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Love Bites: Microbes That Hijack Infection
- Heather McSharry, PhD
- 4 days ago
- 5 min read
Updated: 3 days ago
Summary
Love isn’t always candlelight and chocolate. Sometimes it’s snail slime, zombie ants, and microbes quietly rewriting the rules of attraction.
In this Outbreak After Dark post-Valentine’s special, Heather is joined by Kate and Sam around the campfire to explore parasites and viruses that manipulate fear, flirtation, mating behavior, and occasionally entire nervous systems. From rodents that lose their fear of cats to caterpillars that climb and liquefy for viral gain, this episode asks an unsettling question: How much of what we call “chemistry” is actually biology?
The science is real. The stories are deeply strange. And yes—the snacks are themed.
Listen here or scroll down to read the episode overview or download the full transcript.
Episode Overview
Heather’s Note: This episode uses humor and anthropomorphism for storytelling. Parasites are not conscious villains plotting your dating life. Their behaviors evolved through natural selection—efficient, not evil.
Recipes and References are at the end of the post after the signature.
👉Download Transcript PDF:
This transcript reflects the original episode draft and closely follows the final audio. Because this episode includes conversational ad-libs and live exchanges, minor phrasing may differ slightly from what you hear.
Love Bites begins with a microscopic mastermind: Toxoplasma gondii.
This parasite infects rodents and selectively dampens their fear of cats—the only host where it can reproduce sexually. Infected mice may lose their aversion to feline scent, making them far more likely to become prey. It’s not chaos. It’s evolutionary precision.
From there, things escalate.
We travel through the meticulously orchestrated life cycle of Dicrocoelium dendriticum, the lancet liver fluke that turns ants into temperature-sensitive grazing bait. We examine densoviruses that tweak moth pheromones, and sigma viruses that sabotage fruit fly courtship songs—because sometimes spreading efficiently just means altering who gets a date.
Then comes altitude.
The infamous Ophiocordyceps unilateralis compels infected ants to climb vegetation and perform a fatal “death grip” before fungal stalks erupt and rain spores below. Meanwhile, baculoviruses trigger “tree-top disease,” liquefying caterpillars at the highest point possible for maximum transmission.
These aren’t horror tropes. They’re documented evolutionary strategies.
We also confront a real-world fungal concern: Candidozyma auris (still commonly referred to as C. auris in infection-control guidelines). Unlike cinematic fungi, this yeast doesn’t hijack behavior, but its antifungal resistance makes it a serious healthcare-associated pathogen. Not apocalypse fuel. Just a reminder that real microbial threats are quieter and more complicated than fiction.
Microbial Love Potions (Human Edition)
After exploring parasites that commandeer ants and rodents, the conversation turns inward. Humans don’t have pheromones in the way moths do. The once-popular 1990s pheromone craze—including books like The Alchemy of Love and Lust—was built on early research that didn’t hold up. Our vomeronasal organ is vestigial. There’s no magic molecule that makes someone fall in love.
But microbes still matter.
Your gut microbiome influences serotonin, dopamine, and stress responses. Skin bacteria help generate body odor cues shaped by your immune genes (MHC). A 10-second kiss can exchange millions of bacteria. Couples begin to share microbial signatures over time.
It’s not mind control. It’s chemistry—with context.
What We Cover
How Toxoplasma gondii selectively alters rodent fear
Why zombie-ant fungi don’t infect humans
Parasites that manipulate mating, pheromones, and courtship songs
The real story behind Candidozyma auris
Why humans don’t actually have pheromones
The gut–brain axis and microbial mood influence
Kissing as a bacterial exchange program
Why attraction often signals immune compatibility—not destiny
“Love may be mysterious, but microbes are always involved—quietly steering your mood, your scent, your bonding chemistry…Just never your mandibles.”
By the end of the night, nothing feels quite as simple as a Valentine’s card. But it does feel clearer. Love isn’t hijacked by parasites in humans—but biology is always in the background, shaping the conditions where connection happens.
And around the fire, clarity is enough.
Heather, Kate, and Sam close in unison:
By the fire we meet
With food, drink, and infectious creep.
This is Outbreak After Dark.
Recipes and references appear below the signature.
Courtship Clusters, Zombie Ant Tapenade Toasts, Parasite Punch, and the Symbiosis Spritz are ready when you are.
Cuddle responsibly. Kiss mindfully. And maybe don’t eat the snail slime.
Thanks for joining us for our campfire conversation about flirty microbes. Next month Kate and Sam return for a conversation on the history & mythology of plague doctors. Until then, stay healthy, stay informed, and spread knowledge not diseases.
RECIPES
REFERENCES
Paywalled papers are provided here as PDFs when possible
Toxoplasma gondii and Rodent Behavior
Berdoy et al. 2000. Fatal attraction in rats infected with Toxoplasma gondii. Proc R Soc B.
Vyas et al. 2007. Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors. PNAS. https://www.pnas.org/doi/10.1073/pnas.0608310104?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub++0pubmed
Webster J. 2007. The effect of Toxoplasma gondii on animal behavior: playing cat and mouse. Schizophrenia Bulletin.
Dicrocoelium dendriticum (Lancet Liver Fluke)
Carney W. 1969. Behavioral and morphological changes in carpenter ants infected with Dicrocoelium dendriticum. Am Midl Nat.
Moore J. 2002. Parasites and the Behavior of Animals. Oxford University Press. (Fascinating Book available as PDF here!!)
Ophiocordyceps (Zombie-Ant Fungus)
Hughes et al. 2011. Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection. BMC Ecology.
de Bekker et al. 2014. Species-specific ant brain manipulation by Ophiocordyceps. BMC Evol Biol. 2014.→
https://pmc.ncbi.nlm.nih.gov/articles/PMC4174324/
Baculovirus “Tree-Top Disease”
Hoover et al. 2011. A gene for an extended phenotype. Science.
Hairworms (Nematomorphs)
Thomas et al. 2002. Do hairworms manipulate the water-seeking behavior of their terrestrial hosts? J Evol Biol.
Ribeiroia and Limb Malformations
Johnson et al. 2010. Linking environmental nutrient enrichment and parasite infection to amphibian malformations. Ecol Appl
MHC and Odor Preference
Wedekind et al. 1995. MHC-dependent mate preferences in humans. Proc Biol Sci. → The original “sweaty T-shirt” study.
Havlíček J & Roberts SC. 2009. MHC-correlated mate choice in humans: a review. Psychoneuroendocrinology.
https://www.sciencedirect.com/science/article/abs/pii/S0306453008002667?via%3Dihub
Gut–Brain Axis
Cryan JF & Dinan TG. 2012. Mind-altering microorganisms: the impact of the gut microbiota on brain and behavior. Nat Rev Neurosci.
Mayer et al. 2015. Gut/brain axis and the microbiota. J Clin Invest.
Kissing & Microbiome Exchange
Kort et al. 2014. Shaping the oral microbiota through intimate kissing. Microbiome.
Vomeronasal Organ & Human Pheromones
Meredith M. 2001. Human vomeronasal organ function: a critical review. Chem Senses.
Wyatt, TD 2014. Pheromones and animal behavior: Chemical signals and signatures (2nd ed.). Cambridge University Press.
Candida auris (Candidozyma auris) Clinical Reality
Association for Professionals in Infection Control and Epidemiology (APIC): Candida (Candidozyma) auris (C. auris)
Chow et al. 2020. Tracing the evolutionary history and global expansion of Candida auris. mBio.
WHO releases first-ever list of health-threatening fungi. 2022.
https://www.who.int/news/item/25-10-2022-who-releases-first-ever-list-of-health-threatening-fungi
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