A 2-year-old girl experiences severe pain, trouble breathing, and vomiting from a bark scorpion sting; a neuroscientist experiences multi-organ failure and nearly dies from a leptospirosis infection that he caught while swimming in Hawaii; a 20-year-old woman suffers from severe vomiting, extreme headaches, twitching and a strange crawling sensation in her head that turns out to be caused by Balamuthia mandrillaris and dies from it.

A young mother expecting her second child suddenly comes down with a stuffy nose and itchy throat. They appear to be typical flu symptoms, but she still feels feverish and soon starts coughing. Her breathing deteriorates to the point where she cant' breathe on her own anymore. It turns out that the young woman has developed an Acinetobacter infection. An energetic college student has been healthy, until she suddenly feels like she can't get enough oxygen and starts wheezing. She develops bouts of coughing so bad that she even coughs up worms. The student learns that she has been infected by the Ascaris worm the whole time. A teenage girl living in the countryside suddenly gets headaches. At first, it appears to be from stress, but she soon becomes irritable and develops triple vision. Worse, she even collapses and experiences a seizure. Only when it's too late that it becomes clear that the teenager has had rabies.

A man suddenly grows a pimple that seems minor at first, but eventually oozes and makes his face swollen. A young man that works at a homeless shelter suddenly starts to feel a sharp pain in his back. At first is seems like a simple back injury, but it eventually gets so sharp it spreads to arms and legs. A school-aged boy starts to get a headache after a visit to a friend's house. It doesn't seem too bad at first, but he eventually develops a fever and lays unconscious. It later turns out he is suffering from a condition called Valley Fever.

A little girl's health begins to deteriorate when she suddenly comes down with a fever. She then develops reddish spots on her body, stops breathing on her own, and even suffers kidney and liver failure. A spinal tap reveals that the little girl has meningococcal disease. Unfortunately, the disease causes too much damage that the doctors have to amputate her left arm. A home contractor has been relatively healthy, until he suddenly begins to gain weight in his abdominal area, which turns out to be caused by a large tumor. After removal of the tumor, the man feels excruciating pain that spreads from his abdomen to his lower back and chest. Initially, it appears to be part of his recovery process, but an x-ray shows that a retractor has been left in his body after the surgery. 7-year old Kyle Lewis's life turns into a living nightmare when he starts complaining of headaches, and starts vomiting.

A California teenager nearly suffocates from hantavirus pulmonary syndrome; a Hawaiian personal trainer suffers years of excruciating neuropathic pain from ciguatera poisoning caused by Gambierdiscus toxicus toxins; a Michigan health worker nearly dies from babesiosis.

A teenage boy starts complaining of nasal pain and fever after a swim in the lake. It eventually turns out that he has been infected by a rare but flesh-eating bacteria called Chromobacterium. A young actress starts to get mastitis while breastfeeding her baby. A teenage college student gets infected by a fungus called Blastomyces.

A young aspiring artist suddenly comes down with flu-like symptoms and a swollen face. To make matters worse, his eyes are yellow, he has trouble breathing, and one of his eyes protrude strangely. It turns out that he has Lemierre's syndrome. An active girl's life is put on hold when she starts feeling fatigue and out of breath. Later, she also starts experiencing extreme joint pain, and she gets diagnosed with Lyme's disease. However, further testing shows that the girl has Babesiosis, in addition to chronic Lyme's disease. An active middle-aged woman becomes concerned when she suddenly feels lumps in her chest. After getting them removed, she then starts experiencing bleeding from her right breast. After getting that taken care of, though, she feels a growing lump in her right breast, which turns out to be two surgical sponges.

A toddler starts worrying her parents when she loses her appetite for the foods she normally eats, but starts craving salt and even cat food. After developing a rash, her parents find out that she has been infected by the Toxocara canis parasite. A middle-aged executive of a company starts to feel pain in his abdomen, not knowing that he has been infected by a bacteria called ESBL E. coli. A married couple start to feel flu-like symptoms, which turns out they've been infected by the plague bacterium. However, the husband's condition is much worse, and even has to get his calves amputated.

