Human parasites are divided into endoparasites, which cause infection inside the body, and ectoparasites, which cause infection superficially within the skin.


How Humans Get Parasites

  • Food or water  (roundworm, amoebae, giardia).
  • Via a vector: Mosquitoes transmit heartworm, filaria, malaria; the flea is a carrier of dog tapeworm; the common housefly transmits amoebic cysts; the sand fly carries leishmaniasis.
  • Sexual contact  (trichomonas, giardia, amoebae).
  • Through the nose and skin where pinworm eggs and Toxoplasma gondii can be inhaled from contaminated dust, hookworms, schistosomes, and strongyloides can penetrate exposed skin and bare feet.


Symptoms of a Parasitic Infection 

  • Fatigue
  • Digestive Problems
  • Bulky stools, or fatty mucous in feces
  • Food sensitivities or allergies
  • Environmental intolerance?
  • Joint/muscle pain
  • Anemia
  • Dermatitis/hives
  • Anxiety
  • Insomnia

Interesting facts

VIRUSES are the smallest of all infectious agents, averaging about 100 nanometers (100 billionths of a meter) in length. They have so few genes and proteins of their own that in order to reproduce they need to commandeer the machinery of the cells they invade.

BACTERIA vary widely in size and shape, but tend to be at least 10 times larger than viruses, or at least 1 micrometer (1 millionth of a meter) long. They are single-cell organisms that reproduce independently.

SINGLE-CELL ORGANISMS tend to be at least 10 times larger than bacteria, or about .01 millimeter long.

MULTI CELLULAR ORGANISMS are so large they can usually be seen with the naked eye. Tapeworms, for instance, can reach a length of 6 meters (20 feet)

85%-95% of adults have parasites in them but don’t know it.

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Round Worms

Round worms are parasites commonly hosted in the intestines of various terrestrial animals, chiefly herbivores. They are typically large worms characterized by a mouth surrounded by three lips. The species Ascaris lumbricoides is probably the most familiar parasite in humans. The intestinal roundworm Ascaris lumbricoides infection in humans follows the ingestion of Ascaris eggs that have contaminated foods or soil. In the small intestine the larvae are liberated and migrate through the intestinal wall, reaching the lungs, where they may produce a host sensitization that results in lung inflammation and fluid retention. Then about 10 days later, the larvae pass from the respiratory passages into the digestive tract and mature into egg-producing worms, which grow to some 15 to 40 cm (6 to 16 inches) in length, in the small intestine. Serious, even fatal, complications of ascariasis result from the infiltration of the larvae into sensitive tissues, such as the brain, and from the migration of the adult worms into various body structures where they produce abcesses and toxic manifestations. Ascariasis round worms exists worldwide and is believed to affect some 660 million persons.

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Pin Worms

Adult pinworms inhabit the cecum and other portions of the large and small intestines. Female worms crawl down the intestines and pass out of the anus to lay their eggs around the anal region at night. Occasionally, they can be found on the first stool in the morning. One female can deposit over 15,000 eggs that become infective immediately or within a few hours.

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The symptoms of hookworm disease ordinarily begin with ground itch, an itchy skin irritation caused by the larvae when they penetrate the skin and marked by papules and vesicles that are often located between the toes. In passing through the lungs, the larvae may produce coughing and fever. In the intestine, the mature worm sustains its life by bloodsucking, and persistent feeding by many worms over many years results in secondary anemia.

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Dwarf Tapeworm

The dwarf tapeworm can infect humans when the eggs are ingested from contaminated food or water, or when infected food handlers pass this organism to others. The eggs also develop in grain beetles and many other insects, who then infect the grains that they eat. When humans eat these grains, they are also eating the organism. Rats, mice, hamsters, and dogs can also be infected by ingesting this organism and passing it along to humans. Most human infections result from human-to-human contact through the fecal-oral route. It is possible to be self-infected with this organism when the eggs pass out in the stool, depending upon a person’s hygiene habits. Learn more at



Infection with whipworm may be in apparent unless noticed when passed in the feces, or, on occasion, crawling up into the throat and trying to exit through the mouth or nose. More info at


 Fish Tapeworm

The fish tapeworm is a broad, long worm, often growing to lengths of 3-7 feet at maturity and capable of attaining 30 feet. You can be infected by eating raw, lightly cooked, under-processed freshwater or certain migratory species of salmon, perch, pike, pickerel, and turbot. Fish tapeworms are found wherever humans, bears, and other fish-eating mammals defecate in the same lakes and streams from which this fish are obtained.

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Intestinal Flukes


The adult worms, 2-7.5 cm (0.8-3 inches) long, attach themselves to the tissues of the small intestine of the host by means of ventral suckers; the sites of attachment may later ulcerate and form abscesses. In the early stage of the infection, there is usually abdominal pain, as well as diarrhea and nausea alternating with constipation. Heavy infestations that go untreated cause general body weakness and fluid retention, which may have serious consequences, especially in children.

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At least six forms of amoeba are parasitic in humans. Most important of these is Entamoeba histolytica, which causes amebiasis and dysentery. The diseases often occur in epidemics when raw sewage contaminates water supplies or when soil is fertilized with untreated wastes.

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