Rising infections from a dusty devil, and nailing down when our ancestors became meat eaters
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This is the Science Podcast for January 17th, 2025. I'm Sarah Crespi. First this week, growing numbers of valley fever cases have researchers looking into its cause: a desert-loving fungus. Staff writer Meredith Wadman joins me to talk about the fungus's potential links to everything from drought and wildfires to climate change and rodent populations.

Next, it's long been hypothesized that eating meat drove big changes in our family tree, like bigger brains and more upright posture. I talked with the researcher Tina Ludeker, who looked at nitrogen in tooth enamel from our ancient relatives, Astropithecus, to see if they preferred meat or veg.

Now we have staff news writer Meredith Wadman. She wrote this week about valley fever, a fungal infection that's on the rise in some of the driest parts of the United States. Hi, Meredith. Welcome back to the podcast. Hi, Sarah. It's great to be here with you. Yeah, there is so much going on in the story. I think we should start with

What we know about this link between valley fever, which is a fungal infection, and the weather and climate. And then we can kind of get into the complexity of the disease and the researchers trying to take it on. So what do we know about valley fever and the weather?

Well, valley fever is caused by a fungus that lives in the soil and it likes hot, dry, dusty climates like the American Southwest. That allows it to out-compete other soil-dwelling bugs that don't do so well in hot, dry situations. So for decades, valley fever has been really largely confined to two states where it's endemic, Arizona and California.

But now, as the desertification and heating up of the U.S. West proceeds, it is likely to spread to almost the entire western half of the nation, is what people who model climate change suggest. Now, it has already been increasing in case numbers.

hugely in California and Arizona. But we can't for certain say that is due to climate change. All we know is that when you look at warming scenarios going forward, the spread of this is likely to continue and become a more serious public health problem.

dogs have actually been serving as kind of the sentinel for valley fever cases. Can you talk a little bit about those numbers and how they think that they're related? Yeah, that is dogs with their noses in the ground, particularly medium-sized dogs who like to dig, are real sentinels for this disease. And they can get very, very sick. In fact, they probably get infected more frequently and severely than humans. There are new findings led by a

Jane Sykes at the University of California, Davis, in which Sykes and her group looked at all canine tests for valley fever over the decade 2012 to 2022. And they found that while in 2012, just 2.4% of counties were

reported positive tests in dogs, by 2022, that number had grown to 12.4% of counties. So a quintupling. Okay, so two to 12, that's quite a bit of an increase. What about people? Can we just go through a few numbers? I want to make sure we know what, like, is there an incidence that people will be able to kind of understand how common is this to get? Is there a good way to put that?

Currently, cases are at around 20,000 per year. Those are reported cases. That's almost certainly an underestimate. But suffice it to say that incidents in California in the decade that ended in 2023 jumped way up and nearly quadrupled, in fact. And in the same period in Arizona, it grew by 73%. So...

In terms of people coming through the doors of urgent care clinics or emergency rooms, that's a real impact. And it's only going to continue growing because guess what? People continue to move to the Sun Belt. What is it like for people who get valley fever? What are the symptoms? Well, 60% of people who are infected by inhaling spores of this fungus, whose long fancy name is coccidioides, but is abbreviated to cocci for short,

end up not even knowing they've been infected. 60%. 40% have some impact. Basically, about 35% of them, that's limited to respiratory disease, feeling cruddy. It can last for weeks. They can have a pneumonia. They can feel extremely fatigued. And then

5% will develop permanent respiratory disease where the fungus basically hides out in their lungs, a little like TB, and they never get rid of it. And then

Of those people who get ill, 1.5% develop what we call disseminated disease, where it can spread to skin and to bones and to joints and to the membranes that envelop the brain called the meninges and give them meningitis. This then is a life-threatening illness and is very, very serious and has, in people who survive, very serious long-term impact. Yeah.

Yeah. And you actually talked to some of those folks for the story. We're going to get to them. But you also went to the places where researchers are studying this in the wild, in the environment. And you met with the researchers who are trying to find coxie in the soil, in the air. You know, can you talk a little bit about what they were sampling and some of the difficulties there are in finding this fungus in the wild?

Yes, the spores of the fungus, which kind of blow up and into the air when dirt is disturbed or, you know, can be carried in some instances long miles or hundreds of kilometers on the air.

tend to disappear and appear. It's like a needle in a haystack if you are going to try to like just grab them from the air in the old place, even in a highly endemic county like Kern County, which is Bakersfield, California, and its environs. That's the hottest coxy county in the nation. But you're not just going to like go along your street and kick up a bit of dust and find it.

