Tapeworm Disease and
Other Worm Infections
Study Tapeworm and Other Worm Diseases
1. What are worm infections?
Worm infections are human diseases caused by platyhelminthes (flatworms) or nematodes (roundworms).
2. What are the most important worm infections?
The most important human worm infections are schistosomiasis, taeniasis, cysticercosis, ascariasis and ancylostomiasis (hookworm infection).
Other important worm infections caused by platyhelminthes are: fascioliasis, caused by Fasciola hepatica, which attacks the liver and the bile ducts; hydatid disease, also known as echinococcosis, caused by a taenia-like parasite and transmitted by feces of dogs in contact with sheep, with a clinical picture similar to cysticercosis. Other important infections caused by roundworms are: strongyloidiasis, agent Strongyloides stercoralis, a common opportunistic disease in AIDS; filariasis, also known as elephantiasis, transmitted by mosquitoes of the Culex genus, caused by Wuchereria bancrofti and other thread-like worms and manifested by obstruction and fibrosis of lymphatic vessels that cause swelling (lymphedema) of limbs; enterobiasis (pinworm infection), caused by Enterobius vermicularis, a worm that parasites the colon and the human perianal region; cutaneous larva migrans, an ancylostomiasis of the skin caused by Ancylostoma braziliensis.
3. What is schistosomiasis?
Schistosomiasis is a worm infection caused by schistosomes, a species of flatworms (platyhelminthes). The disease is prevalent in Latin America and in the Far East. The main species of schistosome found in Latin America is Schistosoma mansoni.
4. How do schistosomes differentiate regarding sex separation?
Schistosomes are dioecious, i.e., the species has separated sexes, male and female individuals.
5. What is the intermediate host of Schistosoma mansoni? Where does that host live?
The intermediate host of the schistosome is a gastropod mollusc, a snail of the Planorbidae family and Biomphalaria genus. The snail vector of schistosomiasis lives in freshwater, as in lagoons and creeks.
6. What is the life cycle of the schistosome?
Male and female adult schistosomes live within blood vessels of the human intestines. The females release eggs that trespass the vessel walls and enter the intestinal lumen being eliminated with the human feces. When in water the egg releases a larva called miracidium that then swims to reach the snail that is the intermediate host. Within the snail miracidia transform into cercariae, another kind of schistosome larva. The cercariae leave the snail and swim until penetrating through the human skin. In humans the cercaria gains the circulation infecting mainly the blood vessels of the intestines, liver or lungs and develops into the adult form of the parasite.
schistosome life cycle
7. What are the main phases and clinical manifestations of schistosomiasis?
Schistosomiasis has acute and chronic phases. Days after the infection the cercarial dermatitis appears at the site where the worm penetrated the skin. In one or two months the acute phase begins and fever, cough, muscle pain and nausea occur but soon disappear; in some people this phase may not manifest. In the chronic phase of the disease the worm infestation can affect the bowels, causing diarrhea, bloody feces, tiredness and hepatosplenomegaly (enlargement of the liver and spleen). The excessive pressure upon the hepatic portal vein produces varix (collateral circulation) in the esophagus and the patient may have hemorrhages and bloody vomiting that may even cause death.
8. What are the main prophylactic measures against schistosomiasis?
The main measures to prevent schistosomiasis are: information for infected individuals to look for treatment and to not disseminate the disease; chemical and biological combat against the vector snail; basic sanitary conditions to avoid contamination of lakes, rivers and other water streams by infected feces; to avoid contact with fresh water suspected of contamination.
9. What are taenias? What are the diseases caused by them?
Taenias, also know as tapeworms, are platyhelminth animals (flatworms). The main diseases caused by taenias are taeniasis and cysticercosis.
10. How do taenias classify according to the division of sexes?
Taenias are monoecious (hermaphrodite), the same individual has female and male reproductive organs and undergoes self fecundation.
11. What are the two main species of taenias that cause human diseases?
The two mains species of taenias that cause disease in humans are Taenia solium, or the pork tapeworm, and Taenia saginata, or the beef tapeworm.
Besides these species there are still the fish tapeworm, or Diphyllobothrium latum, and a tapeworm, Echinococcus granulosus, which lives in dogs and cause in humans the severe disease known as hydatid disease, or echinococcosis.
12. How do taenias obtain food and make gas exchange?
Tapeworms have hooks and sucking structures on their heads (scolex) that fixate the parasite in the gut wall; these structures often do not injure the host tissue. The parasite obtains food and makes gas exchange through absorption and diffusion across its skin; since it is a platyhelminth it does not have a digestive system or a circulatory system.
13. What are the segments that form the body of the tapeworm called? What is their function?
The body of the tapeworm is made of segments called proglottids. The proglottids are reproductive structures of the taenia and contain the organs that produce male and female gametes. As the proglottids become distant from the scolex (head) they mature. Mature proglottids can fecundate themselves or neighboring ones and the eggs formed are stored inside them. Proglottids called pregnant proglottids, full of eggs, detach from the body of the worm and are eliminated with the human feces.
14. Concerning their respective intermediate hosts how different are Taenia solium and Taenia saginata?
The intermediate hosts of Taenia solium are pigs and the intermediate hosts of Taenia saginata are cattle.
