Taenia saginata (T. saginata) and Taenia solium (T. solium) are tapeworms that can live in the human intestine. Infection with these tapeworms is called taeniasis. T. solium can also cause a serious illness cysticercosis. Infection is rare in the UK.
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Life Cycle
 Humans are the only definitive (primary) hosts for T. saginata and T. solium.
- 1. Eggs or gravid (egg laden) proglottids (parts of the worm containing eggs) are passed with faeces; the eggs can survive for days to months in the environment.
- 2. Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids.
- 3. In the animal's intestine, the larvae hatch, invade the intestinal wall, and migrate via the blood stream to certain (striated) muscles, where they develop into cysticerci (cysts). A cysticercus can survive for several years in the animal.
- 4. Humans become infected by ingesting raw or undercooked infected meat. In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years. The adult tapeworms attach to the small intestine by their scolex (the extended anterior end of a tapeworm, which has suckers or hook-like parts for attachment). Adult worms then reside in the small intestine. The length of adult worms is usually 5 m or less for T. saginata (although it may reach up to 25 m) and 2 to 7 m for T. solium.
- 5. The adults produce proglottids which mature, become laden with eggs, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T. saginata adults usually have 1,000 to 2,000 proglottids, while T. solium adults have an average of 1,000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the faeces. T. saginata may produce up to 100,000 and T. soliummay produce 50,000 eggs per proglottid respectively. N.B. The eggs from T. saginata are not infective for humans but the eggs of T. solium are. In the latter case, humans can therefore serve as an intermediate host and suffer the much more serious illness known a cysticercosis.
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Symptoms
Symptoms tend to be more severe in the young, or weakened adults. In addition to the passage of proglottids out of the anus (striking in itself!) symptoms include:
- insomnia
- hunger pains
- anorexia,
- weight loss
- abdominal pain
- sometimes gastroenteritis.
T. solium taeniasis produces symptoms less frequently than T. saginata taeniasis.
Cysticercosis
The most important feature of T. solium taeniasis is the risk of development of cysticercosis. This can arise when the eggs (as opposed to the cysticerci) of T. solium are eaten, for example via:
- contaminated fruits and vegetables
- hands contaminated by infected soil
- from a lack of hand washing by a person carrying the adult worm.
The eggs develop into larvae and migrate to all tissues in the body, where they encyst. When this affects vital organs such as the central nervous system (including the brain), the eyes, the liver, the lungs or the heart, health consequences can be serious. Symptoms depend on where the infection is found, as follows:
Brain - seizures or symptoms similar to a brain tumour.
Eye - decreased vision or blindness.
Heart - abnormal rhythms or heart failure (rare).
Spine - changes in walking or weakness.
The disease can be fatal.
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Control
In the UK all beef and pork carcasses are inspected by the Meat Hygiene Service. Any infected parts are rejected.
Freezing meat, or cooking meat to temperatures above 60oC, will kill any cysts.
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Additional Information
- Travellers and immigrants from endemic regions (e.g. Latin America, Africa, south east Asia, and eastern Europe) are likely to be at higher risk of infection. Incidence is higher in rural areas, particularly where pigs are raised and where poor sanitary conditions exist.
- Taenia infections are under-reported in the UK. Between 1990 and 2003, there were 475 laboratory reports in the UK of Taenia saginata, of which 185 reported recent foreign travel. The most reported region of recent foreign travel was sub-Saharan and southern Africa, 43% of these cases involving Ethiopia. In this same time period, there were 394 laboratory reports of Taenia where the species were not specified and, therefore, the above figure is an underestimate. It is likely, however, that as T. solium is very rarely reported in the UK, the majority of such unspeciated reports were due to T. saginata
- Where cysticercosis is endemic, travellers to these areas should be mindful of possible contamination of fruit and vegetables, and the risk from undercooked pork.
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