It's not just Brain Dead TV!
It’s not just Brain Dead Sci-fi comedy folks! Parasites, of Earth not alien origin, can influence behavior. In order to maintain host infections, several recent studies have determined that the parasite Toxoplasma gondii is capable of manipulating behaviors to favor increased transmission between carrier and host species, not just in rodents but primates too. Really – not just crazy Sci-fi TV, these pathogens can actually alter what we do to gain an advantage in transmission to the next host.
T. gondii – Toxo - is a highly promiscuous and common pathogen, capable of infecting all known mammalian species. The initial host symptoms are typically mild and the parasite then survives as chronic cysts in your brain – the dormant stages. Humans usually acquire the disease through undercooked meats. The disease can reactivate in immune-compromised patients with deadly consequences, but the majority of infected individuals lead, what we think, are typical lives.
Lifecycles for this parasite require sexual stages in all large, small, wild or domesticated cats; Toxo’s natural carrier. The sex drive is strong in these little single celled parasites, calling them back to felines at all costs. But later after unceremoniously leaving the cat, they need to find a way back into hosts quickly. This is why common practice dictates that pregnant women stay away from litter boxes. Infections during pregnancy are known to cause miscarriages.
Through direct parasite actions, studies have shown these manipulative parasites make hosts attracted to rather than repelled by feline urine, putting them in a direct line of fire as host-victims. Mice are normally fearful of anything feline. And with a keen sense of smell, mice know to avoid any cat odors but mice with chronic Toxo infections have lost this ingrained fear. Cats, as it has recently been shown experimentally, are particularly good at using sound to find hidden prey so non-fearful mice are literally dead meat.
A rodent dinner is one thing, but can these results translate to other mammals? Large wild cats rarely prey upon humans in modern times. African lions and Indian-Bengali tigers are the main predators. We are at much greater risk by captive held animals. At least 750 reported attacks, either mauling or killing incidences, are confirmed in the US alone since 1990, by captive large cats. But overall, we have much less need to fear the “roar of the lion” than say, wild chimpanzees. In an analogous study to rodent behavioral experiments, wild chimps infected with encysted Toxo are also drawn to leopard urine, their natural predator. So even our closest cousins are vulnerable to this twisted parasitic trick.
Anecdotal descriptions and early studies in humans infected with Toxo have demonstrated some peculiar human behaviors as well. Continuing analysis of available data confirms chronic Toxo infections are associated with clinical diagnoses of schizophrenia and in failed suicide attempts. Poor impulse control is a leading causative factor in suicide attempts. Extrapolating this finding, humans infected with Toxo could have a much more laissez-faire attitude about personal safety overall. One major difference between human studies and other species; no urine smelling experiments are included in clinical analyses.
Should we worry? Not until we find ourselves sniffing the litter box and we spend quality time in big cat country. We have co-existed with this and many similar parasites peacefully. They live their little singular lives, within ours. But just like us, they struggle for sex, survival and support using the best techniques they have on hand – mind control.