Like something out of a horror movie, the idea of a worm crawling across your eye sends chills down your spine, until you realize it’s actually happening. There is a parasitic worm slowly making its way across your eyeball, and you can feel it. In the dead of night, you wake up, in a cold sweat, pitch black and feel a burning sensation on your skin, reaching for the light switch you locate the source of the burning; a festering ulcer on your leg. This is when you realize you have a parasite using your skin as a womb to gestate its young.
Fact is, there are parasites everywhere, in most living matter. The majority of these parasites don’t infect and make hosts of humans, they simply leave us alone and focus on our pets or our livestock instead. There are a select few parasites, however, lurking in the filthy waters, contaminated soil and even in our pets that will gladly make a new home inside our skin, stomachs, eyes and brains, doing everything from merely using us as a vessel for their own means, to outright killing us.
In homage to Halloween and Nick Cutter’s gruesome (and topical) new horror novel The Troop, here are the ten most horrific parasites that infect humans.
10 Dicrocoelium Dendriticum
While Dicrocoelium Dendriticum is a relatively rare parasitic infection in humans, preferring to settle into the stomach of a cow or another animal out for a late night graze, the parasite is known to occasionally infect humans too. Also known as the Lancet Liver Fluke, the parasite's initial host is an ant. In fact, ants seem to be the primary method of infection. There was even a case of a man who contracted Dicrocoelium Dendriticum from bottled water that was contaminated with infected ants. When one contracts the parasite, it settles in the bile ducts typically only causing mild symptoms like bowel disturbances. In more severe cases the Dicrocoelium Dendriticum parasite can become more harmful however, potentially swelling the tissue in the bile ducts, causing enlargement and inflammation of the liver. Even though Dicrocoelium Dendriticum is not common, it may still be wise to check your water bottle next time you take a drink.
9 Giardia Intestinalis
One of the most common parasites in humans, good old Giardia Intestinalis is a truly global, equal opportunity parasite. In fact, Giardia Intestinalis will infect your pet dog, cat or even bird as well. Transmitted by ingesting tiny microbial cysts found in stagnant, unclean water, contaminated food or faeces (yup), Giardia Intestinalis causes a host of symptoms, ranging from the easy enough to deal with bloating, fatigue and loss of appetite to the utterly disgusting; noxious, uncontrollable gas with a smell that may cause you or anyone near you to throw up, rampant diarrhea, which may contain blood or pus and violent vomiting with again, the potential for blood or pus. The good news? In healthy people, the parasite usually takes a hike after a few weeks. The bad news? Giardia Intestinalis is only symptomatic in about 50% of those who have it, meaning it could be dormant in you right now…
8 Tunga Penetrans
Tunga Penetrans is an ectoparasite that goes by many names: Chigoe, the Sand Flea or Jiggers. Regardless of what you want to call this parasite, you do not want to get it. It's a tropical bug that will make your feet its host while it gives birth to its spawn. After the male fleas feed like vampires on a potential host's blood, the female flea digs its way into the bottom of the foot, leaving only her feet and reproductive organs exposed. Soon a black blister forms as the female prepares to lay her eggs. After a few weeks, the eggs hatch and the female dies. Best case scenario, the mother flea either falls out of the host's skin or is scraped out. Worst case scenario, the flea is embedded in the skin which can cause loss of toes and gangrene.
7 Toxoplasma Gondii
Do you love your cat? So does Toxoplasma Gondii. Generally regarded as a feline parasite, humans are actually quite susceptible to becoming infected with Toxoplasma Gondii as well. Up to a third of the world's population either has or has been infected with Toxoplasma Gondii. Though eating undercooked meat, and improperly washed fruit and vegetables are potential risk factors, it's most likely through kitty where your exposure to Toxoplasma Gondii will come. As if containing some sort of self-destruct mechanism, rodents infected with the parasite immediately become drawn to cats, making them easy targets. Cats naturally relish in their new, docile prey and kill said rodents with ease, leaving a nice new corpse as a gift on your doorstep, floor or bed. Beyond being exposed through cleaning up kitty’s well-meaning gift, exposure can also occur while cleaning the litter box. The effects of the parasite on humans vary, though it is well established that pregnant women are especially in danger as the parasite can harm an unborn child. Flu-like symptoms are generally all an infection may produce, but current research has even linked Toxoplasma Gondii to schizophrenia.
