Cysticercosis

Cysticercosis

Magnetic resonance image of a patient with neurocysticercosis demonstrating multiple cysticerci within the brain.
ICD-10	B69
ICD-O:
ICD-9	123.1
OMIM	[1]
MedlinePlus	000627
eMedicine	emerg/119
DiseasesDB	3341

Cysticercosis is a parasitic disease caused by infection by the pork tapeworm, Taenia solium, which enters the body and forms cysticerci (cyst, or larval form of the tapeworm with a protective capsule). When the infection results in cysticerci in the brain, the condition is known as neurocysticercosis. Cysticercosis is the most common parasitic infestation of the central nervous system worldwide.

Humans develop cysticercosis when they ingest eggs or larvae of the pork tapeworm. While the tapeworm is found worldwide, infection is most common in areas with poor hygiene. Tapeworm eggs are passed through the bowel movements of an infected person, and then spread when fecally-contaminated water is drank, undercooked pork of infected pigs is eaten, or contaminated fingers are placed in the mouth. The tapeworm can travel though the bloodstream, with cystercerci forming in various places, including the muscles, eyes, and brain. With heavy infections involving the brain, death can occur.

Cysticerci often occur in the central nervous system, which can cause major neurological problems like epilepsy and even death.

issue of personal and social responsiblity, awareness cooking food contamination

.the larva emerges in the digestive tract. It bores through the intestinal wall into a blood vessel and is carried to muscle tissue in which it forms a protective capsule (encysts) and is called a cysticercus, or bladder worm. If the cysticercus is eaten alive in raw meat, it attaches itself to the host’s intestine and develops directly into a mature adult.

Description

Taenia solium, also called the pork tapeworm, is a cyclophyllid cestode in the family Taeniidae. It infects pigs and humans in Asia, Africa, South America, parts of Southern Europe, and pockets of North America. Like all cyclophyllid cestodes, T. solium has four suckers on its scolex ("head"). T. solium also has two rows of hooks.

T. solium has a very similar life cycle to Taenia saginata,. Cysticerci has three morpholocially distinct types. The common one is the ordinary "cellulose" cysticercus which has a fluid filled bladder that is 0.5cm to 1.5 cm in length and an invaginated scolex. The intermediate form has a scolex while the "racemose" has no evident scolex but are believed to be larger and much more dangerous. They are 20cm in length and have 60ml of fluid and 13% of patients might have all three types in the brain. Though humans usually serve as a definitive host, eating infected meat, fostering adult tapeworms in the intestine, and passing eggs through feces, sometimes a cysticercus (a larva sometimes called a "bladder worm") develops in the human and the human acts like an intermediate host. This happens if eggs get to the stomach, usually as a result of contaminated hands, but also of vomiting. Cysticerci often occur in the central nervous system, which can cause major neurological problems like epilepsy and even death. The condition of having cysticerci in one's body is called Cysticercosis, and is discussed in its own article.

This infection is caused by ingestion of eggs shed in the feces of a human tapeworm carrier. Pigs and humans become infected by ingesting eggs or gravid proglottids. Humans are infected either by ingestion of food contaminated with feces containing eggs, or by autoinfection. In the latter case, a human infected with adult T. solium can ingest eggs produced by that tapeworm, either through fecal contamination or, possibly, from proglottids carried into the stomach by reverse peristalsis. Once eggs are ingested, oncospheres hatch in the intestine, invade the intestinal wall, and migrate to striated muscles, as well as the brain, liver, and other tissues, where they develop into cysticerci. In humans, cysts can cause serious sequelae if they localize in the brain, resulting in neurocysticercosis. The parasite life cycle is completed, resulting in human tapeworm infection, when humans ingest undercooked pork containing cysticerci. Cysts evaginate and attach to the small intestine by their scolex. Adult tapeworms develop, (up to 2 to 7 m in length and produce less than 1000 proglottids, each with approximately 50,000 eggs) and reside in the small intestine for years.

