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.

The second episode of the series to be Christmas-themed – a saleswoman gets a stabbing headaches and a constant burning sensation in her right eye from a Dirofilaria immitis worm that is in her eye; a store manager gets stomach pains, fatigue, nausea, vomiting and even a constantly moving stomach from a surgical sponge being left and forming a hole in his colon; a grandmother working in the forest service gets abdomen pains, fatigue, and pneumonia from Strongyloides stercoralis worms invading her intestines.

A war veteran suffers fatigue, high fevers, night sweats, strange rashes, bloody urine and jaundice from babesiosis; a 15-month-old baby girl suffers fever, dry mouth, vomiting and bloody diarrhea from E. coli O157:H7, whom she got from drinking raw milk; a biologist suffers extreme fatigue, back pains, anxiety, and vertigo from Aspergillus-contaminated breast implants

A special episode with three cases that happened during the holidays – A newlywed woman gets a constant pain in her scalp from botfly larvae; a Virginia man gets sharp back pains and develops a hole in his heart from Streptococcus viridans; a female business consultant and part-time photographer gets valley fever.

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 teenager gets coughing, shoulder pains, dizziness, and nausea from Cryptococcus gattii fungi invading her lungs; a saleswoman gets extreme pain in her breast from a brown recluse spider (Loxosceles reclusa) bite; a religious youth organizer gets swelling of multiple parts of the body over the course of three years from the Loa loa worm.

A 23-year-old athlete/construction worker suffers multiple grand mal seizures and high fevers from eastern equine encephalitis; a hard-edged tough guy suffers severe stomach pains and loss of appetite from accidentally swallowing a grill bristle; a 17-year-old cheerleader who recently got her driver's license suffers a swollen, itchy eye and excruciating eye pains from Acanthamoeba keratitis she got from contact lenses.

During a fishing vacation, a soccer coach goes into septic shock from Vibrio vulnificus necrotizing fasciitis after banging his ankle on a barnacle; a 7-year-old girl gets facial tics, bouts of anxiety, and turns suicidal after a streptococcal brain infection; a makeup artist gets severe stomach cramps and watery diarrhea from Giardia lamblia.

A contractor gets hit in the head with a tool, and later starts getting a pounding headache, dizziness, spotty vision, and nausea from having a nail punctured into his brain; a football player in college gets extreme headaches, a stuffy nose, and blurred vision from Aspergillus fungi entering his brain; in 2012, an 8-year-old boy suffers constant vomiting, fatigue, seizures, and eventually dies from amoebic meningitis after being infected with Naegleria fowleri.

A 6-year-old boy suffers a nasty cough, fever, and vomiting from valley fever; a newlywed husband becomes paralyzed from the waist down due to the West Nile virus; an international journalist suffers extreme stomach cramps, night sweats, chills, nausea, and fever from Entamoeba histolytica.

A teenage boy develops stomach pains, starts vomiting blood and fecal matter, and has nausea from accidentally swallowing a bristle from a grill brush, which got lodged in his intestines; in 2011, a 16-year-old girl who swam in a Florida river experiences a headache, fever, vomiting, mental confusion, unusual behavior and dies from amoebic meningitis; an industrial painter has difficulties breathing and walking from Blastomyces dermatitidis.

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.

The show's fourth Christmas-themed episode, and the second episode of the series that looks back at three past cases, including: a baby whose brain was infected with Cytomegalovirus in utero (All I Got For Christmas Is Brain Surgery); a woman whose eye is infected with the worm Dirofilaria immitis (A Holiday in the Hospital); and a man who has a surgical sponge left in his colon (also A Holiday in the Hospital).

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 newlywed woman gets extreme headaches, memory problems, sinus pressure, and painful rashes, while her husband gets endless nosebleeds, breathing problems, and brain fog, both from Aspergillus; a councilman loses his spleen to visceral leishmaniasis; a 6-year-old gets a fever, red spots, a swollen mouth, loss of appetite, leg weakness, and breathing difficulties from rat bite fever caused by Streptobacillus moniliformis.

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.

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.

An 11-month-old boy experiences wheezing and vomiting after swallowing a button battery; a landscaper becomes infected with Paragonimus kellicotti; a female boxer gets a severe headache, a 105 fever, and impaired vision from cat scratch fever caused by Bartonella henselae.

A 29-year-old man gets tooth pain and almost dies of necrotizing fasciitis caused by the bacteria Streptococcus intermedius and Peptostreptococcus; a female financial adviser gets fatigue, joint pain, mental confusion, hair loss, and muscle weakness for over three years from Lyme disease; a 7-year-old boy gets a loss of appetite, abdominal pains, a fever, diarrhea, constant vomiting, and weight loss from Cryptosporidium.

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 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.

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.

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

A man coughs up blood; a newlywed husband is struck down by a rare disease; and a father struggles with abdominal pain.

A man falls comatose; a college student has a sore throat; and a young woman's symptoms confound experts.

An Idaho 17-year-old football player is struck with a sore throat, breathing difficulties/lung pain, confusion, kidney failure and even tackles his own mother from Group A streptococcus bacteria infecting his blood; an Illinois mother of three kids develops an itchy eye which leads to face numbness, loss of depth perception and blindness as the result of an Acanthamoeba keratitis infection; a dockmaster develops crippling pain in his hand from a Mycobacterium marinum infection along with pimples on his palm from barnacles growing in his hand.

A teenager develops mysterious blotchy sores; an athlete is hit by a rare infection; and a woman battles strange bouts of vomiting.

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.

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 young boy has a strange condition; a woman's symptoms push her to madness; and a toddler falls into a trance-like state when something begins eating his brain.

An infant falls mysteriously ill; a biology professor becomes an unexpected host; and a family man is brought to the brink.

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 13-year-old boy gets a cut on his leg that nearly leads to amputation when it becomes infected with Staphylococcus aureus, causing necrotizing fasciitis; a couple move into their new home, but over the course of three years, the man suffers a spreading/oozing rash, poor coordination, body aches, breathing difficulties, and weight loss, while his girlfriend suffers memory loss, fatigue, and suicidal depression, both from chronic low grade carbon monoxide poisoning; an 8-year-old girl from Hawaii gets a growing mass in her eye from Toxocara canis.

A new mother is in critical condition; a young boy has an ailment that no antibiotics can cure; and a young man has an invader in his brain.

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.

After a man hits his head, he's left fighting a one-on-a-million medical mystery; a boy's wounded knee becomes home to an uninvited guest; a man unwittingly feeds his own intended killer.

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

A young girl is brought to the hospital with stabbing pains in her scalp; a mother's mysterious symptoms threaten to tear a family apart; a deadly invader turns a relaxing vacation into a nightmare.

A Canadian science-lover and traveler suffers a painful lesion caused by botfly larvae; a video game programmer gets suffers from constant vomiting and coughing. When doctors find a large mass in his chest, it is discovered that he has histoplasmosis, which was contracted from inhaling bat droppings in a cave; a 15-year-old girl gets an extremely sore throat, a headache, nausea, and body pains from Lemierre's syndrome.

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 woman is struck down by a dangerous parasite; an infant falls mysterious ill; and a fungus brings a young man to the brink of death.

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.

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.

This episode looks back at three cases from past episodes: a teenage boy with a grill bristle in his intestines (A Deadly Swim); another teenage boy with leprosy (Help! My Son is a Leper); and a teenage girl whose lungs are afflicted with Cryptococcus gattii fungi (My Body Is Rotting).