Poultry and cattle and swine, oh my
For this week's Microbial Mondays, I was inspired by a paper (also published open-access here on BioRxiv) that I saw presented at the Dutch Annual Virology Symposium a few weeks back. These scientists have been hard at work tracing back the origins of a virus that has been at the root of many an outbreak throughout history: the measles virus.
Measles isn't very high on most people's lists of terrifying diseases at the moment, but that's mostly due to the fact that we've had a highly effective vaccine since 1960s, and not so much due to the severity of the disease. It's caused by a highly contagious virus that, even half a century after the vaccine's release, caused about 110,000 deaths in 2017.
The authors of the paper that I found so intriguing set out to determine exactly when humans first ran across measles - i.e. when measles jumped over from infecting cows to infecting humans.
It's long been thought that measles is a close relative of the cattle-infecting virus "rinderpest", which was recently successfully eradicated because cows can't refuse life-saving vaccines (sorrynotsorry, I am tired and therefore I sass). In the past, scientists had assumed that an ancient strain of rinderpest jumped over to humans and evolved into measles somewhere around the 9th century CE. However, the discovery of measles genomes preserved in a lung specimen from 1912 changed all of that.
The scientific team of Sébastien Calvignac-Spencer were able to isolate the most ancient measles genome to date from this lung, which was preserved in Berlin. The lung belonged to a two-year-old child who died of measles in Germany more than a century ago - and her lung still harboured some (inactivated) virus. The team was able to isolate the virus' genetic material, and analyse it in comparison with other isolated measles genomes, which allowed them to build the most complete timeline of measles evolution to date - and thereby extrapolate when measles evolved from Rinderpest.
The results were surprising - but also totally make sense. Based on the timeline constructed by Calvignac-Spencer 's team, it looks like measles became measles - i.e. rinderpest infected humans, a loooooong time ago. A lot longer than we thought - around the 3rd millennium BCE in fact. The authors suggest that, most likely, rinderpest could have crossed over and infected humans many times throughout history, but that things got serious when humans started living in cities. As long as humans were relying on animal agriculture, there was a chance for the virus to evolve and infect us - but when we humans started to live very close to each other, and in large numbers, we provided a sort of feast for the virus.
You see, when viruses hop over to humans, infections can be somewhat self-limiting if the virus simply runs out of humans naïve to the disease to infect. As long as we were living in small settlements, one human could be infected from a cow, and then all of their human friends would be infected. Some would die, and the rest would develop an immune response and have some protection from future infections. And that would be the end of measles in that settlement.
In big cities, though, there is a seemingly endless supply of new humans immigrating or being born - the perfect situation for a virus to become endemic (i.e. to stick around pretty much forever). It could very well be that some ancient epidemics, some of which were documented to effect both cows and humans, could have been caused by an earlier, ancestral form of measles.
And now, for the rant section of this piece. Strong opinions coming, consider yourself forewarned.
Part of the reason that I wanted to write this particular piece today is because of the rise in anti-Asian hate crimes associated with the current SARS-CoV-2 pandemic. Some people seem to erroneously think that it is the fault of "Asians" (in quotation marks because this is a ridiculously massive and varied group of people to blame in the first place) that we are currently dealing with COVID-19. I would invite such people to take a look at their own pandemic-encouraging actions.
To me, all of this - a virus crossing over from animals raised for food, to humans - sounds eerily familiar. We're talking not only measles likely arising from rinderpest or SARS-CoV-2 from an unknown animal coronavirus (but clearly from meat markets), but also the likes of influenza pandemics jumping from poultry or swine, HIV-1 from simian immunodeficiency virus, S and most recently, a mysterious and terrifying Creutzfeldt-Jakob-like prion disease in New Brunswick, Canada, the likes of which typically arise from eating contaminated meats. So, not such a unique situation. And that's not even getting into the problem of antibiotic resistance, which is hugely driven by over-use of antibiotics in the animal agriculture industry.
Before we go around blaming one particular group of people for the type of meat they eat or the way in which they prepare it or whatever people are going on about these days, let's all consider the actual root cause here. The meat-eating. Not the people. It's an action. And at that, an action that people all around the world take. I mean look at the prion disease in Canada right now. Are we going to start blaming Canadians for mad cow disease? Because that would be ridiculous, right?!?
So yeah - personally, I'm pretty critical of (modern) animal agriculture for several reasons, but a big one is that eating animals consistently seems to lead to outbreaks. To be clear, I'm not criticizing what we used to historically do as humans here, in terms of animal agriculture. Pre-modern nutritional requirements is not my area of expertise and I don’t want to get into it. What I'm saying is, based on what we know now, why wouldn't we adjust our behavior accordingly? The cost/benefit analysis of eating mostly plants seems clear to me. In terms of individual health, I am no nutritionist but according to all the science I've seen that isn't sponsored by the meat or dairy industries, plant-based diets seem to be at least as healthy as omnivorous diets for humans, and definitely healthier than high-meat diets. In terms of population health, cardiovascular diseases and cancers are reduced upon switching to plant-based eating, and we would remove a major source of emerging infectious diseases.
Me? I'm gonna stick to my greens.
Until next week... 🌱