What Is A Parasite? What Do Parasites Do?

A parasite is an organism that lives in another organism, called the host, and often harms it. It is dependent on its host for survival - it has to be in the host to live, grow and multiply. A parasite cannot live independently. Although a parasite rarely kills the host, in some cases it can happen. The parasite benefits at the expense of the host - the parasite uses the host to gain strength, and the host loses some strength as a result.

Parasites, unlike predators, are usually much smaller than their host. They reproduce at a faster rate than the host.

The word "parasite"comes from the Greek "parasitos", with para meaning "alongside", and sitos meaning "food" - therefore meaning "eating at the side of, as one would when seated at the same table". It was in the 18th century that the word parasite entered the English language as a biologic term; before that it referred to humans, such as a relative or friend who lived at the expense of another person.

There are three main types of parasitic diseases:
  • Protozoa - this parasite is a single-cell organism. Plasmodium, which causes malaria, is an example. A protozoa can only multiply (divide) within the host.
  • Helminths - worm parasites. Schistosomiasis is caused by a helminth. Other examples include roundworm, pinworm, trichina spiralis, tapeworm, and fluke.
  • Arthropods - includes insects and spiders (arachnids). The insect is not the parasite, but it carries it, it is a vector of parasitic diseases.
Types of parasites There are several types of parasites. Below are examples of some.

Ectoparasite - a parasite that lives on the host's surface, examples include some mites and hair and body lice.

Endoparasite - one that lives inside the host, examples include heartworm, tapeworm, and flatworms. One that inhabits the spaces inside the host's body is an intercellular parasite, while an intracellular parasite inhabits the cells of the host's body, these include bacteria or viruses, and they rely on a third organism known as the vector (carrier). The vector transmits the endoparasite to the host. The anopheline mosquito is a vector, it transmits a protozoan of the genus Plasmodium, which causes malaria.

Epiparasite - this one feeds on another parasite, a relationship known as hyperparasitism. A flea which lives on a dog may have a protozoan in its digestive tract, the protozoan is the hyperparasite.

Parasitoid - the larval development takes place in/on another organism, the host usually dies. In this case there are characteristics of predation, because the host dies.

List of parasites that affect humans

Endoparasites - Protozoan organisms

- (Latin name: Acanthamoeba). Affects the eye and/or brain. It exists all over the world. People can become infected if they clean contact lenses with tap water.

Babesiosis - (Latin Names: Babesia B. divergens, B. bigemina, B. equi, B. microfti, B. duncani). Affects the red blood cells. Different species live in various parts of the world. Transmitted by tick bites.

Balantidiasis - (Latin name: Balantidium coli). Lives in the intestinal mucosa.

Blastocystosis - (Latin name: Blastocystis). Affects the intestines. Enters humans through ingested food contaminated with human/animal feces.

Coccidia - (Latin name: Cryptosporidium). Affects the intestines. Exists worldwide. Enters humans through ingested food contaminated with human/animal feces.

Amoebiasis - (Latin name: Entamoeba histolytica). Affects the intestines. More likely in areas with high population density, poor sanitation, and tropical regions. Fecal oral transmission.

Giardia - (Latin name: Giardia lamblia). Affects the lumen of the small intestine. If humans ingest food/water contaminated with feces, dormant cysts may infect the body.

Isosporiasis - (Latin name: Isospora belli). Affects the epithelial cells of the small intestine. Exists all over the world. Fecal oral route.

Leishmaniasis - (Latin name: Leishmania) - Affects the skin and/or viscera. Exists worldwide in various forms. Transmitted by types of sandflies.

Primary amoebic meningoencephalitis (PAM) - (Latin name: Naegleria fowleri). Affects the brain. Insufflation of contaminated soil, swimming pools and contaminated water.

Malaria - (Latin name: Plasmodium falciparum (80% of cases), Plasmodium vivax, Plasmodium ovale, Plasmodium malariae. Affects the red blood cells. Exists in tropical regions. Transmitted by the anopheles mosquito.

Rhinosporidiosis - (Latin name: Rhinosporidium seeberi). Affects the nose and nasopharynx. Exists in India and Sri Lanka. People who are bathing in common ponds can become contaminated when the nasal mucosa is in contact with infected material..

Toxoplasmosis. Parasitic pneumonia - (Latin name: Toxoplasma gondii). Affects the liver, heart, eyes and brain. Widespread worldwide. People can become infected after ingesting raw/undercooked pork, lamb, goat, milk. Also may exist in contaminated food or soil with cat feces.

