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 fact sheet refers to the transmission and health impacts of T. solium only.
Infection with the T. solium tapeworm occurs when a person eats raw or undercooked, infected pork. Infection with the tapeworm causes few clinical symptoms. Tapeworm eggs passed in the faeces with the tapeworm carrier are infective for pigs. T. solium eggs may also infect humans if they are ingested by a person (via the fecal-oral route, or by ingesting contaminated food or water), causing infection with the larval parasite in the tissues (human cysticercosis).
Human cysticercosisi 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. In specific communities the association between neurocysticercosis and epilepsy can be up to 70%. In poor remote settings where the disease is present, epilepsy is difficult to diagnose and treat, and causes major stigma, especially in girls and women (where it is commonly associated to witchcraft).
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 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. Although 70% of patients with epilepsy could lead a normal life if treated correctly, poverty, ignorance of the disease, inadequate infrastructure in health or lack of access to medication, cause 75% people with this condition to be treated poorly, if treated at all.
Symptoms
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.
Treatment
The treatment of taeniasis by Taenia solium is important to prevent neurocysticercosis and as a tool to assist in controlling or stopping the parasite transmission cycle. The treatment can be done on an individual bases, or as Mass Drug Administration depending on the local circumstances and the control approaches being implemented. Taenaisis can be treated with single doses of praziquantel (10 mg/kg) or niclosamide (adults and children over 6 years: 2 g, children aged 2–6 years: 1 g). Albendazole at 400 g for 3 consecutive days has also been used.
In neurocysticercosis, since the destruction of cysts may lead to an inflammatory response, specialised treatment of active disease is required and may include long courses with high doses of 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.
Reliable epidemiological data on the geographical distribution of T. solium taeniasis/cysticercosis in people and pigs remains 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.
There are several interventions for the control of T. solium that can be used in different combinations. In a meeting of experts in 2009, they were identified as:
Core “rapid impact” interventions:
- treatment of human taeniasis;
- intervention in pigs (vaccination plus anthelmintic treatment);
Supporting measures:
- community health education, including hygiene and food safety;
- improved sanitation - ending open defecation;
Measures requiring more fundamental societal changes:
- improved pig husbandry - no free-roaming pigs; and
- improved meat inspection and processing of meat products.
There are several mathematical models that determine the probability of success of the different strategies’ combinations and the implementation period required to achieved sustained control, but they are still based in many assumptions and unknowns. However, they usually coincide in that integrated One-Health interventions, are the ones more likely to achieve a faster sustainable control.
WHO’s response
Promoting better clinical management of neurocysticercosis
Epilepsy is one of the most common clinical signs in patients with neurocysticercosis (NCC). WHO recognises that people with epilepsy frequently suffer stigmatization and discrimination. WHO urges the Member States to support the establishment and implementation of strategies for the management of epilepsy, and promote actions to prevent the causes of epilepsy (Resolution WHA 68.20 of 2015).
In this context, clinical management of patients with NCC to prevent and manage epilepsy is an essential component, and the countries are requesting clear guidance to improve case detection and management of neurocysticercosis. WHO has conducted a landscape analysis on the management of neurocysticercosis with an emphasis on low-and middle income countries and is now in the last steps of completing and finalising the diagnosis and treatment guidelines for Taenia solium NCC.
Providing guidance for improved diagnostics and supporting countries diagnostic capacity
Improved, simple, cost-effective diagnostic tools for Taenia solium are still needed:
- A point-of-care test for the diagnosis of human cysticercosis is required, especially a test able to be used in symptomatic patients in remote areas in order to detect those with viable systs who need to be referred for imaging and further management.
- Better test for the diagnosis of taeniasis by T. solium are also needed. Current test lack sensitivity and/or specificity, are not commercially available, are expensive or have not been adequately validated.
- Detection of porcine cysticercosis can also be extremely useful, as the prevalence of the disease is higher in pigs than humans (reducing the required sample size for surveillance). It provides a valuable alternative to sampling humans for confirmation of endemic areas and for monitoring and evaluation of control programs to be confirmed by necropsy.
WHO has been facilitating the development of diagnostic tools, and 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 and identify priorities. Following this, WHO developed Target Product Profiles (TPPs) for the diagnosis of neurocysticercosis, taeniasis and porcine systicercosis. TPPs are process tools that provide product requirements to guide researchers, developers and manufacturers in their efforts to develop effective diagnostics based on the needs of the different stakeholders. After drafting the different TPPs, a consultation was held with global stakeholders, and the TPPs were published in 2017.
