Taenia solium, the pig tapeworm, can induce two different types of infection in humans in different stages of its biological development cycle.

Taeniasis is an intestinal infestation of adult tapeworms. It is acquired by humans through the ingestion of tapeworm larval cysts (cysticerci) in raw or undercooked pork. The tapeworms’ eggs are excreted with human faeces, mostly without showing symptoms in the host. One tapeworm carrier can excrete tens of thousands of eggs per day and has therefore a special importance in the epidemiology of the parasite. Cysticercosis develops when humans or pigs ingest the excreted tapeworm eggs. This happens most likely as a result of poor hygiene, through contaminated food or water and when pigs have access to human faeces. Ingested eggs develop to larvae (called cysticerci) and migrate through the body.

In porcine cysticercosis, the larvae mostly remain in muscles and the parasite’s cycle is completed when humans eat the undercooked meat (see taeniasis). Characterizing the transmitting host, data about pigs and pig keeping can serve as a proxy for human infection.

In humans, the cysticerci have an affinity to migrate to the central nervous system where they can cause neurological symptoms, including epileptic seizures. This specific form of cysticercosis is called neurocysticercosis and has a specific importance as a potential severe and long-lasting disease. It is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in close proximity.

Due to the frequently asymptomatic nature of taeniasis, most tapeworm carriers remain unidentified or are only diagnosed incidentally or in the frame of targeted surveys. For a definitive diagnosis of neurocysticercosis, sophisticated neuro-imaging techniques like CT or MRI scanners are required, which are not available in many locations where the tapeworm infection is frequent. These circumstances lead to taeniasis and cysticercosis being under-reported and mis- and under-diagnosed, and thus data on human cases and occurrence in animal populations is limited. Currently, these data are more likely to indicate the presence of the disease rather than its full extent. As control programmes scale up towards control of Taenia solium, surveillance is expected to increase, leading to subsequent improved data quality.