Cysticercosis is a tissue infection caused by the young form of the pork tapeworm. People may have few or no symptoms for years. In some cases, particularly in Asia, solid lumps of between one and two centimeters may develop under the skin. After months or years, these lumps can become painful and swollen and then resolve. A specific form called neurocysticercosis, which affects the brain, can cause neurological symptoms. In developing countries, this is one of the most common causes of seizures.
Cysticercosis is usually acquired by eating food or drinking water contaminated by tapeworms' eggs from human feces. Among foods, egg-contaminated vegetables are a major source. The tapeworm eggs are present in the feces of a person infected with the adult worms, a condition known as taeniasis. Taeniasis, in the strict sense, is a different disease and is due to eating cysts in poorly cooked pork. People who live with someone with pork tapeworm have a greater risk of getting cysticercosis. The diagnosis can be made by aspiration of a cyst. Taking pictures of the brain with computer tomography (CT) or magnetic resonance imaging (MRI) is most useful for the diagnosis of disease in the brain. An increased number of a type of white blood cell, called eosinophils, in the cerebral spinal fluid and blood is also an indicator.
Infection can be effectively prevented by personal hygiene and sanitation: this includes cooking pork well, proper toilets and sanitary practices, and improved access to clean water. Treating those with taeniasis is important to prevent spread. Treating the disease when it does not involve the nervous system may not be required. Treatment of those with neurocysticercosis may be with the medications praziquantel or albendazole. These may be required for long periods. Steroids, for anti-inflammation during treatment, and anti-seizure medications may also be required. Surgery is sometimes done to remove the cysts.
The pork tapeworm is particularly common in Asia, Sub-Saharan Africa, and Latin America. In some areas it is believed that up to 25% of people are affected. In the developed world it is very uncommon. Worldwide in 2015 it caused about 400 deaths. Cysticercosis also affects pigs and cows but rarely causes symptoms as most are slaughtered before symptoms arise. The disease has occurred in humans throughout history. It is one of the neglected tropical diseases.
Signs and symptoms
Muscles Cysticerci can develop in any voluntary muscle. Invasion of muscle can cause inflammation of the muscle, with fever, eosinophilia, and increased size, which initiates with muscle swelling and later progress to atrophy and scarring. Usually, it is asymptomatic since the cysticerci die and become calcified.
Nervous system
The term neurocysticercosis is generally accepted to refer to cysts in the parenchyma of the brain. It presents with seizures and, less commonly, headaches. Cysticerca in brain parenchyma are usually 5–20 mm in diameter. In subarachnoid space and fissures, lesions may be as large as 6 cm in diameter and lobulated. They may be numerous and life-threatening.
Cysts located within the ventricles of the brain can block the outflow of cerebrospinal fluid and present with symptoms of increased intracranial pressure.
Racemose neurocysticercosis refers to cysts in the subarachnoid space. These can occasionally grow into large lobulated masses causing pressure on surrounding structures.
Spinal cord neurocysticercosis most commonly presents symptoms such as back pain and radiculopathy.
Eyes In some cases, cysticerci may be found in the eyeball, extraocular muscles, and under the conjunctiva (subconjunctiva). Depending on the location, they may cause visual difficulties that fluctuate with eye position, retinal edema, hemorrhage, decreased vision, or even vision loss.
Skin
Subcutaneous cysts are firm, mobile nodules, occurring mainly on the trunk and extremities. Subcutaneous nodules are sometimes painful.
Cause
Human cysticercosis develops after ingestion of the egg form of Taenia solium (often abbreviated as T. solium and also called pork tapeworm), which is transmitted through the oral-fecal route. The eggs enter the intestine where they develop into oncosphere larvae by hatching. The larvae enter the bloodstream and invade host tissues, where they further develop into larvae called cysticerci. The cysticercus larva completes development in about two months. It is about 0.6 to 1.8 cm–long, translucent, ellipsoidal, and shiny white, containing one developing scolex.
Diagnosis The traditional method of demonstrating either tapeworm eggs or proglottids in stool samples diagnoses only taeniasis, carriage of the tapeworm stage of the life cycle. Only a small minority of patients with cysticercosis will harbor a tapeworm, rendering stool studies ineffective for diagnosis. Ophthalmic cysticercosis can be diagnosed by visualizing parasite in eye by fundoscopy.
In cases of human cysticercosis, diagnosis is a sensitive problem and requires biopsy of the infected tissue or sophisticated instruments. Taenia solium eggs and proglottids found in feces, ELISA, or polyacrylamide gel electrophoresis diagnose only taeniasis and not cysticercosis. Radiological tests, such as X-ray, CT scans which demonstrate ring enhancement and MRIs, can also be used to detect diseases. X-rays are used to identify calcified larvae in the subcutaneous and muscle tissues, and CT scans and MRIs are used to find lesions in the brain.
