U.K. report ties hepatitis in kids to dogs — an immunologist points out a major flaw

A sudden spike in cases of severe hepatitis in children around the world has recently been widely reported. Recently, several news outlets have highlighted a possible link between the cases and exposure to pet dogs. However, the data suggest that this association is extremely weak – in fact, probably much weaker than most of the alternative hypotheses that have been proposed.

The spike in hepatitis cases in children was first noted in the UK but has now been reported in Europe, Asia and the Americas. Although the worldwide numbers are still very low, the disease has become serious and some children need a liver transplant. At least 11 children have died, and it is suggested that it could continue for some time.

Hepatitis in humans is usually caused by toxicity, such as alcohol, or by infection with one of several different viruses. However, no common virus has been identified in these children.

The UK Health Security Agency (UKHSA), the agency responsible for protecting public health in the UK, is working to find out the cause of the disease so that it can be effectively controlled and treated.

Contact with dogs and hepatitis

In a recent briefing, the agency reported a large number of “dog exposures” in cases of severe childhood hepatitis. However, before parents prevent their children from getting close to their family dog, it’s a good idea to look at the results in detail.

UKHSA found that 70 per cent of patients (64 out of 92, where data are available) were from families with dogs or had “other dog contact”. However, 33% of UK households with dogs and many other children from non-dog households will come into contact with dogs when they visit or play with their friends. 70% of contact with dogs can be completely normal.

To suggest an association, it is important to show not only higher levels of dog exposure in patients but also higher levels in unaffected children. Until tested in so-called case-control studies, any link is only a suggestion.

The second problem with data is that if you ask enough questions, chances are the answers to one or more questions seem to be related to the circumstances.

When we retrospectively collect a very large amount of data, this type of false association can easily occur. There is a website devoted to collecting them. Here’s an example: the divorce rate in Maine from 2000 to 2009 appears to be strongly related to per capita margarine consumption.

The important point about associations identified by retrospective data is that they are hypothetical. They always need to be tested by gathering more data around new cases. If the link is real, it will continue to show up in the new data. If it’s fake, it won’t.

One of the links on the pseudo-correlation site reveals another important problem. Between 2000 and 2009, per capita, cheese consumption in the US appeared to be linked to deaths from getting messy in bed sheets.

It’s not hard to think that this could be due to cheese-induced nightmares. The fact that we can think of a mechanism underlying the link gives us more confidence that it might be true, even if the mechanism is rather remote. We tend to place more weight on associations for which we can think of reasons, even when the evidence is poor.

So what are the possible causes of the spike in hepatitis cases in children, and could any of them be related to dogs? A virus, specifically adenovirus, was detected in the blood of 72% of the patients tested (for comparison, SARS-CoV-2 was detected in only 18%).

When the virus could be identified, it was found to be adenovirus 41 (Ad41), a human virus that commonly causes diarrhea in children. Although dogs have adenoviruses that cause respiratory illness or hepatitis, they are not known to infect humans and Ad41 has no known association with dogs.

The cases in children do not suggest that the infection is being transmitted between children – there are too few, too widely distributed cases for that. Similarly, the distribution of cases does not suggest that this is a new virus that is transmitted from dogs to children. Cases have emerged in other countries much faster than the canine virus would have spread between dogs.

The reason may be

Are there other possible causes? It is suggested that the severity of hepatitis is the result of the immune system not working correctly – either too strong or not strong enough. Social distancing during a pandemic has reduced the transmission of many diseases, and not being exposed to them may leave some children unprepared for infections that would not normally cause them. What’s the problem.

Similarly, failure to come into contact with dirt through hand washing, disinfecting surfaces, and other hygiene practices may predispose children to excessive immune responses (as has been suggested for allergic diseases). ) and hepatitis may be caused by an immune response. not a virus. Finally, and not surprisingly, it is thought that previous Covid infections may have made children more susceptible to hepatitis.

All of this is not theoretical at present, and the available data are insufficient to prioritize any of these problems or use them to recommend control measures. Fortunately, the incidence remains extremely low, and until better data are available, parents should probably focus more on monitoring for any symptoms in their child than reducing exposure. with dogs.

This article was originally published on Conversation by Mick Bailey at the University of Bristol. Read the original text here.

https://www.inverse.com/mind-body/child-heptatis-dog-link U.K. report ties hepatitis in kids to dogs — an immunologist points out a major flaw

Emma James

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