86 Disgusting Facts about Human Parasites

By Karin Lehnardt, Senior Writer
Published December 12, 2016
  • Parasites are the most common form of life on Earth. Scientists believe that over 80% of all living things are parasites.[4]
  • Modern parasitologists recognize that they have not found all human parasites. They estimate that hundreds if not thousands of human parasites will be found in the coming years.[3]
  • The most deadly human parasites are protozoa, which are single-celled organisms. Some of these tiny creatures (there are over 80,000) have brought humans more misery and death than anything else in history, including wars and famine. The most well known deadly parasitic protozoa is plasmodium, which causes malaria.[7]
  • Microscopic, single-celled protozoans make up about 90% of all parasitic infections in the U.S.[2]
  • Malaria, which is caused by the parasitic protozoa plasmodium, is the deadliest disease of all time. No disease, including the plague or smallpox, has killed more people. It has also killed more people than all wars, famines, and natural disasters combined.[11]
  • John Matthews of Iowa went to the doctor when his vision became spotty and hazy. He had a parasitic worm in his eye eating away at his retina. Doctors were able to kill the worm with a laser, but not before the parasite did permanent damage to his retina and optic nerve.[3]
  • A roundworm can produce as many as 200,000 eggs in a single day
  • In the United States, at least 70 people, most of them children, are blinded by the parasite (a roundworm) that causes toxocariasis, which is transmitted to humans through infected dog and cat feces.[8]
  • In 2013, an Iowan woman told her doctor she had bought a tapeworm on the Internet and ingested it in an attempt to lose weight. While tapeworms can cause anemia and malnutrition, it can’t absorb enough food to significantly affect weight.[14]
  • The Gnathostoma spinigerum is a helminth, or worm-type parasite. Because humans are accidental rather than direct hosts, the worms can’t reproduce in a human body, so they live out their 10- to 12-year life cycle migrating throughout the body, causing swelling under the skin.[4]
  • Malaria (Italian for “bad air”), which is caused by the plasmodium parasite, kills between 1.5 and 2.7 million people worldwide per year. Additionally, it kills more than 3,000 children under age 5 every day, or one child every 30 seconds, mostly in Africa.[4]
  • It is estimated that over 50 million children in America are infected with worm parasites but only a small number of those are detected and reported.[1]
  • Parasites are separated into three groups: 1) protozoa, which are tiny, one-celled organisms; 2) helminths, or worm parasites, such as tapeworms and pinworms; and 3) arthropods, which aren’t parasites themselves, but these insects and spiders are common hosts of parasitic diseases.[4]
  • Most parasitic infections happen in warm climates, such as Southeast Asia or other tropic or subtropic regions.[3]
  • The top three parasitic infections in the U.S. are 1) trichomoniasis, a sexually transmitted disease caused by the protozoan trichomoniasis vaginalis, with about 7.4 million cases annually; 2) Giardia, a protozoan that causes intestinal problems, with about 2 million infections annually; and 3) cryptosporidium, a protozoan infection with about 300,000 infections per year.[8]
  • There are two kinds of human parasites: endoparasites, which cause infection inside the body, and ectoparasites, which cause infection outside the body on the skin.[4]
  • Humans are hosts to over 300 species of parasitic worms and over 70 species of protozoa.[4]
  • A parasitic infection called Chagas disease has been dubbed the “new AIDS” of the Americas and is caused by a blood-sucking insect. Like AIDS, the illness is difficult to detect and has a long remission period. It spreads through blood transfusions and from mother to child. It enlarges the heart or intestines so much that they can burst—causing sudden death.[12]
  • The long, threadlike worms block the body's lymphatic system, which causes great swelling
  • Elephantiasis is caused by roundworm and infects at least 120 million people worldwide. Worms can grow between 1.5 and 4 inches long and bunch up in vessels by the lymph nodes, creating grossly swollen limbs.[4]
  • The word “leech” comes from the Old English word for physician because bloodletting, often via leeches, was a mainstay of treatment for over 2,000 years. Because barbers often used to act as surgeons, the red stripes on barber poles symbolize this bloodletting.[7]
  • Tourism and globalism have increased the spread of parasites.[4]
  • Trichomoniasis is a parasite that is also an STD. Considered the most common curable STD, over 3.7 million people have the infection in the U.S. but only about 30% develop any symptoms. Common symptoms include itching, burning, redness, or soreness of the genitals. The infection can last for months or years if not treated.[13]
  • There are over 30,000 species of mites and they live almost everywhere. The earliest mite fossil dates to about 400 million years ago.[3]
