These killers lie dormant, waiting for the right time to strike. Eleven-month-old Garrett Richardson ingests the eggs of a worm, and within days the creature travels to his brain and goes about feeding on its tissue. A Vietnam veteran survived the enemy attacks on the front lines, but back at home — unknown to him — a killer is stealthily working its way through his body, laying waste to his organs and lymph system. By the time the medical evidence reveals the source many years later, the killer is long gone. And John Figge and many of his family members live for six years with unwanted hitchhikers from Africa traveling around in their bodies. Only when one of these creatures begins to attack John's brain are they discovered. Can the family get rid of these deadly parasites before the damage is critical? These are all stealthy predators that get inside their hosts, yet work on very different timetables. Dangerous and often hard to detect, this is the story of the war on sleeper cell parasites.

Across the United States, doctors and scientists are fighting a war against some of nature's deadliest creatures — parasites. It is a race against time when a mysterious organism strikes a mid-western city causing the worst parasitic outbreak in the history of the United States. Before the culprit is contained, 100 innocent people have died. In Chicago, doctors must track down a hidden killer that attacks a group of students on a spring break trip, and a flesh-eating monster is on the loose in a Texas community.

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.

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.

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.

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.

A fit and active dance instructor is suddenly stopped in her tracks by unbearable abdominal pain and vomiting, and a mysterious mass in her colon is revealed to have decaying worms. A middle-aged banker gets seizures from a parasite he picked up from traveling to his home country, Haiti. A scientist finds worms from Africa that threaten to damage his sight living in his skin and eyes.

A schoolteacher deals with an amoeba that eats at his liver and causes him high fever, abdominal pain, sweating, and chills. A young dancer gets worms from eating contaminated pork in her muscle tissue, causing her to get hives all over her body and her limbs to become stiff and painful. A retiree gets scabies from mites he got from staying in the hospital in the past.

A nine-year-old hockey player comes down with encephalitis from the Acanthamoeba, which causes him to lose his concentration and balance, almost killing him. A computer programmer gets severe malaria from the Plasmodium parasite that makes him lose control of his mind and post-malarial neurological symptoms two weeks after an apparent recovery. A marathon runner deals with Leishmaniasis, which causes his spleen to swell.

The Crytosporidium parasite infects a little girl, causing her severe vomiting and diarrhea. A microscopic amoeba kills a firefighter with an autoimmune disorder by causing him meningitis. A rare, vicious tapeworm detaches the retina in a teenaged girl, destroying vision in her left eye.

A cat scratch leads to a horrifying result for a veterinary volunteer; strange liquid oozes from a college student's arm.

Stories of parasites that reside inside their traveling hosts; an Iraq war veteran pulls a foot-long worm from his body.

Daily stomach cramps reveal some of the most common parasites in nature.

A man tries hookworms to cure his allergies; a bloodsuckers gets into a writer's nose.

A middle-aged man who has been caring for his ailing mother gets Babesiosis from walking barefoot to the mailbox. Since he lost his spleen from cancer, he gets severe diarrhea, in addition to fever, fatigue, and night sweats. An active, busy middle-aged woman experiences stomach cramps, explosive diarrhea, lightheadedness, and blurred vision from the Toxocara parasite, which she probably got from contaminated food. An older mother of five children deals with nausea, loss of appetite, muscle spasms, and vomiting from the Strongyloides worm, which she may have picked up from being in contact with infected soil. Because of steroids she took for her breathing problems, her body became more vulnerable to the parasite.

A seven-year-old girl suffers from seizures from a pork tapeworm after being adopted at the age of three from Nepal. A forty-five-year-old machinist deals with blurry and double vision, leaving him legally blind in his left eye, from a raccoon roundworm that he picked up from his turkey hunting. A forty-one-year-old anaethesiologists, along with twenty-eight other anaethesiologists from two different counties, suffer from stomach cramps and crippling diarrhea from the Cyclospora parasite after eating raspberries infected with human feces.

A 7-year-old girl contracts the bubonic plague and suffers a 107 fever, vomiting, painful buboes, and seizures; a yoga instructor finds out that what she thought was influenza is actually necrotizing fasciitis caused by Streptococcus intermedius and Peptostreptococcus; a state wrestling champion contracts angiostrongyliasis.

A teenage ballerina suffers from painful migraines and muscle failures; a young missionary's skin crawls when he uncovers an unholy revelation.

A mother suffers with abdominal pain and nausea for four years until the true cause of her condition is discovered; a 2-year-old girl develops a mysterious lump on her neck.

A small-town boy's summer fun is cut short by a life-threatening Neisseria meningitidis infection. An oil rig worker and daredevil experiences sensitivity to light, muscle pain and horrifying hallucinations from Trichinella spiralis after eating bear meat. A former beauty queen suffers an extreme case of asthma for one year from a nasal packing contaminated with Aspergillus niger fungi.

A Peace Corps volunteer traveling to Burkina Faso suddenly suffers from excruciating bouts of nausea and diarrhea from Entamoeba histolytica, and must find medical help before it is too late; a young woman almost suffocates due to hantavirus pulmonary syndrome she got from breathing dust while cleaning up contaminated with mouse feces; an 18-month-old boy gets infected with Baylisascaris procyonis worms which cause his brain to swell and have neurological damage, eye fluttering, and unresponsiveness.

A newborn baby develops hydrocephalus from a parasitic disease called toxoplasmosis, which was contracted from his mother; an 11-year-old boy suffers headaches, vomiting, seizures, and starts speaking gibberish from being infected with the eastern equine encephalitis virus; a teenager living on a farm suffers a severe cough and fever from Paragonimus kellicotti.

A Canadian 13-month-old toddler gets breathing difficulties and mild vomiting from accidentally swallowing a button battery (for what the doctors originally thought was a coin); a college freshwoman gets migraines, nausea, on-and-off blindness, hallucination-like partial seizures, repulsive taste and two lesions in her brain from infection with Taenia solium; in 2008, a 6-year-old girl gets a headache, a rash, high fevers, and dies from Rocky Mountain spotted fever.

A 4-year-old boy literally drowns in his own mucus, being a victim of an outbreak of the Enterovirus D68 virus; a 7-year old scrapes his knee on a rock at the beach, but when his father puts a liquid bandage on it, it causes it to swell the size of an orange – then, his mother squeezes the wound and finds a sea snail (Littorina scutulata) inside; a college student experiences loss of appetite, fatigue, fever, jaundice, and repetitive nightmares that turn into a reality from getting infected with malaria caused by the Plasmodium falciparum parasite after returning from a trip to Ghana.

An athlete gets headaches, stomach pains, breathing difficulties, and a liver mass from Entamoeba histolytica from a trip to Nicaragua; a teenager develops a leg welt and then gets fatigue and red spots on his body over the course of several years. When the spots open, the doctors discover he has leprosy from coming into contact with an infected nine-banded armadillo (Dasypus novemcinctus). A woman suffers severe headaches, nausea, vomiting, and seizures from Exserohilum rostratum fungi invading her brain.