696 Modern Food Microbiology
of the tongue, heart, diaphragm, jaw, and hindquarters, where they are transformed into larval forms
designated cysticerci. Cysticercosis is the term used to designate the existence of these parasites in
the intermediate hosts. The cysticerci usually take 2 or 3 months to develop after eggs are ingested
by a herbivore. When present in large numbers, the cysticerci impart a spotted appearance to the beef
issue. Humans become infected upon the ingestion of meat that contains cysticerci.
The infection caused by the pork tape (T. solium) is highly similar to that described for the beef
tape, but there are some significant differences. Although humans are also the definitive hosts, the
larval stages develop in both swine and humans. In other words, humans can serve as intermediate
(cysticercosis) and definitive (taeniasis) hosts, thus making autoinfections possible. For this reason,
T. solium infections are potentially more dangerous than those of T. saginata. The infection caused
by larval forms of T. solium is sometimes designated Cysticercus cellulosae. The T. solium scolex
has hooks rather than sucking discs, and the strobila may reach 2–4 m and contain only about 1000
proglottids. Embryos of T. solium are carried to all tissues of the body, including the eyes and brain in
contrast to T. saginata. Although T. saginata exists in both the United States and many other parts of
the world, T. solium has been eliminated in the United States. However, it does exist in Latin America,
Asia, Africa, and eastern Europe. The incidence of T. saginata in beef in the United States is below
1% as a result of federal and local meat inspections.
Symptoms, Diagnosis, and Treatment
Most cases of taeniasis are asymptomatic regardless of the Taenia species involved, but symptoms
differ when humans serve as intermediate host. In these cysticercosis cases, the cysticerci develop in
body tissues, including those of the central nervous system, and generally lead to eosinophilia.
Human taeniasis is diagnosed by demonstration of eggs or proglottids in stools and cysticercosis
by tissue biopsies of calcified cysticerci or by immunological methods. Complement fixation, indirect
hemagglutination, and immunofluorescence tests are valuable diagnostic aids.
A single-dose oral treatment with niclosamide, which acts directly on the parasites, is effective
in ridding the body of adult worms. This drug apparently inhibits a phosphorylation reaction in the
worm’s mitochondria. Another effective chemotherapeutic agent is praziquantel. With cysticercosis,
surgery may be indicated.
Prevention
The general approach in the prevention and elimination of diseases that require multiple hosts is to cut
the cycle of transmission from one host to another. Because the eggs are shed in human feces, taeniasis
can be eliminated by the proper disposal of sewage and human wastes, although T. solium infections in
humans present a more complex problem. Cysticerci can be destroyed in beef and pork by cooking to a
temperature of at least 60
◦ C.
52 The freezing of meats to at least −10
◦ C for 10–15 days or immersion in
concentrated salt solutions for up to 3 weeks will inactivate these parasites. Freezing times and temperatures necessary to ensure the death of all cysticerci from infected calves were found by one group to
be as follows: 360 hours at −5
◦ C, 216 hours at −10
◦ C, and 144 hours at −15, −20, −25, or −30
◦ C.
46
ROUNDWORMS
The disease-causing roundworms of primary importance in foods belong to two orders of the
phylum Nematoda. The order Rhabditida includes Turbatrix aceti (the vinegar eel), which is not a
human pathogen and is not discussed further.
of the tongue, heart, diaphragm, jaw, and hindquarters, where they are transformed into larval forms
designated cysticerci. Cysticercosis is the term used to designate the existence of these parasites in
the intermediate hosts. The cysticerci usually take 2 or 3 months to develop after eggs are ingested
by a herbivore. When present in large numbers, the cysticerci impart a spotted appearance to the beef
issue. Humans become infected upon the ingestion of meat that contains cysticerci.
The infection caused by the pork tape (T. solium) is highly similar to that described for the beef
tape, but there are some significant differences. Although humans are also the definitive hosts, the
larval stages develop in both swine and humans. In other words, humans can serve as intermediate
(cysticercosis) and definitive (taeniasis) hosts, thus making autoinfections possible. For this reason,
T. solium infections are potentially more dangerous than those of T. saginata. The infection caused
by larval forms of T. solium is sometimes designated Cysticercus cellulosae. The T. solium scolex
has hooks rather than sucking discs, and the strobila may reach 2–4 m and contain only about 1000
proglottids. Embryos of T. solium are carried to all tissues of the body, including the eyes and brain in
contrast to T. saginata. Although T. saginata exists in both the United States and many other parts of
the world, T. solium has been eliminated in the United States. However, it does exist in Latin America,
Asia, Africa, and eastern Europe. The incidence of T. saginata in beef in the United States is below
1% as a result of federal and local meat inspections.
Symptoms, Diagnosis, and Treatment
Most cases of taeniasis are asymptomatic regardless of the Taenia species involved, but symptoms
differ when humans serve as intermediate host. In these cysticercosis cases, the cysticerci develop in
body tissues, including those of the central nervous system, and generally lead to eosinophilia.
Human taeniasis is diagnosed by demonstration of eggs or proglottids in stools and cysticercosis
by tissue biopsies of calcified cysticerci or by immunological methods. Complement fixation, indirect
hemagglutination, and immunofluorescence tests are valuable diagnostic aids.
A single-dose oral treatment with niclosamide, which acts directly on the parasites, is effective
in ridding the body of adult worms. This drug apparently inhibits a phosphorylation reaction in the
worm’s mitochondria. Another effective chemotherapeutic agent is praziquantel. With cysticercosis,
surgery may be indicated.
Prevention
The general approach in the prevention and elimination of diseases that require multiple hosts is to cut
the cycle of transmission from one host to another. Because the eggs are shed in human feces, taeniasis
can be eliminated by the proper disposal of sewage and human wastes, although T. solium infections in
humans present a more complex problem. Cysticerci can be destroyed in beef and pork by cooking to a
temperature of at least 60
◦ C.
52 The freezing of meats to at least −10
◦ C for 10–15 days or immersion in
concentrated salt solutions for up to 3 weeks will inactivate these parasites. Freezing times and temperatures necessary to ensure the death of all cysticerci from infected calves were found by one group to
be as follows: 360 hours at −5
◦ C, 216 hours at −10
◦ C, and 144 hours at −15, −20, −25, or −30
◦ C.
46
ROUNDWORMS
The disease-causing roundworms of primary importance in foods belong to two orders of the
phylum Nematoda. The order Rhabditida includes Turbatrix aceti (the vinegar eel), which is not a
human pathogen and is not discussed further.