  • The earliest known human parasite is a lung fluke, and it was found in fossilized feces in northern Chile dating from 5900 B.C. Additionally, ancient Egyptian mummies from as early 2000 B.C. contain tapeworm eggs.[3]
  • Approximately 209 million people around the world are infected with pinworm, or seatworm. More than 30% of children worldwide are infected.[1]
  • The pinworm (a.k.a. seatworm, threadworm) lives mainly in the cecum of the large intestine. A female worm migrates at night onto the perineum where she will lay up to 15,000 eggs. Eggs on the host’s perineum can spread to other people and can infect everyone in the house.[6]
  • Giardia (G. lamblia) is the most common parasite infection in the world and the second most common in the United States after pinworm. It is also known as “Backpacker’s diarrhea” and “beaver fever.”[6]
  • The Guinea worm can grow 2–3 feet inside the human. After it reaches that length, it burrows to the surface of the skin, creates a blister, and then emerges along with hundreds of thousands of larvae. The most effective way to remove it is to pull it out of the body, slowly winding it around a stick for days or even weeks.[11]
  • About one year after the infection, one or more worms emerge from an agonizingly painful blister, often in the lower leg
  • Loa loa, or “eye worm,” is a parasitic worm that lives in human and other mammal eyes. Creepily, a human can feel it moving around in his or her eye and may even seen the worm if its big enough. It can live inside a human for 17 years.[10]
  • Allegedly, the largest human parasite ever extracted from the body of a human being was a 37-foot tapeworm. On September 5, 2001, doctors extracted the monster worm from Sally Mae Wallace’s mouth.[2]
  • When Sanju Bhagat from India went to the doctor complaining of a distended abdomen, shortness of breath, and severe pain, the doctors were shocked to find a partially formed fetus. An absorbed twin, his fetus in fetu,fed off its host until doctors intervened.[4]
  • A person cannot starve a tapeworm, but they may try to eat foods that tapeworms dislike such as garlic and onions. It may be unpleasant, though, to feel and then see, several feet of squirming tapeworms pass from the body. Doctors can also treat tapeworms with drugs. However, if the scolex (head) and neck of the worm are not destroyed, the parasite will regrow itself.[4]
  • Toxoplasmosis is a parasitic disease caused by a protozoan most commonly found in cats. Toxoplasma can cause brain damage to human fetuses and, more recently, it has been linked to schizophrenia, ADD, OCD, and suicide behavior in humans.[9]
  • The vampire fish, or V. cirrhosa or Candiru, can swim up a urine stream into the human victim’s penis, where it shoots out its sharp spine and lodges itself in. Once inside the body, the vampire fish feeds on a human’s blood. Only a very invasive and painful surgery can remove it.[10]
  • A human botfly is a spine-covered larva that burrows into living humans and feeds on their flesh. While its nesting site may look like a mosquito bite, poking from a hardened lump on the skin are two little breathing tubes, which allow the larvae to breathe and remain under the skin while it feeds.[10]
  • Sometimes group hugs aren't all they're cracked up to be
  • Researchers found that 9- and 10-year-old girls are most likely to get head lice because they like to do group hugs.[7]
  • Scabies, or the human itch mite, is transferred by physical contact. The female mite lays her eggs on the skin of a human, causing irritation. The inflammation is exacerbated when the mother begins burying her eggs under the skin, causing intense itching. Other symptoms include soreness and pus-filled nodules.[3]
  • Most humans have follicle mites that live directly on the human body. As many as four mites live head down in a single follicle, gripping the hair with the claws on their legs.[3]
  • Lyme disease, a serious infection carried by ticks, is named from the Connecticut town that reported the first cases, among children, in 1975.[7]
  • Flies have been around for at least 225 million years and they live everywhere except Antarctica. There are about 125,000 species of flies. The earliest flyswatter was found in Egyptian tombs dating from about 2500 B.C. Israelites referred to the devil as “the lord of the flies.”[7]
  • There are over 2,380 flea species worldwide. The oldest fossil flea ever found is about 200 million years old and doesn’t appear to differ from modern fleas. A human-body flea can jump 13 inches, or over 104 times its own body length. In human terms, that would mean a 4-foot-tall child could jump 416 feet, more than the length of a football field.[7]
  • Fleas have parasites of their own, including various mites. A single flea was found carrying 150 mites of the same species, some of which may be harmful to humans. Fleas are also host to tapeworms, protozoa, and bacteria as well as the black plague.[7]
  • There are over 2,600 species of lice.[7]
  • The phrase “nitpicker,” or one who harps on tiny details, is from the word “nit,” or lice eggs.[7]
