The pork tapeworm (Taenia solium) is a parasite that is transmitted to humans by eating raw pork. Humans are a definitive host for Taenia solium, whereas pigs are only an intermediate host.
What is pork tapeworm?
Tapeworms live as parasites in the intestines of humans or other vertebrates. There are many different types of tapeworms. Each species can cause different symptoms, although only a few species could become a danger to humans. In the picture, the head of a tapeworm. Click to enlarge. Taenia solium is one of the most important representatives of the tapeworms (cestodes). Cestodes belong to the worms (helminths). They colonize the intestine parasitically and have a white to yellowish color. The worms have a head, the so-called scolex. This is equipped with suction cups and a hooked crown. A single pork tapeworm consists of several tapeworm limbs. Several thousand of these proglottids form a long chain. This chain is also called a strobila. The pork tapeworms can thus reach a length of between two millimeters and 20 meters. The cestodes and thus also the pig tapeworm belong to the endoparasites. Endoparasites are parasites that live inside the host. They do not have their own intestines, but absorb nutrients from the host’s digestive tract. Absorption occurs through the surface of the body. The outer skin layer of the pork tapeworm is also called tegument. It protects the worm from aggressive substances and at the same time serves to absorb nutrients. The tapeworms grow by molting. To do this, they shed the old tegument and form a new skin.
Occurrence, distribution and characteristics
In humans, the pork tapeworm lives as a parasite in the intestine. Infection occurs through the consumption of meat contaminated with the larvae of the pork tapeworm. The cycle of infection begins with the ingestion of the tapeworm eggs by the pig. The eggs are shed by other tapeworm carriers and enter pasture or pig feed through feces. Larvae hatch from the tapeworm eggs in the small intestine of the pig. These bore through the intestinal wall and reach the muscles of the pig via the bloodstream. There, the so-called fins form. Fins are thin-walled blisters that are filled with fluid. Inside the blister are the head and neck of the future pork tapeworm. The fins of the pork tapeworm are also called cysticerci. A single fin contains only one tapeworm attachment at a time. The respective fins can grow to the size of a walnut. A special form of the pig fin is Cysticercus racemosus. This is a pig fin in a brain ventricle. This can grow as large as 20 centimeters. The pig serves as an intermediate host for the pork tapeworm. Both domestic and wild pigs are possible intermediate hosts. Humans now ingest the tapeworm with infected meat. In the intestine, the skin of the fin is digested from the pig muscle, releasing the head and neck of the worm. The tapeworm then hooks itself with its suckers and hooked head into the mucosa of the small intestine and grows there. In the process, new tapeworm limbs are constantly formed. The individual limbs gradually become sexually mature and are able to fertilize themselves. The last two members form eggs. They detach together with the eggs and are excreted in the stool. An infected person excretes up to nine tapeworm limbs and eggs per day. If eggs reach an intermediate host, fins develop there again. In humans, on the other hand, no fins normally develop.
Diseases and complaints
Normally, infection with a pig tapeworm in an adult human goes unnoticed. However, certain symptoms may occur. However, there may be a loss of appetite or nausea. The affected person may lose weight. They may also vomit. In addition, if the pork tapeworm causes injuries to the intestinal mucosa that are accompanied by blood loss, anemia may develop. The eggs, which are excreted in the stool, can cause itching at the anus. If hygiene is poor, serious self-infection can occur. If the affected person scratches his anus because of the itching, the worm eggs stick under his fingernails.If he now touches himself in the facial area, the worm eggs from his own digestive tract can enter the mouth. This can result in what is known as cysticercosis. Cysticercosis refers to infestation of humans with cysticerci, i.e. with the larvae of the pork tapeworm. In cysticercus cellulosus, numerous pea-sized fin vesicles form and settle in various places in the body. They can infect skeletal muscle, the eye, the skin, and the central nervous system. When the skin and muscles are affected by the fins, it manifests itself as rheumatoid symptoms. Nonspecific general symptoms such as headache or dizziness may also occur. In cysticercosis with Cysticercus racemosus, the fin vesicles collect in bunches. The individual clusters may be of considerable size. If the central nervous system is affected, various neurological symptoms may occur. Over the years, the individual vesicles may also calcify as the fins die. These calcifications are also visible on x-ray. Cysticercosis with Cysticercus racemosus is often fatal. In the blood, cysticercosis shows a so-called eosinophilia. Eosinophilic granulocytes are increased in the blood serum. The disease is diagnosed by serological detection using immunofluorescence tests, immunoblots or ELISA. Microscopic examination for tapeworms is also used. If cysticercosis is confirmed, surgical isolation of the larva is attempted. Supportive medications such as anthelmintics and corticosteroids are used. To prevent infection with pork tapeworm, it is recommended to either cook the pork or freeze it at -20 ° Celsius for at least one day. This will kill the fins in the meat.