Faecal screening tests such as Kato-Katz that are used for other diseases (e.g. soil-transmitted helminths), can also be used to identify Taenia eggs and hence areas in which the parasite may be endemic. WHO is supporting countries such as Cambodia to increase their testing capacity using Kato-Katz.
Supporting countries in their cysticercosis control efforts
WHO has been asked by countries affected with cysticercosis, to support efforts in order to control the disease.
Donation of taenicides
An important component of the control strategy is the treatment of patients who harbor the T. solium tapeworm. This is most often undertaken by implementing preventive chemotherapy (mass drug administration or MDA) to reach all the eligible population. The most effective drugs at a single dose are praziquantel or niclosamide. However, until now, these drugs were not easily available in many countries that wished to control the disease. Under the umbrella of universal health coverage, and with the aim of providing access to quality medicines, WHO has negotiated with Bayer the donation of these two drugs and they are now available for the control of T. solium through the WHO.
Supporting the validation of control programs
To meet the need for clear guidance on a step-wise approach for the development of control programmes, WHO with countries and key partners have taken steps towards identifying a validated strategy to interrupt transmission of T. solium. Several countries are mounting pilot programmes while conducting operational research to measure impact and refine strategies.WHO has supported a 3-year pilot project in Madagascar where cysticercosis is endemic as conditions are very favorable for the transmission of the parasite. A preventive chemotherapy for taeniasis was implemented in Antanifotsy district for 3 consecutive years, and is continuing to support further integrated projects in the country to achieve a sustained control.
In the Americas, PAHO has released a manual on the “Practical considerations for the control of taeniasis and cysticercosis caused by Taenia solium – contribution to the control of T. solium in Latin America and the Caribbean
Identification of endemic areas (mapping)
Cysticercosis is a focal disease, affecting the poorest communities in which basic sanitation is deficient and pigs roam free. One of the first steps to control the disease is to identify those communities or endemic areas where control measures need to be implemented. WHO is assisting countries by providing protocols for mapping (identifying the endemic or high risk areas), as well as assisting countries such as Cambodia in training of diagnostic techniques that can be used for mapping.
Strengthening prevention and control through a One-Health approach
The transmission cycle of T. solium involves pigs as intermediate hosts. Infected pigs look normal, and infected animals suffer little, if any productive loss. Heavily infected pigs may have cysts in their tongues, but the farmers may not notice them. Porcine cysticercosis is not a production disease of pigs, and farmers in these poor communities where the disease is transmitted often do not have the understanding or the incentive to control the disease.
As part of an integrated control strategy to break the transmission cycle of the parasite it is important to implement control measures in pigs. Several mathematical control models have shown that interventions in pigs can greatly accelerate achieving human health benefits.
Advocating a multi-sectorial approach with key partners
WHO is working closely with partner agencies such as the World Organization for Animal Health (OIE) and the Food and Agriculture Organization of the United Nations (FAO) to promote animal interventions and meet the needs for interdisciplinary collaboration to control T. More countries are interested in joining the WHO network for the control of taeniasis/cysticercosis. solium, with the final goal to prevent human suffering due to neurocysticercosis. Tri-partite joint meetings have been organised to promote concerted actions between the different sectors, such as the meeting to accelerate prevention and control of neglected foodborne parasitic zoonoses in Asian countries held in Lao PDR in 2018.
Promoting pig interventions
Specific control measures in the pig population include the vaccination of pigs with the TSOL18 vaccine and the treatment with oxfendazole. Vaccination prevents the pigs getting infected; oxfendazole cures the pigs already infected at the time of vaccination, and both can be given simultaneously.
Working with veterinary authorities as well as key partners in the animal sector, WHO is supporting pilot projects incorporating pig interventions, essential to attain long-term outcomes.
Improving data on T. solium and identifying endemic and high-risk areas
Robust surveillance data is fundamental to assess disease burden, take action and to evaluate progress of control actions. As for other neglected diseases which occur in underserved populations and remote areas, data is especially scarce. WHO is active in counters this situation by collecting and mapping data on T. solium distribution and risk factors associated with the occurrence of the parasite, such as like information on pig keeping, food safety and sanitation. This information has been incorporated into the WHO Global Health Observatory. WHO is also working on developing a protocol to better map the disease and identify the endemic and high-risk areas within countries. This protocol is now being validated in several countries.
Indicators are specific variables that assist with data analysis and provide tools for health authorities and people involved in disease control. WHO has defined a new set of indicators at country and global level for T. solium and is developing reporting systems to guide and assist the countries on data collection and reporting.
At global level, the indicators are 1- Number of endemic countries for T. solium, and 2- Number of countries with intensified control in hyper endemic areas for T. solium. Intensified control means implementation of any core “rapid impact” interventions.