Dear Mark: The Origin of Human Infectious Disease

Just a light and playful topic for your Tuesday morning…. What can I say? Since my posts on human longevity, I’ve had germs on the mind. Aaron Blaisdell’s response to Part 2, however, truly inspired today’s topic:

Excellent post! I wonder how much infection afflicted human populations prior to the adoption of animal domestication. Jared Diamond has discussed how animal domestication led to an increased transfer of viral infections (e.g., colds, flu, small pox, TB, etc.) from farm critter to human. Prior to the domestication of animals such viral transfers were probably rare. Death from viral infection may have been much lower in pre-pastoral times.

So, what kind of infectious landscape did our paleo hunter-gatherer ancestors inhabit? Did their living conditions do more to imperil or spare them? And how did their chances change once they acquired agriculture and animal husbandry? How does it compare to the picture in our modern age?

To understand Grok’s exposure to infectious disease, we can look to Grok’s lifestyle, his interaction with the environment, and his social organization. Grok’s kind, of course, lived in small, nomadic bands that had little interaction with other groups. They killed and ate animals but didn’t keep them. They didn’t cultivate or significantly alter the land they lived on. Although disease existed on some level, broad exposure to a large number of diseases wasn’t what it became later when humans settled into larger, stationary communities.

That all changed when humans took up agriculture and animal husbandry. These novel practices allowed the human population to increase but the added numbers and density of settled communities created the perfect scenario for certain disease transmission (a.k.a. “crowd diseases). Add to this picture the introduction of livestock animals, and suddenly you have a whole new infectious potential.

Experts generally agree that animal husbandry had a hand in introducing new diseases to the human population. Human “crowd diseases” are evolutionary derivatives of animal pathogens as molecular studies have shown. Nonetheless, the picture is more complex than it first appears. As one review of the research suggests, the ultimate catalyst for the boost in pathogen transmission to the human population appears to have been the ecological changes related to animal husbandry and related agricultural practices. In other words, it wasn’t just the increased proximity to animals themselves but the way our farming and herding ancestors manipulated the immediate environment to support their livestock and additional crops. The way they modified the land for their use altered the “transmission ecology” for disease. Issues regarding animal and human waste, food and water sources likely figured into the equation. Changes in the environment and the introduction of livestock also altered these humans’ indirect interaction with wildlife. In some parts of the world and in the case of some diseases, interaction with wildlife was the more primary threat and remains so to this day.

Today, approximately 60% of new human pathogens are acquired from animal sources, and more than 70% of those are based in wildlife. With our species’ continuing movement into new wild habitats, we expose ourselves to the unique pathogens that exist there. Just as our agricultural ancestors interacted and manipulated the land in new ways, we continue to do so today. Humanity’s pathogenic web keeps growing.

Our modern infectious landscape, of course, is something akin to a stepped up version the Kevin Bacon game. With our penchant for international travel, there aren’t very many steps (or hours really) between an outbreak in one part of the world and its introduction here. The Journal of Travel Medicine just recently published the results of a survey showing that some 38% of international travelers from Boston’s Logan Airport were traveling to low and middle income countries, where infectious disease is typically more common and less monitored. Of that 38%, an unnerving 46% didn’t bother to learn about serious infectious risks – like malaria, typhoid, hepatitis, and dengue fever – common to their destinations or what they could do to help prevent contracting these infections. That probably doesn’t bode too well for the rest of us.

Closer to home, we deal more often with the likes of E. coli and MRSA from hospital transmission and modern agricultural practices. As if E. coli in beef and salmonella in chicken weren’t enough, now we’re seeing MRSA in pork. (I guess you can add bacon to the Kevin Bacon game.) Although we see less of the tropical diseases that plague much of the rest of the world, diseases like TB are on the rise, and we now have million people living with HIV/AIDS. For more information on infectious disease numbers and policy in the U.S., check out the Kaiser Foundation’s website for a truly impressive (although sobering) array of interactive maps, reports, and comparative graphs.

