EPISODE 6 of 6: Hijackers

Nature is a war zone and parasites are the ultimate fighters. They are hungry, they are ruthless and they don't play by the rules. Parasites have evolved countless ways of hijacking their hosts' bodies: some steal food from inside the gut, others lurk in the blood sapping their host's nutrients and some even target their host's brain. These are some of the most horrific cases of parasitic infection in the United States. In Virginia a vicious creature is on the rampage, its next victim is an innocent child. In Michigan a brutal killer has invaded a traveler's blood, and a summer's day at a Florida lake turns into a nightmare when a ruthless monster attacks a young boy's brain.

EPISODE 5 of 6: Living With the Enemy

Across the planet, a battle is raging, between parasites and their hosts. There is hardly an organism on this planet that doesn't have parasites that are trying to get at it. Some parasites destroy their hosts with terrifying speed, while others have a more cunning strategy: they keep their host alive for as long as possible. They lurk inside the body and steal their host's nutrients. Some of these parasites are almost impossible to kill. They can evade the immune systems. They can hide in the darkest recesses of the body, and they can survive the most powerful drugs. Once they strike, their victims are condemned to a life sentence of living with the enemy inside them. In Virginia a young woman is attacked by an invincible brain-eating monster that threatens to take her life. A Midwestern farmer does battle with a beast that cannot be killed and a New Yorker is infected with the deadliest parasite on the planet. Three parasites that are almost impossible to destroy; three victims, fighting for their lives. If doctors cannot cure them their only hope of survival is by living with the enemy inside them.

EPISODE 4 of 6: Masters of Disguise

Parasites are ruthless, single-minded and above all devious. To become the most prolific life forms in the world takes a degree of cunning that others can only marvel at. Meet the most deceptive parasites on the planet, the "Masters of Disguise." Teenager Mallorie Greiner has Acanthamoeba keratitis, a parasite that's intent on eating her cornea. Doctors are bewildered at first because her symptoms look just like herpes. Runner Rick DiMichele is struck down with a debilitating disease. Initially, doctors think it's cancer, then malaria; eventually, they discover he has a tick-borne disease called Babesiosis. And not until he's staring death in the face do Mohammed Meah's doctors find the real cause of his problem: a parasitic worm called Strongyloides that's been lurking undetected in his small intestine and living off the steroids he was taking to combat his colitis.

EPISODE 3 of 6: Sex Maniacs

Perfecting the art of reproduction have made parasites the most successful life form on the planet. There are some who are violent, manipulative and have taken sex to the extreme. These parasites are sex maniacs. A New Jersey woman finds her apartment infested with one of the most ubiquitous parasites on earth — bed bugs. Part of the reason for their success is the males' aggressive approach to sex, a method known as "traumatic insemination." A cyclist from Colorado discovers that the insect bites on his head are from botflies. In Oklahoma, a chemical sprayer's cough turns out to be the result of parasitic worms that multiply in the human lung.