Written by andreajn

Modified & Updated: 28 May 2024

Jessica Corbett

Reviewed by Jessica Corbett

green aphid, parasite facts

Parasites can go from being the tiniest, most unnoticeable beings to being the cause of death of millions of people around the world, and everything in between. You might not know it, but you already have thousands of them inside or on your body. While they are not causing you any harm now, it is always best to know about the things in your surroundings. Here are the parasite facts that are essential for your knowledge and daily survival.

  1. Parasites exist on or in a host from whom they get their food or at least at its expense.
  2. The Greek word ‘parasitos’ which means ‘beside the food’ is the origin of the term parasite.
  3. Parasites are believed to be the most common life form on Earth, making up more than 80% of living things.
  4. The biology division that studies parasite is called Parasitology.
  5. Globalization and tourism progressed the spreading of parasites worldwide.
  1. In the U.S., around 90% of the parasitic infections are single-celled protozoans.
  2. Warm-climate countries or tropic/subtropic regions like Southeast Asia host the most parasitic infections.
  3. The 3 different categories that parasites fall into are the protozoa, helminths, and arthropods.
  4. Protozoa are the tiny ones and only have one cell.
  5. Helminths are also known as worm parasites, and examples are pinworms and tapeworms.
  6. While arthropods are not technically parasites, they are insects from which common parasitic diseases begin.
  7. The two kinds of parasites that can be found in parasites are the endoparasites and the ectoparasites.
  8. Endoparasites are the causes of infection that occur inside the body.
  9. Ectoparasites are the causes of infection that occur outside the body, like on the skin.
  10. Humans serve as host to more than 300 parasitic worm species and more than 70 protozoa species.
  1. The term ‘nitpicker,’ which refers to someone who pesters on tiny details, got its name from the word ‘nit’ meaning lice eggs.
  2. Head lice are common in 9 to 10 years old girls due to the age group’s fondness of group hugs.
  3. More than 2,600 lice species exist.
  4. Head lice outbreaks among children in the U.S. are responsible for 12-24 million lost school days each year.
  5. A female hookworm is capable of producing 20,000 eggs per day and can produce up to 217 million eggs in her lifetime.
Table of Contents

Dutchman Anton van Leeuwenhoek was the first human to observe red blood cells, bacteria, and microscopic parasites.

It was the 18th century when he examined his own feces. Leeuwenhoek discovered a parasite called Giardia lamblia that dwells in water.

grass lice, parasite facts
Photo from Needpix

A German researcher performed an experiment using tapeworms on a live convict in the early 1880s.

The criminal was sentenced to death when Friedrich Küchenmeister fed him pig meat carrying immature tapeworms. Eventually, Küchenmeister obtained adult tapeworms from the intestines of the dead man weeks after his execution.

The earliest recorded mite fossil could be traced to around 400 million years ago.

Today, more than 30,000 mites species exist all over the world.

The first reported presumed parasite diseases date to about 3000-2500 BC.

It came from Egyptian records from which Greek physicians like Hippocrates later described the infections to be parasite-induced. Arab and Chinese physicians expressed similar findings as well.

The earliest identified parasite in humans is the lung fluke.

lung fluke, parasite facts
Lung fluke; Photo from Getty Images

Fossilized feces recovered from northern Chile measuring 5900 BC showed indications of the organisms. Moreover, even the ancient Egyptian mummies from 2000 BC revealed carried tapeworm eggs.

Flies have existed for as long as 225 million years.

Around 125,000 flies species exist all over the world, but none of them can be found in Antarctica. The earliest sighting of the flyswatter, or as known to Israelites as ‘the lord of flies,’ was in 2500 BC in Egyptian tombs.

Science claims to have identified the earliest mosquito from 144 million years ago.

More than 2,700 species of the insect fly everywhere in the world, 150 of which dwelling in the U.S. The average speed of a mosquito’s beating wings is 1,000 times per second.

Despite their small size, mosquitos are held responsible for numerous human deaths exceeding those of other creatures.

Mosquitos serve as hosts to parasites as well. Accordingly, these parasites transmitted through feeding cause diseases like dengue fever, yellow fever, malaria, and encephalitis or the inflammation of the brain.

Discovered 200 million years ago, the oldest flea fossil shows little to no difference from the modern fleas.

Over 2,380 species hop around the world. Fleas in the human body can jump up to 104 times its body length, which is equivalent to around 13 inches. Comparing to a human, this capacity is similar to a 4-foot-tall child jumping over the length of a football field.

It is impossible to intentionally doom a tapeworm to starvation.

