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As of March 22, 1995, an addendum has been appended to this article.

While performing routine postmortem meat inspection procedures, a Texas Department of Health meat inspector found numerous cysts in the myocardium, diaphragm, and masseter muscles of several cattle from a West Texas feedlot. The inspector notified the supervising veterinarian, who identified the cysts as the larval stage of Taenia saginata. The latter was confirmed by the Parasitology Department of the College of Veterinary Medicine at Texas A & M University.

Of the 126 cattle submitted for slaughter from this particular lot, 119 were affected. In accordance with the USDA Meat Inspection Regulations, 26 extensively affected carcasses were condemned and 93 lesser-affected carcasses were passed for human food consumption after removal and condemnation of the lesions and freezing the carcasses at -10 C (15 F) for 10 days.

The feedlot of origin was quarantined, and during the next 5 months, 3,599 cattle were slaughtered under intensified inspection. Of the 3,164 (87.9%) affected with cysticercosis, 406 (12.8%) carcasses were condemned and 2,758 (87.2%) were passed after trimming and freezing or heating in accordance with regulations.

The feedlot operator had several questions, which he posed to the supervising veterinarian.

Q: How is infection acquired?

A: Taenia saginata (the beef tapeworm) is an obligate intestinal parasite of man. Infected people may expel several segments daily; each segment contains thousands of eggs, which can survive for 33 days in water or 159 days on grass.¹ Cattle develop cysticercosis by ingesting T saginata eggs in silage, cattle pens, feed bins, pastures, and/or water supplies that have been contaminated with infected human feces, sewage, or sewage effluent. After ingestion, the eggs hatch and eventually become larval tapeworms (cysticerci) in the tissues of the animal. The life cycle is completed when a person ingests raw or undercooked beef containing cysticerci.

Q: Are such episodes typical?

A: The numbers and percentages of infected animals in this case were much larger than usual. Most cases are indicative of enzootic cysticercosis, which is reflected by the occasional finding of an affected animal. Finding several affected animals indicates a common source exposure, which typically develops in commercial feedlots or in pastures that have been contaminated with sewage.

Q: How is bovine cysticercosis recognized?

A: Typically subclinical, cysticercosis is identified at slaughter by meat inspection procedures. However, not all affected animals are identified. Standard meat inspection procedures may not detect light infestation in about one fourth of the carcasses.²

Q: How common is bovine cysticercosis in the United States?

A: In 1986, the USDA Meat and Poultry Inspection Program inspected 34,822,173 cattle, of which 7,897 carcasses (0.023%) were affected with cysticercosis.³

Q: How can infections in feedlot cattle be prevented?

A: Prevent the contamination of feed, water, and pens by educating employees about the transmission of bovine cysticercosis and personal hygiene practices, by providing adequate and convenient toilet facilities, and by excluding unauthorized personnel from the premises.

Q: What are the costs of infection in a feedlot?

A: The costs may be high. Consider our case. Once the problem was recognized, many packing plants refused to accept animals from the feedlot, and plants that did accept them did so only at reduced prices, because they knew that slaughter rates would be slowed, increasing labor costs. They also anticipated that some carcasses would be condemned and others would have to be heated or frozen, increasing energy costs and yielding a product that could only be used for manufactured products such as sausage. The final cost in our case was $500,000 to $800,000.

Q: Are losses caused by swine cysticercosis common?

A: Swine cysticercosis is a major problem in many developing countries, but it is rare in the United States. According to USDA slaughter statistics for 1986, only 6 swine with cysticercosis were identified in 77,245,836 swine slaughtered in federal establishments.³ Zoonotic transmission of T solium has not been established in the United States.

Q: Why is T solium (the pork tapeworm) more dangerous to people than T saginata?

A: Although a person ingesting either cysticerci will develop taeniasis, the increased public health importance of T solium is because man also can be infected by T solium eggs. The eggs hatch in the small intestine, burrow into venules, and eventually localize in the brain, eye, muscle, or other tissues. Most of the morbidity and mortality in human cysticercosis results from CNS involvement.⁴ Human cysticercosis caused by ingestion of T saginata eggs is not known to develop.⁵

Q: Are human cases of cysticercosis being diagnosed in the United States?

A: Human cysticercosis is particularly common in Mexico, Central America, South America, Africa, and Asia, and is being diagnosed more frequently in the United States because of a large immigrant population from endemic areas, improved diagnostic technology, and increased physician awareness.⁶

A study conducted at 4 Los Angeles hospitals identified 497 patients treated and 11 deaths recorded for cysticercosis from 1973 through 1983. Hospital records classified 95% of these patients as Hispanic.⁶

Q: Is the transmission of human cysticercosis occurring in the United States?

A: Yes. Cysticercosis was diagnosed in a 10-month-old child in Los Angeles who apparently was infected by a Mexican maid with taeniasis⁷ and in 12 people in Los Angeles County that had not traveled to countries endemic for T solium taeniasis/cysticercosis.⁶

A large immigrant population from T solium-endemic areas, especially in US/Mexico border states, may contain several individuals harboring T solium and passing thousands of eggs daily. Human cysticercosis could occur from the direct transfer of T solium eggs from the feces of a person harboring an adult worm to their own or another's mouth or could result from indirect transfer by ingestion of food or water contaminated with eggs.

References

1. Jepsen A, Roth H. Epizootiology of Cysticercus bovis--resistance of the eggs of Taenia saginata, in Proceedings. 14th Int Vet Congr 1952; 2:43-50.

2. Dewhirst LW, Cramer JD, Sheldon VV. An analysis of current inspection procedures for detecting bovine cysticercosis. J Am Vet Med Assoc 1967; 150:412-417.

3. Statistical summary of federal meat and poultry inspection for fiscal year 1986, USDA publication No. FSIS-14. May 1987.

4. Nash TD, Neva FA. Recent advances in the diagnosis and treatment of cerebral cysticercosis. N Engl J Med 1984; 311:1492-1496.

5. Acha PN, Szyfres B. Zoonoses and communicable diseases common to man and animals, World Health Organization scientific publication No. 354. 1980; 498-506.

6. Richards FD, Schantz PM, Ruit-Tiben E, et al. Cysticercosis in Los Angeles County JAMA 1985; 254:3444-3448.

7. Cysticercosis acquired in Los Angeles County Los Angeles County Dep Health Serv Public Health Lett 1982; 4:33-34.

Addendum (1995)

Prepared by Lee C. Jan, DVM, Director of the Meat Safety Assurance Division, Texas Department of Health, Austin, TX 78756-3199, on recommendation by the original author Dr. Weedon and by William W. Rosser, DVM of the Texas Department of Health.

In response to the question, "How common is bovine cysticercosis in the United States?", the updated answer is that, in 1994, the USDA FSIS inspected 34,370,227 cattle, of which 4,619 carcasses (0.013%) were affected with cysticercosis.¹

In response to the question, "Are losses caused by swine cysticercosis common?", the updated answer is that, in 1994, only 3 swine with cysticercosis were identified of 90,206,024 swine slaughtered in federal establishments.¹

Reference

1. United States Department of Agriculture. Livestock slaughtered and cysticercosis dispositions. 1994.