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Monday, December 2, 2013

On 5:29 AM by Zufar M Ihsan in ,    No comments

"The germ seems to especially like infesting the brain, parasites hijacking the mind"

We have an innate fear for snakes or spiders as have rats for cats. 

So much that cat urine triggers fear response in rats that have never encountered a feline even by generations. 

But after being infected with the brain parasite Toxoplasma gondii, however, rats turned attracted to cat urine, raising the chance to be preyed upon. 

But a new research revealed the amazingly mechanism by which the parasite, which also infects over 50 % of the world's human population, operates with almost surgical precision, not affecting other behaviors. 

"This discovery could shed light "on how fear is generated in the first place" and how people can potentially better manage phobias," said researcher Ajai Vyas, a Stanford University neuroscientist.

Toxoplasma's primary hosts are the felines, the only hosts in which it reproduces sexually, but this protozoan infects a large array of mammals, including humans, with about 50 million infected people in the US. 

Some scientists say the parasite has affected human behavior enough to change entire cultures. 

"The germ seems to especially like infesting the brain, parasites hijacking the mind," Vyas said.

In humans this disease is rarely deadly, but in pregnant women, if they get infected during pregnancy, can provoke abortion and the infection can be risky for infants and persons with depressed immune systems. 

Some connect Toxoplasma to schizophrenia and even neuroticism. 

The parasite could change the brains of rats to turn them into easier preys for cats, so they can jump into felines to start their sex life. 

Vyas' team found that infected rats turn mildly attracted to bobcat urine, but they remained fearful of open spaces as uninfected rats and kept their fear response to sound cues predicting mild electrical shocks. 

Rats are prudent enough when it comes to touch food that smells unfamiliar. 

Infected rats, like the normal rats, rejected food smelling like coriander.

"One would thus assume that if something messes up with fear to cat pee, it will also mess up a variety of related behaviors. We do not see that. Toxoplasma affects fear to cat odors with almost surgical precision. We show that parasites are a little more likely to be found in amygdala [a region of the brain] than in other brain areas," Vyas said. 

"This is important because the amygdala is involved in a variety of fear-related behaviors."

Other potential targets of the parasite could be the stress hormone corticosterone and the brain chemical dopamine. 

Scientists will test if infected rats turn less afraid of cat images or scents of various rat predators.

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On 5:25 AM by Zufar M Ihsan in ,    No comments

-Parasites can experience an extremely rapid evolution that turns them helpful

We know that parasites are the bad guys that trigger diseases. Some are lethal, like malaria, others just decrease fitness (like gut worms). Those attacking the sexual apparatus affect fertility. Wolbachia is a bacterium encountered in over 20 % of all insects and known to decrease female fertility. 

But a new research found that parasites can experience an extremely rapid evolution that turns them helpful, due to an opposite effect of boosting host fertility, a process meant to spread further the parasites themselves. It's a type of example showing how parasites can turn into symbionts, the way mitochondria, involved in cell's oxygen respiration, turned from an infectious bacterium into a crucial organelle. 

"It may be that the Wolbachia in this case is well on the way to having a relationship that will eventually develop into a dependency by the host on the Wolbachia for survival," said evolutionary biologist Andrew Weeks at the University of Melbourne in Australia. 

Wolbachia already parasitizes a human parasite worm, which cannot reproduce without these bacteria; this is also the situation of certain wasps. The insects get Wolbachia bacteria from their mothers, but usually the bacteria induce a wide array of reproductive impairments, like turning males to females, parthenogenesis (virgin females lay eggs), higher female promiscuity and male sexual exhaustion, lowered female fertility (eggs number). But the bacteria would rather necessitate higher number of host offspring to flourish themselves. 

"We had a very thorough theoretical analysis which suggested that this could and should evolve, but we had no idea of the timeframe that this might take," said Weeks. 

His team investigated the populations of the Californian fruit fly Drosophila simulans. 
Wolbachia was detected in this species 20 years ago and have monitored the disease's spread, which occurred over 400 miles (640 km) from south to north. In the lab the bacteria decrease female fertility by 15 to 20 %. But now, the parasite was found to cause an average 10 % increase in fertility in the lab. 

By now, researchers can just guess that the parasites could deliver to their hosts some nutritional benefits. The researchers were shocked by the rhythm of this evolution, thought to take thousands to millions of years and not in just two decades, "although it is becoming clearer that evolution does work on such short time scales," Weeks said. 

"The fact that Wolbachia can alter itself so quickly might also help explain why the germs have such a diversity of effects on their hosts," he explained.

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