The recent surge in cases of sudden and severe hepatitis in children has been widely reported around the world. Recently, several media outlets have highlighted a possible link between these cases and contact with pet dogs. However, the data suggesting such an estimate is very limited – in fact, perhaps more limited than most of the other hypotheses proposed.
The surge in cases of hepatitis in children was first seen in the UK, but is now reported in Europe, Asia and the Americas. Even though the numbers are still very low around the world, the disease is proving to be severe and some children have to undergo liver transplants. At least 11 children have died, and it looks like the incident is likely to continue for some time.
Hepatitis in humans is usually caused by a toxic substance, such as alcohol, or by infection with one of several different types of viruses. However, none of the usual viruses were found in these children.
The UK Health Security Agency (UKHSA), the body responsible for protecting public health in the UK, is working to identify the cause of the disease so that it can be effectively controlled and treated.
dog showed up
In a recent briefing, the agency reported a high number of “dog exposure” in these cases of severe childhood hepatitis. However, before parents can prevent their children from approaching the family dog, the results should be examined in detail.
The UKHSA found that 70% of patients (64 of 92, where data are available) were from families who owned a dog or were “exposed to other dogs”. However, 33% of UK households have a dog, and many more children from non-owner homes are exposed to them when visiting friends or playing with them. 70% exposure in dogs would be completely normal.
To suggest a link, it is important to show that not only the exposure of dogs in patients is high, but also that it is much higher than in unaffected children. Until this is confirmed in the so-called case-control study, any link is nothing more than a suggestion.
The second problem point with these data is that by asking enough questions, there is a high probability that the answers to one or more of these questions will appear to be relevant to the cases.
If we collect a lot of data, this kind of false association can easily happen. There is also a website dedicated to collecting these statistics. Here’s an example: Maine’s divorce rate between 2000 and 2009 seems to be strongly related to per capita margarine consumption.
The point to remember about links identified in historical data is that they are assumptions. They should always be proven by collecting more information on new cases. If the link is true, it will continue to appear in the new data. If it goes wrong, we will never see it again.
One of the associations on the dummy correlations website reveals another important problem. Between 2000 and 2009, every person consuming cheese in the United States may have been linked to deaths due to binding to bed sheets.
One can easily imagine that this could be the result of dreams triggered by cheese. The fact that we can think of a mechanism that suppresses the link reinforces our idea that it can be true, even if the said mechanism is very far away. We give more weight to associations where we can think of an explanation, even if the evidence is weak.
So what are the possible reasons for the reversal of hepatitis cases in children? Could any of this have anything to do with dogs? One virus in particular, an adenovirus, was found in the blood of 72% of the patients tested (for comparison, SARS-CoV-2 was found in only 18% of cases).
In cases where it is possible to identify the type of virus, it is similar to human adenovirus serotype 41 (Ad41), which often causes diarrhea in children. Even if dogs can secrete their own adenoviruses that cause respiratory illness or hepatitis, they are not known to infect humans. In addition, Ad41 has no known connection to dogs.
The cases seen in children do not suggest that the infection was passed from one individual to another-the number of cases is small and the distribution is much wider for that. Similarly, the distribution of cases does not suggest that it is a new virus transmitted from dogs to children. In other countries, cases have shown to be much faster than a canine virus to spread between dogs.
Is there another possible cause? It has been suggested that the severity of hepatitis is the result of malfunction of the immune system – too fast or not strong enough. Social isolation during a pandemic reduces the transmission of various diseases, and lack of exposure to these conditions may make some children unprepared for infections that are usually not a problem.
Similarly, lack of exposure to dirt resulting from hand washing, sterilization of surfaces, and other hygiene measures may predispose children to overactive immune responses (e.g. suggested in allergic diseases). So hepatitis may be due to the immune response rather than the virus. Finally, and not surprisingly, the likelihood is raised that previous Covid-19 infections have a predisposition in children to hepatitis.
These are all just theories at this time, and there is not enough data available to prioritize them or use them to suggest control measures. Fortunately, the incidence remains extremely low, and until better data is available, parents should focus more on observing any symptoms in their children than on reducing their exposure. of dogs.
The original version of this article was published on The Conversation, a nonprofit news site dedicated to sharing ideas between academic experts and the general public.