Cat lovers and rare beef eaters may be easy prey for automobiles ...

BBC NEWS | Health | Eat worms - feel better

One third of Britons carry the toxoplasma parasite in their brain.

Its natural home is the cat and it's spread in cats' faeces. It can be picked up by any mammal, from rats to cattle. The main way we get it is by eating undercooked meat (which is why 80% of the French are estimated to have it, with their love of rare meat).

Once we have it we have it for life, there's no way we can get rid of it.

Research shows it somehow manipulates rats' behaviour - it makes rats attracted to cats - their natural predator, so they're more likely to be eaten by a cat and the parasite can complete its life cycle.

For years scientists thought it had no effect on our behaviour, but now the parasite's changing their minds. Recent research suggests that people with toxyplasma have slower reaction times than those without and are also more than twice as likely to be involved in a traffic accident than those who aren't carrying the parasite.

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The BBC news story is a tie in to a BBC broadcast. The broadcast sounds gruesome and fascinating. I've been following the UC/hookworm studies for years and I'm looking forward to the study publications. This Toxoplasma data is new to me though, and it's rather unsettling. It's not good news for people who have pet cats or who like their meat rare. Personally, I'm switching to well done, though it may be too late for me! Good news for dog loving cat hating vegetarians though ... (I think dogs don't get toxoplasma ...)

Reflections on my personal bacterial companions

I stopped a puck the other day.

With my leg. That's what comes with playing against these dad-gum college kids. They don't know their own strength.

The hematoma became infected, and since antibiotics aren't what they used to be my personal physician/spouse recommended diligent attention. So now the infection is mostly better.

This gave me the opportunity to wonder about three things:

1. Who creates the tough sealant (scab) atop the wound? I used to think my body did that, but, really, it's a stupid response. I need the sucker to drain, not seal. Maybe the scab is built by the bacteria?
2. Why don't infected wounds hurt more? I whack my finger and it sure hurts, but my body doesn't complain much about infections. Seems illogical ... unless the bacteria are turning off pain signals.
3. We know Toxoplasma makes rats dumb and happy - the better for cats to munch 'em and spread the infection. We think it does something similar to humans. So shouldn't bacterial infections make us feel kind of laissez-faire, less prone to aggressively treat the infection?

That was yesterday. I was inspired in part by a gruesome science fiction story of some years back about emergent sentience in bacteria (can't remember author, but I don't think it was Greg Bear).

I don't think these are original ideas, but I didn't expect to see a Carl Zimmer essay on the topic today!

I For One Welcome Our Microbial Overlords | The Loom | Carl Zimmer | Discover Magazine

.... Very often, the parasites cause hosts to do things that help the parasites, instead of themselves. For example, a protozoan called Toxoplasma needs to get from rats to cats, and to help the process along, it makes rats lose their fear of cats. Parasites can also change the diet of their host as well as the way in which their hosts digest their food....

I was reminded of this sinister manipulation by a paper that was published in Science today by Rob Knight and his colleagues. They built on previous research that revealed that mice genetically engineered to be obese have different kinds of microbial diversity in their guts than normal mice...

... Knight and his colleagues discovered a different–and more disturbing–way that microbes can make mice fat....

... Mice with a genetic make-up that alters the diversity of their gut microbes get hungry, and that hunger makes them eat more. They get obese and suffer lots of other symptoms. Get rid of that particular set of microbes, and the mice lose their hunger and start to recover. And that distinctive diversity of microbes can, on its own, make genetically normal mice hungry–and thus obese, diabetic, and so on.

When I first learned of this work, I asked Knight–with a mix of dread and delight–whether the microbes were manipulating their hosts, driving them to change their diet for the benefit of the microbes. He said he thinks the answer is yes...

If gut bacteria can change diet, then skin bacteria could make people with chronic skin infections apathetic -- the better to discourage treatment of the thriving bacterial colonies ...

Update 3/24/2010 - See also a 2006 post on viruses changing dietary behaviors ... Why would a virus fatten an animal?

