What is cysticercosis (pork tapeworm infection)?
Cysticercosis is a systemic parasitic infestation caused by ingesting the eggs of the pork tapeworm, Taenia solium. The symptoms of this illness are caused by the development of characteristic cysts (cysticerci) which most often affect the central nervous system (neurocysticercosis), skeletal muscle, eyes, and skin. Many individuals with cysticercosis never experience any symptoms at all (asymptomatic).
The pork tapeworm responsible for causing cysticercosis is endemic to many parts of the developing world, including Latin America, Asia, and sub-Saharan Africa. The World Health Organization (WHO) estimates that cysticercosis affects about 50-100 million people worldwide. The incidence of cysticercosis has increased in the United States due to increased immigration from developing countries. Approximately 1,000 new cases of cysticercosis in the United States are reported annually. The majority of cases in the United States occur in Latin American immigrants. Neurocysticercosis is a leading cause of adult-onset seizures worldwide, and it is estimated to cause 30% of all epilepsy cases in countries where the parasite is endemic. The Centers for Disease Control and Prevention (CDC) has designated cysticercosis as one of five "neglected parasitic infections" in the United States, and the WHO has designated cysticercosis as one of 17 "neglected tropical diseases" worldwide.
Historically, the disease has been recognized since about 2000 B.C. by the Egyptians, and later it was described in pigs by Aristotle. The disease was also recognized by Muslim physicians and is thought to be the reason for Islamic dietary prohibition of eating pork. In the 1850s, German investigators described the life cycle of T. solium.
What causes cysticercosis?
Cysticercosis in humans is caused by the dissemination in humans of the larval form of the pork tapeworm, Taenia solium, which then form cysts in various organs. When the eggs of Taenia solium are ingested by humans, the tapeworm eggs hatch and the embryos penetrate the intestinal wall and reach the bloodstream. The formation of cysts in different body tissues leads to the development of symptoms, which will vary depending on the location and number of cysts.
Risk factors associated with acquiring cysticercosis include living in areas where the parasite is endemic (most commonly in rural developing countries where pigs roam freely and come into contact with human feces), drinking water or eating food contaminated with tapeworm eggs, and living in a household where another family member has intestinal tapeworm infection (taeniasis). Individuals who have taeniasis and poor hygiene are also at increased risk of infecting themselves.
How does cysticercosis spread?
Humans are the host for Taenia solium, and they may carry the tapeworm in their intestine (taeniasis), often without symptoms. The tapeworm eggs are periodically shed in the feces by the human reservoir, and typically pigs ingest the tapeworm eggs in contaminated food or water. The pigs subsequently become infected and develop cysticerci in their body tissue. When humans eat infected raw or undercooked pork, the life cycle of the tapeworm is complete and the cycle continues.
Human cysticercosis, however, develops after humans ingest Taenia solium eggs. The eggs are typically spread via food, water, or surfaces contaminated with infected feces. Oftentimes, the eggs may be spread from the hands of infected food handlers who do not clean their hands or from fruits and vegetables fertilized/irrigated with water containing infected human feces. Though the source of this fecal-oral transmission most often occurs from other infected individuals, it is also possible for individuals who carry the tapeworm to infect themselves.
Cysticercosis is not contagious. However, people who carry the intestinal tapeworm (taeniasis) can shed the tapeworm eggs in their feces, and if they practice poor hygiene (not washing their hands after using the bathroom), they can infect others or themselves if the eggs are accidently ingested.
What is the incubation period for cysticercosis?
The incubation period for taeniasis (intestinal tapeworm infection) can vary, and some individuals may be asymptomatic. Some individuals with taeniasis may develop nonspecific symptoms such as abdominal discomfort, nausea, diarrhea, or constipation about six to eight weeks after ingesting pork containing cysticerci, when the tapeworm has become fully developed.
The incubation period for cysticercosis is variable. Many individuals may remain completely asymptomatic, while others may not develop symptoms from cysticercosis until many years after infection.
What are the symptoms of cysticercosis?
The symptoms will depend on the location and the number of cysticerci, though many individuals with cysticercosis will never develop any symptoms at all. The majority of patients with cysticercosis who present to a health care professional have central nervous system involvement (neurocysticercosis or NCC). Symptoms of neurocysticercosis may include the following:
- Nausea and vomiting, abdominal pain
- Vision changes
- Balance problems
- Weakness or numbness
- Seizure (often the presenting symptom, occurs in about 70% of people with NCC)
Involvement of other body tissues may cause skeletal muscle swelling, subcutaneous cysts, and vision changes from cysts infecting the eyes.