However, rodent burrows have a much higher chance of harboring cocci spores, and that's where Jennifer Head and Jim Marquis are.

leaders of a project I visited in Bakersfield last October were searching for cocci spores, even as at the same time they were flying drones above this area with rodent holes to try to capture spores from the air on filters. They would take the filters back to the lab and look for cocci DNA. Right. Now, it's interesting that they're having to do this, right? Because

One of the big questions is if Coxie is expanding its area, if it's invading these new counties, these new regions, how is it getting there? And we don't ask that question about a bacteria or a virus that infects people. We don't tend to say,

How is this virus getting into this neighborhood? We kind of have ideas about it. But this fungus has the potential to travel on the wind or maybe be dispersed by wildfires. Or as we just talked about, it could be riding on rodents or spreading from dead rodents. So there's a lot of questions here in how it gets around, right?

So many questions that are unanswered. And these scientists are really, to use an overused phrase, at the cutting edge of trying to work out how these spores spread in the environment. Because there's huge public health implications, right? You're not going to send out a bunch of construction workers unmasked if you know that they're digging in an area with rodent holes and that cocci has been identified in that area. Or even if you don't know it has been.

Yeah. Like, as you point out in your story, there are all these correlations between wildfires and valley fever, between certain weather patterns of drought and then recovery.

All of these different weather patterns are out there. And then you have your coccyx cases and you need to make this mechanism work. But just even finding it in the environment to show levels are going up or down is a real challenge. It is. And not only that, we don't know how many spores you have to inhale to get really sick. There's kind of been conventional scientific wisdom that only one or two can make you very sick. Just

Jennifer Head, this infectious disease model at the University of Michigan, really is skeptical of that. And that's one of the things she's trying to chase down in this work she was doing in Kern County last October. Yeah. And because it has such a wide range of effects, too, you don't know if it's the dosage or a vulnerability in the person.

Right. And there are certain people, particularly with a couple of genetic mutations, who are definitely more vulnerable to getting disseminated disease if they should become infected with this fungus. So are Black people for reasons that are not well understood. You know, the other thing I noticed about the cases that you describe in your story, besides kind of these symptoms that are all over the place, is

How difficult it is to diagnose. Like, why is it so tricky for this to get picked up by medical personnel? Well, because you have to think of it. Someone comes in the door of your clinic with what they call a community-acquired pneumonia, a lung infection.

that is making them feel sick, fever, cough, fatigue. There's many possible causes of that. And unless you are thinking about coccidioides or cocci, this fungus, you are not likely to test for it. More common bacterial and viral causes are going to be at the top of your list. And the result is that it takes on

on average, 38 days from the time a person first seeks out medical care until they actually get a firm diagnosis. And those are important days in which the fungus can really establish a foothold in the body. And it does respond to antifungal treatment, but you got to be getting the treatment for it to respond. Some of the people that you mentioned in your story ended up with that, like,

like kind of chronic infection that doesn't go away and they're just on antifungals for the rest of their life. Yes, that's particularly true for people who get meningitis. One of the folks I met, Jose Sanchez, who was an architect in Mexico before immigrating to the U.S. where he became a construction worker in dusty areas of Southern California and who came down with valley fever that manifested as a meningitis infection.

and has been very, very ill since. It's been more than four years. And the result is that he has to have this port, this reservoir under the skin on top of his head into which are injected really powerful antifungal drugs every four weeks to keep it in check. Wow. But he already suffered a stroke.

due to the meningitis. And he is, you know, seriously disabled and will not be able to work again. Now, this is, as we said at the beginning, a fraction of a fraction, less than 50 percent of the people who are infected get sick. And then going down from there, you get these more and more severe cases. But as numbers go up, you know, we're going to see that small fraction increase in actual size. What about a vaccine? Like this is something that

isn't going away. We can barely find any environment. You can wear a mask, but, you know, it's dust. Dust gets everywhere. Is there any potential way of combating it preemptively? Already, researchers at University of Arizona have developed a dog vaccine that hopefully is going to be approved by the USDA.

The University of Arizona group is also now hoping to develop this vaccine into a human vaccine. At the same time, Bridget Barker at Northern Arizona University and colleagues at the University of Washington are working on what they hope will be a messenger RNA vaccine for humans. Its prototype is going to be tried in monkeys this year, they hope.

So there are vaccine lights on the horizon. It's just that the horizon is always off.