These days we’re all too accustomed to thinking about massive pandemics. Some go underreported for their impact and others get hyped far beyond the legitimate toll they take. (H1N1, anyone?) Media field days aside, we hold both historic and recent scourges in our collective consciousness: the Bubonic Plague, Spanish influenza, TB, AIDS, cholera, malaria, Ebola. (Light reading as promised…) Just as growing population density put our ancestors at increased risk, the same trend holds true today. Add to the population angle our continuing settlement into deeper wild habitats and the modern – yet decidedly unsanitary – livestock conditions that put farmers, handlers, and eventual diners at risk. As a result of these and other influences, the World Health Organization warns we humans have been “gaining” a disease a year on average since the 1970s. Not the kind of progress we thought we were signing up for… To boot, we’re exposed to new and virulent disease while medical overprescribing and agricultural exploitation hampers the effectiveness of the antibiotic and antiviral drug armory designed to protect us. Hmmm.

Modern living, as I’ve always said, is an exchange of risk for reward. The benefits we embrace aren’t free. (In fact, they aren’t cheap either, as WHO’s financial breakdown of recent epidemics shows. The best infectious disease prevention includes part general health, part common sense, part sanitation, and part education. Although, I’m not a fan of alarmists who declare that the sky and accompanying bird flu-laced droppings will fall any minute, and I’m hardly one to suggest that people don’t travel where they want to travel. Infectious disease to some degree has always been with us and is something to control rather than hope to thoroughly eliminate. Nonetheless, I believe it’s prudent to educate ourselves and scrutinize the practices that contribute to its spread. From my perspective, investing in good overall health is a place each of us can start. Choosing – when possible – not to support farms/facilities that use routine antibiotics for their livestock is yet another option. Our age is a far cry from Grok’s, but there’s plenty of room for common sense on the path to progress.

Thanks for reading today, and be sure to let me know your thoughts. Have a great week, everyone!?

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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32 thoughts on “Dear Mark: The Origin of Human Infectious Disease”

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  1. First rule on how to not acquire an infection: stay out of the hospital! It’s the WORST place to be. Nosocomial infections (infections acquired in the hospital) are rampant, and kill thousands per year. A 2000 JAMA article states 80,000 deaths every year!! EIGHTY THOUSAND!!!

  2. I’m moving away from conventionally raised meat, but what does this mean in regards to eating wild meat(I’m specifically thinking of deer):

    “Today, approximately 60% of new human pathogens are acquired from animal sources, and more than 70% of those are based in wildlife.”

    1. Most of the new diseases I’ve read about are from bush meat in Africa and tropical areas. I don’t think it’s as much of a problem here.

      1. It might be a factor of diversity, africa has a higher diversity of animals in general, being that it is hotter and more ecologically diverse. Deer hunting could expose you to ticks, which could expose you to things like lyme disease, but take everything with a grain of salt. Moderation is key.

    2. I eat deer/elk/caribou, wild caught ocean and freshwater fish, or wild fowl almost everyday and have had zero incidence of illness, nor have my husband or child.

      “Pathogens” is a catch-all term that means not only bacterial or viral infections, but also those that come from fungi, parasites (worms, etc.) and pria (the altered proteins that cause mad cow/chronic wasting disease). 70% is a big number, but consider that you can catch Rocky Mountain Spotted Fever from a tick bite, but not from eating deer meat. Similarly, well-cooked wild fish will not transmit any parasites to your body, but undercooked or raw fish could definitely do so. It’s all in the processing and handling of your meat, and in the judgement of the hunter/fisherman to discard meat that looks suspect. I’ve tossed many a fish carcass in disappointment after seeing the flesh riddled with worms, and had to destroy a deer carcass once because the meat was infected with something (I don’t know what) – the deer had been gored by another buck and some sort systemic infection took over and made the muscle tissue smell awful. We erred on the side of caution, and have no regrets. For one, we did not get sick from the meat, and two, we eliminated a sick animal from the herd and reduced the possibility of spreading an infection.

