Science in Small Bites
Watch Out for the Real Zombies this Halloween
“People try to crush your soul and destroy your happiness, but zombies just want to have a little nibble of your brain.” — J. Cornell Michel
Zombie #1, The New World Screwworm
Move over, Robert Kennedy Jr.; that tapeworm in your brain is passé. (BTW, you might want to consider cooking your pork in the future.)
With Halloween coming up, I want to introduce readers to a couple of the world’s most macabre, gruesome, and dangerous lifeforms: the screwworm and a species of amoeba called Naegleria fowleri.
If creepy-crawlers give you the heebie-jeebies, skip this article and go straight to the School Menus, or 100-Years-Ago, long before zombies dominated post-apocalyptic films.
I don’t think I have ever used the word “Zombie” in a previous article, so I need to clarify before proceeding. From a theatrical standpoint, zombies didn’t develop a taste for human brains until the 1985 film “The Return of the Living Dead.” Previously, they ate only human flesh and blood, as depicted in the 1968 film “Night of the Living Dead.” Why the sudden change in diet? Brain tissue seems to be a good source of endorphins, which, as all informed zombies know, mitigate the pain of decomposing.
Now, let’s move on to the factual, sciencey part of this story, starting with the dreaded screwworm. What people often call a screwworm is actually the larval stage of a New World Blowfly (Cochliomyia hominivorax), a maggot, if you will. This single insect has plagued farmers and ranchers, costing billions of dollars in livestock damage.
NOTE: The New World Screwworm is called that not because it is a new species, but because it is native to the Western Hemisphere.
Many years ago in a rural part of Ohio, I noticed one of our barn cats had what first appeared to be a shot in the stomach with a pellet gun, or had punctured its belly while crossing the lower portion of a barbed wire fence that surrounded the barn. Still, clearly something had caused a deep hole in her flesh.
The cat let me get a better look by rolling her over on her back, and I was shocked and disgusted by what I saw deep in the wound – some sort of grub or larva wiggling its way deeper into her body. I went to the house and returned with some rubbing alcohol, tweezers, and an old Army blanket, which my wife wrapped around the cat’s body to reduce the chance of getting scratched or bitten.
The larva, which I later found was from the screwworm blowfly, became quite active when I poured alcohol into the hole, apparently trying to back out. When I finally grasped it with the tweezers and pulled it out, I saw that the 3/4-inch-long maggot had a pair of hooks on its front end. We took the cat to the vet and were told that this particular invasive worm eats its way through the body of any warm-blooded mammal, eventually killing it.
It never occurred to me at the time that because I am a warm-blooded mammal, I too could be the victim of the parasitic screwworm. Most blowflies feed on carrion, whereas the New World Screwworm feeds on living flesh, which makes it even more horrendous. It also doesn’t differentiate between humans and other mammals; as long as an open wound is present, the screwworm will burrow in and begin feasting.
If the screwworm invades a head wound, it can and will burrow through the tissue and bone to feast on the brain. This is rare in humans, but it does happen occasionally.
Management programs such as the Sterile Insect Technique have successfully eliminated the New World Screwworm in certain locations. This is accomplished by sterilizing millions of male blowflies with gamma radiation and dropping them en masse over infected areas. The female blowfly only mates once in its life, so it effectively prevents most, if not all, of the potential screwworms
Zombie #2 Naegleria fowleri
Wikipedia describes the premise of the TV series “The Last of Us as”: “A post-apocalyptic drama set decades after a mutated Cordyceps fungus collapses modern civilization by turning humans into aggressive, zombie-like creatures.”
If you’ve seen or heard of this series, remember it is a Hollywood product and pure fiction. Cordyceps is a real fungal genus, and it does horrible things to some insects; it turns them into zombies controlled by an invasive spore. This parasitic fungus has not evolved to zombify humans, at least not yet.
One cordyceps species attacks carpenter ants. When spores settle on a carpenter ant, they invade its brain and take control of its behavior. It forces the ant to climb a plant or tree, then makes it grasp the plant with a death grip. Soon, the cordyceps fruit (the mushroom) sprouts from the ant’s head, releasing another generation of spores.
But as stated earlier, we humans don’t have to worry about this happening to us; in fact, cordyceps spores are commercially available to kill destructive carpenter ants. However, the next tiny zombie we will explore is definitely a danger to humans: a microscopic amoeba called Naegleria fowleri.
I’m writing this article about Naegleria fowleri not to alarm you, but to make you aware of this extremely dangerous organism with few boundaries; it is found globally, and infection from this amoeba carries a 98% chance of death.
Referred to as a “brain-eating amoeba,” Naegleria fowleri (Nf) is a single-celled organism that enters the human brain and quite literally makes a meal of it. Few organisms can easily infect the brain, but Nf has evolved a unique shapeshifting strategy that lets it do so.
Nf is a thermophile, meaning it thrives in warm freshwater. If you’re unlucky enough to bump into an Nf, you may do so while swimming in a warm pond or lake. Nf is also found in hot springs, rivers, and even in unchlorinated swimming pools. There have been cases of infection from using a neti pot with warm, untreated tap water. Because of Nf’s shapeshifting abilities, it can even adapt to living in dirt and be inhaled.
That said, you cannot get infected by contact with other people or by merely drinking water; the Nf amoeba can reach the brain only through the olfactory system, specifically, through the nose. Our brain is well protected from most parasites, but this single-celled organism has evolved strategies to overcome these barriers and reach the brain to feast on our Gray matter, even the cribriform plate. The cribriform plate is a porous bone at the base of the skull that makes up the roof of the nasal cavity.
Once the Nf amoeba enters the nose, it attaches to the mucosa and follows the olfactory nerve fibers. It wiggles through the cribriform plate to the olfactory bulbs and enters the brain.
Having arrived, it causes a generally fatal infection called primary amoebic meningoencephalitis, which causes swelling of the brain. Unfortunately, the symptoms are identical to meningitis, so treatment is often delivered too late to save the patient. And, indeed, the fatality rate is a whopping 98%. According to the CDC, of the 180 cases in the U.S. from 1937 through 2025, only 4 victims survived.
In preparing for this article, I listened to a podcast interviewing a mother whose only child, a young boy, was infected by Naegleria fowleri after swimming with some other lads in a warm body of freshwater. The story was heartbreaking as she described how her son began complaining of a frontal headache followed by fever, vomiting, seizures, and hallucinations, and died after 5 days of a living hell, all because of a microscopic organism.
To be clear, primary amoebic meningoencephalitis is a rare disease. People will, of course, keep swimming in warm freshwater, lounging in hot springs, and even filling their neti pots with warm tap water. However, there are signs that global warming may help Naegleria fowleri proliferate, as it has other lifeforms; it could be an emerging parasite, and that wouldn’t be good.
Here’s wishing you a spooky yet enjoyable Halloween.
Ken Springer
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