It pays to be a parasite: The cat

I've half-jokingly praised the parasitic brilliance of the dog. Arguably, however, dogs are symbiotes. We gave them our garbage, they cleaned the premises. Physically weak humans could ally with physically strong dogs, given evolution more playgrounds to tweak the mind.

Domestic cats, on the other hand, are pure[1] parasites:

DNA Offers New Insight Concerning Cat Evolution - New York Times

With each migration, evolutionary forces morphed the pantherlike patriarch of all cats into a rainbow of species, from ocelots and lynxes to leopards, lions and the lineage that led to the most successful cat of all, even though it has mostly forsaken its predatory heritage: the cat that has induced people to pay for its board and lodging in return for frugal displays of affection.

How did evolution shape the cat, so it was so able to prey so effectively upon human weaknesses? One clue (also from this week's NYT Science) is that human's are programmed to respond to anything resembling a helpless infant. Cats appear to have evolved to take advantage of that weak point.

One can only speculate on the alliance that evolution might build between cats and toxoplasma. It would make sense that toxoplasma, a rapidly evolving parasite, could alter the behavior of both cats and humans to further its own agenda ...

I do love ecology.

[1] Ok, so they killed rats, mice and other "vermin". Sigh. Guess they were symbiotes once too ...

Toxoplasma infection alters personality?!

Dangerrrr: cats could alter your personality - Health - Times Online

The claim is that toxoplasma infection alters human personality. I don't believe it, but it's fascinating. We do know that parasites change personality and behavior in many species. (via Metafilter)

The joy of parasitism and the strategic wisdom of the cat

I'm a dog person, but I'm kindly inclined to the Dog's historic rival in exploiting the human host. Not that Dogs and Cats are pure parasites, though the cat's role as a toxoplamsa vector arguably moves them closer to the dark side. Dogs do eat garbage and thus reduce disease (like toxoplasma, which can't live in dogs), cat's do kill pests, which reduces disease (do cats get plague?) and food loss.

Quibbles aside, as a happy host to my current canine parasite, I'll raise a toast to the strategic brilliance of the cat, an animal that went from chewing on primates to switching sides when the time was right ... (emphases mine)

The Near Eastern Origin of Cat Domestication (Science)

... Some 10,000 years ago, somewhere in the Near East, an audacious wildcat crept into one of the crude villages of early human settlers, the first to domesticate wheat and barley. There she felt safe from her many predators in the region, such as hyenas and larger cats.

The rodents that infested the settlers’ homes and granaries were sufficient prey. Seeing that she was earning her keep, the settlers tolerated her, and their children greeted her kittens with delight.

At least five females of the wildcat subspecies known as Felis silvestris lybica accomplished this delicate transition from forest to village. And from these five matriarchs all the world’s 600 million house cats are descended....

a subsequent NYT editorial comments:

Cats Among Us - New York Times

... This new genetic evidence resolves the puzzle of cat remains turning up in Cyprus before the rise of the Egyptian civilizations that were supposed to have domesticated the cat.

The wild subspecies that gave up their DNA for these tests still exist, though barely. That is one of the painful ironies of domestication. Creatures who come in from the wild eventually prosper — domestic cats number, after all, in the hundreds of millions — while those who don’t almost inevitably fall upon hard times...

Humans are the ultimate predator, compared to which the old saber tooths were ... pussy cats. We may not last long, but in the meantime we are pretty sure to wipe out every large animal that doesn't find a way to serve us. The cat made a good strategic move. With luck they might outlast us, and return to having primates for lunch long after we're gone ...

Our fiends the toxoplasma

Carl Zimmer updates us on the diabolical machinations of the mind controlling parasites that infest half of humanity: The Loom : Parasites as Neuropharmacologists. Maybe this explains tiger petting in Thailand.

PS. I do recommend the Thailand travelogue link, which has more than one connection to micro-organisms. I spent most of a year near the old fish market as a feckless youth. There is more continuity than I might have imagined, though I think the writer is over simplifying a wee bit ...

Why would a virus fatten an animal?

We know parasites such as toxoplasma change the behavior of their hosts [1]. That seems to make nice evolutionary sense. But why would a virus induce obesity in some animals?