A fairly young part-time student starts feeling a throbbing headache, which causes her to have the flu and then meningitis. When she starts hallucinating, it's clear she has a teratoma on her ovary that contains brain cells. An eight-year-old boy starts getting a pain in his stomach and vomiting. It seems that the cause is food poisoning at first, but he soon starts to feel intense pain and swelling in his legs, leading to the discovery that he is suffering from a disease where the flu virus attacks the muscle cells. A self-employed plumber starts to vomit just after starting to work night shifts. He tries to hide the condition, but he soon starts misspelling words.

A 1-year old boy who survived a premature birth starts resisting food, suffering a fever, and coughing up blood. After being rushed to the emergency room, the doctors find out that the cause was the boy swallowing a button battery, which burned a hole in his esophagus. A 21-year-old college student from Canada starts suffering a headache that lasts longer than it should. And soon, she starts getting hallucinations, her head starts twitching, she forgets what her age is, and she even starts having grand mal seizures. While resting in the preparation room for brain surgery, she suddenly gets up and yells, then passes out. Eventually, it is discovered that she has an abscess in her brain that caused an infection caused by Streptococcus milleri, which was caused by getting her tongue pierced. A mother/wife starts to get a headache, and soon she also experiences fever, body aches, dizziness, and foul-smelled urine. Her doctor soon discovers that she has an infection called Dengue fever.

A teenage girl has been enjoying her life of gymnastics and nature, when she suddenly receives a scratch on her hand. The problem seems minor, but the scratch fails to heal and becomes several lesions, which also spread to her eyes. The infection appears to be caused by the MRSA bacteria, but it turns out that it is actually caused by Mycobacterium marinum. A middle-aged man suddenly feels as if he's choking and coughs hard. Initially, it appears to be a case of pneumonia, but after a surgery to fix his spine, he develops stabbing pain in his throat. The coughing returns, and it turns out that he did, indeed, swallow a can tab. A young man suddenly starts complaining of itchiness in his body. He develops a headache, nausea, body aches, and an inability to urinate. Tests show that the man has developed meningitis from rat lungworm disease.

A middle school teacher has been having a healthy pregnancy until suddenly, she starts experiencing abdominal cramps and diarrhea. It initially appears to be a case of the flu, but she soon starts bleeding during episodes. At this point, the young woman appears to have hemorrhoids, which progressively worsen. Tests show that she has been infected by the Cryptosporidium parasite. A retired schoolteacher enjoys his retirement with his wife, when suddenly, he feels a lack of appetite for his favorite food. It doesn't appear to be an issue at first, but his appetite continues to decline, and he starts coughing frequently. His coughing fits worsens to the point where breathing becomes incredibly difficult. It appears to be pneumonia, but it turns out that a pea has been lodged in his lung. A young truck driver has been fairly healthy, when suddenly, discovers a strange speck in his vision. Later, he develops pain, irritation, and blurry vision in his right eye.

A four-year-old Pennsylvania boy gets a runny nose with red discharge, stomach pains, pale skin and extreme pain from accidentally putting a button battery up his nose; an Idaho college student gets a cut on her knee, but then develops agonizing leg pain followed by septic shock from an Aeromonas hydrophila infection; a Pennsylvania woman has strange outbursts and appears to lose her mind from a teratoma growing on her ovary giving her Anti-NMDA receptor encephalitis.

During a family vacation cruise, a Louisiana 2-year-old is restless and drools, which leads to vomiting and kidney and liver failure due to abrin poisoning after accidentally eating a bead from a necklace made of the rosary pea plant on a trip to Jamaica; a California mother-of-two develops a bloated and descended stomach and colon, a body-wide rash, fluid in her abdomen and meningitis from valley fever caused by Coccidioides immitis; a 6-year-old boy suffers a headache, vomiting, blindness and bizarre neurological symptoms which include crossed eyes, that prove fatal. Only when it is too late is it discovered that he was infected with the Balamuthia mandrillaris amoeba.

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 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 Canadian woman suffers a piercing pain in her throat and vomiting from accidentally swallowing a grill bristle (for which she thought was a sprig of rosemary) which got caught in her throat during a barbecue; an Arizona retired firefighter vacationing in Belize develops growing and eventually opening purple bumps on his limbs, lethargy, and hand pain from cutaneous leishmaniasis; a Nebraska 14-year-old girl is struck with swollen lymph nodes in her neck, dizziness, fatigue, blackouts, and body pain from Tularemia.

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.

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.

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 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 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.

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.