Space & Innovation

Parasite Infection Linked to Road Rage

People who often fly off the handle at the slightest provocation may be infected with a parasite that may alter human behavior.

People who display frequent bouts of extreme, impulsive anger, such as road rage, are more than twice as likely to be infected with a common parasite than are individuals who do not exhibit such explosive behavior, according to a new study.

The findings, reported in the Journal of Clinical Psychiatry, suggest that the parasitic infection toxoplasmosis could lead to increased aggressiveness and associated mental illness in some people.

People who repeatedly fly off the handle with little provocation and who overreact to stress are often diagnosed with a condition known as intermittent explosive disorder.

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"Our work suggests that latent infection with the Toxoplasma gondii parasite may change brain chemistry in a fashion that increases the risk of aggressive behavior," senior author Emil Coccaro of the University of Chicago said in a press release.

"However, we do not know if this relationship is causal, and not everyone that tests positive for toxoplasmosis will have aggression issues," Coccaro added, saying that additional studies are needed.

Nevertheless, the researchers did find - via blood tests - that individuals diagnosed with intermittent explosive disorder were more than twice as likely to test positive for toxoplasmosis exposure compared to healthy people with no such prior diagnosis. The study involved 358 adult subjects.

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The researchers also evaluated the test subjects' levels of anger and aggression, and found that toxoplasmosis-positive individuals scored significantly higher than did the other participants.

It is believed that around 30 percent of all humans carry the Toxoplasma gondii parasite, but most show no symptoms at all. The parasite seems to be similar to prevalent pathogens like staphylococcal bacteria, in that it is very common and does very minor, if any, damage to most people. When the immune system weakens or conditions somehow otherwise become more favorable for the pathogens, they can strengthen in numbers and pose significant health threats.

Prior research has shown that the Toxoplasma gondii parasite can break through the blood-brain barrier and may then reside in brain tissue. Infection with the parasite has been linked to several psychiatric diseases, including schizophrenia, bipolar disorder and suicidal behavior.

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Transmission can occur through many different ways, such as drinking contaminated water, eating undercooked meat (especially pork, lamb, or venison), or accidentally swallowing the parasite through contact with cat feces and/or dirt. It can also be transmitted through an organ transplant or a transfusion, although this is rare.

"We don't yet understand the mechanisms involved–it could be an increased inflammatory response, direct brain modulation by the parasite, or even reverse causation where aggressive individuals tend to have more cats or eat more undercooked meat," co-author Royce Lee of the University of Chicago said. "Our study signals the need for more research and more evidence in humans."

A scanning electron micrograph of the protozoan parasite Toxoplasma gondii from a tissue cyst in the brain of an infected mouse.

Insects and other creepy crawlies may be tiny, but their lineages are mighty, finds a new study that determined the common ancestor of mites and insects existed about 570 million years ago. The study, published in the latest issue of the journal Science, presents an evolutionary timeline that settles many longstanding uncertainties about insects and related species. It found that true insects first emerged about 479 million years ago, long before dinosaurs first walked the Earth. Co-author Karl Kjer, a Rutgers entomologist, explained that mites are arthropods, a group that's distantly related to insects. Spiders and crustaceans are also arthropods.

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Spiders such as the huntsman spider can, like mites, trace their lineages back to about 570 million years ago, according to the new study. The researchers believe that the common ancestor of mites, spiders and insects was a water-dweller.

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Millipedes, such as the one shown here, as well as centipedes are known as myriapods. The most recent common ancestor of myriapods and crustaceans lived about 550 million years ago. Again, this "mother of many bugs" would have been a marine dweller. Kjer explained, "You can't really expect anything to live on land without plants, and plants and insects colonized land at about the same time, around 480 million years ago. So any date before that is a sea creature." Moving forward in time, the most common ancestor of millipedes and centipedes existed a little over 400 million years ago. The leggy body plan has proven to be extremely successful.

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"This is an early insect that evolved before insects had wings," Kjer said. Its ancestry goes back about 420 million years. The common ancestor of silverfish living today first emerged about 250 million years ago. Dinosaurs and the earliest mammals likely would have then seen silverfish very similar to the ones that are alive now.

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Dragonflies and damselflies have family histories that go back about 406 million years. Kjer said that such insects looked differently then, however. "For example," he said, "they had visible antennae." Their distant ancestors were among the first animals on earth to fly.

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"Parasitic lice are interesting, because they probably needed either feathers or fur," Kjer said. As a result, they are the relative newbies to this list. Nonetheless, the researchers believe it is possible that ancestors of today's lice were around 120 million years ago, possibly living off of dinosaurs and other creatures then.

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Crickets, katydids and grasshoppers had a common ancestor that lived just over 200 million years ago, and a stem lineage that goes back even further to 248 million years ago. A trivia question might be: Which came first, these insects or grass? The insects predate the grass that they now often thrive in.

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Dinosaur Era fossils sometimes include what researchers call "roachoids," or wing impressions that were made by ancestors to today's roaches, mantids (like the praying mantis) and termites. "Some cockroaches are actually more closely related to termites than they are to other cockroaches," Kjer said, explaining that this makes tracing back their lineages somewhat confusing. He and his colleagues determined that the stem lineage goes back about 230 million years, while the earliest actual cockroach first emerged around 170 million years ago.

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Termites and cockroaches have a tightly interwoven family history. Termites similar to the ones we know today were around 138 million years ago. Now we often think of termites as pests, but they are good eats for many different animals, which back in the day would have included our primate ancestors.

Flies like houseflies that often buzz around homes belong to the order Diptera, which has a family tree that goes back 243 million years ago. The most recent common ancestor for modern flies lived about 158 million years ago, according to the study. There is little doubt that the earliest humans, and their primate predecessors, had to contend with pesky flies and all of the other insects mentioned on this list. All of these organisms are extremely hardy. The researchers determined that, in the history of our planet, there has only been one mass extinction event that had much impact on insects. It occurred 252 million years ago (the Permian mass extinction), and even it set the stage for the emergence of flies, cockroaches, termites and numerous other creepy crawlies.

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