Cysticercosis is caused by infection with the larval stage of the pork tapeworm, *Taenia solium*. This disease occurs when a person ingests the eggs of *T. solium*, which are shed in the feces of someone who carries the adult tapeworm in their intestines. Unlike taeniasis, where a person harbors the adult tapeworm after eating undercooked pork containing cysticerci (the larval cysts), cysticercosis happens when the eggs themselves are swallowed, leading to the development of cysts in various tissues of the body.
The life cycle of *Taenia solium* is central to understanding how cysticercosis develops. The adult tapeworm lives in the human intestine and releases eggs into the environment through feces. These eggs can contaminate food, water, or hands, especially in areas with poor sanitation. When another person accidentally ingests these eggs, the eggs hatch in the intestine, releasing larvae that penetrate the intestinal wall and travel through the bloodstream to different parts of the body. These larvae then form cysts, called cysticerci, in muscles, skin, eyes, or the central nervous system.
The most serious form of cysticercosis is neurocysticercosis, where cysts develop in the brain. This can cause a wide range of neurological symptoms, including seizures, headaches, and even life-threatening complications. The severity depends on the number, size, and location of the cysts, as well as the host’s immune response.
Transmission of cysticercosis is closely linked to hygiene and sanitation conditions. In regions where open defecation is common or where pig farming is done near human dwellings without proper waste management, the risk of egg contamination increases. People can become infected by consuming food or water contaminated with tapeworm eggs or through direct contact with a tapeworm carrier, such as via contaminated hands.
It is important to note that cysticercosis is not caused by eating undercooked pork alone—that leads to intestinal taeniasis, not cysticercosis. Instead, cysticercosis results from ingesting the eggs, which can come from fecal contamination. This means that a person with taeniasis can be a source of cysticercosis for others if hygiene is poor.
In rare and emerging cases, there is evidence suggesting that adult tapeworms themselves might have the potential to invade tissues beyond the intestine, including the central nervous system, especially in immunocompromised individuals. This challenges the traditional understanding that only the larval stage causes tissue infection and highlights the complexity of *T. solium* infections.
Preventing cysticercosis involves improving sanitation, ensuring proper handwashing, cooking pork thoroughly to kill cysticerci, and treating tapeworm carriers to stop the spread of eggs. Public health measures focusing on education, hygiene, and pig management are crucial in breaking the cycle of transmission.
In summary, cysticercosis is caused by ingesting *Taenia solium* eggs from human feces, leading to larval cysts forming in tissues. Poor sanitation and hygiene facilitate this transmission, making it a significant health issue in areas where these conditions prevail.
