A mysterious strain of hepatitis, first detected in UK children, has been recorded in four more European countries and the US, the EU health agency said on Tuesday.
On Friday, the World Health Organization said it was monitoring 84 cases of severe acute hepatitis reported in Britain since April 5 and added that it expected more cases in coming days.
There are five main strains of the hepatitis virus. At present, these have not been detected in the children, and the exact cause remains unknown.
Hepatitis is an inflammation of the liver. Six British children, and two US children, have received liver transplants.
Cases have also now been recorded in children in Denmark, Ireland, the Netherlands and Spain, the European Center for Disease Prevention and Control (ECDC) said.
Nine suspected cases have also been recorded in the US state of Alabama, among children aged one to six, two of whom needed liver transplants.
“Investigations are ongoing in all countries reporting cases. At present, the exact cause of hepatitis in these children remains unknown,” the ECDC said.
In most cases the children did not have a fever. But some of the cases have been so severe that patients had to be transferred to specialist children’s liver units and receive liver transplants, both the WHO and ECDC have said.
A specialist in virology at Imperial College London, who wished to remain anonymous, told The Telegraph that it is “very unusual and rare” for children to develop severe hepatitis, especially to the degree that they require a liver transplant.
He said: “The number of cases is exceptional. It makes people think there is something unusual going on – such as a virus that has mutated or some other cause. It has sent alarm bells ringing.”
The infection has mainly affected children aged under 10 and symptoms included jaundice, diarrhoea, vomiting and abdominal pain.
The virologist cautioned that in descriptions he has read, children are presenting with jaundice alone. “Usually with hepatitis, symptoms begin with feeling unwell, shivery and feverish, and then you develop jaundice. But in some of the descriptions for this, children are presenting with jaundice and little evidence of prior illness. This is highly unusual,” he said.
British health authorities have examined a link to common viruses, or other possible causes like Covid-19, infections or environmental factors, but remain puzzled by what has caused it.
“No link to the Covid-19 vaccine was identified and detailed information collected through a questionnaire to cases about food, drink and personal habits failed to identify any common exposure,” the ECDC said.
One potential line of inquiry is whether a group of viruses called adenoviruses could be causing the illnesses. Adenoviruses usually cause a range of mild illnesses and most people recover without complications. They can cause a range of symptoms, including colds, vomiting and diarrhoea.
The WHO said: “The United Kingdom has recently observed an increase in adenovirus activity, which is co-circulating with SARS-CoV-2, although the role of these viruses in the pathogenesis (mechanism by which disease develops) is not yet clear. ”
Dr Meera Chand, director of clinical and emerging infections at the UKHSA, called on parents to be alert to the signs of hepatitis, including jaundice. She added: “Normal hygiene measures such as good handwashing, including supervising children, and respiratory hygiene, help to reduce the spread of many of the infections that we are investigating.”
The virologist added that parents should not be alarmed, and that cases are still exceptionally rare.