- Taeniasis is an intestinal infection caused by adult tapeworms.
- Three tapeworm species cause taeniasis in humans, Taenia solium, Taenia saginata and Taenia asiatica. Only T. solium causes major health problems.
- T. solium taeniasis is acquired by humans through the ingestion of tapeworm larval cysts (cysticerci) in undercooked and infected pork.
- Human tapeworm carriers excrete tapeworm eggs in their faeces and contaminate the environment when they defecate in open areas.
- Humans can also become infected with T. solium eggs by ingesting contaminated food or water or as a result of poor hygiene.
- Ingested T. solium eggs develop to larvae (called cysticerci) in various organs of the human body. When they enter the central nervous system they can cause neurological symptons (neurocysticercosis), including epileptic seizures.
- T. solium is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in close proximity.
- More than 80% of the world's 50 million people who are affected by epilepsy live in low and lower-middle income countries.
- A combination of control measures is available, and their implementation depends on the local setting and resources.
Transmission and burden
Taeniasis is an intestinal infection caused by 3 species of tapeworm: Taenia solium (pork tapeworm), Taenia saginata (beef tapeworm) and Taenia asiatica.
Humans can become infected with T. saginata or T. asiatica when they consume infected beef meat or pig liver tissue, respectively, which has not been adequately cooked, but taeniasis due to T. saginata or T. asiatica has no major impact on human health. Therefore, this factsheets refers to the transmission and health impacts of T. solium only.
Infection with the T. solium tapeworm occurs when humans eat raw or undercooked, infected pork. Tapeworm eggs pass with the faeces and are infective for pigs. Infection in humans with the T. solium tapeworm causes few clinical symptoms. However as well as being infective for pigs, T. solium eggs may also infect humans if they are ingested, causing infection with the larval parasite in the tissues (human cysticercosis). This infection can result in devastating effects on human health. The larvae (cysticerci) may develop in the muscles, skin, eyes and the central nervous system. When cysts develop in the brain, the condition is referred to as neurocysticercosis. Symptoms include severe headache, blindness, convulsions, and epileptic seizures, and can be fatal. Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide, and is estimated to cause 30% of all epilepsy cases in in countries where the parasite is endemic.
Cysticercosis mainly affects the health and livelihoods of subsistence farming communities in developing countries of Africa, Asia and Latin America. It also reduces the market value of pigs and cattle, and makes pork unsafe to eat. In 2015, the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases, resulting in a considerable total of 2.8 million disability-adjusted life-years (DALYs). The total number of people suffering from neurocysticercosis, including symptomatic and asymptomatic cases, is estimated to be between 2.56–8.30 million, based on the range of epilepsy prevalence data available.
T. solium cysticercosis was added by WHO to the list of major Neglected Tropical Diseases (NTDs) in 2010 with NTD roadmap goals of making available a validated strategy for control and elimination of T. solium taeniasis/cysticercosis and those interventions to be scaled up in selected countries by 2020.
Taeniasis due to T. solium, T. saginata or T. asiatica is usually characterized by mild and non-specific symptoms. Abdominal pain, nausea, diarrhoea or constipation may arise when the tapeworms become fully developed in the intestine, approximately 8 weeks after ingestion of meat containing cysticerci.
These symptoms may continue until the tapeworm dies following treatment, otherwise it may live for a number of years. It is considered that untreated infections with T. solium tapeworms generally persist for 2–3 years.
In the case of cysticercosis due to T. solium, the incubation period prior to the appearance of clinical symptoms is variable, and infected people may remain asymptomatic for many years.
In some endemic regions (particularly in Asia), infected people may develop visible or palpable nodules (a small solid bump or node that can be detected by touch) beneath the skin (subcutaneous). Neurocysticercosis is associated with a variety of signs and symptoms depending on the number, size, stage, and location of the pathological changes as well as the host’s immune response, but 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 meal followed after 2 hours by a laxative; children aged 2–6 years: 1 g; children under 2 years: 500 mg).
In neurocysticercosis, 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
To prevent, control and possibly eliminate T. solium, proper public health interventions with an approach spanning veterinary, human health and environmental sectors are required. Eight interventions for the control of T. solium can be used in different combinations designed on the basis of the context in the countries:
- mass drug administration for taeniasis;
- identification and treatment of taeniasis cases;
- health education, including hygiene and food safety;
- improved sanitation;
- improved pig husbandry;
- anthelmintic treatment of pigs (Oxfendazole at doses of 30 mg/kg – commercially produced and registered for the treatment of cysticercosis in pigs);
- vaccination of pigs (TSOL18 vaccine – commercially available); and
- 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 these areas.
Working with veterinary and food safety authorities as well as with other sectors is essential to attaining the long-term outcomes of reducing the burden of disease and safeguarding the food value chain. The WHO Neglected Tropical Diseases (NTDs) team is working closely with other WHO departments in the areas of mental health, research and development, food safety, water, and sanitation, as well as partner agencies such as the Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) to meet the needs for interdisciplinary collaboration to control T. solium, with the final goal to prevent human suffering due to neurocysticercosis.
To meet the need for clear guidance on a step-wise approach for the development of control programmes, WHO with countries and key partners has taken the first steps towards identifying the “best-fit” strategy to interrupt transmission of T. solium and improve case detection and management of neurocysticercosis using the tools currently available.
Improved, simple, cost-effective and rapid diagnostic tools are still needed for use in field conditions to detect T. solium carriers as well as human and porcine cysticercosis cases, and to direct programme planning and monitoring. In December 2015, a stakeholder meeting on T. solium taeniasis/cysticercosis diagnostic tools was held at WHO headquarters to address the lack of a suitable diagnostic toolbox for taeniasis, cysticercosis and neurocysticercosis.
WHO programmes for the control of neglected tropical diseases and of mental health are also steering the development of evidence based standard guidelines for diagnosis and treatment of T. solium neurocysticercosis to support clinical management and inform national policies and programmes.
Several countries are mounting pilot programmes with the available tools while conducting operational research to measure impact and refine strategies. More countries are interested in joining the WHO network for the control of taeniasis/cysticercosis. Robust surveillance data is fundamental to assess disease burden and to evaluate progress.. As for other neglected diseases which occur in underserved populations and remote areas, data is especially scarce. WHO counters this situation by collecting and mapping data on T. solium, and risk factors associated with the occurrence of the parasite, like information on pig keeping, food safety and sanitation.
Sustainable funding and anthelmintic drug donations are urgently needed to progress towards the control goals of T. solium.