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Stanford University School of Medicine

Cat guts, car crashes, and warp-speed Toxoplasma infections

Between one-quarter and half of the people on Earth are infected with Toxoplasma gondii. This is one widespread parasite: The versatile protozoan can infect most warm-blooded creatures. Yet it can sexually reproduce only within the intestines of members of the cat family. (Toss that fact off at your next dinner party.)

It gets weirder. Strangely, T. gondii-infected rats seem to have an altered sense of... well, something. Instead of experiencing dread at the smell of cat feces, as would any rat in its right senses, infected rats experience something akin to falling in love, in a manner Stanford biologist Robert Sapolsky, PhD, has described.

Apparently, evolution has favored T. gondii over rats, because the latter's newfound fondness for feline feces increases their risk of being devoured - and of their microbial manipulators' scoring a five-star honeymoon hotel room inside a cat gut.

As for us people, immune-compromised individuals can suffer great harm from a T. gondii infection but the vast majority of those infected experience no obvious symptoms - although people with T. gondii residing in them are 2.5 times as likely to get into car accidents, and pregnant women probably should be screened for the pest's presence. There are also indications that T. gondii infection is associated with an increased risk for schizophrenia.

This, then, is a bug deserving of some serious study. Speaking of which, in a study published in Nature Chemical Biology, Stanford microbiologists Matt Bogyo, PhD, and John Boothroyd, PhD, and their colleagues have revealed another item in the bag of burglar tools the pathogen uses to invade cells.

They found a small molecule (so, a good candidate drug) that causes the parasite to invade victims' cells more efficiently. Yep, I said that correctly: A dose of this stuff enhances the parasite's invasion capacity.

"Hmmmm," you may be thinking. "Okayyyy ... so why should I get excited about a compound that increases the number of parasites that are invading a person's or animal's cells?"

Bogyo gave me an answer in the form of an analogy. "It's easy to find ways to make a car go slower. But a lot of those ways of slowing it down don't tell you much of anything about how the car works. If you find something that makes the car go faster, you're on the road to cracking that car's operating system."

There are other reasons, Bogyo theorized, why the compound Bogyo, Boothroyd and company identified could prove useful. Here's one:

Inducing increased invasion of the host may actually result in poorer overall fitness for the parasite. Increasing the speed of the invasion process will prevent [T. gondii] from being able to disseminate away from the point of exit from a previously infected host cell. This will prevent the spread of the parasite throughout the body and actually reduce the productivity of the infection. So, ultimately, compounds that stimulate the parasite invasion pathway might be viable therapeutic agents.

Previously: Patrick House discusses Toxoplasma gondii, parasitic mind control and zombies, Compound clogs Plasmodium's in-house garbage disposal, hitting malaria parasite where it hurts and NIH study supports screening pregnant women for toxoplasmosis
Photo by flackjack

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