Trichomoniasis - (Latin name: Trichomonas vaginalis). Affects the female urogenital tract. Can exist in males, but without symptoms. This is an STI (sexually transmitted infection).

Sleeping sickness - (Latin name: Trypanosoma brucei). Affects the central nervous system, blood lymph. Transmitted by the tsetse fly.

Chagas disease - (Latin name: Trypanosoma cruzi). Affects the blood, muscle, nerves, heart, esophagus and colon. Transmitted through an insect bite.

Helminths organisms (worms)

Ancylostomiasis/Hookworm - (Latin name: Ancylostoma duodenale, Necator americanus). Affects the lungs, small intestine, and blood.

Anisakiasis - (Latin name: Anisakis). The human has an allergic reaction. Human can become infected when eating contaminated fish and seafood.

Roundworm. Parasitic pneumonia - (Latin name: Ascaris sp. Ascaris lumbricoides). Affects the intestines, lungs, pancreas, liver, appendix (the patient develops Löffler's syndrome). Tropical and subtropical regions.

Roundworm - (Latin name: Baylisascariasis, Baylisascaris procyonis). Affects the brain, lungs, liver and intestines. Infection comes from contaminated raccon stools. North America (rare).

Tapeworm. Tapeworm infection - (Latin name: Cestoda). Affects the intestine. Today this parasite is rare.

Clonorchiasi - (Latin name: Clonorchis sinensis; Clonorchis viverrini, Dicrocoelium dendriticum). Affects the gall bladder. Humans can become infected after ingesting contaminated ants.

Dioctophyme renalis infection - (Latin name: Dioctophyme renale). Usually affects the right kidney. Exists all over the world. Humans can become infected after eating raw or undercooked freshwater fish.

Diphyllobothriasis. Tapeworm - (Latin name: Diphyllobothrium latum). Affects the intestines and blood. Exists in Chile, Peru, Japan, Uganda and Europe. Humans can become infected after eating raw freshwater fish.

Guinea worm. Dracunculiasis - (Latin name: Dracunculus medinensis). Person gets blisters and ulcers, affects subcutaneous tissues and muscle.

Echinococcosis .Tapeworm - (Latin name: Echinococcus granulosus, Echinococcus multilocularis, E. vogeli, E. oligarthrus). Affects the spleen, kidneys, lungs and liver. Mediterranean region. The human can become infected after eating foods contaminated by the feces of a carnivore, or eating offal from a herbivore.

Pinworm. Enterobiasis - (Latin name: Enterobius vermicularis, Enterobius gregorii). Affects the intestines and anus. This bacteria is more common in temperate regions.

Liver fluke. Fasciolosis - (Latin name: Fasciola hepatica, Fasciola gigantic). Affects the gall bladder and liver. Common in various parts of the world. Contamination comes from freshwater snails.

Fasciolopsiasis. Intestinal fluke - (Latin name: Fasciolopsis buski). Affects the intestines. Common in East Asia. When humans ingest infested water plants or water they can become infected.

Gnathostomiasis - (Latin name: Gnathostoma spinigerum, Gnathostoma hispidum). Affects people under the skin. It is rare, and occurs in Southeast Asia. Caused by eating freshwater fish, pigs, snails, frogs, and chicken.

Hymenolepiasis - (Latin name: Hymenolepis nana, Hymenolepis diminuta). Humans can become infected by ingesting material contaminated by cockroaches, meal worms and flour beetles.

Loa loa filariasis, Calabar swellings - (Latin name: Loa loa filarial). Affects the eyes, lungs and connective tissue. Mainly in West Africa. Transmitted by horsefly bites.

Mansonelliasis. Filariasis - (Latin name: Mansonella streptocerca). Affects the subcutaneous layer of the skin.

Metagonimiasis. Intestinal fluke - (Latin name: Metagonimus yokogawai. Caused by eating undercooked or salted fish. Found in Siberia, Balkan states, Israel, Spain and Manchuria.

River blindness - (Latin name: Onchocerca volvulus, Onchocerciasis). Affects the eyes, skin, and tissue. Found in Africa, Central/South America, near fast flowing, cool rivers. Transmitted by a fly.

