Taenia solium cysticercosis, caused by infection with T. solium larval cysts, occurs in both humans and swine, resulting in significant public health and economic hardship. T. solium, also referred to as the pork tapeworm, is a helminth that exists in both a mature tapeworm form and a larval form. The lifecycle of T. solium begins when swine, the intermediate hosts, ingest tapeworm eggs excreted in the feces of a tapeworm carrier. The larvae hatch from the eggs and invade most tissues of the swine, giving rise to the disease cysticercosis.
When humans ingest raw or undercooked meat from cysticercotic swine, tapeworms, or taeniasis, develop. Patients with taeniasis may exhibit epigastric discomfort, nausea, irritability, diarrhea, and weight loss. In addition, proglottids, or individual segments of the tapeworm that are self-contained hermaphroditic reproductive units, may obstruct the appendix, biliary duct, or pancreatic duct.
Humans may also ingest T. solium eggs present in contaminated food and water and become infected with the larval form. After T. solium eggs are ingested, cysticerci may develop in the subcutaneous tissues, muscles, heart, lungs, liver, brain, and eye. Although small numbers of viable cysticerci may fail to produce symptoms in the infected host, death of the larvae stimulate a marked inflammatory reaction, fever, muscle pains, and eosinophilia. If the larvae invade the central nervous system, a single cyst may cause disease. The host may develop meningoencephalitis, epileptic seizures, dementia and other neurologic or psychiatric manifestations, and death can result from acute intracranial hypertension. The various manifestations of neurologic dysfunction caused by T. solium infection are collectively termed neurocysticercosis. Although neurocysticercosis can include many neurological symptoms, epilepsy is the most common symptom. In fact, T. solium is considered the leading infectious cause of epileptic seizures worldwide. Additionally, T. solium neurocysticercosis has a current worldwide toll of 50 million cases with 50,000 deaths each year.
Neurocysticercosis is rarely acquired in the United States; however, the disease is common in Latin America, Asia, Russia, and Eastern Europe. In Mexico, the mean rate for cysticercotic pigs in inspected slaughterhouses during 1980-1981 was 1.55%, and in rural areas of Mexico and South America, where sewage disposal is limited, the proportion of cysticercotic pigs can be in excess of 50%. In these and other developing countries, the parasite causes a substantial economic burden to the pork industry. Additionally, due to the increased travel and immigration from highly endemic areas, detection and treatment of T. solium related diseases has become a U.S. public health priority.
Diagnosis historically relied on histological identification of the parasite by biopsy or autopsy. The recent development of radiologic and serologic methods has improved diagnosis. However, while radiologic methods such as computed tomography (CT) or nuclear magnetic resonance imaging are useful in diagnosing neurocysticercosis, they are often too expensive or inaccessible in developing countries.
Although some diagnostic tests are currently available to identify T. solium infection and diagnose neurocysticercosis, these tests lack specificity and sensitivity. A more specific and sensitive assay for diagnosing human neurocysticercosis by detecting the presence of T. solium larvae using immunoelectrotransfer blot (EITB) is described in U.S. Pat. No. 5,354,660 to Tsang et al. This test is the only test approved by the Pan American Health Organization. However, the assay utilizes purified, naturally-occurring T. solium larval glycoproteins, which makes the assay reagents expensive and difficult to produce.
In developing countries where T. solium-related diseases are endemic, access to diagnostic assays may be limited due to the high cost of using antigens that are produced using complicated purification procedures. Furthermore, because cysticercosis is most prevalent in rural areas of developing countries, a field test is needed for epidemiological studies and surveillance. A field assay using inexpensive and reliable reagents could be an important tool in breaking the transmission cycle of the parasite, enabling the on-site diagnosis of infected pigs and immediate treatment with anti-helminthic agents such as oxfendazole. A field diagnosis of cysticercosis would also serve as an economic benefit to pig farmers, because uninfected pigs command a higher price.