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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–26. Life cycle of Paragonimus westermani (lung fluke). The eggs are excreted unembryonated in the sputum, or alternately, they are swallowed and passed with stool . In the external environment, the eggs become embryonated , and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues . Miracidia go through several developmental stages inside the snail : sporocysts , rediae , with the latter giving rise to many cercariae , which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, where they encyst and become metacercariae. This is the infective stage for the mammalian host . Human infection with P westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite . The metacercariae excyst in the duodenum , penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (7.5–12 mm by 4–6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this takes place completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65–90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of P westermani.

Current Medical Diagnosis & Treatment 2024 > Paragonimiasis

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eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

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eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

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eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

View in Context

eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

View in Context

eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

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eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

View in Context

eFigure 37–27. Life cycle of cestodes. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, Taenia solium, or T asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment. Cattle (T saginata) and pigs (T solium and T asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids . In the animal’s intestine, the oncospheres hatch , invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat . In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine . Length of adult worms is usually 5 M or less for T saginata (however, it may reach up to 25 M) and 2–7 M for T solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T saginata adults usually have 1000 to 2000 proglottids, while T solium adults have an average of 1000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T saginata may produce up to 100,000, and T solium may produce 50,000 eggs per proglottid respectively. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Taeniasis species.

Current Medical Diagnosis & Treatment 2024 > Noninvasive Cestode Infections

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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eFigure 37–43. Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species . After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms . Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst . Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.) A flowchart of the life cycle of Trichinella spiralis, or trichina worm.

Current Medical Diagnosis & Treatment 2024 > Trichinosis

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