Tapeworm infections can occur when a person consumes food that is contaminated with tapeworm larvae. If the larvae of the tapeworm are ingested in improperly cooked meat, they can infect the intestines and develop into adult tapeworms; the infections are known as taeniasis. If the eggs of the pork tapeworm, Taenia solium, are ingested, they hatch, and the parasite can move outside the intestine, developing larval cysts in the body tissues and organs, thereby infecting them and causing a disease known as cysticercosis. Only Taenia solium causes cysticercosis in humans.
Taenia saginata, T. solium, and T. asiatica, the tapeworms that cause taeniasis are found throughout the globe. Worldwide, about 50 million people are infected by T. saginata or T. solium. The only one of medical relevance is T. solium as it causes neurocysticercosis. Nearly 50,000 human deaths occur due to cysticercosis.
T. solium is prevalent in non-Islamic areas of Southeast Asia, India, parts of China, Central and South America, Africa and is present in Eastern Europe. The infection is particularly prevalent in parts of Africa and Latin America.
T. saginata is common in the cattle-breeding areas. It is highly prevalent (i.e. >10%) in the Near East, central and eastern Africa, and central Asia. It is least prevalent in (i.e.1%) in the regions Central and South America, Europe and Southeast Asia.
T. asiatica, on the other hand, is prevalent in Asia and is commonly seen in China, Indonesia, Taiwan, Thailand, and Republic of Korea.
In India, tapeworm infections occur in all states, but the prevalence among the states vary. Both taeniasis and cysticercosis is believed to be highly prevalent in northern India than southern India. Unfortunately, the population-based epidemiological data on taeniasis and cysticercosis are lacking from India. (1)
According to a report by The National Institute of Mental Health and Neuro Sciences (NIMHANS), Bengaluru, neurocysticercosis occurred in 2% of unselected series of epilepsy patients. A study from New Delhi reported that 2.5% of all intracranial space occupying lesions were caused due to neurocysticercosis. More than 95% of Indian patients with neurocysticercosis were vegetarians. (2)
A study reported that a rural pig farming community in Lucknow district, Uttar Pradesh, had a high prevalence of taeniasis, which was 18.6%. In this community, active epilepsy occurred in 5.8% of the population and 48.3% of the population with epilepsy met the probable or definitive diagnostic criteria for neurocysticercosis. (2)
There are various studies conducted to estimate the prevalence of porcine cysticercosis in the different states of India. The prevalence of cysticercosis was found to range between 3.33% to 17.8% according to these studies. The incidence varied according to the regions and other factors. (3-8)
Tapeworm gets its name from its shape, which is like a tape measure. It is a flat, segmented parasite, which lives in the intestine of some animals and humans; it cannot live freely on its own.
An adult tapeworm has a head, neck and a chain of segments (called proglottids). The head helps the tapeworm to attach to the intestine; the neck helps in regeneration of the worm, and the proglottids may contain eggs. While causing an intestinal tapeworm infection, the tapeworm head attaches to the intestinal wall, and the proglottids produce eggs and grow. An adult tapeworm can survive in a host for up to 30 years.
There are several species of tapeworms that infect the humans; including:
Tapeworms can grow upto 4.5 to 9 meters (15 to 30 feet long.
Other species of tapeworm, Echinococcus multilocularis and Echinococcus granulosus (dog tapeworms) survive in the intestine of dogs and other canines, which can infect humans by causing cysts in the liver and other organs.
Pigs or humans can be infected with the larval stages of Taenia solium by ingesting the proglottids or the eggs, via consuming contaminated food.
When one consumes raw or undercooked pork or other meat, which contains the cysts of the tapeworm, they become infected. These cysts mature and develop into adult tapeworms in the intestine of the host. The tapeworms attach themselves to the wall of the intestine.
The proglottids of the adult tapeworm can produce eggs, which may be released into the intestine. Sometimes, the proglottids detach themselves from the rest of the tapeworm and move into the anus. The proglottids and eggs are passed in the stool.
The pigs, rarely humans, can be infected by ingesting the proglottids or the eggs, via consuming the food contaminated with human stool.
The consumed eggs hatch in the intestine of the individual and release spheres (known as oncospheres) which penetrate the intestinal wall. These spheres travel through the bloodstream to muscles, liver, brain and other organs, where they form cysts and further infect those organs.
If the cysts develop in the brain (condition referred as neurocysticercosis), it can cause serious complications.