SciSun: The Foolish and the Brave   Leave a comment

Mice, generally, aren’t known for their bravery. ‘Run away to live another day’ is probably a motto they live by, for as long as they live; because, in natural conditions, most mice live less than two years. It’s not their fault; the behavior of individual mice, within the mouse world, probably ranges from timid to adventurous (who else would be brave enough to try and take all that cheese); yet compared to other larger, stronger, and less preyed-upon animals, mice are unfortunately toward the bottom of the predator-prey scale. Which makes it unusual to see mice all over the world confronting their main adversaries – primarily cats – in confident bravado and what seems to be a complete loss of fear.

It would be encouraging to know mice have decided to stand up for themselves, won’t be victims any longer and aren’t going to take it anymore (Are you a Mice, or a man!); but regrettably, that doesn’t seem to be what’s happening. A few weeks ago we wrote about Toxoplasma gondii, a single-cell, parasitic organism that causes the often-deadly disease toxoplasmosis. In order for this organism to live and reproduce, it must spend a part of its life both inside a prey animal; and a cat. Dogs, bears, snakes, cloned T-Rexes, or other predators won’t do; just like that strange woman down the street, Toxoplasma must live with cats.

The fearlessness of these mice is not that they must sit on a narrow elevated ladder.  Nor that they must remain still as a black cat walks over them.  Their true bravery is they must perform in a show with two men dressed like this.

The fearlessness of these mice is not that they must sit on a narrow elevated ladder. Nor that they must remain still as a black cat walks over them. Their true bravery is they must perform in a show with two men dressed like this.

And if cats do anything (just what, exactly, do cats do?); is chase and eat mice, small birds, and other easy to catch animals. Feral cats (those that roam freely without a home); and cats with a home that are still allowed to roam freely have been identified as the worst offenders in the toxoplasma war: Within the two weeks that newly infected cats can actively shed the parasite (it’s all in the poop!), a single cat can distribute more than 20 million of the infective organisms, which remain viable 18 months or more waiting for an unsuspecting new host. One cat can infect thousands of animals – including humans – that come into contact with contaminated food, soil or water. Despite generations of mothers warning their children to wash our vegetables, wash your hands, and don’t put dirt in your mouth, it’s estimated over thirty percent of humans have the virus laying dormant in their nervous system. Once triggered by illness or even more frightening, a genetic marker that scientists haven’t yet identified, toxoplasmosis leads to serious illness or death.

But that doesn’t explain the fearless mouse, who, if he knew better, would be very fearful of both cats and the diseases they carry. Countless years of evolution created this symbiotic relationship between the cat and the taxo organism that permanently removes all fear from an infected mouse. Once infected, mice never fear cats again – of course ‘never’ is relative, because the goal of this single-celled manipulator is not to embolden rodents toward their main enemies, but rather to cause mice to loose all concern for danger, so it’s easier to be caught and eaten. The only way taxoplasma can complete its life cycle is in the intestines of a cat (which shows living conditions might not be all that good for the virus, either). Without a cat ingesting the current host – fearless mice – the parasite can’t live.

Just as taxoplasma has developed into an opportunistic hanger-on (which, itself, is the definition of ‘parasite’); mice, perhaps, were never intended to be brave and generations of caution has enabled countless generations of mice, rather than easy meals for cats. What benefits the cat and the taxoplasma is a liability to the mice, sheep, cattle, bird, wildlife or human hosts that become ill by the tens of thousands each year. Maybe not an example of fearlessness among mice, who once infected can’t help themselves, this is more a story of humans who allow countless cats to roam free, risking the spread of disease and illness. And that’s a decision more foolish, than brave.


Michonne Says: Marmots never wash our food, and we dig in the dirt all the time! I hope we don’t get sick from that toxi-cat sickness. And if the sickness hurts other animals, why doesn’t it make cats sick? That doesn’t seem fair.

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