Although a parasite rarely kills the host, in some cases it can happen. To a certain extent, if a parasite does kill its host it has failed as this means it will need to find a new home. 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.
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Here are some key points about parasites. More detail and supporting information is in the main article.
- Parasites live within other organisms and thrive to the detriment of their host
- Malaria is caused by a parasite
- There are at least 1,000 species of parasite capable of living in or on humans
- Parasites that live on the surface of their hosts are known as ectoparasites
- Sleeping sickness is caused by a parasite transmitted by the tsetse fly
- Some parasitic worms can grow to over 30 m in length
- Epiparasites are parasites that live on other parasites
- Babesiosis is a parasitic disease that affects the red blood cells
- Trichomonas vaginalis is a sexually transmitted parasite
- Humans can become infected with clonorchiasi after ingesting contaminated ants.
What is a parasite?
Malaria is caused by a Plasmodium parasite.
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.
In general, a parasite is an organism that live within another, using the resources of the host to fuel its life cycle.
Parasites are an incredibly varied group of organisms. Around 70% of parasites are microscopic in size, such as the malarial parasite; however, some worm parasites can reach over 30 m in length.
There are three main types of parasitic diseases:
- Protozoa: a single-celled 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
- Ectoparasites: these live on, rather than in their hosts, these include lice and fleas.
Symptoms of parasitic diseasesBecause there are so many species of parasite there is a wide array of potential symptoms. Sometimes the symptoms may appear similar to hormone deficiency, pneumonia or food poisoning. These are some of the potential symptoms that might occur:
- Itchy anus or vagina
- Weight loss and/or increased appetite
- Abdominal pain
- Diarrhea, and vomiting
- Sleeping problems
- Aches and pains
- General malaise
Types of parasiteThere are over 1,000 known parasite species that can infect humans. These are some examples:
Endoparasite: live inside the host (as opposed to ectoparasites), examples include heartworm, tapeworm, and flatworms. Those that inhabit the spaces within the host's body are called intercellular parasites, while an intracellular parasite live within the host's cells.
Intracellular parasites include bacteria and viruses; they rely on a third organism, known as the vector (carrier). The vector transmits the endoparasite to the host. The mosquito is a vector for many parasites including the protozoan of the genus Plasmodium that causes malaria.
Epiparasite: these feed on other parasites, 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 or on another organism, the host usually dies. In this case there are characteristics of predation, because the host dies.
Head lice are called ectoparasites because they live on the exterior of their host.
Babesiosis: (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: (Blastocystis). Affects the intestines. Enters humans through ingested food contaminated with human/animal feces.
Coccidia: (Cryptosporidium). Affects the intestines. Exists worldwide. Enters humans through ingested food contaminated with human/animal feces.
Amoebiasis: (Entamoeba histolytica). Affects the intestines. More likely in areas with high population density, poor sanitation, and tropical regions. Fecal oral transmission.
Giardia: (Giardia lamblia). Affects the lumen of the small intestine. If humans ingest food/water contaminated with feces, dormant cysts may infect the body.
Isosporiasis: (Isospora belli). Affects the epithelial cells of the small intestine. Exists all over the world. Fecal oral route.
Leishmaniasis: (Leishmania) - Affects the skin and/or viscera. Exists worldwide in various forms. Transmitted by types of sandflies.
Primary amoebic meningoencephalitis: (PAM) - (Naegleria fowleri). Affects the brain. Insufflation of contaminated soil, swimming pools and contaminated water.
Malaria: (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: (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: (Toxoplasma gondii). Affects the liver, heart, eyes and brain. Widespread worldwide. People can become infected after ingesting raw/undercooked pork, lamb, goat or milk. Also may exist in contaminated food or soil with cat feces.
Trichomoniasis: (Trichomonas vaginalis). Affects the female urogenital tract. Can exist in males, but without symptoms. This is an STI (sexually transmitted infection).
Sleeping sickness: (Trypanosoma brucei). Affects the central nervous system, blood and lymph. Transmitted by the tsetse fly.
