Taenia saginata

The beef tapeworm, Taenia saginata, is a cestode parasite acquired in humans through the ingestion of raw or poorly cooked meat of infected cows. These cows have been infected via the ingestion of human feces containing the eggs of the parasite and these cows contain viable cysticercus larvae in the muscle. Humans act as the host only to the adult tapeworms and can grow up to 25 meters in the lumen of the intestine, but are usually closer to 5 meters in length

Binomial name: Taenia saginata 

Kingdom         : Animalia
Phylum            : Platyhelminthes
Class                : Cestodes
Order               : Cyclophyllidea
Family             : Taeniidae
Genus              : Taenia
Subgenus         : Taeniarhynchus
Species            : saginata

Morphology

Adult Worm

Taenia saginata attaches to the surface of the small intestine via four suckers located on the scolex (see image below). Unlike T. solium, no hooks are present on the scolex of T. saginata. The scolex has a maximum diameter of 1.5 to 2 mm while each sucker is approximately 0.7 to 0.8 mm in diameter. The worms have been observed to attain a length upwards of 25 meters, though are usually closer to 5 meters in length. Attached to the scolex is the neck and then thousands of proglottids (segments); the gravid proglottids have eggs in them. Aside from the gravid proglottids, which tend to brake off and leave in the feces, mature and immature proglottids are also present. Mature proglottids are close to 12 mm in bredth, while immature proglottids are longer (20 mm) but narrower (6 mm). Mature proglottids each have genital organs consisting of about 300 to 400 testes and a vaginal sphincter. The gravid proglottids are found in the last fifth of the worm and contain 15-20 lateral branches. T. solium, on the otherhand, contain only 7-13 lateral branches. The difference in the branching of the gravid proglottids is a method of diagnosis in determing which tapeworm is infecting the individual.

Eggs

The eggs of both T. solium and T. saginata are indistinguishable. Eggs develop in hyaline capsules and are shed after leaving the proglottid. The eggs contain an outer membrane and are roughly 31-43 um in diameter. These eggs are ingested by cattle or other intermediate hosts and once they reach the duodenum, hatch and penetrate the intestinal wall.

Cysticercus

The cysticercus (for image click "Transmission" on left frame) develop and appear in striated muscle and is more concentrated in certain muscle, particularly the pterygoid, tenderloin, and myocardium areas. The mature cysticercus are in the shape of an oval and are milky-white. They are 7.5-10 mm in breadth and 4-6 mm in length.

Scolex of T. saginata

 

Infection

Taenia saginata is transmitted to humans through ingestion of contaminated beef. The contaminated beef contain cysticercus in the striated muscle of cows and when ingested by humans, will develop into adult tapeworms. In the cow, the ingested embryo penetrates the intestinal wall and is carried to striated muscle. 

Reservoir and Vector

The host for this parasite (more specifically the adult worm) is the human while the inetermediate host is the cow as well as buffalo, giraffe, llama, sheep, and likely raindeer. There is no vector for this particular parasite. 

Diagnostic Tests

To diagnose, one usually can see gravid proglottids in the stool or can feel motile proglottids in the anal region. Using microscopy, the proglottids can be viewed to determine which type of Taenia is present. These proglottids placed between two slides should be placed in 10% formaldehyde solution and the branches injected with India ink. If 12 or more branches are seen, this will positively diagnose T. saginata. To obtain the proglottids, transparent adhesive tape should be used in the anal region. Using microscopy to view the eggs will only diagnose Taenia, but cannot definitively specificy which tapeworm (beef or pork) is present. 

Management

T. saginata is usually relatively benign, so the important thing is simply to make a diagnosis. Once a diagnosis is made, treatment can begin soon after.

Therapy

Niclosamide or quinacrine hydrochloride has been used to get rid of the tape worm. Niclosamide damages the worm to the point of dissolution and is the preferred treatment. Praziquantel is often added to this regiment at a single dose of 10 mg/kg body weight. Mebendazole at 300 mg twice daily for three days has also been reported to be effective. 

Epidemiology

In most countries, T. saginata is more common than T. solium. It is associated with areas of poor sanitation and high consumption of beef. Many of the cases seen in the United States are from immigrants who came from a country that has higher rates of beef tapeworm. The number of cases in the United States are much higher than that of T. solium. Eggs may remain viable in human feces for several weeks such that cattle who ingest them will become infected. Of 40 cows that were exposed to contaminated sewage, 18 were found to have cysticerci in the tissues. Some insects (coprophagous) are able to disperse the eggs to other places. Rates of cysticercosis is around 0.37% nationwide.

References
 http://www.stanford.edu/class/humbio103/ParaSites2006/Taenia_saginata/index.html