15. What is the life cycle of a tapeworm?
Pregnant proglottids with taenia eggs are released together with human feces. If ingested by the intermediate hosts, swine or bovine, the eggs break inside their intestines and the larva trespass the mucosa and gains the circulation to settle on muscles, heart, brain and other organs of these animals and then differentiate into cystic larvae called cysticerci. Humans become infected when eating raw or badly cooked swine or bovine meat contaminated by cysticerci. In the human intestines the cysticerci develop into adult worms and the cycle goes on.
taenia life cycle
16. What is the difference between taeniasis and cysticercosis?
Taeniasis is the parasitic disease caused by the adult tapeworm installed within the human intestine.
Cysticercosis occurs when humans ingest eggs or pregnant proglottids of taenias, for example, through badly washed food or self infection. In cysticercosis humans assume the role of intermediate hosts of the parasite and the cysticerci develop within human organs like muscles, brain, eyes and subcutaneous tissue. The brain infestation by cysticerci, a condition known as neurocysticercosis, is extremely severe and may lead to death.
In the normal life cycle of taenias the humans are the definitive hosts and develop taeniasis, a less serious disease, and not cysticercosis.
17. If a person eats raw or badly cooked meat infected by Taenia solium or Taenia saginata will this person develop taeniasis or cysticercosis?
If a person eats raw or badly cooked meat infected by Taenia solium or Taenia saginata he or she will develop the disease taeniasis. The ingestion of contaminated raw or badly cooked infected meat means that cysticerci are being ingested. The human then will be affected by taeniases since in his or her gut the cysticerci may develop into an adult tapeworm.
18. How does self infection by tapeworms occur?
Taeniasis patients may develop the most severe form of the worm infection, cysticercosis, because their feces contain eggs and pregnant proglottids of the taenia and there is risk of self infection due to bad hygienic habits, like not washing the hands after defecation. If these individuals ingest the eggs of the parasite they can develop cysticercosis too.
19. What are some prophylactic measures for tapeworm infections?
The main prophylactic measures against taeniasis and cysticercosis are: not to ingest raw or badly cooked swine or bovine meat; sanitary education of the people; appropriate destination of feces; adequate treatment of infected people.
20. What is ascaris? What is the disease caused by this worm?
Ascaris, or Ascaris lumbricoides, is an animal of the nematode phylum, i.e., a roundworm. Ascaris causes ascariasis, a common worm infection of the intestine.
21. How do ascaris obtain food?
The ascaris live within the human gut and feed from the food ingested by the infected person.
22. Does Ascaris lumbricoides present an intermediate host?
Ascaris is a monoxenous parasite, its life cycle is dependent only on one host and so it does not have intermediate host.
23. What is the life cycle of ascaris?
Adult ascaris that live within the human intestine can release up to 200 thousand eggs a day. The eggs are eliminated with human feces and mature in the environment under some heat and moisture conditions. Humans may ingest mature eggs through food contaminated by human feces or through bad hygienic habits. The eggs again inside the human intestine release larvae that cross the enteric mucosa and gain the circulation reaching the lungs. In the lungs the larva mature and go to the airway and to the pharynx when they are then swallowed. Within the gut the larvae develop into adult worms.
ascaris life cycle
24. What are the main symptoms of the pulmonary and of the intestinal phases of the ascaris infestation?
In the pulmonary phase the ascaris infestation causes cough, hemoptysis, dyspnea, fever, fatigue and may cause a special kind of pneumonia called eosinophilic pneumonia. In the intestinal phase the symptoms are due to spoliation of nutrients of the host and thus hunger and weight loss may appear. Masses of ascaris inside the bowels can cause severe intestinal obstruction.
25. What are some prophylactic measures against ascariasis?
The main prophylactic measures against ascariasis are: efficient washing of vegetables and other foods; basic sanitary conditions and appropriate destination of feces; hygiene education for people; combat against insects that can carry the eggs of the parasite, like flies and cockroaches.
26. What is ancylostomiasis?
Ancylostomiasis is a disease caused by Ancylostoma duodenale or Necator americanus, both hookworms belonging to the nematode phylum (roundworms). Ancylostomiasis caused by these worms is also called hookworm disease.
Since the parasites nourish themselves on human blood the infection causes anemia, hypoproteinemia and the patient often seems pale.
27. Which is the typical feature of the hookworms related to the way they obtain food and explore the host?
Both Ancylostoma duodenale and Necator americanus have mouthparts with hooks or “teeth” that help the fixation of the parasite in the human intestine wall and facilitate the tissue injury necessary to drain blood from the host. The structures are evolutionary adaptations for the parasitic way of life of these animals.
28. Are hookworms monoxenous or heteroxenous?
Hookworms are monoxenous, i.e., their life cycle depends only on one host.
29. What is the life cycle of the hookworms?
Adult hookworms within the human intestine release eggs that are eliminated with the human feces. Under adequate conditions of moisture and temperature the eggs mature in the soil and generate larvae. The larvae differentiate into thread-like infective larvae that can penetrate the human skin, generally through the feet. The larvae them gain the human circulation and reach the lungs from where they go to the airway and the pharynx. When the larvae are swallowed they enter the small intestine and develop into adult worms and the cycle restarts.
hookworm life cycle
30. What are the main prophylactic measures against hookworm disease?
The main prophylactic measures against hookworm disease are: to avoid walking barefoot on soils suspected of contamination; basic sanitary conditions and appropriate destination of feces; treatment of infected people.
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