Chinese Liver Fluke - (Latin name: Opisthorchis viverrini, Opisthorchis felineus, Clonorchis sinensis). Affects the bile duct. In Russia 1.5 million people are affected. Caused by eating raw, slightly salted or frozen fish.

Paragonimiasis, Lung Fluke - (Latin name: Paragonimus westermani; Paragonimus africanus; Paragonimus caliensis; Paragonimus kellicotti; Paragonimus skrjabini; Paragonimus uterobilateralis). Affects the lungs and sputum. Causd by eating undercooked or raw freshwater crabs, crayfishes and other crustaceans.

Schistosomiasis, bilharzia, bilharziosis or snail fever - (Latin name: Schistosoma sp.). Affects the skin. Caused by exposure to fresh water snail infested waters. Found in South America (eastern), Africa, the Caribbean, and the Middle East.

Intestinal schistosomiasis - (Latin name: Schistosoma mansoni). Affects the skin, spleen intestine, liver, and lungs. 83 million people are affected. Found in the Middle East, Asia, South America, Africa and the Caribbean. Human skin exposed to water infested with a type of fresh water snail can become infected.

Urinary schistosomiasis - (Latin name: Schistosoma haematobium). Affects the skin, lungs, ureters, bladder and kidneys. Found in the Middle East and Africa. Humans can become infected if their skin is exposed to water contaminated with a type of snail.

Schistosomiasis by Schistosoma japonicum - (Latin name: Schistosoma japonicum). Affects the intestine, skin, spleen, and liver. Humans can become infected if their skin is exposed to water contaminated with a type of snail.

Asian intestinal schistosomiasis - (Latin name: Schistosoma mekongi). Found in southeast Asia. Humans can become infected if their skin is exposed to water contaminated with a type of snail.

Sparganosis - (Latin name: Spirometra erinaceieuropaei). Humans can become infected if they eat foods tainted with dog or cat feces.

Strongyloidiasis.Parasitic pneumonia - (Latin name: Strongyloides stercoralis). Affects the lungs, skin and intestines. The parasite penetrates through the skin.

Beef tapeworm - (Latin name: Taenia saginata). Exists all over the world. Affects the intestines. Caused by eating undercooked beef.

Pork tapeworm - (Latin name: Taenia solium). Caused by eating undercooked pork.

Toxocariasis - (Latin name: Toxocara canis, Toxocara cati). Affects the eyes, brain and liver. Caused by eating Toxocara egg tainted foods.

Trichinosis - (Latin name: Trichinella spiralis, Trichinella britovi, Trichinella nelsoni, Trichinella native). Affects muscle, small intestine and periobital region. Caused by eating undercooked pork.

Swimmer's itch - (Latin name: Trichobilharzia regenti, Schistosomatidae). Affects the skin. Caused by going into contaminated water.

Whipworm - (Latin name: Trichuris trichiura, Trichuris vulpis). Affects the large intestine and anus. It is common all over the world. Humans can become infected when ingesting the eggs in dry goods, for example rice, several grains, beans, or soil tainted with human excrements.

Elephantiasis Lymphatic filariasis - (Latin name: Wuchereria bancrofti, lymphatic system). Caused by mosquito bites.


Bedbug - (Latin name: Cimicidae Cimex lectularius). Affects the skin and vision. Found all over the world. Sharing clothing and bedding can spread infection.

Head louse. Pediculosis - (Latin name: Pediculus humanus). Affects the hair follicles. Common all over the world. Spread by head-to-head contact.

Body louse. Pediculosis - (Latin name: Pediculus humanus corporis). Common all over the world. Infection can spread by sexual activity, skin-to-skin contact, and sharing bedding and/or clothing.

Crab louse. Pediculosis - (Latin name: Phthirus pubis). Affects the pubic area and eyelashes. Common all over the world. Infection can spread by sexual activity, skin-to-skin contact, and sharing bedding and/or clothing.

Demodex. Demodicosis - (Latin name: Demodex folliculorum/brevis/canis). Affects the eyebrow and eyelashes. Common all over the world. Caused by prolonged skin contact.

Scabies - (Latin name: Sarcoptes scabiei). Affects the skin. Common all over the world. Infection can spread by sexual activity, skin-to-skin contact, and sharing bedding and/or clothing.

Screwworm. Cochliomyia - (Latin name: Cochliomyia hominivorax). Affects skin and wounds. Found in Central America and north Africa. Transmitted by a fly.

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