Chagas disease: (Trypanosoma cruzi). Affects the blood, muscle, nerves, heart, esophagus and colon. Transmitted through an insect bite.
Helminths organisms (worms)Ancylostomiasis/Hookworm: (Ancylostoma duodenale, Necator americanus). Affects the lungs, small intestine, and blood.
Anisakiasis: (Anisakis). The human has an allergic reaction. Human can become infected when eating contaminated fish and seafood.
Roundworm. Parasitic pneumonia: (Ascaris sp. Ascaris lumbricoides). Affects the intestines, lungs, pancreas, liver and appendix (the patient develops Löffler's syndrome). Tropical and subtropical regions.
Roundworm: (Baylisascariasis, Baylisascaris procyonis). Affects the brain, lungs, liver and intestines. Infection comes from contaminated raccon stools. North America (rare).
Tapeworm: (Cestoda). Affects the intestine. Today this parasite is rare.
Clonorchiasi: (Clonorchis sinensis, Clonorchis viverrini, Dicrocoelium dendriticum). Affects the gall bladder. Humans can become infected after ingesting contaminated ants or snails.
Dioctophyme renalis infection: (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: (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: (Dracunculus medinensis). Patient develops blisters and ulcers, affects subcutaneous tissues and muscle.
Echinococcosis .Tapeworm: (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.
Bacteria are sometimes considered parasites.
Liver fluke. Fasciolosis: (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: (Fasciolopsis buski). Affects the intestines. Common in East Asia. When humans ingest infested water plants or water they can become infected.
Gnathostomiasis: (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: (Hymenolepis nana, Hymenolepis diminuta). Humans can become infected by ingesting material contaminated by cockroaches, meal worms and flour beetles.
Loa loa filariasis, Calabar swellings: (Loa loa filarial). Affects the eyes, lungs and connective tissue. Mainly in West Africa. Transmitted by horsefly bites.
Mansonelliasis. Filariasis: (Mansonella streptocerca). Affects the subcutaneous layer of the skin.
Metagonimiasis. Intestinal fluke: - (Metagonimus yokogawai. Caused by eating undercooked or salted fish. Found in Siberia, Balkan states, Israel, Spain and Manchuria.
River blindness: (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: (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: (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: (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: (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: (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: (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: (Schistosoma mekongi). Found in southeast Asia. Humans can become infected if their skin is exposed to water contaminated with a type of snail.
Sparganosis: (Spirometra erinaceieuropaei). Humans can become infected if they eat foods tainted with dog or cat feces.
Strongyloidiasis.Parasitic pneumonia: (Strongyloides stercoralis). Affects the lungs, skin and intestines. The parasite penetrates through the skin.
Beef tapeworm: (Taenia saginata). Exists all over the world. Affects the intestines. Caused by eating undercooked beef.
Pork tapeworm: (Taenia solium). Caused by eating undercooked pork.
Toxocariasis: (Toxocara canis, Toxocara cati). Affects the eyes, brain and liver. Caused by eating Toxocara egg tainted foods.
Trichinosis: (Trichinella spiralis, Trichinella britovi, Trichinella nelsoni, Trichinella native). Affects muscle, small intestine and periobital region. Caused by eating undercooked pork.
Swimmer's itch: (Trichobilharzia regenti, Schistosomatidae). Affects the skin. Caused by going into contaminated water.
Whipworm: (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: (Wuchereria bancrofti, lymphatic system). Caused by mosquito bites.
Flukes often have complex life cycles utilizing at least two different hosts.
Head louse. Pediculosis: (Pediculus humanus). Affects the hair follicles. Common all over the world. Spread by head-to-head contact.
Body louse. Pediculosis: (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: (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: (Demodex folliculorum/brevis/canis). Affects the eyebrow and eyelashes. Common all over the world. Caused by prolonged skin contact.
Scabies: (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: (Cochliomyia hominivorax). Affects skin and wounds. Found in Central America and north Africa. Transmitted by a fly.
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