'Shocked' scientists find brain parasites in baby lizards still in shells

Female common wall lizard
Female common wall lizard (Podarcis muralis) (Image credit: Nathalie Feiner)

A newfound species of parasitic worm wiggles its way into the brains of baby lizards long before the reptiles hatch. 

How do the nematodes break into developing lizard brains? They sneak in through the lizard mothers' ovaries, a surprising new study finds.

Parasitic nematodes that prey on mammals can sometimes jump from mother to offspring through the placenta in utero or through breast milk after birth, the study authors noted in an article-in-press to be published in the May 2020 issue of the journal The American Naturalist. But until now, no one thought that reptiles could pass down their parasites from mother to offspring; evidence suggested that, because they lay eggs, animals like lizards are less vulnerable to certain routes of parasitic transmission. 

But much to scientists' surprise, the discovery of worms in lizard embryos suggests that reptilian eggs aren't as impenetrable as once thought.

Related: 8 awful parasite infections that will make your skin crawl

Common wall lizard embryo

Common wall lizard embryo (Image credit: Nathalie Feiner)

"I was shocked when I saw something moving in the embryo's brain, despite having dissected many lizard eggs before," lead author Nathalie Feiner, an evolutionary biologist at Lund University in Sweden, said in a statement. While studying common wall lizards (Podarcis muralis) across Europe, Feiner and her colleagues routinely dissect and examine developing lizard embryos and find most to be worm-free. However, one population of common wall lizards in the Pyrenees mountain range turned out to be riddled with nematodes.

Wondering where the worms came from, the researchers examined the lizard mothers and found nematodes wriggling in the animals' ovaries. Typically, nematodes invade the intestines of common wall lizards, but the authors hypothesized that this newfound species adapted to thrive in the reproductive system of females. The worms in the ovary infiltrate the embryos of the the developing lizards and enter their brains before a hard egg shell forms around the animal. 

The authors allowed several infected lizard embryos to develop to maturity, noting that "infected lizard embryos develop normally and hatch with nematodes residing in their braincase." The animals appear healthy when first hatched, parasites aside, but the researchers did not monitor the lizards further to see how their health and behavior might be affected as they mature, the authors added. 

"It would be exciting to know if this vertical transmission [between mother and embryo] is unique to the nematodes we found in the common wall lizards or if this occurs in other species, as well," Feiner said. "It would also be interesting to find out if the lizard’s behavior is affected by having worms in their brains."

Originally published on Live Science. 

OFFER: Save at least 53% with our latest magazine deal! (opens in new tab)

OFFER: Save at least 53% with our latest magazine deal! (opens in new tab)

With impressive cutaway illustrations that show how things function, and mindblowing photography of the world’s most inspiring spectacles, How It Works (opens in new tab) represents the pinnacle of engaging, factual fun for a mainstream audience keen to keep up with the latest tech and the most impressive phenomena on the planet and beyond. Written and presented in a style that makes even the most complex subjects interesting and easy to understand, How It Works (opens in new tab) is enjoyed by readers of all ages.

Nicoletta Lanese
News Editor, Health

Nicoletta Lanese is a news editor on Live Science's health desk. She first joined the publication in 2019 as a staff writer. She holds degrees in neuroscience and dance from the University of Florida and a graduate certificate in science communication from the University of California, Santa Cruz. Her work has appeared in The Scientist Magazine, Science News, The San Jose Mercury News and Mongabay, among other outlets.

  • Sylas
    Maybe this is a step in evolution. Maybe the lizards are evolving to include a symbiotic relationship with a higher intelligence. These are extremely intelligent worms to figure out the ONE way into an egg shell without breaking it. This means that the "newmatodes" have some very disturbing traits: Extremely intelligent with strategic thinking and generational planning skills, They possess a thorough working knowledge of physiology, as well as reproductive endocrinology in different species. They have demonstrated an execrable nature because they made the calculated decision to feast upon baby brains. In conclusion, we really have no choice but to rid the world of these sycophants before they master the technology to invade human baby brains in utero.
  • Hayseed
    Maybe they were following their nose, like a pig does.