Four months after the world sounded the alarm, here’s what we know about the mysterious childhood hepatitis

On April 12, 2022, the European Center for Disease Control issued an alarm for an acute hepatitis of unknown origin that already affected more than 60 children in England. In a few days, a dozen and a half countries began to detect cases of this strange disease. Almost 20 children had to receive emergency transplants.

The alarm lasted just a few weeks and there were dozens of theories about the origin of the mysterious disease. However, we have had to wait until now, with all the data on the table, for scientists to begin to explain what really happened on those days.

The explosion of a new disease. On April 5, 2022, the World Health Organization reported ten cases of severe acute hepatitis in central Scotland. As of April 8, the UK had 74 cases. It was not uncommon for cases of hepatitis of unknown origin to appear. It is, in fact, quite common and every year hundreds (or even thousands) of patients with liver disorders of unclear aetiology are received in emergency services. What was striking was that all the patients were less than ten years old, hepatitis viruses (A, B, C, E and D) had been ruled out, as well as other similar possible causes and the cases had appeared suddenly. What was happening?

It was an adenovirus, but not the one we thought. After much thought, scientists zeroed in on the adenovirus family, but none seemed to fit. That’s when they realized there were very high levels of human adeno-associated virus type 2 (AAV2). Until then, this virus had never been associated with a disease; fundamentally because AAV2 cannot replicate itself, it never occurs in high concentrations and that greatly limits its ability to do damage.

Why now? It is curious, but everything seems to indicate that AAV2 can indeed replicate in the presence of another virus (a normal adenovirus or, in rarer cases, a herpes virus called HHV6). Until now, those viruses did not “match in time.” In other words, the seasonal circulation of viruses kept them separate and the possible epidemics of these different viruses did not overlap at any time: there would be cases, of course, but they were so isolated that they did not attract attention until this year.

But the COVID arrived. COVID, as we have seen half a dozen times, has caused all infectious diseases to “run wild” and show up on unexpected dates. What until now seemed innocuous has become a time bomb.

Why is all this important? Beyond finding the key to the mysterious childhood hepatitis, the truth is that this is a wake-up call about how small social changes can have enormous consequences. In recent days, we have seen data on the increase in strokes in Andalusia without the reason being very clear, and this is just one of the examples of changes in the “geography” of diseases that are beginning to emerge. It’s time to be vigilant, be creative and work to find some order in the chaos that the pandemic has left us.

Image | Ian Taylor