Health officials investigating a spike in hepatitis cases among children in the UK increasingly believe it could be linked to a common virus known as adenovirus.
Adenoviruses are a group of viruses that can affect different parts of the body depending on the type.
The range of illnesses associated with adenoviruses include common cold or flu-like symptoms, a fever and sore throat, according to the US Centers for Disease Control and Prevention website.
Acute bronchitis, pneumonia, conjunctivitis and acute gastroenteritis – including vomiting and diarrhoea – can also result from infection.
Bladder inflammation or infection and neurological disease are less common but are also listed as symptoms.
The UK Health Security Agency has recorded 111 cases of unexplained hepatitis in children under 10 since January, with 10 of the children needing liver transplants.
The UN health agency said it has so far received reports of at least 169 cases of "acute hepatitis of unknown origin", and that one death had been reported.
The World Health Organisation (WHO) said the majority of the cases it was aware of had been in the UK, but an unexpected increase in cases has now been reported by several other countries, notably Ireland and the Netherlands.
Doctors are still investigating what is causing the illnesses, but adenovirus is a leading suspect, having been detected in 75 per cent of the confirmed cases tested.
One possible explanation is that the outbreak is linked to a surge in common viral infections after Covid restrictions ended.
Experts believe children who were not exposed to adenovirus over the last two years may now be getting hit harder when they are exposed to the viruses.
The WHO said that “while adenovirus is currently one hypothesis as the underlying cause, it does not fully explain the severity of the clinical picture”.
In a statement, the organisation said: “Infection with adenovirus type 41, the implicated adenovirus type, has not previously been linked to such a clinical presentation.
“Adenoviruses are common pathogens that usually cause self-limited infections. They spread from person-to-person and most commonly cause respiratory illness, but depending on the type, can also cause other illnesses such as gastroenteritis (inflammation of the stomach or intestines), conjunctivitis (pink eye), and cystitis (bladder infection).
“There are more than 50 types of immunologically distinct adenoviruses that can cause infections in humans. Adenovirus type 41 typically presents as diarrhoea, vomiting, and fever, often accompanied by respiratory symptoms.
“While there have been case reports of hepatitis in immunocompromised children with adenovirus infection, adenovirus type 41 is not known to be a cause of hepatitis in otherwise healthy children.”
The WHO added: “Factors such as increased susceptibility amongst young children following a lower level of circulation of adenovirus during the Covid-19 pandemic, the potential emergence of a novel adenovirus, as well as SARS-CoV-2 co-infection, need to be further investigated.
“Hypotheses related to side effects from the Covid-19 vaccines are currently not supported as the vast majority of affected children did not receive Covid-19 vaccination. Other infectious and non-infectious explanations need to be excluded to fully assess and manage the risk.”
