Cysticercosis

Synonyms and related keywords: Taenia solium infection

Overview
Cysticercosis, or neurocysticercosis, is the most common parasitic infestation of the central nervous system worldwide. Humans develop cysticercosis when they ingest eggs or larvae of the tapeworm Taenia solium. The eggs and larvae are usually found in fecally-contaminated water and undercooked pork. When cysticerci are found in the brain, the condition is called neurocysticercosis (NEW-row SIS-tuh-sir-KO-sis).

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.

Epidemiology and Demographics
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. Taeniasis and cysticercosis are very rare in Muslim countries. 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.

Cysticercosis is widely endemic in rural areas of Latin America, Asia, and Africa. During the 1980s, however, neurocysticercosis has been increasingly recognized in the United States through improved brain imaging by CAT and MRI. Most cases have been diagnosed in the western states among immigrants from areas with endemic cysticercosis. In addition, from 1988 through 1990, 7.3% of 138 cases reported to the Los Angeles Department of Health Services were acquired locally (i.e., in patients born in the United States who had not traveled to foreign countries with endemic cysticercosis). Epidemiologic investigation of these cases identified as possible sources of infection household contact with persons who had imported tapeworm infections.

Can infection be spread from person to person?

No. Cysticercosis is not spread from person to person. However, a person infected with the intestinal tapeworm stage of the infection (T. solium) will shed tapeworm eggs in their bowel movements. Tapeworm eggs that are accidentally swallowed by another person can cause infection.

Locally Acquired Neurocysticercosis -- North Carolina, Massachusetts, and South Carolina, 1989-1991 From October 1989 through November 1991, three persons with neurocysticercosis acquired in the eastern United States (North Carolina, Massachusetts, and South Carolina) were reported to CDC. This report summarizes clinical and epidemiologic information for these cases.

Patient 1. On October 4, 1989, a previously healthy man residing in New Jersey had a syncopal episode while at work. Although physical examination was normal, magnetic resonance imaging (MRI) at a New York City hospital revealed multiple ( greater than 20) cystic lesions throughout the brain. A serum specimen was positive for cysticercosis by immunoblot assay. The patient was asymptomatic on anticonvulsant medication until June 1991, when left-sided hemiparesis and weakness were noted. In July, he was treated with albendazole (10 mg/kg per day for 28 days) administered with dexamethasone. His condition improved, and he remains asymptomatic.

The patient was born and raised on a farm in North Carolina and had moved to New Jersey in July 1989; he had never traveled outside the United States. Although there was no family history of neurologic illness or tapeworm infection, some of the workers who were hired seasonally to assist on the farm had immigrated from countries with endemic cysticercosis.

Patient 2. On August 26, 1990, a 16-month-old girl in Boston had a seizure. Cranial contrast-enhanced computerized axial tomographic (CAT) scan showed ring-enhancing lesions in the left parietal and frontal cortex and a solid right parietal lesion. The immunoblot assay for cysticercosis was positive in both serum and cerebrospinal fluid. Stool examination for ova and parasites showed Giardia. The patient was treated with metronidazole for giardiasis, but no specific anthelminthic medication was given. In November 1989, the lesions were resolving, and the patient remains asymptomatic on anticonvulsants.

The patient had always resided in Boston and had never traveled out of Massachusetts. Her parents had emigrated from the Cape Verde Islands 18 months before her birth. Although no immediate family members had been acutely ill, serum specimens obtained from three of four family members were positive for cysticercosis in the immunoblot assay. Stool specimens obtained from the patient's father contained eggs of Taenia sp. All family members were treated with a taeniacidal dose of niclosamide.

Patient 3. In February 1990, a previously healthy girl in South Carolina developed generalized seizures. A CAT scan revealed a single contrast-enhancing right parietal lesion consistent with a tumor. Biopsy of the lesion showed nonspecific inflammation. In May, follow-up examination by MRI demonstrated a recurrence of the lesion, which was resected. The lesion was identified as a cysticercus (larval cyst) of Taenia solium. The patient remains asymptomatic on anticonvulsant medication.

