Cysticercosis

Primary reference(s)

WHO, 2020. Taeniasis/cysticercosis. World Health Organization (WHO). Accessed 29 September 2020.

Additional scientific description

Taenia solium causes taeniasis which is acquired by humans through the ingestion of the parasite’s 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 due to poor hygiene (via the faecal-oral route) or ingesting contaminated food or water. When the parasites enter the central nervous system, they can cause neurological symptoms (neurocysticercosis), including epileptic seizures. Human cysticercosisi can result in devastating effects on human health. The larvae (cysticerci) may develop in the muscles, skin, eyes and central nervous system (WHO, 2020).

Cysticercosis due to T. solium is usually characterised 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 several years. It is considered that untreated infections with T. solium tapeworms generally persist for two to three years. In the case of cysticercosis due to T. solium the incubation period prior to the appearance of clinical symptoms varies, 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) (WHO, 2020).

Taenia solium is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in proximity. In high risk communities it can be associated with as many as 70% of epilepsy cases. More than 80% of the world’s 50 million people who are affected by epilepsy live in low and lower-middle income countries. 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 with witchcraft) (WHO, 2020). In 2015, the World Health Organization (WHO) Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases, and resulting in a 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 at 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% of people with this condition to be treated poorly, if treated at all (WHO, 2020).

Metrics and numeric limits

Not applicable.

Examples of drivers, outcomes and risk management

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 (WHO, 2020).

To prevent, control and possibly eliminate T. solium, public health interventions with an approach spanning the veterinary, human health and environmental sectors are required. However, reliable epidemiological data on the geographical distribution of T. solium taeniasis/cysticercosis in people and pigs remains scarce (WHO, 2020).

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 to focus prevention and control measures in these areas (WHO, 2020).

There are several interventions for the control of T. solium that can be used in different combinations. In a meeting of experts in 2009, these were identified as (WHO, 2020):

• 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
  • improved meat inspection and processing of meat products.

The WHO response includes: supporting the validation of control programmes; identification of endemic areas (mapping); strengthening prevention and control through a One-Health approach; advocating a multi-sectorial approach with key partners; promoting pig interventions; and improving data on T. solium and identifying endemic and high-risk areas (WHO, 2020).

Indicators are specific variables that assist with data analysis and provide tools for health authorities and people involved in disease control. The 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 the global level, the indicators are the number of endemic countries for T. solium, and the number of countries with intensified control in hyper endemic areas for T. solium. Intensified control means implementation of any core ‘rapid impact’ interventions (WHO, 2020).