Foodborne Animal Parasites 695
Prevalence
Although the first human case was reported in 1906, it was the scattering of cases during the early
1980s that brought new attention to this disease in the United States and Canada. The cases in question
resulted from the consumption of sushi, a raw fish product that has long been popular in parts of Asia but
only relatively recently has become popular in the United States. The incidence of diphyllobothriasis
is high in Scandinavia and the Baltic regions of Europe. It is estimated that 5 million cases occur
in Europe, 4 million in Asia, and 100,000 in North America. However, only 1 of 275 asymptomatic
natives of Labrador, Canada, examined in 1977 had a positive stool culture for this organism.
100
Symptoms, Diagnosis, and Treatment
Although most cases of diphyllobothriasis are asymptomatic, victims may complain of epigastric
pain, abdominal cramps, vomiting, loss of appetite, dizziness, and weight loss. Intestinal obstruction
is not unknown. One of the consequences of this infestation is a vitamin B-12 deficiency, along with
macrocytic anemia.
This disease is diagnosed by demonstrating eggs in stools. Treatment is the same as for taeniasis.
The absence of overt symptoms does not mean the absence of the tapeworm in the intestines because
the worms may persist for many years.
Prevention
Diphyllobothriasis can be prevented in humans by avoiding the consumption of raw or undercooked
fish. Although the elimination of raw sewage from waters will undoubtedly help to reduce the incidence,
it will not break the life-cycle chain of this organism, as humans are not the only definitive hosts.
Cooking fish products to an internal temperature of 60
◦ C for 1 minute or 65
◦ C for 30 seconds will
destroy the organism,
6 as will freezing fish to −20
◦ C for at least 60 hours.
56,57
Cysticercosis/Taeniasis
This syndrome in humans is caused by two species of flatworms: Taenia saginata (also Taeniarhynchus saginatus; beef tape) and Taenia solium (pork tape). They are unique among both flatworm
and roundworm parasites in that humans are their definitive hosts; the adult and sexually mature stages
develop in humans, whereas the larval or juvenile stage develops in herbivores. These helminths have
no vascular, respiratory, or digestive systems nor do they possess a body cavity. They depend on the
digestive activities of their human hosts for all of their nourishment. Their metabolism is primarily
anaerobic.
The structure of a T. saginata proglottid is illustrated in Figure 29–1. The adult worm consists of a
scolex (head) that is about 1 mm in size and lacks hooks but has four sucking discs. Behind the scolex is
the generative neck, which segments to form the strobila composed of proglottids. The latter increase
in length, with the oldest being the farthest away from the scolex. Each proglottid has a complete set
of reproductive organs, and an adult worm may contain up to 2000 proglottids. These organisms may
live up to 25 years and grow to a length of 4–6 m inside the intestinal tract. T. saginata sheds 8–9
proglottids daily, each containing 80,000 eggs. The eggs are not infective for humans.
When proglottids reach soil, they release their eggs, which are 30–40 µm in diameter, contain fully
developed embryos, and may survive for months. When the eggs are ingested by herbivores, such
as cattle, the embryos are released, penetrate the intestinal wall, and are carried to striated muscles
Prevalence
Although the first human case was reported in 1906, it was the scattering of cases during the early
1980s that brought new attention to this disease in the United States and Canada. The cases in question
resulted from the consumption of sushi, a raw fish product that has long been popular in parts of Asia but
only relatively recently has become popular in the United States. The incidence of diphyllobothriasis
is high in Scandinavia and the Baltic regions of Europe. It is estimated that 5 million cases occur
in Europe, 4 million in Asia, and 100,000 in North America. However, only 1 of 275 asymptomatic
natives of Labrador, Canada, examined in 1977 had a positive stool culture for this organism.
100
Symptoms, Diagnosis, and Treatment
Although most cases of diphyllobothriasis are asymptomatic, victims may complain of epigastric
pain, abdominal cramps, vomiting, loss of appetite, dizziness, and weight loss. Intestinal obstruction
is not unknown. One of the consequences of this infestation is a vitamin B-12 deficiency, along with
macrocytic anemia.
This disease is diagnosed by demonstrating eggs in stools. Treatment is the same as for taeniasis.
The absence of overt symptoms does not mean the absence of the tapeworm in the intestines because
the worms may persist for many years.
Prevention
Diphyllobothriasis can be prevented in humans by avoiding the consumption of raw or undercooked
fish. Although the elimination of raw sewage from waters will undoubtedly help to reduce the incidence,
it will not break the life-cycle chain of this organism, as humans are not the only definitive hosts.
Cooking fish products to an internal temperature of 60
◦ C for 1 minute or 65
◦ C for 30 seconds will
destroy the organism,
6 as will freezing fish to −20
◦ C for at least 60 hours.
56,57
Cysticercosis/Taeniasis
This syndrome in humans is caused by two species of flatworms: Taenia saginata (also Taeniarhynchus saginatus; beef tape) and Taenia solium (pork tape). They are unique among both flatworm
and roundworm parasites in that humans are their definitive hosts; the adult and sexually mature stages
develop in humans, whereas the larval or juvenile stage develops in herbivores. These helminths have
no vascular, respiratory, or digestive systems nor do they possess a body cavity. They depend on the
digestive activities of their human hosts for all of their nourishment. Their metabolism is primarily
anaerobic.
The structure of a T. saginata proglottid is illustrated in Figure 29–1. The adult worm consists of a
scolex (head) that is about 1 mm in size and lacks hooks but has four sucking discs. Behind the scolex is
the generative neck, which segments to form the strobila composed of proglottids. The latter increase
in length, with the oldest being the farthest away from the scolex. Each proglottid has a complete set
of reproductive organs, and an adult worm may contain up to 2000 proglottids. These organisms may
live up to 25 years and grow to a length of 4–6 m inside the intestinal tract. T. saginata sheds 8–9
proglottids daily, each containing 80,000 eggs. The eggs are not infective for humans.
When proglottids reach soil, they release their eggs, which are 30–40 µm in diameter, contain fully
developed embryos, and may survive for months. When the eggs are ingested by herbivores, such
as cattle, the embryos are released, penetrate the intestinal wall, and are carried to striated muscles