  • Parasitic body lice may carry a parasite belonging to group of bacteria called Rickettsia, which causes typhus. Next to malaria and the plague, typhus is the greatest killer of people in history. Unless treated with antibiotics, 4 in 10 victims die.[7]
  • An adult tapeworm can live 30 years or more. About 175 million people worldwide have tapeworm infections.[1]
  • Tapeworms have 1,000 to 2,000 body segments, called proglottids, each containing 80,000 to 100,000 eggs
  • In the last six centuries, typhus (caused by the parasite Rickettsia) has killed more soldiers than all weapons combined.[3]
  • In the United States alone, outbreaks of head lice among children account for the loss of 12 to 24 million school days each year.[7]
  • Tapeworms do not have eyes. Rather the indentions on each side of their heads are suction cups used to attach it to a victim’s intestines.[4]
  • Hookworms are the only worms known to have teeth. Its Latin name, Necator americanus, means “American murderer.” It can spend 15 years or more in the intestine, feeding and reproducing.[4]
  • A female hookworm produces 20,000 eggs a day.[3]
  • Hookworms infect more than 1 billion people worldwide, or 1/6 of the human race.[1]
  • People heavily infected with hookworm may have thousands of worms in their intestines. It causes diarrhea, weight loss, breathing difficulty, and heart problems. Children may also suffer mental retardation because of loss of blood and oxygen to the brain.[7]
  • Because parasites dampen the body’s immune system, some doctors have given volunteer hay fever sufferers a drink containing upward of 300 hookworm eggs, which greatly improved hay fever symptoms. Because hookworms become a problem only when they enter the body as larvae through the skin, the eggs passed harmlessly out of the volunteer in the feces.[4]
  • Mosquitoes are the most dangerous animals on Earth
  • The earliest mosquito known to science lived 144 million years ago. Mosquitoes can beat their wings about 1,000 times per second. There are over 2,700 species of mosquitoes throughout the world; about 150 live in the U.S.[7]
  • Ascaris, known as “small intestinal roundworms,” are a type of parasite that multiply fast, grow long, and may emerge from a person’s anus similar to string confetti.[6]
  • Roundworm is transferred by ingestion. The eggs hatch and quickly penetrate the intestinal wall, where they enter the blood stream. From there, the worm enters the lungs, where it is coughed up, swallowed, and returned to the gut. Symptoms include fever, tiredness, allergic rash, vomiting, diarrhea, nerve problems, and wheezing/coughing.[6]
  • While the leeches’ nearest relative, the earthworm, eats decaying plant matter, all 650 species of leeches prey on other creatures.[4]
  • While most animals with jaws have two jaws that form the framework of the mouth, leeches have three jaws holding razor-sharp teeth arranged to make a Y-shaped bite.[4]
  • A leech’s saliva has a numbing chemical so that its victim cannot feel its bite. Its saliva also has a chemical that dilates blood vessels around the wound, allowing more blood to flow. A third chemical, hirudin, prevents blood from clotting. When the leech is full, it drops off—but because of hirudin, the wound can ooze blood for up to 24 hours. Leeches can eat five times their body weight in blood.[4]
  • The flatworm blood fluke can live in the bloodstream of its host for decades and can cause schistosomiasis, or bilharzia. Chronic infection can cause liver damage, kidney failure, infertility, or bladder cancer. In children, it can cause learning problems and poor growth.[4]
  • Tapeworms can survive up to 25 years in humans. They are transmitted through infected food and attach themselves to the host’s intestines with hooks on their “head” or scolex.[4]
  • Onchocerca volvulus is a parasitic worm that causes “river blindness,” the world’s second leading infectious cause of blindness. It can live up to 15 years in the human body and is transmitted by the bite of the black fly. The worms spread throughout the body, and when they die, they cause intense itching and an immune response that can destroy tissue, such as eye tissue.[11]
  • The O. volvulus emerging from the antenna of a black fly
  • Mosquitoes have been and still are responsible for more human deaths than any other creature that has existed. Mosquitoes have their own parasites, which they transmit while feeding, causing such diseases as yellow fever, dengue fever, and encephalitis, or swelling of the brain, and malaria.[7]
  • A vector-borne parasitic disease, “sleeping sickness” is fatal without treatment. Transmitted through the bite of an infected tsetse fly, the parasite multiplies in subcutaneous tissue, blood, and lymph and then passes across the blood-brain barrier to infect the central nervous system. Symptoms include confusion, poor coordination, sleep, and sensory disturbances.[11]
  • The Naegleria fowleri ameba, or the “brain-eating amoeba,” makes its home in people’s brains. Infection causes brain inflammation, extensive destruction of brain tissue, vomiting, stiff neck, hallucinations, and seizures. After the onset of symptoms, the disease progresses rapidly and causes death within 3–7 days.[10]
