Dozens of children in Europe and the United States have been infected with acute hepatitis of unknown origin since the beginning of April. European health authorities have begun to investigate this mysterious disease which, in a few rare cases, has required a liver transplant. The point with several experts based in the United Kingdom, where the first cases were detected. “Very strange”, “extremely surprising” or even “really unusual and disturbing”. These are the qualifiers used by virologists and pediatricians interviewed by France 24 about the appearance for almost a month in young children of cases of hepatitis – that is to say inflammation of the liver – of unknown origin. The European Center for Disease Prevention and Control announced on Tuesday April 19 that it had been observed in five European countries. The first infections date back to early April in Scotland. Then children fell ill in the rest of the British Isles. There have been officially just under 80 patients – aged between 22 months and 13 years – in the UK, according to the UK Health Security Agency, which opened an investigation into the phenomenon two weeks ago. Very rare acute hepatitis in childrenSince then, cases of childhood hepatitis have been observed in Spain, Denmark and the Netherlands, according to the European Center for Disease Prevention and Control. Even the United States is affected, since nine sick children have been treated in Alabama. The number of infections certainly appears low in a world which is still fighting against an epidemic of Covid-19 which has affected more than 500 million people . But it was enough to alert the World Health Organization, which warned that the number of cases is expected to rise in the “coming days” now that health authorities around the world are actively looking for them. But the total number of affected children is not the most worrying factor for specialists. “What shocks me is first of all that hepatitis is a rather rare condition in children, and that in addition it is acute cases, which is even rarer”, summarizes Will Irving , virologist at the University of Nottingham, contacted by France 24. Hepatitis often has causes that have nothing to do with the world of children. They can occur with excessive alcohol consumption, be transmitted during sexual intercourse if one partner is a carrier (hepatitis A) and are more common among intravenous drug users who use uncleaned shared needles (hepatitis C).The various forms of hepatitis are, moreover, often of benign evolution and the main symptoms – fevers, diarrhoea, pains in the stomach, jaundice – are resorbed or remain weak. Not so with this hepatitis since “almost all the children had very damaged livers”, underlines Will Irving. Six of them even had to undergo a liver transplant, “which is very rare”, recalls Graham Cooke, specialist in infectious diseases at Imperial College London, contacted by France 24. To top it off, he acts for the moment of a “mystery” hepatitis. None of the main suspects – the viruses that cause hepatitis A to E – were found in the bodies of the young patients. No potential environmental factor common to all cases, such as consumption of contaminated food or exposure to certain toxic substances (toxic hepatitis), could not be identified at this stage. The geographical distribution of cases – on both sides of the Atlantic – further reduces the chances of finding an explanation linked to a local environmental factor. A link with Covid-19 unlikelyPandemic obliges, the Sars-CoV-2 virus has also been suspected. “Two hypotheses have been raised: either it is a still unknown effect of the latest Omicron variant, or we only realize now, after two years during which the children were protected by confinements and other social distancing measures. , that Covid-19 can cause hepatitis in some young people”, summarizes Alastair Sutcliffe, pediatric researcher at University College London, contacted by France 24. A link between the coronavirus and these cases of acute hepatitis which leaves this dubious specialist. First, because several affected children were not infected with Covid-19 at the same time. Then, if it was a still unknown symptom of Covid-19, “there would probably have been many more cases of hepatitis, given the speed of spread of Sars-CoV-2”, estimates Will Irving. British health authorities have even investigated whether it could be an adverse effect of a vaccine against Covid-19. But none of the sick children were vaccinated. “That may be the only good news in this story. At least the antivax won’t be able to get hold of it,” notes Alastair Sutcliffe. There may also be a more indirect link with the pandemic. The successive confinements could have played a role, suggest all the experts interviewed by France 24. “We have an abnormal disease which appears in an abnormal health context, it is logical to wonder if there is no link”, emphasizes Alastair Sutcliffe. In this case, “children develop their immune system in contact with viruses, but for two years the youngest have been protected by confinements and distancing measures, which means that their immune system has not adapted to certain viruses,” says Graham Cooke. The trail of the AD-41 adenovirusSome even think they have identified a possible culprit: AD-41. It is an adenovirus – a large family of viruses most often responsible for very mild symptoms such as colds or fatigue – “which is known to cause gastroenteritis in children, but which does not has so far never been associated with a risk of hepatitis”, notes Will Irving. The presence of this adenovirus has been detected in several children affected by “mystery” hepatitis in the United Kingdom and “we know that it There is currently a sharp increase in infections with this adenovirus in the British population”, recognizes Graham Cooke. “It is quite frightening to think that the confinement and then the relaxation of sanitary measures [qui a permis de favoriser la propagation de l’adénovirus] may have led to the discovery of a new cause of hepatitis”, notes Alastair Sutcliffe. But again, nothing is certain. AD-41 was not, in fact, present in all young people with hepatitis. “It is not necessarily a refutation of the thesis of a link between this adenovirus and cases of hepatitis – we could, for example, not look in the right place – but it weakens it”, recognizes Graham Cooke. There remains the hypothesis of the discovery of a brand new virus at the origin of these infections. “It would still be extraordinary, given that we are still in a pandemic context due, precisely, to a new virus”, estimates Alastair Sutcliffe. All the more surprising since we would go from a new virus which has largely been harmless for the youngest to another pathogenic agent which seems to target children, or at least cause severe forms exclusively in them. This last hypothesis would be the easier to check. “We have advanced techniques to identify the presence of foreign DNA or RNA – which suggests the existence of a virus – in tissue taken, in this case, from pieces of liver of infected children”, summarizes Will Irving . On the other hand, if it is a question of discovering if all these children were exposed to the same toxin or to a contaminated food, it will be a much more complicated matter.