What you can do is consume food that they dislike, some of which are onions and garlic. Another option is for doctors to handle tapeworms using drugs. Either way, it is important to destroy the head or ‘scolex’ and the neck for it will only grow back otherwise.

tapeworm, parasite
Tapeworm; Photo from Adobe Stock

Tapeworms are eyeless beings.

Instead, they have indentations on each side of their heads which serve as suction cups attached to the intestines of a victim.

Even on the adult stage, a tapeworm can survive to up to 30 more years.

Tapeworm infections affect nearly 175 million people around the world.

Protozoa parasites are considered to have the most deadly effects on humans.

These unicellular organisms befell more misery and death upon humans compared to anything else in an extensive history of famine and wars. The most commonly known among this type is the plasmodium, the basic cause of malaria.

Helminths are invertebrates with multiple cells defined by their bodies with flattened, tube-like forms.

Aside from being a general term for ‘worm,’ helminths also have distinct bodily bilateral symmetry. They are triploblastic, meaning that they have endo-, ecto- and mesodermal tissues. However, flatworms are free of body cavities while roundworms and segmented annelids like earthworms have body cavities enclosed in the mesoderm.

Ectoparasites infest human skin as well as that of some animals.

Common members of this taxonomically diverse assortment are the head lice and scabies mites. Numerous reports from the past 20 years narrate ectoparasitic disease outbreaks such as scabies, myiasis, and tungiasis.

The name ‘leech’ came from the Old English designation for ‘physician.’

It started when leeches were used in bloodletting procedures for more than 2000 years. Additionally, barber poles had red stripes signifying the so-called bloodletting since barbers were often acting as surgeons.

The invention of the microscope paved the way for the discovery of many parasites.

If not for the valuable machine, doctors from back then would not have any idea how these tiny creatures caused too many diseases until today.

Worms in humans would either eat the exact same food you intake or eat you.

They can enter your body through the consumption of water and food, via agents for transmission like mosquitos, through sexual activities or into the nose and skin.

Some parasites are like intellectual alien invaders that can perform many things in the body upon entry.

For example, some species can fool their host’s bodies that they are natural parts of a tissue or organ. This way, the immune system would not do its job of fighting off the intruders.

tick on hair, parasites
Tick on hair; Photo from Getty Images

Parasites can turn your organs into Swiss cheese.

The physical trauma that worm infections might cause you can lead to the perforation or breaking of your circulatory system, the lungs, the intestines, or the liver. Worst, it can affect the whole body.

Parasites that lump together in balls may cause bigger problems for the entire body.

Not only can they block, erode or damage specific organs, they can also appear as cancer tumors. What’s worse is that they may enter the lungs, heart, and brain.

Parasites can have adverse effects on your digestion.

It happens when they strip you of vitamins, minerals and amino acids that are vital for the process. In some cases, these parasites can make you anemic and even drowsy after meals.

Parasites secrete toxic waste which is poison to your body.

This condition with metabolic waste products is known as ‘verminous intoxication.’ As a result, most of your body’s vitamin content stress on the disposal of the toxins due to their reabsorption through the intestines. This struggle makes your body work harder than ever just to be able to oust the toxic waste products.

The largest recorded human parasite extracted from a human body was a tapeworm that is 37 feet long.

It was the 5th of September 2001 when doctors successfully plucked the freakishly long worm from the mouth of a woman named Sally Mae Wallace.

Parasites can also live in or on their fellow parasites.

Further, those organisms can also host their own parasites. Scientists name this relationship ‘hyperparasites’.

Whether a plant or animal is living or dead, fungi can feed off of it.

However, fungi cause disturbing infections to humans. Some of these are the jock itch, athlete’s foot, and ringworm.

The ringworm counts as a fungus.

It has the physical appearance of a parasitic worm and dwells in a curled-up position under the surface of the skin.

Toxoplasma gondii is a parasite usually found in cats but can cause diseases to humans.

This protozoan stimulates toxoplasmosis which is known to induce brain damage to a human fetus. Recently, the parasitic disease was also found to have links to ADD, OCD, schizophrenia, and even suicidal behavior among humans.

Toxoplasma gondii tissue cyst in mouse brain
Toxoplasma gondii tissue; Photo from Wikimedia Commons

Toxoplasma gondii has reverse effects on rats.

Such parasitic infection in rats makes them lose their natural fear of the feline species, especially of their urine. Moreover, a 2011 PLOS ONE study showed that infected rats might even feel sexually attracted to the scent of cat urine to which they are usually defensive.

A helminth named Gnathostoma spinigerum causes swelling under the skin.