6 Dermatobia Hominis
Dermatobia Hominis, or the human Botfly is a tropical parasite that makes an incubator out of human skin before unleashing their offspring into the world. The Botfly ingeniously lays eggs in insects that feed on human blood like ticks and mosquitoes. Once the bloodsuckers find a human meal, not only do they draw blood and leave an itch, they also leave a squirming mass of minute larvae that burrow a hole into a host's skin. Once the larvae are warm and snug inside an arm, neck or thigh, they incubate for up to ten weeks, all the while breathing through a hole the resilient parasite tunnelled through the host's skin. Oh, and the host can feel the larvae moving inside them as well. If the larvae reach maturation, they will eventually exit the body to continue their journey to parasitic adulthood; if not, an infection in the affected area can occur requiring surgery to remove the larvae.
5 Dracunculiasis Medinensis
One of the more famous parasites in the world, Dracunculiasis Medinensis, better known as the Guinea Worm, is caused by drinking unclean water that is infected with fleas containing Guinea Worm larvae. For up to a year the parasite toys with its host producing no symptoms at all while mating inside the stomach until one day a sharp burning pain and the formation of a blister begin a long and perilous battle with “the fiery serpent.” While the blister forms, the host suffers from burning pain, fever, nausea and rashes; the worm is merely migrating. Once the blister pops the female Guinea Worm uses the break in the skin to attempt to release her larvae to repeat the evolution. More than one worm infects many people at a time and the only way to remove the worm is the tedious process of winding it around a stick. If unsuccessful the worm may die in the host's body causing arthritis, abscess and even paralysis.
4 Loa Loa
Ever had something in your eye? Well, unless you’ve had Loa Loa it probably wasn’t a worm; a worm that can be felt crawling inside your eyeball. Infected through the bite of certain types of flies, the Loa Loa nematode will begin migrating through a host’s body from the site of the initial fly bite, leaving painful swelling and ulcers on the skin as it moves from place to place, but it is always heading for the eyes. As horrific as Loa Loa sounds, it is actually easy to cure with either a minor surgery or antibiotics clearing up the infection. If untreated, the worm can live up to 17 years in a human being. At least it only takes an average of 15 minutes for the worm to crawl from one side of the eye to other.
Caused by the different types of Filial Worm, Filariasis is a collection of diseases all with various serious complications. Spread by a bite from either mosquitoes or black flies, the most serious infections a host can acquire from these worms living inside their body include river blindness, which yes, indeed, can cause blindness, and the more well known and sensationalized elephantiasis. Though over 120 million people are suspected to be infected with the Filial Worm that can cause Elephantiasis, the majority are asymptomatic. For the unfortunate, Elephantiasis causes the extreme swelling, thickening of the skin in many infected people, most often in the legs and arms. Pain is also usually present in people with Elephantiasis; coupled with the swelling of their limbs the diseases makes daily life routinely difficult. Arguably an epidemic, Elephantiasis accounts for nearly 40 million disfigurements and incapacitations around the globe.
2 Vandellia Cirrhosa
A vampire fish if ever there was one, the Vandellia Cirrhosa is a tiny catfish that lives in the Amazon. Its method of survival is by attaching itself to larger fish in order to drink their blood. Vandellia Cirrhosa hunts its victims by smell; the fish is attracted to the smell of ammonia and follows the ammonia scent secreted by larger fish to attach its razor sharp spine into its gills to feed. Funny thing is, humans release ammonia too; when we urinate. When out for a leisurely swim in the Amazon with nary an outhouse in site, well… the water is as good a place to go as any, right? If you want a vicious vampire fish swimming into your urethra and painfully attaching itself inside you to drink your blood then yes, have at it. The extremely painful, invasive and humbling surgery required to rid yourself of the vampire fish may make you think twice, and give new meaning to the idea of treating nature as a toilet.
1 Naegleria Fowleri
A relative newcomer on the parasitic scene, Naegleria Fowleri has wasted no time in making itself one of the deadliest parasites on the planet. Literally a brain eating amoeba that causes Primary Amoebic Meningoencephalitis, Naegleria Fowleri lives in water and enters the body through the nose. Within a week living inside the body, it begins to eat at the tissue in the brain, causing symptoms that at first manifest as fever, nausea, vomiting and hallucinations, and quickly lead to seizures, respiratory failures and the mass destruction of brain cells resulting in death. Though Primary Amoebic Meningoencephalitis is rare, and Naegleria Fowleri not overly common, the mortality rate is 95%, and even worse, it has caused deaths in every demographic of people from all across the globe, making it a truly indiscriminate and terrifying parasite.