- Taeniasis is an intestinal infection caused by adult tapeworms.
- Taeniasis is acquired by humans through the inadvertent ingestion of tapeworm larval cysts (cysticerci) in undercooked pork or beef.
- Human tapeworm carriers contaminate the environment with tapeworm eggs which pass out with faeces.
- Cysticercosis is the infection of tissues caused by cystercerci as a result of ingesting Taenia eggs. Cysticerci of T. solium, but not T. saginata, can infect humans.
- Cysts that develop in the central nervous system cause neurocysticercosis – the most severe form of the disease and one of the main preventable causes of epilepsy (seizures) in many developing countries.
- More than 80% of the world’s 50 million people who are affected by epilepsy live in low-income and lower-middle-income countries, many of which are endemic for T. solium infections in people and pigs.
Taeniasis is an intestinal infection caused by 2 species of tapeworms. The most important human Taenia tapeworm infections are caused by Taenia solium (pork tapeworm) and T. saginata (beef tapeworm).
Humans become infected with T. saginata when they consume beef which has not been adequately cooked. Taeniasis due to T. saginata usually has a minor impact on human health.
Infection also occurs in humans when they eat raw or undercooked pork (T.solium). Taenia solium tapeworm infection is of significant importance as it can cause cysticercosis – a serious disease.
Cysticercosis is the infection with the tapeworm at the larval stage (cysticerci). Inside the body, cysticerci can develop in a number of tissues such as the muscles, subcutaneous tissues, eyes and brain; those that are located in the central nervous system cause neurocysticercosis, the most severe form of the disease.
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 low-income and lower-middle income countries, many of which are endemic for T. solium infections in people and pigs.
Cysticercosis mainly affects the health and livelihoods of subsistence farming communities in developing countries of Africa, Asia and Latin America since it can lead to epilepsy and death in humans. It also reduces the market value of pigs and cattle and makes pork and beef unsafe to eat.
Although theoretically amenable to control and declared eradicable by the International Task Force for Disease Eradication in 1993, T. solium cysticercosis remains a neglected disease and was added by WHO to the list of major neglected tropical diseases in 2010.
Taeniasis is acquired by humans through the inadvertent ingestion of their cysticerci in undercooked pork or beef.
Once in the human body, cysticerci develop into adult tapeworms that live in the intestine and release egg-bearing gravid proglottids (segments) which are passed out with faeces.
Cysticercosis is acquired when proglottids or eggs are ingested. It is a natural infection of pigs and cattle, but, in the case of T. solium, it can also affect humans, usually when they swallow T. solium egg-contaminated soil, water or food (mainly vegetables).
Taeniasis and cysticercosis are common in areas where animal husbandry practices are such that pigs and cattle come into contact with human faeces.
Taeniasis due to T. solium or T. saginata is usually characterized by mild and non-specific symptoms. Abdominal pain, nausea, diarrhoea or constipation might arise, 6-8 weeks after ingestion of the cysticerci when the tapeworms become fully developed.
These symptoms may continue until the tapeworm dies following treatment (otherwise it may live many years).
In the case of cysticercosis due to T. solium, the incubation period is variable, and infected people may remain asymptomatic for years.
In some endemic regions (in particular Asia), infected people may develop visible or palpable nodules (a small bump or node which is solid that can be detected by touch) beneath the skin (subcutaneous).
When cysts are recognized by the host following spontaneous degeneration or after treatment, an inflammatory reaction may occur.
Neurocysticercosis is associated with a variety of symptoms and signs depending on the number, size, stage and location of the pathological changes as well as the host’s immune response and the parasite’s genotype, but it can also be clinically asymptomatic. Symptoms may include chronic headaches, blindness, seizures (epilepsy if they are recurrent), hydrocephalus, meningitis, dementia and symptoms caused by lesions occupying spaces of the central nervous system.
Taenaisis can be treated with praziquantel (5-10 mg/kg, single-administration) or niclosamide (adults and children over 6 years: 2 g, single-administration after a light breakfast, followed after 2 hours by a laxative; children aged 2-6 years: 1 g; children under 2 years: 500 mg).
Currently there are no standard treatment guidelines for neurocysticercosis and treatment has to be tailored to the individual case. Since the destruction of cysts may lead to an inflammatory response, treatment of active disease may include long courses with praziquantel and/or albendazole, as well as supporting therapy with corticosteroids and/or anti-epileptic drugs, and possibly surgery. The dosage and the duration of treatment can vary greatly and depend mainly on the number, size, location and developmental stage of the cysts, their surrounding inflammatory edema, acuteness and severity of clinical symptoms or signs.
Prevention and control
Infections with T. saginata can be managed through an individual clinical approach due to its low pathogenicity (low ability to spread from host to host).
By contrast, infections due to T. solium require proper public health interventions aimed at their prevention, control and possibly elimination.
Eight key interventions for the control of T. solium are:
- access to preventive chemotherapy;
- identification and treatment of taeniasis cases;
- health education;
- improved sanitation;
- improved pig husbandry;
- anthelmintic treatment of pigs;
- vaccination of pigs;
- improved meat inspection, and processing of meat products.
Reliable epidemiological data on geographical distribution of T. solium taeniasis/cysticercosis in people and pigs is still scarce.
Appropriate surveillance mechanisms should enable new cases of human or porcine cysticercosis to be recorded in order to help identify communities at high risk and focus prevention and control measures in such areas. A mandatory reporting system of cases is highly warranted, to target effective strategies of intervention.
Building on the WHO Expert Consultation on Foodborne Trematode Infections and Taeniasis/Cysticercosis of 2009, the WHO Neglected Tropical Diseases (NTD) roadmap seeks to pilot a strategy for controlling T. solium taeniasis/ (neuro) cysticercosis by 2015 and scale it up in selected endemic countries by 2020.
An informal consultation will take place in WHO in July 2014 with select countries, experts and strategic partners. The consultation will aim to identify a ‘best-fit’ strategy with countries to interrupt transmission of Taenia solium and to improve case detection and management of neurocysticercosis using the tools currently available. Evidence is being collated through a systematic review of the literature with a focus on low resource settings.
Preliminary findings reinforce that a single intervention to control diseases caused by T. solium is insufficient. Working with the veterinary and food safety authorities and other sectors will be necessary to attain a long term reduction in the burden of disease and safeguarding the food value chain.