Taenia Solium - Pork Tapeworm

The pork tapeworm, Taenia solium, is the most harmful tapeworm in humans. Taenia solium infection is acquired either from human feces that contains Taenia solium eggs or from uncooked pork which contains larval cysts. If larvae are ingested, they mature into adults in the small intestine. This infection type is called taeniasis and is often asymptomatic. If eggs are ingested, the resulting disease is cysticercosis. It gets its name from larval Taenia solium called cysticercus. Both diseases are common in Africa, Asia, South America and Southern Europe. Taeniasis is rare in Muslim countries since people there do not consume pork.

Taeniasis

Taenia solium, as its Latin name suggests, uses pigs as intermediate hosts for its larval stage. A pig gets infected with cysticercosis. If a human eats pork without cooking it, the dormant larva excysts in the bowel. The larva matures into an adult tapeworm which absorbs nutrients from the passing food.

The flat body of an adult Taenia solium consists mostly of segments, proglottids. Pork tapeworm is attached to the intestinal wall with its head, the scolex. Its head has four suckers and two rows of hooks. It has a neck that produces the segments which grow bigger as they move towards the rectum. They absorb nutrients from the surrounding food. Each segment produces eggs that remain inside it until the segment is passed out in the feces. The segment is less than 1 cm long and 2 cm wide and contains up to 50000 eggs. Taenia solium grows up to 7 meters. A full grown pork tapeworm consists of 1000 segments and sheds six gravid proglottids per day. The segments are detached from the tail. Out in the nature they can be accidentally eaten by pigs or humans.

Taeniasis diagnosis is made by an endoscopic examination or by finding segments (or eggs) from the feces. Taeniasis is usually treated with niclosamide or endoscopic removal.

Cysticercosis

Microscopic tapeworm eggs are ingested by a human or pig due to poor hygiene. Tiny larvae called oncospheres hatch in the small intestine. They penetrate the intestinal wall and enter the bloodstream. They travel to muscles or other tissue such as the liver or the brain. Lastly, oncospheres transform into cysticerci and encyst. The smallest cysticerci are 0.5–1.5 cm long whereas the biggest forms are 20 cm long. About 60 % of patients with cysticercosis have cysticerci in the central nervous system which is called neurocysticercosis. Cysticerci molt into adults only in the intestine. Immune system does not recognize the cysts. They can live in the tissue for many years without causing any symptoms. Eventually they get old and their shell structures start to leak causing an inflammatory response. Common symptoms include: muscle spasms, dizziness, headaches and seizures. Major cysticerci infections can lead to a sudden death.

As the cysticerci die, the infected areas, lesions, shrink. The swelling goes down and symptoms start to go away. The area of the organ where they sited will be covered with fibrosis. Vital functions of the organ may be lost. If oncospheres travel to the eyes the developed cysticerci can float in the eye and cause disturbed or blurry vision. Infection in the eyes can also cause swelling or detachment of the retina.

The definitive host, human, can get infected with the same tapeworm over and over again. This autoinfection can occur in two ways. In some rare cases the mature segments dissolve too early releasing the eggs. It can happen, if the large intestine is not working properly. This retro-peristalsis reverses the direction of the stool and the gravid proglottids are carried back to the stomach. The larvae hatch and cause cysticercosis. Another way to autoinfect oneself with cysticerci is to scratch the anus and then put fingers into the mouth. This too requires that some microscopic eggs have been released from the segments before exiting the body. Normally the segments stay intact in the colon.

Cysticercosis diagnosis is possible from Magnetic Resonance Imaging scans or X-rays. The cysts resemble tumours so the diagnosis is not foolproof. Cysticercosis is generally treated with albendazole in combination with anti-inflammatory drugs. Drug treatment is not necessary, if the cysticerci are already dead. Surgical removal is possible, if the location of the cyst is known. All cases of cysticercosis are not treated. The decision of whether or not to treat neurocysticercosis is based upon symptoms and the number of cysticerci found in the brain. If only one is found, treatment is often not given.

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