Cysticercosis
Human cysticercosis is caused by the development of Taenia solium cysticerci in human tissues. Cysticerci that develop in the central nervous system cause neurocysticercosis.
Neurocysticercosis is considered to be a common infection of the human nervous system and is the most frequent preventable cause of epilepsy in the developing world. More than 80% of the world’s 50 million people who are affected by epilepsy live in developing countries, many of which are endemic for T. solium infections in people and pigs.
Cysticercosis mainly affects the health and livelihoods of subsistence farmers in developing countries of Africa, Asia and Latin America as it can lead to epilepsy and death in humans, reduces the market value of pigs and makes pork unsafe to eat.
Although theoretically amenable to control and declared eradicable by the International Task Force for Disease Eradication in 1993, cysticercosis remains a neglected disease.
This is mainly because of a lack of information about its burden and transmission, the lack of diagnostic tools available for use in the field, and the lack of validation of simple intervention packages used as part of integrated helminth control strategies.
Transmission
Humans acquire cysticerci, the larval stage of T. solium, by ingesting the tapeworm’s eggs.
Cysticerci also develop in the muscles of pigs that have swallowed T. solium eggs.
The consumption of undercooked pork by humans completes the tapeworm’s lifecycle. The frequency of the disease has decreased in developed countries owing to stricter meat-inspection standards, improved hygiene and better sanitary facilities.
Symptoms, prognosis and treatment
The incubation period is variable, and infected people may remain asymptomatic for years. When cysts are recognized by the host following spontaneous degeneration or after treatment, an inflammatory reaction may occur; this usually results in clinical symptoms, including chronic headaches, blindness, seizures (epilepsy if they are recurrent), hydrocephalus, meningitis, symptoms caused by lesions occupying spaces of the central nervous system, dementia and even death.
Symptoms include epileptiform attacks, headaches, learning difficulties and convulsions. In severe cases, neurocysticercosis may be fatal and it has been noted as a cause of death among young adult Hispanics and Latinos in the United States. Oedema around calcified cysticercal granulomas also has been found to cause symptoms.
The duration of symptoms associated with neurocysticercosis, and the proportion of patients that will fully recover with or without treatment, are ill-defined.
The location of infection that most often prompts a medical consultation is the central nervous system, followed by the eye and its surrounding tissues. Treating cysticercosis is difficult, and not always successful. Morbidity mostly occurs when the cysticerci develop in the brain causing neurocysticercosis.
Treatment of cysticercosis is very difficult with varying success: praziquantel+corticosteroids+albendazole. Treatment of taeniasis is easy using praziquantel.
Surveillance, prevention and control
One of the main obstacles to controlling and eliminating T. solium infection is the lack of reliable epidemiological data on infections in people and pigs. Preventing the disease requires strict meat inspection regimens, health education, thorough cooking of pork, sound hygiene, and adequate water and sanitation.
Appropriate surveillance mechanisms should enable new cases of human or porcine cysticercosis to be reported to national authorities in order to facilitate the identification and treatment of tapeworm carriers and the people who are in close contact with them.
Options available for detecting human cysticercosis include biopsy of subcutaneous cysts (a common manifestation of cysticercosis in Asia), immunodiagnosis (detection of antibodies or parasite antigens in serum samples) and imaging (radiography, computed tomography and magnetic resonance imaging ).
Methods for detecting cysticercosis in pigs include the rapid, inexpensive method of detecting lingual cysts, but this has low sensitivity, or more sensitive immunodiagnostic tests and postmortem inspection. One dose of the drug oxfendazole has been found to cure porcine cysticercosis though it may take several months for the cysts to disappear.
In 2009, all aspects of controlling T. solium infections and disease were discussed during an expert consultation on foodborne trematodiasis and taeniasis and cysticercosis held in Vientiane, Lao People’s Democratic Republic. The meeting issued guidance that focused on using improved preventive chemotherapy in humans and pigs, and the vaccination of pigs. These tools should be ready for use in the field within 2–3 years.
The consultation group further acknowledged that community-led total sanitation (that is, the provision of adequate water and sanitation organized by the community itself) is a novel approach to behavioural change and has the potential to be scaled up with minimal investment.