24Broadfish Tapeworm Operculated eggs contain ciliated coracidium. Copepods eat the coracidium.They become procerocoid larvaeMinnows eat the copepod.Predator fish eat the minnows.Humans eat the predator fish.The infective stage is in the fish.
25Broadfish Tapeworm The larvae are released from the cysts. They invade the intestines and mature.They attach by bilateral grooves called brothria.The proglottids are passed in the feces, and return to the water.They become embryonated and become operculated eggs.
37Schistosoma spp. Eggs are eliminated with feces or urine. The eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts. The stages in the snail include 2 generations of sporocysts and the production of cercariae (which have a forked tail). Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and shed their forked tail, becoming schistosomulae.
40Schistosoma spp. The schistosomulae migrate to the veins: S. japonicum and S. mansoni inhabit the mesenteric veins draining the intestines.S. haematobium inhabit the urinary bladder venous plexus.The females are smaller and live inside the male. They deposit eggs in the small venules. The eggs are moved progressively toward the lumen of the intestine and are eliminated with feces or urine.
43Schistosoma spp.Human contact with water is thus necessary for infection by schistosomes. Skin penetration is required.Various animals, such as dogs, cats, rodents, pigs, horse and goats, serve as reservoirs, but skin penetration is still required.Geographic Distribution: Schistosoma mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East; S. haematobium in Africa and the Middle East; and S. japonicum in the Far East. Schistosoma mekongi and S. intercalatum are found focally in Southeast Asia and central West Africa, respectively.
44Schistosoma spp.Symptoms include: Katayama fever, granulomas (occasionally in brain or spinal cord). S. haematobium schistosomiasis also includes: hematuria, and bladder cancer.
56PinwormEggs are deposited on perianal folds. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens or contact with contaminated curtains, carpeting, etc.Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs. Following ingestion of infective eggs, the larvae hatch in the small intestine and the adults establish themselves in the colon. Gravid females migrate nocturnally outside the anus and deposit their eggs while crawling on the skin of the perianal area.
57PinwormGeographic Distribution: Worldwide, with infections more frequent in school- or preschool- children and in crowded conditions. Enterobiasis appears to be more common in temperate than tropical countries. The most common helminthic infection in the United States (an estimated 40 million persons infected).
66Trichuris trichiuraThe unembryonated eggs are passed with the stool. In the soil, the eggs become infective. After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine, and release larvae that mature and establish themselves as adults in the colon. Female worms in the cecum shed up to 20,000 eggs per day. The life span of the adults is about 1 year.Geographic Distribution: The third most common round worm of humans worldwide, with infections more frequent in tropical areas and poor sanitation practices, and among children. It is estimated that 800 million people are infected worldwide. Trichuriasis occurs in the southern United States.
75HookwormEggs are passed in the stool. The released rhabditiform larvae grow in the feces and/or the soil, and after 5 to 10 days they become filariform larvae that are infective.These infective larvae contact the human host, penetrate the skin and are carried through the veins to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed.The larvae reach the small intestine, where they reside and mature into adults. Adult worms attach to the intestinal wall with resultant blood loss by the host.
76HookwormGeographic Distribution: The second most common human helminthic infection (after ascariasis). Worldwide distribution, mostly in areas with moist, warm climate. Both N. americanus and A. duodenale are found in Africa, Asia and the Americas. Necator americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe.
88AscariasisAdult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the fecesAfter infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried to the lungs. The larvae penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms.
89AscariasisGeographic Distribution: The most common human helminthic infection. Worldwide distribution. Highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation. Occurs in rural areas of the southeastern United States.
97TrichinellosisTrichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella. After exposure to gastric acid, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms.The females release larvae that migrate to the striated muscles where they encyst. Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Pigs or bears feed on infected rodents. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).Geographic Distribution: Worldwide. Most common in parts of Europe; in the United States, it is most common in Alaska from eating infected bear meat.
98TrichinellosisEosinophilia develops in response to the presence of the worm. Patients who develop neurologic and cardiac dysfunctions have marked hypereosinophilia associated with arteriolar microthrombi leading to areas of cerebral and myocardial infarction. Immunologic reactions also are deemed responsible for one of the hallmark clinical findings—palpebral edema.The direct trauma of the larva encysting in muscle cells, coupled with the immunologic response, is responsible for other clinical features (eg, fever, myalgias). Ultimately, the intramuscular cysts typically calcify.
104ElephantitisDuring a blood meal, an infected mosquito introduces filarial larvae onto the skin of the human host, where they penetrate into the bite wound. They develop in adults that commonly reside in the lymphatics. The microfilariae migrate into lymph and blood channels moving actively through lymph and blood. Another mosquito ingests the microfilariae during a blood meal and work their way to the mosquito's midgut and develop into infective larvae. The infective larvae migrate through to the mosquito's prosbocis and can infect another human when the mosquito takes a blood meal.
108River BlindnessDuring a blood meal, an infected blackfly (genus Simulium) introduces filarial larvae onto the skin of the human host, where they penetrate into the bite wound. In subcutaneous tissues the larvae develop into adult filariae, which commonly reside in nodules in subcutaneous connective tissues. Adults can live in the nodules for approximately 15 years. Some nodules may contain numerous male and female worms. Some of them get into the bloodsteam.Another blackfly ingests the microfilariae during a blood meal and migrate to the thoracic muscles. There they develop into infective larvae and migrate to the blackfly's proboscis and can infect another human when the fly takes a blood meal.
114Guinea WormHumans become infected by drinking unfiltered water containing copepods (small crustaceans) which are infected with larvae of D. medinensis.Following ingestion, the copepods die and release the larvae, which penetrate the host stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space. After maturation into adults and copulation, the male worms die and the females migrate in the subcutaneous tissues. Approximately one year after infection, the female worm induces a blister on the skin, generally on the distal lower extremity, which ruptures. When this lesion comes into contact with water, the female worm emerges and releases larvae. The larvae are ingested by a copepod and develop into infective larvae.
118Loa loaThe vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata. During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces filarial larvae onto the skin of the human host, where they penetrate into the bite wound. The larvae develop into adults that commonly reside in subcutaneous tissue but can migrate into spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs. The fly ingests microfilariae during a blood meal, which migrate to the thoracic muscles and develop into infective larvae. They migrate to the fly's proboscis and can infect another human when the fly takes a blood meal.