Right. Yeah. And I mean, especially looking at, you know, the news today, we're recording in the Los Angeles wildfires are incredibly intense. Like we're seeing a lot of change in that landscape that's encouraging fires. And it very likely is going to increase the occurrence of valley fever. Yes. Well, a really eye-popping study on the heels of other California wildfires found that high

Hospital admissions for valley fever increased 20% in the two to three months immediately after a wildfire event in a certain area. And this wasn't like in typical coccy country. This was in the main major coastal cities like San Francisco, LA and San Diego, where coccidio mycosis is not an everyday occurrence. Right.

Yeah.

40 years old, healthy, out training for a marathon and came down with valley fever that actually ended up giving her a very serious meningitis. So people in these

Counties in these endemic areas are really at risk just by the fact of existing and living there. Okay, Meredith, this has been super fascinating. I really appreciate you talking with me about it. Thanks, Sarah. It was really good to talk to you. Meredith Wadman is a staff news writer for Science. You can find a link to the story we discussed at science.org slash podcast.

Stay tuned for a look at Astropithecus' diet 3 million years ago. Was it mainly meat, mainly plants, or perhaps termites?

A switch to a more meat-heavy diet has been theorized to drive big changes in the human lineage in our ancient relatives. Bigger brains, smaller guts, maybe upright stature. This week in science, Tina Ludica and colleagues explore this idea by analyzing a diet of the ancient human ancestors Australopithecus over three million years ago in South Africa. Hi, Tina. Welcome to the Science Podcast. Hi, Sarah. Thank you for having me. Thank you for coming.

What's the thinking behind linking diet and these big changes in our forebears? Like why would consuming more meat

potentially trigger these kinds of things? So a diet that includes a lot of animal resources like meat or milk or anything else, of course, has very high energy. And it's extremely difficult to get this through a diet that just contains low quality savanna foods. So if we look at monkeys today, like

Baboons, for example, they eat all day long. They're vegetarian, mostly vegetarian, omnivores, but they eat a lot of low quality food, vegetarian usually, a lot of seeds and everything. And they eat all day long. They don't have much time for anything else. And they have still comparatively small brains compared to us, of course. So I'm not saying we should all eat more meat to get more intelligent or have bigger brains. But living in a savannah and not being able to cook probably already is, of course, a big challenge.

disadvantage, then you have to eat over a lot of things to just fuel big brains. So with meat and later, of course, with cooking, of course, it's much easier with this high energy, like the densely packed

basically to get all the resources to power our brains to increase in size. Okay, so to grow really elaborate brains, you need a lot of... and to power them. And power them, exactly. So if you look at brains today, our brains have about...

are only 2% of our body weight, but they use about 20% of our energy. So we need a lot of energy to power these strains. For early hominins, it's really important that brain development and cranial capacity and the growth of it is linked to a high protein, energy-rich diet, which is easiest to get from meat, of course, or other animal proteins.

or animal resource uses. So the question is, of course, when did this start? In which hormone and taxidermy did it start? How is it linked to this brain development and other adaptations, of course, that are really important, like dental adaptations, for example? Is it just something that early HOMO did and then re-evolved from it? Or is it something that also Ocelopithecus, which I worked on, already explored, for example, which was still a fairly small-brained early hormone and

Right. That was what I was going to ask. Yeah. So Australopithecus did not have a giant brain. Australopithecus brains are about like 500 cubic centimeters and ours is about three times as big, like 1,300 cubic centimeters. So much, much bigger. In terms of Australopithecus, can you place them in, where are they in time and in the family tree in relation to us?

Of course, yeah. The most famous Australopithecus, I think, is Lucy from Ethiopia. Most of us know Lucy. So they lived for a long, long time, about four million years to two million years, roughly. So two million years they occupied across the East African Rift and also South Africa, of course, where my study is based. Different habitats, different niches and habitats.

The individuals I work on are from Steppfontein, a cave in southern Africa in the so-called cradle of humankind. And a lot of specimens have been found down there. These are dated to roughly three and a half million years. Dating is an issue in caves, but about three and a half million. It could be a little bit younger to two and a half million.

Are they kind of our ancestors? Because there's lots of other hominins that we say are cousins or we investigate them and maybe they interbred, but maybe not. So how does Astropithecus fit into that? This sounds like such an easy question and surprisingly, it's still not.

