Gross, gross, gross, gross, gross.

When a rat lungworm finds itself in a human, it does what it usually does in rats—it heads to the central nervous system and brain. Sometimes the migration of the worms to the central nervous system is asymptomatic or only causes mild transient symptoms. But, sometimes, they cause severe neurological dysfunction. This can start with nonspecific symptoms like headache, light sensitivity, and insomnia and develop into neck stiffness and pain, tingling or burning of the skin, double vision, bowel or bladder difficulties, and seizures. In severe cases, it can cause nerve damage, paralysis, coma, and even death.
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It’s often thought that the worm can’t complete its life cycle in humans and that it ends up idly wandering around the brain for a month or two before it’s eventually killed off by immune responses. However, there has been some evidence of adult worms reaching the human lungs.