Taenia solium is found worldwide. Because pigs are intermediate hosts of the parasite, completion of the life cycle occurs in regions where humans live in close contact with pigs and eat undercooked pork. Cysticercosis is often seen in areas where poor hygiene allows for contamination of food, soil or water supplies. Prevalence rates in the United States have shown that immigrants from Mexico, Central and South America and Southeast Asia account for most of the domestic cases of cysticercosis. Taeniasis and cysticercosis are very rare in predominantly Muslim countries, as Islam forbids the consumption of pork. It is important to note that human cysticercosis is acquired by ingesting T. solium eggs shed in the feces of a human T. solium tapeworm carrier, and thus can occur in populations that neither eat pork nor share environments with pigs.

Humans are the definitive host for T. solium, which means that the adult tapeworms are found only in the intestine of humans. It is possible for a human to be infested by T. solium (taeniasis) without having cysticercosis; in this case the tapeworm lives in the jejunum and regularly lays its eggs. These eggs do not have the capacity to invade tissue, and they are excreted with the rest of that person's feces. In areas of poor sanitation, swine (and humans) ingest the eggs, which may contaminate the water supply.

The eggs are capable of hatching once ingested. The larvae of T. solium are able to invade tissue, and enter the bloodstream. From there, they are able to spread to many organs (skeletal muscle, heart, eye, brain, spinal cord) and form cysts in tissue called cysticerci. They cannot grow into adult worms in this state, and remain indefinitely encapsulated in tissue. Cysticerci are commonly found at autopsy in asymptomatic inhabitants of endemic areas.

Humans may ingest the eggs or larvae directly from contact with fecally contaminated food or water (common). In rural areas where cysticercosis is common, pigs ingest the eggs by the same means. When pigs eat the eggs, the larvae hatch and disseminate and form cysticerci in the striated muscle, which can be the infective source of cysticercosis for humans who later consume that pork. This describes why swine are the intermediate host of T. solium: pigs eat the eggs laid by the tapeworms that live in the gut of infested humans.

Humans with taeniasis contract cysticercosis in the same manner; they are also capable of autoinfection by vomiting. In the latter case, eggs laid by their infesting tapeworm are pushed back into the stomach. When these eggs pass back into intestines, the larvae hatch and the infestation proceeds as usual.

See also Taenia solium and Taenia saginata.

Symptoms

In muscles, cysts cause painless swelling or create nodules under the skin. If cysts form in the eye, they can impair vision by floating in the eye and can cause blindness by causing swelling and detachment of the retina. Heart lesions can lead to abnormal rhythms or heart failure (rare). The most dangerous symptoms are a result of encystment in the central nervous system.

According to a Centers for Disease Control and Prevention Division of Parasitic Diseases, in neurocysticercosis (cysticercosis of the brain), "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.

When death occurs, it is most often due to involvement of the brain resulting in hydrocephalus, cerebral edema, cerebral compression, or epileptic seizures.

Diagnosis

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.

Treatment

The anti-parasitic drugs Praziquantel and Albendazole may be used to treat neurocysticercosis. Steroid anti-inflammatory medication is also often used in conjunction to reduce the swelling (brain edema) that results from immune system attacks on dead worms. 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. A meta-analysis of 11 trials suggests that there is probably some small benefit to patients who have active lesions, but no benefit to those with only dead or inactive lesions.

If the cyst is in certain locations, such as the eye or the brain, steroids may be started a few days before the antiparasitic, in order to avoid problems caused by swelling. If swelling and immune response are not controlled, the treatment itself can be lethal, so the medication is given in low dosages over several days. Sometimes surgery may be needed to remove the infected area or cysts, but this may be impossible when they are located in areas of difficult or dangerous surgical access. Also, some medications may treat symptoms, such as seizures or irregular heartbeat without affecting the worms.

If the cysticerci have calcified in the brain, or if there is only one lesion, treatment is not considered beneficial.

Prevention

It is possible to avoid infection with T. solium by avoiding 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.

If a person is already infected with T. solium, they can avoid cysticercosis by treating the infection in the small intestine early, by not ingesting their own feces, and by not vomiting, as this brings eggs to the stomach so they form cysticerci in the small intestine.

References

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http://www.cdc.gov/ncidod/dpd/parasites/cysticercosis/factsht_cysticercosis.htm Cysticercosis (SIS-tuh-sir-KO-sis) Centers for Disease Control and Prevention National Center for Zoonotic, Vector-Borne, and Enteric Diseases Division of Parasitic Diseases 2008 CDC 2008

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