💥💩Fun with explosive diarrhoea

“There were no public health laws in Ankh-Morpork. It would be like installing smoke detectors in Hell.” — Terry Pratchett, Feet of Clay

It’s a funny thing, isn’t it? Nature is pretty much always trying to kill us, or at least make us uncomfortably ill, especially now that we number over 8 billion and we’re all packed together on our little blue planet. We depend on boring, irritating things like food safety laws and continual checks that we’re not being fed (say) contaminated lettuce. And yet, people seem to take every opportunity to dump on competent epidemiologists and infectious disease experts.

If I’d put a picture of, say, Anthony Fauci up there instead of pictures of a few potentially dodgy foods and Cyclospora cayetanensis, the brickbats would already be flying from about one third of the US population. And although even they surely know at some visceral level that dumping on the people who protect you from infection is dumb, they pretty much can’t help themselves. It seems.

Cyclospora cayetanensis is not a bacterium or a virus. It’s a tiny spherical parasite—specifically, an apicomplexan—measuring no more than about 10 millionths of a metre (µm) across.1 Because it’s a eukaryote, it shares a lot of our internal molecular mechanisms, despite its tiny size. Its life cycle—shown above—is a bit weird, but not that weird compared to some parasites.^⌘

Cyclospora seems to pretty much infect only people. And—you guessed it—shit is involved. You eat food that is contaminated by faeces containing the parasite, and it settles down in the upper part of your small bowel, especially the jejunum. It invades the lining cells, breeding there, and after about a week, produces (a) the now well-known explosive diarrhoea that can carry on for weeks, and (b) lots of oocysts that carry on the infection.

Tracing the story of Cyclospora is as murky as trying to trace that lettuce back from Taco Bell to Taylor Farms. It wasn’t even called ‘Cyclospora’ when it was first seen in the poo of people from Papua New Guinea in 1979. There was a lot of confusion3 until, between 1992 and 1994, Ortega and colleagues first named and then described it in detail in the Journal of Parasitology, after isolating specimens from the poo of people in Peru4 and the US. The oocysts fluoresce blue under ultraviolet light at 330–365 nm, using concentrated stool wet mounts.

Here’s the thing. This little bugger is resistant to chlorine. It’s resistant to hand sanitisers and chemical treatments used on farms. It’s wise to wash fruit anyway, but it’s so tiny and the infective dose is so small, some of the Cyclospora may well slip through. It sticks to the tiny hairs on raspberries through mechanisms we don’t understand.

Best thing is not to get poo on your lettuce! Over 158°F (70°C) for 1.5 minutes will apparently kill Cyclospora, but that will also kill your salad! Microwaving is less reliable, as there may be cold spots. You can also get it from contaminated water, so boil away if this is a potential source.

Even detecting it is tricky. It doesn’t stain well with standard stains for parasites and their eggs. You can’t culture it in the lab. And nobody keeps food for ten days just on the off-chance that later you might want to test it for Cyclospora. Some labs have a polymerase chain reaction (PCR) test for it in stool.

But what you really need is good surveillance—and when cases are detected, then you need an army of epidemiologists to go out and interview everyone. Although it’s difficult and time-consuming to work out whether you ate at Taco Bell a week or more ago, with enough information, we can piece together a pattern, and stop the flow of, well, er … clears throat.

Once you are infected, the trots (and intermittent explosions) can last for weeks or longer. Specific antibiotics seem to work, though.

There’s been a flood of cases in the United States recently. There seem to be at least two distinct clusters. It’s easy to blame the Trump administration. They present such a large target. But let’s be fair here: they stuffed up.

We know they’ve crippled the CDC.⌘ As with those screwworms,⌘ you can again blame DOGE. And as of July 1, 2025, Foodnet cut back its surveillance to just two pathogens. Before then, they were on the lookout for Campylobacter, Listeria, Shigella, Vibrio, Yersinia and—yep—Cyclospora. Now they just look for STEC and Salmonella.5 Here’s a quote:

“Essentially, CDC is backing off on one of their best surveillance systems,” said Dr. J. Glenn Morris, director of the Emerging Pathogens Institute at the University of Florida. Morris, a former Agriculture Department official, was instrumental in helping create FoodNet in 1995.

To their credit, the CDC still did manage to produce an alert on July 14, 2026. According to them, about one in eleven infected people have been hospitalised, but there have been no deaths so far.6

They’re just doing their best. But there’s another problem. Once there’s poo in your salad, you need to turn off the poo tap. I’m sure you’ve watched things unfold: an ongoing rise in cases following lack of clarity, arse-covering and denial on the part of the major lettuce distributor who was fingered as, well, having at least metaphorically dirty fingernails.

You can predict this: more of the same. Not just Cyclospora, but also Campylobacter, Listeria, Shigella, Vibrio, Yersinia. They can all give you the trots, but they can do a lot more. For example, Campylobacter can give you Guillain-Barré syndrome, where your nerves stop working (they may recover). Oh wait! Cyclospora might do that too. Listeria is particularly nasty in pregnant women, as their immune system struggles to fend it off, and it can cause devastate or kill the unborn baby. Come to think of it, we’re not too keen on cyclosporiasis in pregnancy either.

With food safety, coordination has now failed. We can expect this in other areas. Scarier still are the millions of viruses out there that we haven’t yet met. If our surveillance mechanisms are down, then something resembling ebola^⌘ or Nipah^⌘ virus—but far more dangerous—could slip through. We may not know until it’s too late. Are you feeling lucky?

Meanwhile, American politicians are too busy doing other things they consider important, like putting the boot into transgender athletes, facilitating ICE, and using up their remaining munitions futilely bombing Iran.

What a shithole country the USA has become :(

My 2c, Dr Jo.

^{⌘ This symbol is used to indicate posts where I’ve discussed the flagged topic in more detail.}