It might be due to humans being accidental hosts instead of direct ones. Nonetheless, the worms have no capacity to reproduce inside a human body. Instead, they cause skin swellings as they migrate all over the body until they live out their lifespan of 10-12 years.

Leeches have 650 different species and all of them live off other creatures.

On the other hand, its nearest relative earthworm feeds on decaying plant matter.

Leeches can consume as much blood as 5 times their body weight.

Their saliva contains a chemical that can numb the victim from its bite. Another content is a chemical that expands the blood vessels surrounding the wound, thus more blood flow. Lastly, leech saliva also releases hirudin which hinders blood from coagulating. While a full leech would easily drop off, the hirudin release will keep oozing blood even until 24 hours.

Leeches possess 3 jaws with razor-sharp teeth.

These teeth are in a formation that produces a Y-shaped bite. On the contrary, most animals only have 2 jaws to form the structure of their mouths.

A parasitic worm named eye worm or ‘Loa loa’ resides in the eyes of humans and other mammals.

As creepy as it may seem, patients with this condition can sense the movement of the worm in their eye. A big enough Loa loa can even be seen by the host itself. This worm can survive inside a human body for up to 17 years.

Follicle mites can live directly on a human body.

Up to 4 mites can live in a single follicle with their heads down. They grip the hair with their legs claws.

Mites could also be parasites on fleas, another species of parasites.

Once, a flea was found a host to 150 mites under the same species. Some of them are even harmful to humans. Aside from mites, fleas can also be host to bacteria, protozoa, tapeworms, and even the black plague.

scabies mite on human skin
Scabies mite; Photo from Getty Images

Physical contact is the main transfer system for the human itch mite, scabies.

The main cause of irritation is the eggs that a female mite lays on the human skin. Eventually, the mother would start to bury her eggs under the skin, intensifying the inflammation. Symptoms can also take form in pus-filled nodules and soreness.

The second most prominent cause of blindness in the world is a parasitic worm named Onchocerca volvulus.

From transmission via a black fly bite, this worm can last up to 15 years in a human body. The worms scatter to different parts of the body. Upon its death, it causes ‘river blindness,’ intense itching and an immune response that destroys tissue like eye tissue.

Bloodworms are beneficial in serving as a primary menu in the aquatic food chain.

They retain their red-colored larvae form before turning into the non-biting midge fly. What gives them their red color is the iron-porphyrin protein that they carry in their tissue and blood. Their hemoglobin content helps them survive even polluted waters that have low levels of oxygen. Many carnivorous fish, crabs, frogs, salamanders, shrimps, snails and turtles eat this worm.

The pinworm inhabits the cecum of the large intestine of its host.

It is also known as the threadworm or seatworm. At night, a female worm transfers to the perineum to lay 15,000 eggs. These eggs can later reach other people and even infect the host’s housemates.

A parasitic worm called Guinea worm can grow up to 2-3 feet inside a human body.

Upon reaching this length, it would then drill into skin surfaces. It forms a blister from which it would emerge alongside thousands of larvae. The most effective removal method is by pulling it out of the host while slowly coiling it around a stick for days or weeks.

The only worms known to possess teeth are the hookworms.

It spends its life feeding and reproducing inside the host’s intestine for at least 15 years. The Latin name of hookworm is Necator Americanus which translates to ‘American murderer’. True to its name, hookworms infect about ⅙ of humanity, equivalent to over 1 billion humans all over the world.

Hookworm; Photo from Getty Images

Hookworm infection might also mean the existence of thousands of other worms in the infected person’s intestines.

Symptoms include difficulty in breathing, diarrhea, weight loss, and heart problems. However, infected children are also prone to mental retardation due to the lack of oxygen and blood to the brain.

Hookworm infection raises grave concern due to blood loss.

A hookworm holds an organic anticoagulant which helps it to easily consume around 0.25 milliliters of blood from the host every day.

A flatworm blood fluke can last for decades in its host’s bloodstream.

It generates bilharzia or schistosomiasis, and other chronic infections. Further, it can lead to bladder cancer, infertility, kidney failure, and liver damage, as well as problems in learning and growth in children.

Hookworms were found to alleviate hay fever.

In a previous study, doctors handed hay fever patients volunteers a drink that contains more than 300 hookworm eggs. Results showed that the process lightened the symptoms of hay fever. While hookworm entry through the skin is a problem, it is okay for them to pass a host in feces without any harm caused.

A spined larva named human botfly digs into living human hosts and feasts on their flesh.

Its nesting site might appear similar to a mosquito bite, but it also has two breathing tubes on the hardened skin lump. These hollows allow breathing for the larvae while it feeds under the skin.

