After a woman suffers having cysts surgically removed from her right breast, things get even worse when surgical sponges are accidentally left inside of her.

A dream vacation to South America becomes a nightmare when a man's face begins to be eaten away by a parasite.

Tara keeps feeling stabbing pains in her scalp, so she investigates the Internet for answers. What she finds is almost unbelievable - botflies. She decides to cut open her scalp.

Boil-like legions lead to a diagnosis of lung cancer, just in time for Christmas. But during surgery, doctors are surprised to find a different sort of infection.

Found in contaminated food and water, Entamoeba histolytica is a parasite that feeds on living cells in the human gut.

After eating some raw sushi, a woman begins a fight for her life as a mass containing parasitic worms creates a blockage in her colon. The woman has Anisakiasis, a disease caused by Anisakis worms.

A disease begins eating a boy's face from the inside, forcing doctors to begin removing the infected flesh to save his life.

A happily married couple's trip to New York becomes a nightmare when they learn that they have been infected with the Bubonic Plague, not only putting their lives in danger but anyone who comes into contact with them.

Leishmaniasis kills skin cells in mass numbers, causing prominent skin sores. In extreme cases, it attacks the face itself, leaving the victim disfigured.

The Leishmania parsite feeds directly on the vital organs from the inside-out. It's spread through infected sand flies.

Acanthamoeba is a voracious parasite that enters the body through the skin or the nose, then devours brain cells.

While swimming with a friend a man has a seizure and collapses. Shortly after, he finds out that a pork tapeworm has been slowly eating away at his brain!

Even dead, the larvae of parasitic roundworms can cause river blindness, or Onchocerciasis. These parasites are transmitted through the saliva of blackflies.

Burrowing through the skin and internal organs, gnathostoma worms can eventually cause paralysis and death.

The pork tapeworm is a particularly vicious parasite because it can end up in the most important organ in the human body: the brain.

A fitness fanatic cannot understand why he is too fatigued to work out until he learns an infection in his colon has created a tear, causing e-coli to spread through his body.

Mark Johnstone is having a very unusual sensation near his scrotum. What could it be?

After being diagnosed with multiple different diseases, this patient’s symptoms still won’t get better.

A man contracts something while in Belize, which turns out to be Cutaneous Leishmaniasis.

After Lauren is diagnosed with encephalitis, doctors finally discover the cause: a teratoma, or parasitic twin, on her ovary.

A button battery has burned a hole the size of a quarter in this patient’s nose.

Mark had been experiencing a tingling sensation that turned into a stabbing pain. What he thought were cramps suddenly escalated to a much more serious condition.

Stephanie noticed her 4-year-old son, Alex, came home with less energy than usual. But what seemed like the result of a long day at school quickly turned into a race to the emergency room.

When a high school football star begins to experience odd symptoms, his parents take him to the hospital.

Doctors have to act fast when an apparent infection is spreading fast on one woman's arm. When they discover it's the work of a vicious type of flesh-eating bacteria, the clock is ticking to save her.

A journalist just back from West Africa is experiencing night sweats and fever-induced nightmares among other terrifying symptoms. WHAT could he have picked up on his travels abroad?

When Rich, a journalist just back from West Africa, is feeling so ill he needs to race to the hospital, doctors soon learn it's a parasite called 'Entamoeba histolytiche,' the world's deadliest parasite after Malaria.

When an EMS' own son starts having seizures, a nightmare begins for their entire family. The eventual diagnosis is heartbreaking and doctors are not hopeful.

SNEAK PEEK: When one woman is convinced she has a worm in her eyeball - yet her doctor is not - she decides to take matters into her own hands. Literally. With a pair of tweezers. *shudder*

Medical sponges left in your body after surgery can be deadly. Each year as many as 6,000 patients have medical equipment left in their body after surgery. Up to 35% of those with sponges left in their body will die.

Well, hopefully you won't experience the kind of horrific discovery one woman made when doctors found a parasite living in her eyeball.

When a doctor discovers a worm in a woman's eyeball, they immediately perform surgery to remove it. Everyone's SHOCKED when they extract a 7- to 8-inch-long worm.