Beef tapeworm

Taenia saginata

ORDER Cyclophyllidea

FAMILY

Taeniidae

TAXONOMY

Taenia cucurbitina grandis saginata Goeze, 1782, Germany. Tae-niarhynchus saginatus (Goeze, 1782) Weinland, 1858.

OTHER COMMON NAMES

French: Ténia inerme; German: Rinderbandwurm. PHYSICAL CHARACTERISTICS

Body usually 9.8-16 ft (3-5 m) long (exceptionally, some specimens reach a length of 66 ft [20 m]), with maximum width (0.20-0.28 in [5-7 mm]) at gravid proglottides. Scolex lacks rostellum and hooks. Gravid proglottides (found in feces of humans) can be distinguished from those of the other common human Taenia, T. solium, by the uterus having 15-20 (or more) lateral branches (versus 7-13 lateral branches in T. solium).

DISTRIBUTION

Cosmopolitan.

HABITAT

The microhabitats of this species are the intestines of humans (for adult worms) and the body musculature of cattle (for larvae). The macrohabitats can be all places where uninspected raw or undercooked beef is eaten, or where cattle graze on grass contaminated by eggs released with human feces.

FEEDING ECOLOGY AND DIET

Internal parasite absorbing nutrients through the tegument. BEHAVIOR

The gravid proglottis can migrate out of the anus of the infected human and then can be found in the bed or in the underpants. However, it is usually released with feces. It actively crawls and can go at some distance from feces. With drying up, a rupture appears on the ventral surface of the proglottis, allowing eggs to disperse in the environment.

REPRODUCTIVE BIOLOGY

Russian researchers carried out a long-term study on the egg production of T. saginata in infected humans, including by provoking experimental self-infections during the period 1930-1940. They found that the adult parasite could live in the human intestine for more than 10 years. The daily output can reach up to 28 proglottides. Each proglottis may contain up to 175,000 eggs. Thus, an infected person may release up to 5

million eggs per day. Eggs are eaten by cattle with contaminated grass. They hatch in the duodenum. Oncospheres penetrate through the intestinal wall and enter blood vessels. They reach the musculature and turn into infective larvae (cysticerci) in about 8-10 weeks. Humans become infected by eating beef containing alive cysticerci (raw or undercooked). The adult worms start to produce gravid proglottids about one to three months after entering the final host.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

Among tapeworms, T. saginata is the most widespread agent of parasitic diseases of humans in the world. The parasitic disease caused by it is known as taeniiasis or taeniarhynchiasis. The latter originates from the name of the genus Taeniarhynchus where this parasite was placed before 1994. The validity of this genus is not supported by most authors publishing since then.

Most of the infected people have no symptoms (except releasing gravid proglottides). Sometimes symptoms such as abdominal pain, diarrhea, headache, loss of appetite, and allergic reactions may occur. Several anthelmintic drugs are very efficient against this worm. The prevention is not difficult: beef is not dangerous when fully cooked and no longer pink inside. Cysticerci are killed at 131-140°F (55-60°C).

An alternative viewpoint of the significance of T. saginata (and the other two species using humans as final hosts, T. solium and T. asiatica, both with larvae developing in pigs) to humankind may be relevant. The traditional opinion among scientists is that with the domestication of intermediate hosts (cattle and swine) the species of Taenia have become associated with humans (some 10,000 years ago). However, phylogenetic studies during 2000-2001 based on comparative morphology and gene sequences suggest that hominids obtained taeniids before the origin of the modern humans. Probably some 2 million years ago, large African hominids preyed on antelopes and other bovids in the savanna, where large cats and hyenas also lived. They were parasitized by taeniid tapeworms because of their similar diet with that of the carnivore mammals. Once hominids acquired taeniid tapeworms, they also contributed to the rate of the infestation of herbivore mammals by providing additional tapeworm eggs in the grasslands. Wild bovids, with their musculature heavily infected by cysticerci, were probably easier prey than uninfected animals. Thus, T. saginata (or its ancestor living in our ancestors) helped early hominids have meat on their menu more frequently. At least part of the evolutionary success of our species may be due to tapeworms!

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