So we say one of our early ancestors, and there's a lot of evidence out there that they actually are ancestors of early Homo and with that Homo sapiens. But of course, it's still fairly difficult to directly reconstruct all of this. But it is one of our ancestors. And what is really unusual today, actually, that we are the only permanent species existing. So the only one that is living on the

whole face of the planet right now. In the past, there were a lot of different genuses living coexistently, like Australopithecus, Plantopus and Homo, for example, around 2 million. Of course, then a lot of different species within this genus. So we had multiple hominins living coexistently

You just had a brilliant podcast a few weeks ago about these footsteps of Homo Implantibus, for example, that were found in the mud. So they have to be within a few hours to days or something like this. We knew these guys coexisted. So one of the interesting things is also like, why did some of these hominins, most of these hominins, all but us, died out?

And why did other one make it to be humans today? Right. And the reason this is so difficult is we just don't have access to the kind of materials that you would need to investigate this question. Like we don't have their DNA. No. Maybe we can see like behind structure of proteins, like fossilized into what we have. But there's just not a lot of

molecules left from these ancient beings. And that makes looking at their diet, what they were eating, really difficult. And so up until this point,

The focus has been on maybe they were butchering things. Maybe there's evidence of tools, but even that, it's not necessarily their stone knife, right? We don't know how much tool use they had. And we don't know, you know, it's just so long ago. There's so little left over. So here's where I want to kind of get into your technique. This is based on nitrogen isotope ratios in tissues. What

which has been done in collagen for Neanderthals, for example. But this approach kind of taps out around 200,000 years ago. Like we can't look at collagen that's older than that. So how are you able to go back so much further and look at something that was over 3 million years ago and say something about

the isotope ratios in its body. So nitrogen isotope, as you said, has been measured for many, many years in many tissues. 200,000 is actually the uppest limit. We have to be really lucky. Often the nitrogen, which you want to measure within the organics, is gone within thousands of years. In Bronze Age already, we can't really measure it anymore. It depends on the setting, of course.

So now we explore tooth enamel to measure nitrogen isotopes in. Tooth enamel has been proven to be extremely robust. The isotopic fingerprint in tooth enamel seems to be not changing during fossilization for many of the isotopes. We know that for carbon and oxygen, for example. But this nitrogen problem is that there is almost no nitrogen in tooth enamel.

There's less than 0.007% nitrogen in tooth enamel. So almost nothing. We hope that whatever nitrogen is in there might also be so well preserved within the crystallines of the tooth enamel that it might keep the isotopic fingerprints. But it is just almost impossible to get to that and measure this.

So here now I'm at the Max Planck Institute for Chemistry and together with the Princeton University here, a method was developed already a few years ago, a decade ago now, to measure nitrogen in extreme low compositions, basically with a really high precision on material that

has almost no nitrogen. We use bacteria basically, and we do a very complicated cleaning step to get rid of any organics and any nitrogen that is not mineral bound. And then whatever is left, we feed to a strain of bacteria and they convert this N2 into N2O.

and they excrete it, and we measure that directly with a mass spec. Amazing. Yes. So this method here was developed in the Frida Martinez-Garcia's lab, and as I said, on many different materials. And then I came and was like, hey, tooth enamel, probably we know this, diagenically robust, has almost no nitrogen. Can't we do that? And we started this in 2019, and now it works. How do the proportions of nitrogen isotopes in...

tooth enamel, how could they relate to diet? Like why would they vary depending on whether or not an animal was eating meat? With every step in the food chain, the delta-5 and value increases. So plants have low values, herbivores eating those plants have intermediate values, and then a carnivore has high values because it ate individuals with this intermediate value. Right. So it adds up. So if I'm only eating grasses, then I just get a little boost. But if I'm eating carnivores,

Tigers get a huge boost. Yes, exactly. Your position on the food web relates to this Delta S, this ratio.

Exactly. And in terrestrial food web, it's fairly easy because it's usually three steps in the food chain. But for example, if you look at the oceans, there we can get to extremely high Delta 15N values in sharks, for example, because the food chain is just much longer. So it just adds up basically. So yeah, so then, so you have these values from teeth, but you need to know back in the day, if you were a meat eater, if you were a plant eater, what those Deltas look like, like what those ratios look like. Exactly.

Exactly. So let me go a step back. First, we went to East African ecosystems or sub-Saharan ecosystems, to museums collection mostly, and in Gorongosa National Park. And there we measured a lot of antelopes and giraffes and compared them to lions and hyenas. And again, it made sense. We have these about four per mil differences. And then now we take it into the fossil world, right? What we did is we sampled coexistent herbivores and carnivores. So we have a bunch of bovets of antelopes.

