On 12 April 2022, the European Center for Disease Control issued an alert for an unknown acute hepatitis that currently affects more than 60 children in the UK. Within days, a dozen and a half countries began detecting cases of this strange disease. About 20 children had to have emergency organ transplants.

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

The outbreak of a new disease. On 5 April 2022, the World Health Organization reported ten cases of severe acute hepatitis in central Scotland. As of 8 April, there were 74 cases in the UK. Cases of hepatitis of unknown origin were not uncommon. It is actually quite common, and each year hundreds (or even thousands) of patients with liver disorders of unclear etiology are admitted to emergency rooms. What was striking was that all patients were less than ten years old, hepatitis viruses (A, B, C, E, and D) were excluded, as well as other similar possible causes, and the cases were abrupt. What was going on?

Adenovirus, but not what we thought.. After much thought, the scientists reset the adenovirus family, but none of them seemed to fit. That’s when they noticed very high levels of human adeno-associated virus type 2 (AAV2). Until then, this virus had never been associated with a disease; basically because AAV2 cannot replicate itself, it never occurs in high concentrations, greatly limiting its ability to inflict damage.

Why now? Interestingly, however, 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). So far, these viruses have not “matched in time”. So the seasonal circulation of viruses kept them separate, and possible outbreaks of these different viruses never overlapped: There would be cases, of course, but they were so isolated that they didn’t attract attention until this year.

But COVID has come. As we’ve seen half a dozen times, COVID has caused all infectious diseases to “go crazy” and appear on unexpected dates. What seemed harmless until now has turned into 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 to how small social changes can have huge ramifications. Recently, we’ve seen data on the rise of strokes in Andalusia without being too obvious why, and this is just one example of the changes that are beginning to emerge in the “geography” of diseases. It’s time to be vigilant, be creative, and try to find order in the chaos the pandemic has left us.

Image | Ian Taylor