be in some way linked to the pandemic,鈥� says at the University of Birmingham, UK. Of the 60 children with hepatitis who were tested for the coronavirus on arrival at hospital, 10 were positive, a rate of about 17 per cent.
A from the UK Health Security Agency (UKHSA) says this 鈥渋s not unexpected, given the community prevalence across the period of the investigation鈥�, but it is looking into whether a previous covid-19 infection could be the second factor. 鈥淐ovid may have primed the system for an immune reaction,鈥� says at Imperial College London.
Another idea is that the current cases are merely ones that were 鈥渄elayed鈥� because children had less chance to get infected with the 41F adenovirus during the past two years. When England鈥檚 first lockdown began in March 2020, infection rates of all adenoviruses in 1 to 4-year-olds plummeted. They returned to previous levels in late 2021, shot up to about three times their former rate in February and have since been falling.
But the hepatitis outbreak seems to have been too sudden to just be delayed cases. What is more, the 41F adenovirus doesn鈥檛 normally cause severe hepatitis like this, even rarely, says Kelly.
The idea that the outbreak is connected with lockdowns 鈥� or rather, the return of social mixing after a period when it was lower than normal 鈥� is the UKHSA鈥檚 leading hypothesis. There have been fewer childhood infections going around during the pandemic, not just adenoviruses, and immune responses against some pathogens can give partial protection against others. 鈥淭hese children have not encountered their normal childhood viruses,鈥� says Kelly.
Researchers are also investigating the possibility that the children have been exposed to toxins in the environment or other pathogens at the same time as the adenovirus, or that there is no second factor and the adenovirus is a novel variant that can cause hepatitis.
While the UKHSA and medical bodies in other countries continue their investigations, parents and carers of children are being warned to watch out for signs of hepatitis. In these cases, the condition generally starts with nausea and vomiting, and then progresses to jaundice, where the skin and eyes become tinged with yellow.
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