The vampire fish is a parasite that enters the body by swimming up a urine stream into the human’s penis.

Inside, it releases its sharp spine to fasten itself in. The vampire fish, also known as V. cirrhosa or Candiru, consume human blood for food. You can only have it removed by undergoing painful, and even very invasive, surgery.

Typhus that can come from parasites is one of the most murderous diseases for humans, second only to malaria and plague.

The said parasite is part of a bacteria group named Rickettsia that can hyperparasite on body lice. Out of 10 victims, 4 might die without antibiotic treatment. The last 600 years saw more soldiers killed by typhus than all involved weapons combined.

Ingestion is the most common transmission mode of roundworms.

Upon hatching, the eggs immediately pierce through the intestine walls to gain access to the bloodstream. Worms inside would then enter the lungs that would cough it up, have it swallowed just to return to the gut. Roundworm infection shows an allergic rash, coughing, diarrhea, fever, nerve problems, and tiredness.

Small intestinal roundworms are known as ‘Ascaris’.

This type of parasite reproduces fast, grows long and emerges from the host’s anus like string confetti.

True to its name, the brain-eating amoeba dwells in the host’s brain.

Also known as the Naegleria fowleri ameba, this parasite is a possible reason for stiff neck, vomiting, hallucinations, brain inflammation, seizures and extensive destruction of brain tissue. The onset of symptoms is only the beginning of a rapid death within only 3-7 days.

Naegleria fowleri ameba, parasite
Naegleria fowleri ameba; Photo from Getty Images

Despite the number of recognized parasites today, modern parasitologists revealed that there are still human parasites left undiscovered.

Still, they assumed that hundreds of these organisms would eventually come to light in the years to come.

Approximately 50 million children in the U.S. have parasitic worm infections.

However, only a few cases get detected and reported.

More than 30% of children from around the world are infected with pinworms.

This number is just a part of the estimated 209 million affected people worldwide.

Ticks are the main causes of Lyme disease.

The condition got its name from where the first cases in children were recorded in 1975 – a town in Connecticut.

tick, parasite
Tick; Photo by John Tann on Wikimedia Commons

Ticks were once used to torture the prisoners of Turkestan tribes.

First, they chained the prisoner to a board inside a cell. Then upon it, the tribesmen released swarms of ticks. These parasites then drained the prisoner’s body of blood as the purpose of them being raised and kept hungry.

Amebiasis is a disease that you can get from the Entamoeba histolytica, a unicellular parasite.

Because areas with poor sanitation means are the main dwelling place of this parasite, U.S. cases ordinarily come from people who have had recent travels in remote areas.

Amebiasis can spread from contact with infected dungs or contaminated surfaces that one touches.

Consuming contaminated food and water, or some sorts of sexual contact is another culprit. In 10 infected persons, only 1 ends up sick and developing symptoms like stomach pain and mild diarrhea.

The deadliest disease known to humankind is malaria, a condition caused by plasmodium.

All the famines, wars and natural disasters combined did not beat the kill count of this disease. Not even smallpox or plague has come close to the numbers. Malaria is an Italian term for ‘bad air’ with a kill rate of 1.5-2.7 million people annually worldwide. In Africa, it is responsible for the death of above 3,000 children under 5 years old each day, equivalent to the death of 1 child every 30 seconds.

Humans can get infected by roundworms through dog and cat waste.

This parasite causes toxocariasis which blinded at least 70 people in the United States. Sadly, most of the people infected are children.

Americans consider the Chagas disease, a parasitic infection, as the new AIDS.

Despite coming from a blood-sucking parasite, the disease is like AIDS in many ways. One is that they are both difficult to detect and entails a long abatement period. Both diseases can also be transmitted from the mother to her child, or during blood transfusions. The Chagas disease causes swelling of the heart or intestines to their bursting point, leading to the sudden death of the victim.

Trichomoniasis is among the top 3 parasitic infections that affect U.S. residents.

Also an STD, this disease originates from the trichomoniasis vaginalis, a protozoan parasite. It garners around 7.4 million cases a year but is also the most common treatable STD. Symptoms show through redness, burning, soreness or itching of the genitals. If untreated, the trichomoniasis may persist up to months and years.

A protozoan parasite named Giardia is one of the main causes of intestinal problems.

It infects around 6% to 8% of the chickens and 2% adults worldwide, with an average number of infected people at 2 million.

Giardia, Parasite
Giardia; Photo by CDC/ Dr. Stan Erlandsen on Wikimedia Commons

The second most common parasitic infection in the U.S. is the Giardia or G. lamblia.

