The Parasite
: ex 1) a Rat Love a Cat and chase a Cat.
ex 2) a snail with Crazy eyes lure a bird to be eaten
1. The life cycle of the parasite Toxoplasma gondii goes like this: Toxoplasma reproduces inside the intestine of a cat, which sheds the parasite in its feces. Rats then ingest the parasite when they consume food or water contaminated with cat feces. The parasite takes up residence in the rat’s brain and, once the rat gets eaten by a cat, it starts the cycle all over again.
Researchers have known for a few years that a rat infected with Toxoplasma loses its natural response to cat urine and no longer fears the smell. And they know that the parasite settles in the rat’s amygdala, the part of the brain that processes fear and emotions.
Now a new study in the journal PLoS ONE adds another bizarre piece to the tale: When male rats infected with Toxoplasma smell cat urine, they have altered activity in the fear part of the brain as well as increased activity in the part of the brain that is responsible for sexual behavior and normally activates after exposure to a female rat.
The double messages of “you smell a cat but he’s not dangerous” and “that cat is a potential mate” lure the rat into the kitty’s deadly territory, just what the parasite needs to reproduce. Scientists still don’t know how the parasite works to alter the brain, though there apparently is a link to production of dopamine, an important neurotransmitter in the systems for decision-making and reward.
How the parasite makes the rat brain do what it needs is a particularly interesting question because rats and cats aren’t the only animals that can become infected with Toxoplasma. There is concern, for example, about the parasite’s effect on sea otters. And grazing livestock can become infected after eating contaminated vegetation.
More worryingly, though, is that one-third of humans test positive for exposure to Toxoplasma (the most common ways for humans to come into contact with the parasite is through kitty litter and by consuming undercooked meat).
Not only can pregnant women pass on the parasite to an unborn child (putting the child at risk of blindness or mental disability) but recent studies have also found an association between the parasitic infection and increased risk of schizophrenia and obsessive compulsive disorder.
2. Have you ever had a pet that seemed just a little bit crazy or odd? Can you be sure that it was in control of its own mind and not something else?
Managing the large collection of earthworms, flatworms and leeches at the museum, the relationships between parasites and their sometimes multiple animal hosts. To ensure that they are eaten or picked up by their desired host some crafty parasites use some very disturbing techniques.
Snails can get infected with the parasite when they eat bird droppings filled with the parasite’s eggs. This parasite is a type of trematode—a parasitic flatworm that infects mollusks and vertebrates. Inside the snail, the parasite grows and then tunnels into the eye stalks of the animal. Here it pumps embryos into fat, throbbing brood sacs it builds in the snail’s eyestalks, turning the appendages into bright green-banded, pulsating beacons that look like caterpillars.
While these colorful pulsating eye stalks may be attractive to birds, they still need to be able to find the snail to eat it. The parasite has evolved to help move its host out of the darkness, by influencing the snail’s tiny brain to reduce its natural aversion to daylight.
Once a hungry bird finds and eats the infected snail, the parasite finds itself in an optimal host for reproduction. Even if the snail manages to survive, it may be infected with more parasites, meaning that another trematode can emerge in its other eye stalk, beginning the process all over again!