      Go ahead and eat that delicious, wild roaming, grass fed deer. Savor a wild duck now and then (they are worth the time it takes to pluck them). And by all means if you a hook a decent trout or smallmouth bass, fry it up. It won’t hurt you at all if you just apply some common sense.

      Oh, and I eat my deer meat well on the side of cool and bloody. Rare deer or elk or caribou is not a problem if the meat looks and smells fresh. Same for the organ meats. Deer heart is not so tasty as beef, but deer liver pate is a true delight.

      1. Makes perfect sense…thanks for taking to the time to share that. Deer liver pate, eh? If I get the opportunity, I will definitely try it! (I was so hoping that your name linked to a blog!!)

      2. Might depend where you live. Out here the concern with undercooked deer meat is tape worms. Eww! If you eat raw or under cooked deer (rabbit or prairie dog too) meat you do risk getting tapeworms. Now they are easily cleared up but still. Eww! NOT something I really want!

        So check in with local folks or DOW to find out about specific risks in your area.

        1. If you like eating raw meat and are worried about parasites and their eggs, just put the meat in the deep freeze for 2-3 weeks (or longer but 2 weeks are enough) to kill all pathogens.

          Besides, most parasites evolved to enter AND exit a host without killing it.
          If you do get a tapeworm, let me tell you that in the old days garlic and parsley was used to deworm children.
          Also large amount of citrus fruit works well ( I’ve used that on my dogs, 2 mature tapeworms fell out of his butt ).

          Freezing meat and on top of consuming garlic and parsley, there is NO way you have ANY worms.

          Just don’t go swim in a lake and swallow a bunch of ‘fish’ water…yuck.

  3. A lot of bacteria are zoonotic, meaning they jump species. Probably just a nice adaptation for them but not so nice for us.
    Virus and prions can jump as well…I first thought this was just the way it is. My study of biology and medicine confirmed that this is the way of the world.

  4. An exchange of risk for reward is very true. To advance at this rate, these exchanges are definitely required. However, ‘not advancing’ is also an exchange of risk for reward.

  5. Extremely off-topic:
    I’m a student in college at the moment and would like literate how much I love reading your articles! Listening to two hour lectures with 200+ people in my biology lecture puts me to sleep every time, but your articles inspire me! I’ve also gone Grok and reading the science behind your philosophy has been extremely interesting. Thanks Mark!

  6. Type O blood may be an adaptation to Yersinia spp. They are cold weather bacteria carried by animals. Their surface proteins resemble type A blood. Yersinia pestis, bubonic plague, is one species. The northern European populations have a higher percentage of type O than those of the Mediterranean.

  7. The domestication of plants has also exacerbated plant diseases. Some of the moulds produce mycotoxins which can contaminate grains and seeds. Yet more reasons not to consume these products.

  8. all of these are cycle, we cannot live without other animal and plants, we cant eat other people to stay healthy, o yes we can, but its taboo, all im saying is its better to blame ourselves rather than pointing on other plants mycotoxins or animal dander or virus or anything like that, lets just strengthen our immune system and its that it. we will be keeping away from my mycotoxins etc.

    1. I agree with the population density aspect. We have become as much a scourge upon the earth as these diseases have been to us.

      It’s about balance, and most of society has lost that wisdom.

  9. Thanks, Mark, for expounding so eloquently on my little comment. I don’t remember where I heard these wise words, but they’ve stayed with me: Life is a disease, transmitted sexually and always fatal. 🙂

    1. If someone had not posted this link, I was going too. It fits right in. Of course, we only have urbanization because of agriculture. “The Vegetarian Myth” also brings up some interesting points related to that.

  10. I wonder if disease increased with the agricultural revolution simply because the people weren’t as healthy. For instance, I imagine bubonic plague spread much faster through the poor of Europe, who ate mostly bread and porridge, than it would through a healthy tribe of hunter-gatherers. Just a guess!

    I have a question for you, though: what is your opinion on vaccines? I have (hesitantly) made the choice to delay all vaccines for my son, because I’m simply not convinced that they have more benefit than risk. Obviously they are not “natural,” though I wouldn’t bypass them just because of that. What do you think?

