Hacker News Reader

Comment by eganp | Hacker News Reader

The risk of cow->human BSE transmission is infinitesimal. Species barriers in prions are surprisingly strong and, for practical purposes, nearly impermeable [0]. In fact, the Prion Protein (PrP) in humans causes multiple distinct diseases including CJD, Kuru, and FFI. Infectious prion confirmations are probably highly influenced by glycosylation [1,2]. Even if this testing wasn't god awfully slow, it's unclear one learns anything from it.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2736662/ [1] https://www.cureffi.org/2013/05/05/prion-protein-n-linked-gl... [2] https://www.biorxiv.org/content/10.1101/2021.02.14.431014v2

View on HN

What you are saying is dangerous. We had a serious set of exactly these transmission events in Britain only a few decades ago. Clearly the risk is not infinitesimal.

Didn’t a huge number of cows get infected back then with only a small number of cases?

Dangerous? The hypothesized connection is not remotely clear. In vitro transformation of human PrP into PrP(Sc) by bovine PrP(Sc) is a necessary for the causal model. The fact that a strong species barrier exists, in vitro and in vivo, points towards a spurious association.

It's understandable why one might infer from the correlation that there's a relationship but this is confounded by observation. The baseline expectation for CJD in a population is 1-2 cases/million [0]. vCJD cases in the UK never exceeded 30/yr [1, Fig 2. a]. Yes, vCJD occurs primarily in younger people - but that's circular as vCJD is defined as CJD-like disease with early onset. If cross-species transmission were common, one would expect a similar spike in age >40.

The incidence of vCJD, even at its peak, was exceedingly rare. Many things, such as observation bias, pollution, or rare side-effects from faddish street drugs could be at fault here. It's tempting to jump to conclusions, a la "eating fats makes you fat," but it's totally unwarranted in the face of the in vitro and in vivo data demonstrating strong species barriers.

[0] https://www.cdc.gov/prions/cjd/occurrence-transmission.html [1] https://link.springer.com/article/10.1007/s00401-020-02153-7

What happened in the 1990s in Britain?

>The risk of cow->human BSE transmission is infinitesimal.

I don't think your sources support this conclusion. bovine spongiform encephalopathy (BSE) rarely passes the species barrier, but it is difficult, if not impossible to estimate what the rate is in the absence of mitigations.

Don’t we know already? In the UK weren’t millions of cows infected and eaten for years with only a few hundred human transmissions?

There are a plethora of unknowns that make it very difficult to check transmission rate. Transmission is rare, but this could be impacted by lots of factors. There were hundreds of thousands of cows in the UK, but there were also testing and culling programs to try to prevent them from entering the food supply. There were also regulations on which parts of the cows could be used for human consumption.

Last but not least, there are huge uncertainties around the diagnosis rate of mad cow in humans. For example, a 2013 study (1) found that 1 in 2000 people in the UK now have Creutzfeldt-Jakob disease.

Based on this, it could be possible that transmission rates are very high if a human were to eat mad cow nervous tissue.

1) https://www.bmj.com/content/347/bmj.f5675.full

This study is looking at the appendix, not any brain tissue. Without considering symptoms, it's possible that altered PrP expression and/or folding in the appendix does not cause vCJD or result from exposure to PrP(Sc).

Also, these antibodies are not very selective for a given confirmation. Idk how this made it into the BMJ because standard in the PrP field is a protease resistance assay given the issues with Ab specificity.

This article is from the UK National Centre for Infectious Disease Surveillance and Control and is cited by by the NHS and widely in the literature.

I am not an expert in the field, but it seems relevant to consider latent or asymptomatic PrP expression when assessing how often it crosses the species barrier.

Reply on news.ycombinator.com