Serological Antibodies to cysticerci can be demonstrated in serum by enzyme linked immunoelectrotransfer blot (EITB) assay and in CSF by ELISA. An immunoblot assay using lentil-lectin (agglutinin from Lens culinaris) is highly sensitive and specific. However, individuals with intracranial lesions and calcifications may be seronegative. In the CDC's immunoblot assay, cysticercosis-specific antibodies can react with structural glycoprotein antigens from the larval cysts of Taenia solium. However, this is mainly a research tool not widely available in clinical practice and nearly unobtainable in resource-limited settings.
Neurocysticercosis The diagnosis of neurocysticercosis is mainly clinical, based on a compatible presentation of symptoms and findings of imaging studies.
Imaging Neuroimaging with CT or MRI is the most useful method of diagnosis. A CT scan shows both calcified and uncalcified cysts, as well as distinguishing active and inactive cysts. Cystic lesions can show ring enhancement and focal-enhancing lesions. Some cystic lesions, especially the ones in ventricles and subarachnoid space may not be visible on a CT scan, since the cyst fluid is isodense with cerebrospinal fluid (CSF). Thus diagnosis of extraparenchymal cysts usually relies on signs like hydrocephalus or enhanced basilar meninges. A CT scan with intraventricular contrast or MRI can be used. MRI is more sensitive in the detection of intraventricular cysts.
CSF CSF findings include pleocytosis, elevated protein levels and depressed glucose levels; but these may not be always present.
Prevention Cysticercosis is considered a "tools-ready disease" according to WHO. International Task Force for Disease Eradication in 1992 reported that cysticercosis is potentially eradicable. It is feasible because there are no animal reservoirs besides humans and pigs. The only source of Taenia solium infection for pigs is from humans, a definite host. Theoretically, breaking the life cycle seems easy by doing intervention strategies from various stages in the life cycle.Schantz, P. "Eradication of T. solium Cysticercosis" International Conference on Emerging Infectious Diseases 2002. CDC.ftp://ftp.cdc.gov/pub/infectious_diseases/iceid/2002/pdf/schantz.pdf
For example, Massive chemotherapy of infected individuals, improving sanitation, and educating people are all major ways to discontinue the cycle, in which eggs from human feces are transmitted to other humans and/or pigs. Cooking pork or freezing it and inspecting meat are effective means to cease the life cycle The management of pigs by treating them or vaccinating them is another possibility to intervene The separation of pigs from human feces by confining them in enclosed piggeries. In Western European countries post World War 2 the pig industry developed rapidly and most pigs were housed. This was the main reason for pig cysticercosis largely being eliminated from the region. This, of course, is not a quick answer to the problem in developing countries.
Pigs The intervention strategies to eradicate cysticercosis include surveillance of pigs in foci of transmission and massive chemotherapy treatment of humans. In reality, control of T. solium by a single intervention, for instance, by treating only the human population will not work because the existing infected pigs can still carry on the cycle. The proposed strategy for eradication is to do multilateral intervention by treating both human and porcine populations. It is feasible because treating pigs with oxfendazole is effective and once treated, pigs are protected from further infections for at least 3 months.
Limitations Even with the concurrent treatment of humans and pigs, complete elimination is hard to achieve. In one study conducted in 12 villages in Peru, both humans and pigs were treated with praziquantel and oxfendazole, with a coverage of more than 75% in humans and 90% in pigsGarcia, H.H., 2002. "Effectiveness of an interventional control program for human and porcine Taenia solium cysticercosis in field conditions." In: International Health. Johns Hopkins University, Baltimore, p. 250. The result shows a decrease in prevalence and incidence in the intervention area; however, the effect did not eliminate T. solium. The possible reason includes the incomplete coverage and re-infection. Even though T. solium could be eliminated through mass treatment of human and porcine population, it is not sustainable. Moreover, both tapeworm carriers of humans and pigs tend to spread the disease from endemic to non-endemic areas resulting in periodic outbreaks of cysticercosis or outbreaks in new areas.
Vaccines Given that pigs are part of a life cycle, vaccinating pigs is another feasible intervention to eliminate cysticercosis. Research studies have been focusing on vaccines against cestode parasites since many immune cell types are found to be capable of destroying cysticercus. Many vaccine candidates are extracted from antigens of different cestodes such as Taenia solium, T. crassiceps, T. saginata, T. ovis and target oncospheres and/or cysticerci. In 1983, Molinari et al. reported the first vaccine candidate against porcine cysticercosis using antigen from cysticercus cellulosae drawn out from naturally infected animals. Recently, vaccines extracted from genetically engineered 45W-4B antigens have been successfully tested to pigs in an experimental condition. This type of vaccine can protect against cysticercosis in both Chinese and Mexican type of T. solium. However, it has not been tested in endemic field conditions, which is important because the realistic conditions in the field differ greatly from the experimental condition, and this can result in a great difference in the chances of infection and immune reaction.
Even though vaccines have been successfully generated, the feasibility of their production and usage in rural free-ranging pigs remains a challenge. If a vaccine is to be injected, the burden of work and the cost of vaccine administration to pigs will remain high and unrealistic. The incentives of using vaccines by pig owners will decrease if the vaccine administration to pigs takes time by injecting every single pig in their livestock. A hypothetical oral vaccine is proposed to be more effective as it can be easily delivered to the pigs by food.
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