This post is the 16th in a series highlighting the WHO’s list of 17 Neglected Tropical Diseases (now technically 18 as mycetoma was added to the list at the 69th World Health Assembly in May 2016). To read the previous posts in this series click here.
Today’s post is about taeniasis and cysticercosis, two related human diseases caused by the same parasite. Which disease you get depends on when in the life cycle you ingest the parasite. Taeniasis is an intestinal infection caused when you eat the partially grown tapeworm, Taenia solium, in contaminated pork. Cysticercosis on the other hand, occurs when you ingest tapeworm eggs via contaminated food, water, or poor hygiene. These eggs can migrate throughout the body and form cysts in various tissue. The worst-case scenario is when the eggs form cysts in the brain, causing neurocysticercosis, which can result in epilepsy. Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide. It’s estimated that 30% of all epilepsy cases in areas where the parasite is endemic are caused by the parasite. That’s almost one of out three people with epilepsy in these areas who are only epileptic because of a parasitic infection.
The Taenia solium parasite is endemic in many places around the world. As shown in the figure above, it is endemic in Latin America, South America, sub-Saharan Africa, and part of Asia. The humans who are most affected by the parasite are folks who come into frequent contact with the pigs, usually through animal husbandry practices where pigs come into contact with human feces. Because, remember, in the transmission of taeniasis the humans release the tapeworm eggs in their feces, pigs ingest the human feces and then humans eat the contaminated pig meat. You can obviously imagine that in areas where T. solium is endemic, the market value of pigs is reduced and pork can be unsafe to eat.
Taeniasis can be treated with drugs, but there are currently no standard treatments or guidelines for neurocysticercosis. Treatment for neurocysticercosis is on an individual basis, but can be very invasive, expensive, and time consuming, not to mention dangerous for the patient. To prevent T. solium infections, public health, environmental health, and veterinary medicine must all work together. Interventions for prevention include concepts like access to treatment, health education, improved sanitation, and vaccination of pigs, among others.
Taenia solium is a suitable target for eradication: it has a single definitive host (humans) with one source of infection for intermediate hosts (human tapeworm carriers who infect pigs), domestic animals are the main intermediate source, there are no important wild reservoirs, and we have treatment to cure infection. This parasite was eradicated from most of Europe by improvements in sanitation, education, and commercial pig production. Eradication is possible from the rest of the endemic areas in the world as well, it will just take a concerted effort from all sectors of human and animal health systems. I know folks who have (non-parasite) epilepsy and it can be a debilitating disease that disrupts your entire life. Imagine the lives folks could have if neurocysticercosis was no longer a disease they had to worry about.