Cysticercosis

Cysticercosis is a tissue infection caused by the young form of the pork tapeworm, *Taenia solium*. This condition is a significant global health concern, often classified as a neglected tropical disease. While many people may experience no symptoms for years, the infection can cause serious issues in various body parts. In some regions, such as Asia, it can manifest as firm lumps under the skin. More critically, a specific form called neurocysticercosis affects the brain and is a major cause of seizures in developing countries.

The infection process begins through the oral-fecal route. A person acquires the infection by consuming food or water contaminated with tapeworm eggs. These eggs typically come from the feces of a person carrying adult worms, a condition known as taeniasis. Once ingested, the eggs hatch in the intestine into larvae called oncospheres. These larvae enter the bloodstream and migrate to different host tissues. Over about two months, they develop into cysticerci. These cysticerci are translucent, shiny white, and about 0.6 to 1.8 cm long.

Cysticerci can settle in many different areas of the body, leading to various symptoms. In the muscles, they can cause inflammation, fever, and muscle swelling, which may later lead to scarring or atrophy. Subcutaneous cysts appear as firm, mobile nodules on the skin, often on the trunk or limbs. If the parasites reach the eyes, they can cause vision loss, retinal edema, or hemorrhage. The most severe form is neurocysticercosis, where cysts develop in the brain tissue. These brain cysts are usually 5 to 20 mm in diameter, but those in the subarachnoid space can grow as large as 6 cm.

Diagnosing cysticercosis requires different methods depending on where the cysts are located. For brain infections, doctors rely heavily on neuroimaging like CT scans or MRI scans. A CT scan can show both active and inactive, calcified cysts by looking for ring enhancement. MRI is often more sensitive for detecting cysts inside the ventricles of the brain. Doctors may also look for an increased number of eosinophils, a type of white blood cell, in the blood or cerebrospinal fluid. In some cases, a biopsy of the infected tissue or a fundoscopy to examine the eye is necessary for a certain diagnosis.

History and geography play a major role in how this disease is distributed. Cysticercosis has occurred in humans throughout history and remains common in Asia, Sub-Saharan Africa, and Latin America. In certain areas, up to 25% of the population may be affected. In contrast, the disease is very uncommon in the developed world due to better sanitation. In 2015, the disease was responsible for approximately 400 deaths worldwide.

Prevention focuses on breaking the life cycle of the parasite through improved sanitation and hygiene. One effective method is ensuring pork is cooked thoroughly or frozen to kill any existing cysts. Improving access to clean water and using proper toilets also prevents the spread of eggs. Treating humans with taeniasis is vital to stop them from spreading eggs to others or to pigs. In some regions, managing pig populations by using enclosed piggeries has helped eliminate the disease. This was seen in Western Europe after World War II, where the rapid development of the pig industry helped reduce cysticercosis.

Scientists are also researching ways to eradicate the disease through medical and veterinary interventions. One strategy is the use of vaccines for pigs, which could prevent them from carrying the parasite. While several vaccine candidates exist, such as those using genetically engineered antigens, using them in rural areas remains a challenge. Researchers are even looking into hypothetical oral vaccines that pigs could eat. Another approach involves treating both humans and pigs with medications like praziquantel or albendazole. By treating both populations, it may be possible to stop the cycle of infection entirely.