We have a bunch of hyenas, big cats like the saber-toothed cat, and a few dog-like, jackal-like animals.

taxa. And again, we see a beautiful difference between those herbivores and carnivores of about four to five mil. So you had to look at the astroepithecus in this context and you used what, seven different individuals and you took their teeth. And then we were able to sample with a normal dental drill, basically. So something we all probably know. And so how did they compare with the

herbivores of their time, the carnivores of their time? Like what was their magic ratio? So the magic ratio is low. So they have on average very similar delta fission end values compared to the coexistent herbivores.

They look very much like the herbivores. Okay, so they're not eating a lot of meat. Exactly. They did not eat enough meat to change the Delta 15N value to a meat-based diet, basically. What is extremely interesting, though, that their range in Delta 15N is huge. Between only those seven individuals, we have a huge range, much bigger than any of the carnivores, than any of the herbivore species. So this shows us, yes, it's a plant-based diet, mostly plant-based diet for sure.

But also it looks like individuals had very different diets within these vegetarian niche. So they have the lowest data fit and values we have measured in any of the data sets.

which can point to any diet with anything that has very low Delta 15N values. What kinds of things might they be eating? So we can't say like, oh yeah, this guy ate a lot of rice and this one noodles. That is something we can never do. Plus there was no rice and noodles. But yes, we can see that during tooth development, they actually, some of these had very different diet. Yeah. So what might they have been eating? Like what are some

options to create that ratio. So this shows that some of them with the low delta-phyton end values use resources with delta-phyton end values that were very low. That can be unfixing plants or legions or just termites, for example. And termite fishing is a very important resource with tool use in many of the ites that exist today, like

fish a lot for termites. But termites itself have a very diverse diet. So there's actually a little bit of study out there, but not that much about the delta-15n values of termites. And then it will be really complicated. How did these termites three and a half million years ago, what kind of delta-15n values do they

they have. But we see it in the Isar Valley, for example, in Tanzania, that termites often in sub-Saharan savannas have low Delta 15N values. So this actually, despite it being an animal resource diet, those termites could pull the Delta 15N value down, actually. And this is something we want to explore. But

It's difficult because many insectivores have either no teeth or teeny tiny teeth. And we do need five milligrams. So it's a little bit four to five milligrams. It's a little bit difficult to grow those teeth, but we explore that now in modern ecosystems, actually. So this is not case closed. Australopithecus was vegetarian forever. You know, they lived for millions of years all over the place in Africa. You know, is it possible that some other group,

went for the meat just because it was perhaps easier to do where they were. Yes, this is not case closed at all because actually these results are not really surprising. These very early, early arsola pedicures, we are not surprised that they were mostly plant-based, had a plant-based diet.

But we know today we are omnivores. We know that Neanderthals, for example, were called even hyper carnivores at some point. So it looks like they had a very meat-based diet, at least seasonality. So where did it change?

regionally, which taxon explored meat more than others, or maybe some taxon just never explored it at all. How important was it for the adaptation and then the success of a species or extinction of the species? And how is it linked to habitat, for example? So we are planning in the next few years to do other studies, of course, in other environments in Eastern Africa and Southern Africa, but also maybe in Africa

Southeast Asia or completely other regions to see how this meat eating evolved over time and who might have evolutionary success from it. So I can see this up and down the family tree all over wide time periods, correlating it with environment. It's going to be so fascinating to have this like

marker of meat eating this far back in time. Exactly. And of course, it also doesn't really stop there for my group. So we now try to push it back in time and we are analyzing dinosaurs. Again, it might be not that exciting to hear that T. rex actually was a carnivore, but to be able to explore food webs like a million, a hundred million years ago will make a big difference. It

Thank you so much, Tina. This has just been a really fascinating conversation. Thank you. It was great to be here. Tina Ludica is a group leader at the Max Planck Institute for Chemistry and is an honorary research fellow at the Evolutionary Studies Institute in Johannesburg. You can find a link to the paper we discussed at science.org slash podcast. You can also find the other podcasts we did on ancient hominins overlapping in Africa at the same place.

And that concludes this edition of the Science Podcast. If you have any comments or suggestions, write to us at [email protected]. To find us on podcast apps, search for Science Magazine or listen on our website, science.org/podcast. This show was edited by me, Sarah Crespi, and Kevin MacLean. We had production help from Megan Tuck at Podigy. Our show music is by Jeffrey Cook and Wenkui Wen.

Finally, we're thankful for a generous donation in support of a science podcast from the Jacobs Family Foundation. The Jacobs Family Foundation promotes education, health, and scientific endeavors that make a difference in the lives of others. On behalf of Science and its publisher, AAAS, thanks for joining us.