While it is second to pinworm in the U.S., it is hailed as the most common in the whole world. Other names for it are the beaver fever and the backpacker’s diarrhea.

The leading cause of waterborne diseases in U.S. residents is the cryptosporidium.

This protozoan parasite tallies approximately 300,000 infections annually. It is usually spread through water consumption and causes diarrheal illnesses. Moreover, its outer shell makes it capable of surviving outside the body much longer, thus its tolerance to chlorine disinfection.

Elephantiasis results in the swelling of limbs to a grossly huge size.

Originating from roundworm infection, this condition affects around 120 million victims from all over the world. When the worms grow from 1.5-4 inches long, they clump up in vessels near the lymph nodes.

The ‘sleeping sickness’ is a vector-borne infection that becomes fatal when not treated.

Its transmission comes from an infected tsetse fly bite. Upon entry in the host’s body, it propagates in lymph nodes, blood, and subcutaneous tissue. Then, it passes through the barrier of the blood and brain to contaminate the central nervous system. Symptoms of this disease are sleep, confusion, poor coordination, and sensory disturbances.

tsetse fly, parasite
Tsetse fly; Photo by International Atomic Energy Agency on Wikimedia Commons

The common worm schistosomiasis is dangerous as it can develop HIV/AIDS infection risks.

As women in Africa do their laundry in the waterways, the worm finds its way up their vaginal canal where it forms small sores that pave the way for HIV infection. Hence, researchers believe in the liability of this parasite in the increasing rates of HIV infections for these people. The good thing is that an 8-cents pill can cure the parasitic infection.

Parasite namecalling in humans started in ancient Greece.

Back then, wealthy people faked their generosity by inviting poor people over to share a meal with them. However, they could only earn their food by telling stories, reciting poetry, singing and glorifying the guests. They had the name ‘parasitos’ before, which meant ‘freeloader’ in the 1700s.

An Iowan man received permanent damage from an eye worm in 2010.

John Matthews’ vision started to become hazy and spotty, but he had no idea why. Upon consulting his doctor, they found that a parasitic worm in his eye was feeding on his retina. But by the time the doctors successfully killed the worm through laser treatment, the worm has already done permanent damage to his retina as well as his optic nerve.

Tapeworms were believed to aid in weight loss.

No scientific claims here, but an Iowan woman attempted to reap benefits from the worm species. She bought a tapeworm in 2013 and ingested it for her attempt to shed some weight. Despite the tapeworm’s effects on malnutrition and anemia, it is not capable of absorbing enough food to affect her weight significantly.

Once, an Indian man became ‘pregnant’ due to a host-parasite relationship.

Sanju Bhagat was experiencing severe pain, shortness of breath and swollen abdomen when he went to the doctor. As it turned out, he had an absorbed partially-formed twin inside his body. His fetus in fetu was feeding off of him that the doctors had to remove it.

A leopard frog, despite its tiny size, can host 12 different species of parasites.

Each of them can only live in none other than an autonomous body part. On the other hand, a Mexican parrot carries 30 different parasite species on its feather solely.

Malnutrition and infectious diseases make up 15% to 20% of the deaths of the Crusaders.

Parasites like the tapeworms are at a high in the Crusades expedition. Already encumbered, the body of the victims served as a feeding place for the parasites given the precious nutrients.

A square foot of a single carpet is host to at least 10,000 dust mites.

Likewise, a mattress can hold 100,000 to 10 million of the same bugs.

dust mites, parasites
Dust mites; Photo from Getty Images

Your pillow is home to parasites and other things that you would wish you did not know.

Especially when it is older than 2 years, a pillow has 10% of its mass made up of dead mites and mite feces.

The U.S. National Parasite Collection stores more than 1 million parasite specimens.

Eric P. Hoberg, a former custodian of the collection, described the selection as a “critical resource for exploring patterns of abundance, distribution, diversity, historical interactions, and biogeography of host and parasitic organisms. It provides a repository for specimens that may serve as the foundation for evaluations of biodiversity in North America and other regions of the world.”

An initial objective for building the National Parasite Collection is to produce a complete reference tool.

Scientists who study parasites and diseases in animals can also utilize its materials. However, all researchers can only either request the specimens for a loan in their labs or examine the collection in its location in Maryland.

In Tokyo, Japan, the Meguro Museum of Parasitology only has 45,000 specimen display.

While the U.S. Collection includes protozoans, cestodes, nematodes, lice, ticks, mites, trematodes, and other diverse parasites, this one only displays parasites. It is also home to the fossil of the 30-foot tapeworm extracted from a human’s intestine which museum guests can take pictures.

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