Pathology of Infection of Taenia

 

 

T. saginata

Larvae - Unlike T. solium, T. saginata does not utilise man as an intermediate host, and therefore pathology due to the larval form is not a feature in human disease. In cattle, the cysticercus, referred to as Cysticercus bovis (named before the parasite life cycle had been determined, and the connection between the two forms had been established) is completely asymptomatic.

Adults - The pathology of infection with adult T. saginata is highly variable. Often infections are completely asymptomatic, but in other cases, some degree of pathology may be seen, most seriously intestinal blockage. In some cases, vitamin deficiency may be the result of excessive absorption of nutrients by the parasite, although this aspect of tapeworm pathology is more a feature of infection with the fish tapeworm D. latum. Also infection may be accompanied by a broad
range of non-specific symptoms, including more commonly, (if seen at all), abdominal pain, digestive disturbances, excessive appetite or loss of appetite, weakness and weight loss.

T. solium

Larvae - Infection with the larval form of T. solium Cysticercus cellulose, (called "Cysticercosis") may have severe consequences, the annual world-wide mortality due to cysticercosis having been estimated at approximately 50 000 cases. In man, the cysticerci mainly develop in the subcutaneous tissues, but infections in both the Central Nervous System (C.N.S.) and ocular tissues are also very common. Infection of the C.N.S. may cause severe pain, paralysis, optical and/or psychic disturbances and epileptic convulsions, mainly due to mechanical pressure as the larvae develop. Later there may be loss of consciousness and even death. Infections involving the eye may give rise to discomfort and can cause detachment of the retina.

Adults - Usually only a single adult specimen is present, which may cause a slight degree of mucosal inflammation. The actual effects on the host may vary considerably, often there are few symptoms, but in some cases, a variety of nonspecific symptoms such as constipation, epigastric pain and diarrhoea, are present.

Exceptionally rarely there may be perforation of the intestinal wall, with subsequent peritonitis. However, more seriously, as detailed above, the presence of adult worms carries the risk of autoinfection due to reverse-peristalsis resulting in cysticercosis, it is estimated that approximately 25% of cases of Cysticercus cellulose infections in the man being acquired by this route.

Diagnosis of Infection by Taenia spp

- Demonstration of scolex and proglottids in the faeces. However, scolex are rarely excreted in faeces
- The eggs of T. saginata and T. solium are similar. However, most laboratory diagnosis is through the observation of Taenia spp eggs in a faecal sample.
- Examination of the gravid uterus shows 15-25 lateral branches in T. saginata and 7-13 lateral branches (counted from the main stem) in T. Solium when short chains of 5-8 proglottids passed out in faeces are pressed through glass slides.
- The scolex of T. saginata is easily distinguished from that of T. solium in that it has only 4 suckers but no hooks.
- Radiological examination of the intestinal tract may reveal tapeworm infection.

Epidemiology and control

The prevalence of Taenia infection is on the increase due to the following factors;
1. Intensification of animal production
2. Development of meat industries in several developing countries
3. Consumption of undercooked beef and pork by a tourist visiting highly endemic areas
4. Consumption of semi-cooked meat in manufactured food products like hamburgers, etc.
5. Accelerating urbanisation with decreased efficiency of sewage systems
6. Sewage farming Given the above listed epidemiological factors that favour transmission,

 the following measures can be taken to reduce prevalence;
 
1. Proper meat inspection services before usage in meat industries. Diseased
meat should be condemned and destroyed
2. Lightly infected beef with cysticerci can be rendered safe for consumption
by freezing at -10oC for at least 10 days
3. Cooking of meat well before eating
4. High standards of sanitation will reduce transmission
5. Immunization against bovine cysticercosis.

Other Taenia cestodes

Infection by Adult tapeworms

Taenia taeniformis - This parasite has a cosmopolitan distribution, the adult parasites are normally found in cats and related carnivores, but it has been reported from an Argentinean child. The adult tapeworms are about 60cm long and are unusual in that they lack a neck. The scolex is large and equipped with two rows of hooks, while the posterior gravid proglottids have a characteristic bell shape. The larvae, which is found in wild rodents, is a strobilaceous, development of a
cysticercus where the scolex has evaginated but is still attached to the bladder of the cysticercus by a short segmented strobila.

Taenia Bremner (Syn. T. confusa) - reported from man in Africa, Japan and the United States of America. This parasite may be a synonym of T. saginata. Taenia africanus - published a few times in East Africa. This tapeworm has broad segments and an unarmed scolex with a small apical sucker.

Infection by Larvae (Metacestode Infections)

Taenia multiceps - The adult tapeworms of this species are found in dogs and related canids. The larva is a fluid containing cyst 5cm or more in diameter, containing several hundred protoscolices, and is called a coenurus. It is normally found in the brain or spinal cord of sheep and goats where it is an important pathogen. In these animals, it causes a condition known as 'gid' or 'staggers' as the
coenurus develops along with associated destruction of nervous tissue. The larval form may rarely infect man, where it causes a condition called coenurus cerebralis, on accidental ingestion of tapeworm eggs from the faeces of dogs.

Taenia serialises - A similar parasite to T. multiceps, the coenurus larvae, measuring 4cm in diameter or larger, is usually found in the subcutaneous and intramuscular tissues of lagomorphs. The adult tapeworms are found in dogs and foxes with a cosmopolitan distribution. They measure about 70 cm in length and have a scolex with two rows of about 30 hooks. The larvae have been reported very rarely in man.

Taenia glomerulus - The larvae commonly infect rodents, but the coenurus larvae have also been reported as rarely affecting man in Africa