    1. Actually bubonic plague kills healthy victims quite quickly as well. Once you get it, not much you can do.

      Rats and small vermin which carry the plague are more an urban problem, which is why heading to the hills made some sense.

      IN a larger sense, you can only have plagues with large, densely connected populations otherwise it burns itself out by killing too many hosts.

    2. Don’t forget that the Native North American hunter-gatherers (who were, from what I understand, very healthy upon first contact with Europeans, and also not living in super-dense urban concentrations) were severely affected by diseases introduced by the Europeans like smallpox. They died in droves. The primal lifestyle can’t protect you if a disease is virulent enough.

    3. Sheila, Please get your child vaccinated. There’s little chance that society will revert to a less dense H/G lifestyle in your child’s lifetime. Without vaccines your child becomes a threat to the general population and possibly a burden if he becomes sick.

      Modern vaccines are not natural but that doesn’t mean they are a bad idea. If you broke your leg and a doctor put a cast on it, that is unnatural. But, no one would say that it is a bad idea to have modern medical science fix your broken leg and prevent you from being permanently crippled.

      Don’t throw away a modern tool just because it wasn’t available in the Paleolithic. We live in a unique time where we can pick the best of both worlds.

      1. Like I said, I wouldn’t forego vaccines just because they are not natural. I do use modern medicine. But vaccines do carry a significant risk of adverse reactions, from seizures to Guillan-Barre syndrome to death. Not to mention the vaccine-autism connection has never been satisfactorily researched.

        I’m sorry, I am not putting my child through risk so that he can avoid being “a burden and threat” to the general population. I would only put him through it if I thought it was good for HIM. And when I compare his chances of getting, say, measles, and then the chances of him having the slightest complication from it, to the chance to getting an adverse reaction from a vaccine, I decided that not vaccinating was somewhat less risky. I would give any vaccine that came up more positively in the risk-benefit analysis, but right now none do. When he’s a little older and exposed to more people, I may decide to vaccinate selectively.

        I was just curious what Mark would have thought of this.

        1. The idea that an unvaccinated person “threatens the heard” is specious logic. Think about it for just a moment: the whole idea of vaccination is to protect oneself from disease. An unvaccinated child does nothing to deter from that.

          And I’ll add, the IDEA of vaccines is really just that. the vast majority of studies, and all the ones that support their efficacy, are funded by the FDA/pharmaceutical industry. Their bias is to keep their bottom line healthy (read: profits), NOT to keep the public healthy. In fact, they have more interest in keeping the public UNhealthy since that makes them more money.

          This is not conspiracy theory, this is critical thinking and common sense. Let’s use our intellects like people, not follow fear like sheeple.

          Many diseases for which children are vaccinated today do not exist in this country anymore (such as polio). The risk of the vaccine FAR outweighs the risk of the disease. Polio cases since 1970 in this country have all been from the vaccine. (excuse my lack of references, but the info and studies are very easy to find if you want them).

          Vaccines are not all they’re cracked up to be, not as effective as we’re led to believe, and potentially way more risky than the establishment wants us to know.

          Think about it: the FDA is wrong about diet. Might they be wrong about 1 or 2 other things?

          Follow the money. And listen to your heart, not the reactionary bullshit spouted by the majority.

  11. If everyone here is here because they know that conventional wisdom about healthy diets is totally and utterly wrong and they have found a better way to nourish their brains and bodies, why is it so hard to imagine that the conventional wisdom on vaccines may also be totally wrong, and there could be better ways to protect our children than injecting them with 30+ vaccines? How many studies tell you that eating whole grains is healthy? Not buying it, as I have seen the destruction from eating grains in my own family. Not buying the 30+ pokes are safe and effective for everyone either. My kids will no longer be guinea-pig pincushions for Big Pharma. I wish I could un-vaccinate them both.

    FYI: Never has there been a study on the cumulative effect of all of the vaccines that are now being pushed on the CDC schedule.