  • The greatest concern for hookworm infection is blood loss. Because it has an organic anticoagulant, a hookworm can consume about 0.25 mL of host blood per day.[4]
  • Parasitology is the branch of biology that studies parasites.[3]
  • The Meguro Museum of Parasitology in Tokyo, Japan, displays only parasites and has 45,000 specimens. Museum visitors can even have their picture taken with a 30-foot-long tapeworm taken from a man’s intestine.[3]
  • The U.S. National Parasite Collection in Beltsville, Maryland, has over 1 million parasite specimens.[3]
  • The word “parasite” comes from the Greek word parasitos, meaning “beside the food.”[3]
  • In ancient Greece, wealthy people who wanted to appear generous invited poor people to have a meal with them. These guests were called parasitos and earned their food by praising their guests, singing, reciting poetry, and telling stories. By the 1700s, the word meant “freeloader.”[3]
  • The tiny leopard frog can have 12 different parasites, each living in a separate part of its body and none other. A specific Mexican parrot has 30 different types of parasites on its feathers alone.[3]
  • Van Leeuwenhoek was also known as "the Father of Microbiology" and was considered to be the first microbiologist
  • In the 18th century, Dutchman Anton van Leeuwenhoek became the first human to see bacteria, red blood cells, and microscopic parasites. While examining his own feces, for example, he discovered Giardia lamblia, a parasite that lives in water.[4]
  • One square foot of carpet easily holds at least 10,000 dust mites. A mattress may have between 100,000 and 10 million of them.[4]
  • If your pillow is more than 2 years old, 10% of its weight is mite feces and dead mites.[4]
  • Parasites can have their own parasites, and those parasites can have parasites, too. Scientists call parasites of parasites “hyperparasites.”[3]
  • Fungi feed on plant and animal matter, both living and dead. In humans, fungi can cause annoying infections, such as athlete’s foot, jock itch, and ringworm. Ringworm looks like a parasitic worm curled up under the skin’s surface, but it’s really a fungus.[7]
  • Ancient feces show that human ancestors had parasitic worms. Additionally, scientists have found microscopic worm eggs in hundreds of mummies.[7]
  • The first written accounts of diseases possibly caused by parasites come from Egyptian records from around 3000–2500 B.C. Later, Greek physicians, notably Hippocrates, described infections caused by parasites, as did Chinese and Arab physicians.[3]
  • Before the invention of the microscope, early doctors had no idea that tiny parasites were the causes of many diseases.[3]
  • Early in the 1880s, a German researcher Friedrich Küchenmeister fed pig meat containing immature tapeworms to a criminal condemned to death. Weeks later, after the execution, he recovered adult tapeworms from the man’s intestines.[4]
  • For a hookworm infestation lasting 4 years, each adult female hookworm could end up producing as many as 217 million eggs.[4]
  • During the Crusades, 15%–20% of crusaders died of either malnutrition or infectious diseases while on expedition, aided by an abundance of parasites such as tapeworm and hookworm. Parasites competed with the crusaders’ already taxed body for precious nutrients.[5]
  • Approximately 2% of adults and 6%–8% of children in the developing world suffer from Giardia.[1]
  • Tribes in Turkestan used to torture prisoners to death with ticks. They would chain a prisoner to a board in a cell and release swarms of ticks that were raised and kept hungry for that purpose. Slowly, they would drain the prisoner of his blood.[7]
  • Ticks find their hosts by detecting breath, body odors, or by sensing body heat, moisture, and vibrations
  • The schistosomiasis worm is a dangerous parasite that can increase the risk of HIV/AIDS infection. Researchers believe this common worm may be responsible for the high rates of HIV infections in women in Africa because of the worm’s behavior in the female body. When women do laundry in the waterways, the worm makes it way up the vaginal canal and creates small sores inside, which open the way for HIV infection. The parasite infection can be cured with a pill that costs 8 cents.[9]
  • Three Main Types of Parasites[4]
    EctoparasitesLive on the outside of their host, either in or on the skin. Fleas and lice are well known examples of ectoparasites
    EndoparasitesLive within the bodies of their hosts. Tapeworms are the largest endoparasites.
    Temporary parasitesLive apart from their host most of the time, visiting them only to feed. Ticks, leeches, and bedbugs are examples of temporary parasites
    Parasites and Global Annual Deaths[1]
    DiseaseHuman InfectionsAnnual Deaths
    Malaria489 million1-2 million
    All worms4.5 billionN/A
    Ascaris1.0 billion20 thousand
    Hookworms900 million50-60 thousand
    Whipworms750 millionN/A
    Filarial worms657 million20-50+ thousand
    Schistosomes200 million0.5-1.0 million

