‘Brainwashing’ parasites inherit a strange genetic gap

Horsehair worms are even weirder than scientists thought.
parasitic horsehair worm
The hairworm has a long slender body that entangles itself and form knots. The Field Museum

Deep beneath our feet almost anywhere on the planet, there are parasitic spaghetti-like puppet masters known as horsehair worms or gordian nematodes. 

These sneaky, slimy beings are lacking three major systems: excretory, circulatory or respiratory. To make up for it, they invade crickets, grasshoppers and other invertebrates, tapping into their neurological circuit and eventually brainwashing them. Once inside a body, the adult worm will then take action by controlling their host and forcing them to seek a water body so that the worms can exit and mate. 

[Related: Mind-controlling ‘zombie’ parasites are real.]

These creatures might not just be missing crucial systems for function—but something in their DNA.  Scientists from the Field Museum of Natural History and Harvard University sequenced the genome of the freshwater hairworm Acutogordius australiensis and the saltwater worm Nectonema munidae. They discovered that these animals were missing genes that coded for cilia—hair-like structures found on nearly all cells in animals and humans. 

The researchers published their findings in Current Biology this month.   

“What we found, which was very surprising, was that both hairworm genomes were missing about 30 percent of a set of genes that are expected to be present across basically all groups of animals,” said Tauana Cunha, a postdoctoral researcher at Chicago’s Field Museum and lead author of the study

Cilia are the fuzzy hair-like threads found on eukaryotic cells that help with moving fluid, debris and other materials from one place to another. “Animals use ciliary structures to move, to clean their cells, as sensors (there are cilia in your eyes and ears, for example), in sperm cells. Sponges use these structures to move water and feed, we use them for many of the things,” says co-author Bruno de Medeiros, research associate at the Museum of Comparative Zoology at Harvard University and assistant curator of insects at the Field Museum. “It is crazy that an animal would lose cilia and flagella, since they seem so useful and so entangled into the natural history of an animal.”

The lineage of hairworms has historically been understudied. Hairworm experts are limited, and delving into their genome is an expensive and uncommon process. But, these findings open up a new series of questions over what other creatures may have lost “such a fundamental cell-level structure as the cilia,” Mederios says. 

“So this major lineage of animals was neglected so far. There are others, still. We definitely do not have yet a clear picture of the genome of all animals,” says Mederios. 

[Related: How a peculiar parasitic plant relies on a rare Japanese rabbit.]

While humans don’t need to live in fear of a mind-controlling worm, knowing how these parasites operate is crucial to protecting environmental and human health. For example, the saltwater species sampled was found in a deep-sea lobster, which can be caught for human consumption. Other arthropods pollinate crops, or are even used in feedstocks or experimental human food

“If the trend to use crickets as food keeps up and we start to do mass-production of crickets, we certainly want to be aware of the potential parasites and how to deal with them, which include hairworms,” Mederios says.