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Some internal fish parasites are spectacular, such as the philometrid nematode Philometra fasciati which is parasitic in the ovary of female Blacktip grouper; [14] the adult female parasite is a red worm which can reach up to 40 centimetres in length, for a diameter of only 1.6 millimetre; the males are tiny.
Several species of Trichinella can cause disease, with T. spiralis being the most common. [1] After the infected meat has been eaten, the larvae are released from their cysts in the stomach. [1] They then invade the wall of the small intestine, where they develop into adult worms. [1]
The migration of adult worms in the intestinal epithelium can cause traumatic damage to the host tissue, and the waste products they excrete can provoke an immunological reaction. [2] The resulting inflammation can cause symptoms such as nausea, vomiting, sweating, and diarrhea.
In their Parasite Immunology article on worms and viral infections, Kamal et al. explain why some parasitic worms aggravate the immune response. [13] Because parasitic worms often induce Th2 cells and lead to suppressed Th1 cells, problems arise when Th1 cells are needed. [13] Such cases occur with viral diseases. [13]
Major groups of parasites include protozoans (organisms having only one cell) and parasitic worms (helminths). Of these, protozoans, including cryptosporidium, microsporidia, and isospora, are most common in HIV-infected persons. Each of these parasites can infect the digestive tract, and sometimes two or more can cause infection at the same time.
Diphyllobothrium is a genus of tapeworms which can cause diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriasis is D. latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode that infects fish and mammals.
Each worm causes a mild inflammatory reaction at its site of contact with the intestine. In heavy infections which are common cause damage to the mucosa and produce intestinal pain and mucosa diarrhea. Sometimes eggs can enter the blood and lymph vascular systems through mucosa go into the ectopic sites in the body.
This wound on the fish then heals, leaving almost no scarring. Species of Philometra require two hosts to complete their life cycle. After the larval worms are released from the host fish, they are ingested by copepods which act as an intermediate host. Once inside the copepod, the larvae molt several times. Fish may then eat the infested copepod.