The patient lived in Laurens County, South Carolina, and had never traveled out of state. To identify the source of the infection and possible additional persons with neurocysticercosis, the Upper Savannah District of the South Carolina Department of Health and Environmental Control conducted interviews and voluntary diagnostic tests among 26 family members and contacts. None of these persons had traveled outside the United States or eaten uncooked pork, and none reported previous tapeworm infections, subcutaneous nodules, seizures, or other neurologic symptoms. Serum specimens from all 26 persons were negative in the immunoblot assay for cysticercosis. One contact, a neighbor who had immigrated from Mexico, was seronegative, and the one stool specimen obtained from him was negative for eggs and proglottids of Taenia sp. However, the health department obtained serum specimens from five of the neighbor's friends who also had immigrated from Mexico and who often stayed in the neighbor's residence (often visited by the patient), of which three were positive for cysticercosis by immunoblot assay. One of the seronegative persons reported a history of tapeworm infection several years previously. All five refused stool examination for intestinal parasites. Reported by: LA Lettau, MD, S Gardner, MD, Dept of Hospital Epidemiology and Infectious Diseases, Greenville Hospital System; J Tennis, MD, S Hollis, F Payne, Upper Savannah District, J Jones, MD, State Epidemiologist, South Carolina Dept of Health and Environmental Control. BA Kruskal, MD, DW Teele, MD, Boston City Hospital; L Moths, MD, Upham's Corner Health Center; A DeMaria, MD, State Epidemiologist, Massachusetts Dept of Public Health. K Spitalny, MD, State Epidemiologist, New Jersey Dept of Health. MW Wittner, MD, J Kaplan, MD, HB Tanowitz, MD, Albert Einstein College of Medicine, New York City; K Rowin, MD, New City, New York. Div of Parasitic Diseases, National Center for Infectious Diseases, CDC.

Screening
Patients with cysticercosis and their household and other personal contacts should be screened for tapeworm infection since treatment with a single dose of niclosamide or praziquantel will eradicate the tapeworm and remove a potential source of transmission. Consideration should be given to screening persons at high risk for T. solium infections for intestinal parasites if those persons are to be employed as food handlers or housekeepers. Persons having household or other close contact (i.e., contact that exposes them to inadvertent infection through the fecal-oral route) with a person with a documented tapeworm should be screened for cysticercosis by medical history and serologic testing; if such an assessment suggests cysticercosis, neurologic examination and brain scan is advised.

Pathophysiology & Etiology
The cestode (tapeworm) Taenia solium (pork tapeworm) is the main cause of human cysticercosis. In addition, the larval stage of other Taenia species (e.g., multiceps, serialis, brauni, taeniaeformis, crassiceps) can infect humans in various sites of localization including the brain, subcutaneous tissue, eye, or liver.

Life Cycle:

Cysticercosis is an infection of both humans and pigs with the larval stages of the parasitic cestode, Taenia solium.

This infection is caused by ingestion of eggs shed in the feces of a human tapeworm carrier 1. Pigs and humans become infected by ingesting eggs or gravid proglottids 2, 7.

Humans are infected either by ingestion of food contaminated with feces, 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 3, 8 invade the intestinal wall, and migrate to striated muscles, as well as the brain, liver, and other tissues, where they develop into cysticerci 9.

In humans, cysts can cause serious sequellae 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 4.

Cysts evaginate and attach to the small intestine by their scolex 5. 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 6.

Diagnosis
Diagnosis can be difficult and may require several testing methods. Your health care provider will ask you about where you have traveled and your eating habits. Blood tests are available to help diagnose an infection, but may not always be accurate. If surgery is necessary, confirmation of the diagnosis can be made by the laboratory.

''I have been diagnosed with neurocysticercosis. My health care provider has decided not to treat me. How was this decision made?''

Often, the decision of whether or not to treat neurocysticercosis is based upon the number of lesions found in the brain and the symptoms you have. When only one lesion is found, often treatment is not given. If you have more than one lesion, specific anti-parasitic treatment is generally recommended.

If the brain lesion is considered calcified (this means that a hard shell has formed around the tapeworm larvae), the cysticerci is considered dead and specific anti-parasitic treatment is not beneficial.

As the cysticerci die, the lesion will shrink. The swelling will go down, and often symptoms (such as seizures) will go away.

History and Symptoms

 * Cysticerci in the muscles: Cysticerci in the muscles generally do not cause symptoms. However, you may be able to feel lumps under your skin.


 * Cysticerci in the eyes: Although rare, cysticerci may float in the eye and cause Blurred Vision. Infection in the eyes may cause Swelling or detachment of the retina.


 * Neurocysticercosis (cysticerci in the brain, spinal cord): Symptoms of neurocysticercosis depend upon where and how many cysticerci (often called lesions) are found in the brain. Seizures, and Headache are the most common symptoms. However, confusion, lack of attention to people and surroundings, difficulty with balance, swelling of the brain (called hydrocephalus) may also occur. Death can occur suddenly with heavy infections.

How long will I be infected before symptoms begin?

Symptoms can occur months to years after infection, usually when the cysts are in the process of dying. When this happens, the brain can swell. The pressure caused by swelling is what causes most of the symptoms of neurocysticercosis. Most people with cysticerci in muscles won’t have symptoms of infection.

