Taenia solium, is known as the pork tapeworm. It infects pigs and humans in Asia, Africa, the Philippines, South America, parts of Southern Europe, and pockets of North America. Infection in humans with Taenia solium larvae (cysticerci) is called cysticercosis.
Cysticercosis is rare in most industrialized nations but is endemic in developing areas such as Latin America, Asia and Africa. Most of the cases of cysticercosis in the United States are associated with immigrants from these countries.
Tapeworm infection is acquired by eating raw or undercooked meat of infected animals or ingesting contaminated food and water. Beef generally carries Taenia saginata while pork carries Taenia solium. Certain freshwater fish and salmon may also carry a tapeworm called Diphyllobothrium latum.
The T. solium larvae develop in the human intestine into the adult tapeworm over 2 months and can attain lengths greater than 12 feet. In the intestine, T. solium can survive for years. The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine. Mixed infections of both Taenia saginata and Taenia solium parasites can occur. Humans are the definitive host for T. solium, which means that the adult tapeworms are found only in the intestine of humans.
Tapeworms are segmented, and each segment or proglottid of the female is capable of producing eggs. The groups of proglottids from the beef tapeworm are capable of movement and actively crawl out through the anus. Cattle and pigs can be infected by ingesting vegetation contaminated with eggs or pregnant proglottids. In the animal's intestine, they hatch, invade the intestinal wall, and migrate to the muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat.
Many sites of infection have been documented but the central nervous system has been the most common. Presence of the cysticerci in the brain may cause increased cranial pressure, seizures and altered mental states, epilepsy and even death. When death occurs, it is most often due to involvement of the brain resulting in hydrocephalus, cerebral edema, cerebral compression, or epileptic seizures. Cysticercosis, or neurocysticercosis, is the most common parasitic infestation of the central nervous system worldwide.
With neurocysticercosis seizures, and headaches are the most common symptoms. However, confusion, lack of attention to people and surroundings, difficulty with balance, hydrocephalus (compression of the brain tissue due to obstruction of cerebrospinal fluid flow) may also occur. Often, there are few symptoms until the parasite dies. When the parasite dies, the host's immune system detects the worm's remains and attacks them, causing swelling and scarring. This is what causes most of the symptoms. Spinal cord lesions can lead to partial loss of motor control, weakness, and even paralysis.
It is possible to avoid infection with T. solium by not eating undercooked pork and food and water contaminated with human feces. Extra care should be taken in places with poor hygiene or meat inspection laws. Freezing infested pork for a prolonged period will also kill cysticerci. The following list describes important actions to prevent infection with tapeworm:
Neurocysticercosis is difficult to diagnose in its early stage and may be apparent only when the first neurological symptoms start, or when a CT scan, or an MRI of the brain is performed for other reasons. Antibody tests or a biopsy of the affected area may be necessary to complete the diagnosis.
It is still controversial whether patients benefit from treatment, because live cysticerci do not provoke seizures; only dead or dying parasites invoke an inflammatory response and seizures. In theory, therefore, treating a patient with drugs that kill living parasites can induce seizures in someone who is otherwise well and seizure-free; likewise, treating someone with seizures may not have any effect on outcome as the parasites are already dead and no improvement can be expected.
Reliable diagnosis of cysticercosis requires multiple testing methods such as radiography and the qualitative screening of serum IgG antibodies to Taenia solium using an Enzyme Linked Immunoabsorbant Assay (ELISA) technique.
Although use of cyst vesicular antigen has helped to increase its sensitivity and specificity, significant cross reactions with Echinococcosis occurs. If Echinococcus infection cannot be ruled out in the differential diagnosis, a positive sample should be confirmed by other means (i.e. immunoblot offered by the CDC) or by other non-serological means. Repeated examination and concentration techniques will increase the likelihood of detecting light infections. Nevertheless, speciation of Taenia solium is impossible if solely based on microscopic examination of eggs, because all Taenia species produce eggs that are morphologically identical. Eggs of Taenia species are also indistinguishable from those produced by cestodes of the genus Echinococcus.
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