Diagnosis of cysticercosis
The types of specialists involved in treating individuals with cysticercosis depend on the clinical presentation and the areas of the body involved. An infectious-disease specialist will likely be involved. A neurosurgeon may be consulted if surgical management is necessary. A neurologist may treat patients who experience seizures. Finally, an ophthalmologist may be needed in cases of eye involvement.
The diagnosis of cysticercosis can sometimes be difficult, as many individuals are asymptomatic, and the diagnosis is only made after patients have developed symptoms of the illness. Diagnosis may require a combination of tests and imaging studies. In general, however, the patient's clinical presentation along with abnormal radiographic imaging results (CT scan of the brain/MRI of the brain) lead to the diagnosis of neurocysticercosis. Blood testing can sometimes be used as an adjunct in making the diagnosis, though it is not always helpful or accurate. These tests are usually performed in more specialized labs. Rarely, a biopsy from affected tissue may be needed to make the diagnosis. Stool studies are sometimes also obtained because they may contain identifiable parasite eggs.
What is the treatment for cysticercosis?
The treatment of cysticercosis depends on various factors, including the individual's symptoms, the location and number of cysticerci, and the stage of cyst development. Generally speaking, treatment is tailored to each individual patient and their particular presentation, and treatment regimens may include anthelmintic agents, corticosteroids, anticonvulsant medications, and/or surgery. Asymptomatic patients may not require any treatment at all. Controversy does exist as to which patients require treatment with the various medications.
Active taeniasis can be treated with praziquantel (Biltricide) or niclosamide. Praziquantel should be used with caution if there is the possibility of neurocysticercosis, as it can cause inflammation around dying cysts.
For cysticercosis, the most commonly used anthelmintic agents include albendazole (Albenza) and praziquantel. These antiparasitic medications are effective in eliminating viable cysticerci, though they may cause reactive localized inflammation. Consequently, the use of these medications must be evaluated on a case-by-case basis. More than one course of treatment may be necessary to completely eliminate active cysts.
Corticosteroids may also be used in conjunction with, or instead of, antiparasitic medications. However, corticosteroids are used to decrease inflammation but are not active against the parasite. Again, treatment with these medications must be tailored to each individual case. Consultation with an infectious disease expert is recommended.
Anticonvulsant medications are used in patients with neurocysticercosis experiencing seizures or at high risk for recurrent seizures. Various anticonvulsant medications, such as carbamazepine (Tegretol) or phenytoin (Dilantin), may be prescribed. Consultation with an experienced neurologist may be helpful to determine patient treatment.
Surgical management may also be necessary in select cases of cysticercosis. Surgical removal of central nervous system cysts or placement of a brain shunt (to relieve pressure) is sometimes necessary in some cases of neurocysticercosis. Certain cases of cysticercosis involving the eyes or subcutaneous cysts may also require surgery (ophthalmic surgeon).
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What are the complications of cysticercosis?
The potential complications of cysticercosis may include the following:
What is the prognosis for cysticercosis?
The prognosis for the majority of patients with cysticercosis is excellent with proper medical treatment and management. Many individuals with cysticercosis will never develop any symptoms of the disease. Those individuals who develop neurocysticercosis and/or seizures usually have good outcomes if their disease is promptly treated and if the patients comply with medications. Death from cysticercosis is rare, but it can occur. From 1990-2002, there were approximately 221 cysticercosis-related deaths in the United States.
Is it possible to prevent cysticercosis?
The prevention of cysticercosis can be achieved through various measures including the following:
- Public education regarding the parasite and its route of transmission
- Avoidance of raw or undercooked pork in endemic areas to avoid intestinal infection
- Avoidance of potential fecal-oral routes of transmission through routine hand washing, good personal hygiene, as well as through the proper handling and preparation of foods
- Meat inspection and the proper disposal of infected meat in endemic areas
- Improved sanitary measures for human waste disposal in endemic areas
- Screening contacts of infected individuals and instituting appropriate treatment
- Developing a vaccine for the prevention of cysticercosis which may be used in the future (Currently, there is no vaccine approved for use in humans, though there have been advances in vaccines being used in pigs.)
United States. Centers for Disease Control and Prevention. "Parasites -- Cysticercosis." Sept. 22, 2020. <http://www.cdc.gov/parasites/cysticercosis/>.
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