Laboratory Findings
Laboratory Diagnosis:

The definitive diagnosis consists of demonstrating the cysticercus in the tissue involved. Demonstration of Taenia solium eggs and proglottids in the feces diagnoses taeniasis and not cysticercosis. While suggestive, it does not necessarily prove that cysticercosis is present. Persons who are found to have eggs or proglottids in their feces should be evaluated serologically since autoinfection, resulting in cysticercosis, can occur.

Cysticercosis: Antibody Detection

CDC's immunoblot assay with purified Taenia solium antigens has been acknowledged by the World Health Organization and the Pan American Health Organization as the immunodiagnostic test of choice for confirming a clinical and radiologic presumptive diagnosis of neurocysticercosis. CDC's immunoblot is based on detection of antibody to one or more of 7 lentil-lectin purified structural glycoprotein antigens from the larval cysts of T. solium in an immunoblot format. It is 100% specific and has a sensitivity superior to that of any other test yet evaluated. Serum specimens from 97% of parasitologically confirmed cases of cysticercosis have detectable antibodies. No serum samples from patients with other microbial infections react with any of the T. solium-specific antigens. The most important factors identified as determining positive immunoblot reactions are the numbers and stage of development of cysticerci. Cumulative clinical experience has confirmed that in patients with multiple (more than two) lesions, the test has more than 95% sensitivity. Seropositivity in biopsy-confirmed patients with single, enhancing parenchymal cysts was <50%; in clinically defined patients with a single cyst but who were not biopsied, sensitivity was 70%. Seropositivity in serum and CSF of patients with multiple but only calcified cysts was 82 and 77%, respectively. In all patients, regardless of their clinical presentation, the immunoblot assay is slightly more sensitive in serum than in CSF specimens: consequently, there is no need to obtain CSF solely for use in the immunoblot assay.

CDC's immunoblot is both more specific and more sensitive than enzyme immunoassay (EIA) systems with which it has been compared. Lack of specificity has been a major problem in most EIAs because of cross-reacting components in crude antigens derived from cysticerci; these components react with antibodies specific for other helminthic infections, especially echinococcosis and filariasis. Most partially purified fractions evaluated in an EIA appear to have lower sensitivity than crude antigens and do not necessarily achieve higher specificity. Assays employing crude antigens for the detection of antibody are not reliable for the identification of this disease; all positives and any negative strongly suspected of cysticercosis should be confirmed by immunoblot. Currently available antibody detection tests for cysticercosis do not distinguish between active and inactive infections and thus have not been useful in evaluating the outcomes and prognoses of medically treated patients. Both the CDC immunoblot and an EIA are commercially available in the United States.

Typical antibody reactions in CDC's immunoblot for cysticercosis. Individual sera from patients with either cysticercosis or echinococcosis were analyzed using the immunoblot for cysticercosis.

Cysticercosis-specific antibodies react with glycoproteins derived from T. solium cysts. The positions of the seven diagnostic glycoproteins are marked and designated according to their relative mobilities in SDS-PAGE. Sera from patients with cysticercosis react with at least one of the cysticercosis-specific proteins, whereas sera from patients with echinococcosis do not react with any of the seven diagnostic proteins.

MRI and CT
Diagnosis of neurocysticercosis is usually made by MRI or CT brain scans.

Treatment
Not all cases of cysticercosis are treated and the use of albendazole and praziquantel is controversial.

Pharmacotherapy
Infections are generally treated with antiparasitic drugs in combination with antiinflammatory drugs.

Surgery and Device Based Therapy
Surgery is sometimes necessary to treat infection in the eyes, cases that are not responsive to drug treatment, or to reduce brain edema.

Primary Prevention

 * Avoid eating raw or undercooked pork and other meats.
 * Don’t eat meat of pigs that are likely to be infected with the tapeworm.
 * Wash hands with soap and water after using the toilet and before handling food, especially when traveling in developing countries.
 * Wash and peel all raw vegetables and fruits before eating. Avoid food that may be contaminated with feces.
 * Drink only bottled or boiled (1 minute) water or carbonated (bubbly) drinks in cans or bottles. Do not drink fountain drinks or any drinks with ice cubes. Another way to make water safe is by filtering it through an "absolute 1 micron or less" filter AND dissolving iodine tablets in the filtered water. "Absolute 1 micron" filters can be found in camping/outdoor supply stores.

Acknowledgements
The content on this page was first contributed by: C. Michael Gibson M.S., M.D.

List of contributors:

Pilar Almonacid