1 Amin, Omar M. “Parasites.” Parasitology Center Inc. 2010. Accessed: May 19, 2014.

2 Butcher, Nancy. The Strange Case of the Walking Corpse. New York, NY: Penguin Books, 2004.

3 Drisdelle, Rosemary. Parasites: Tales of Humanity’s Most Unwelcome Guests. Oakland, CA: University of California Press, 2011.

4 Dunn, Rob. The Wild Life of Our Bodies. New York, NY: HarperCollins Publishers, 2011.

5 Heitz, David. “Parasites in Crusaders’ Poop Offer Insight into Medieval Famine.” Healthline. June 27, 2013. Accessed: May 19, 2014.

6 Kucik, Corry Jeb et al. “Common Intestinal Parasites.” American Family Physician. March 1, 2014. Accessed: May 19, 2014.

7 Marrin, Albert. Little Monsters: The Creatures that Live on Us and in Us. New York, NY: Penguin Group, Inc, 2011.

8Neglected Parasitic Infections (NPIs) in the United States.” Centers for Disease Control and Prevention. May 8, 2014. Accessed: May 19, 2014.

9 Pedersen, Marianne G. et al. “Toxoplasma gondii Infection and Self-Directed Violence in Mothers.” JAMA Psychiatry. November 2012. Accessed: May 19, 2014.

10 Plaue, Noah. “10 Parasites that Do Horrifying Things to People and Animals.” Business Insider. June 27, 2012. Accessed: May 19, 2014.

11The Enemy Within: 10 Human Parasites.” New Scientist. July 9, 2009. Accessed: May 19, 2014.

12The ‘New AIDS of the Americas’: Experts Warn of Deadly Insect-Borne Disease that Can Cause Victim’s Hearts to Explode.” Daily Mail. May 29, 2012. Accessed: May 19, 2014.

13 “Trichomoniasis—CDC Fact Sheet.” Centers for Disease Control and Prevention. Updated August 3, 2012. Accessed: May 19, 2014.

14Woman Swallows Tapeworm to Lose Weight; Tells Doctor She Bought It on the Internet.” Huffington Post. Updated August 20, 2013. Accessed: May 19, 2014.

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