Contagious obesity? Identifying the human adenoviruses that may make us fat | Science Blog

Ad-37 third virus implicated in animal obesity

The theory that viruses could play a part in obesity began a few decades ago when Nikhil Dhurandhar, now at Pennington Biomedical Research Center at LSU, noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more fat than non-infected chickens. The discovery was intriguing because the explosion of human obesity, even in poor countries, has led to suspicions that overeating and lack of exercise weren't the only culprits in the rapidly widening human girth. Since then, Ad-36 has been found to be more prevalent in obese humans.

In the current study, Whigham et al. attempted to determine which adenoviruses (in addition to Ad-36 and Ad-5) might be associated with obesity in chickens. The animals were separated into four groups and exposed to either Ad-2, Ad-31, or Ad-37. There was also a control group that was not exposed to any of the viruses. The researchers measured food intake and tracked weight over three weeks before ending the experiment and measuring the chickens' visceral fat, total body fat, serum lipids, and viral antibodies.

Chickens inoculated with Ad-37 had much more visceral fat and body fat compared with the chickens infected with Ad-2, Ad-31 or the control group, even though they didn't eat any more. The Ad-37 group was also generally heavier compared to the other three groups, but the difference wasn't great enough to be significant by scientific standards.

The authors concluded that Ad-37 increases obesity in chickens, but Ad-2 and Ad-31 do not. "Ad-37 is the third human adenovirus to increase adiposity in animals, but not all adenoviruses produce obesity," the study concluded.

There is still much to learn about how these viruses work, Whigham said. "There are people and animals that get infected and don't get fat. We don't know why," she said. Among the possibilities: the virus hasn't been in the body long enough to produce the additional fat; or the virus creates a tendency to obesity that must be triggered by overeating, she said.

It certainly makes sense to try and figure out how host adiposity could benefit a virus, but for no good reason I suspect a tendency to produce fat is a side-effect that's irrelevant to the virus.

[1] BTW, why do some dogs compulsively eat grass? Since grass eating is associated with Giardia infection, one might consider that bug. Or maybe a parasite who's life cycle involves deer ticks and who causes colitis in dogs ...

Parasite and master

I'm addicted to these stories of parasites controlling their hosts. Were we less fussy when we carried worms? Is OCD (obsessive compulsive disorder) an adaptive response to the lassitude and carelessness worms create? (In other words, OCD is the disorder that emerges when the worms are gone, when the worms are present the same neurologic structures counteract the worm effect).

The big focus now is on Toxoplasma. How does this lovely litte brain infesting critter change our behavior? What's the curious relationship to some schizophrenia-like conditions? Carl Zimmer, one of our best science writers, summarizes the stor to date: The Return of the Puppet Masters.

Parasites are cool.

We too are manipulated by our parasites

Manipulative Malaria Parasite Makes You More Attractive (to Mosquitoes) - New York Times

It is becoming clear that many, if not all, parasites alter the behaviors of their hosts. Research shows malaria-infected mosquitoes vary their biting behavior depending on the parasite's life cycle. Now we learn that infected human children smell more attractive to mosquitoes:

After studying 12 sets of children, the scientists discovered a striking pattern. 'Gametocyte-infected children attracted about twice as many mosquitoes as either uninfected ones or ones infected with nontransmissible stages,' Dr. Koella said. 'The results really jump out.'

The infected children did not show symptoms like fever, a common situation in Africa. Nevertheless, the researchers treated them with anti-malaria drugs on the day of their study. Two weeks later, after the medicine had cleared the parasites, the scientists repeated the experiments with the same three children. They found that the cured children were no more attractive to the mosquitoes than the others.

I'm starting to worry that the 'toxoplasma alters personality' claim may be valid.

Throughout most of human history we carried a very large number of parasites in our bodies -- particularly worms. How has losing those worms changed our behavior?

Update 8/10: Still thinking about our friends the worms. Some think the absence of worms is the cause of some inflammatory bowel diseases (ulcerative colitics especially). So if worms would make their hosts careless about hygeine, and probably careless about many things, would removing our parasitic worms give rise to obsessive-compulsive disorder? Does being wormless make some people unusually rigid and puritanical? Does having worms promote careless behavior?