Taenia solium
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p685-686
2025-11-03
51
GENERAL CHARACTERISTICS
T. solium, the pork tapeworm, is the intestinal cestode capable of causing serious pathologic damage to the human host. Humans serve as the definitive host, whereas pigs serve as the intermediate host. Humans can also serve as the intermediate host. T. solium may result in an intestinal infection in which the larvae mature and reside in the small intestine for up to 25 years. The organisms can grow to be 1.5 to 8 m long and produce more than 1000 proglottids, each containing about 50,000 eggs. Cysticercosis is the extraintestinal form of the disease and can be much more severe. The disease is life threatening if the organism invades the central nervous system.
EPIDEMIOLOGY
T. solium has a worldwide distribution. Higher rates of illness have been seen in Latin America. The parasite is found in the United States, typically among Latin Ameri can immigrants and Mexican agricultural workers. The tapeworm is more prevalent in underdeveloped communities with poor sanitation and when pork is ingested undercooked or raw.
PATHOGENESIS AND SPECTRUM OF DISEASE
T. solium infection can result in the presence of both adult and larval stages in the human host (Figure 1). Infection begins when the intermediate host ingests embryonated eggs in feces. Once the egg is ingested, the hexacanth embryo is released into the intestine where the embryo penetrates the mucosa. The embryo then matures into a cyst (cysticercus) in the tissue. Humans may become infected when they eat raw or undercooked pork containing embedded cysts. Pork tapeworm infection is usually caused through the ingestion of multiple worms. During ingestion and subsequent digestion of the infected meat, the cysticercus is released and attaches to the mucosa within the small intestine of the human host. The cysticercus matures into an adult worm within approximately 5 to 12 weeks. The eggs are then released in the host’s feces. Accidental ingestion of the eggs by the human host may also result in migration of the embryo through the intestine to other areas of the body, including the eyes, brain, muscle, or bone. In addition, the proglottids are motile and may migrate out of the anus. Infection of the adult tapeworm causes few clinical symptoms, although abdominal pain, diarrhea, indigestion, and loss of appetite may be present as a result of irritation to the mucosa of the intestinal wall. The major complication with T. solium is cysticercosis (larval forms throughout the body), in which the human host becomes the intermediate host and harbors the larvae in tissues as previously described.
Fig1. Life cycle of Taenia saginata and Taenia solium.
LABORATORY DIAGNOSIS
Serologic diagnosis is unreliable for infections with T. solium. Diagnosis of Taenia tapeworm infection is through the examination of stool samples. Individuals suspected of infection with T. solium should be asked if they have passed any notable tapeworm segments in their stool. Stool specimens should be collected on 3 different days and microscopically examined for the presence of Taenia eggs (see Figure 2). Tapeworm eggs can be detected in the stool 2 to 3 months after the tapeworm infection is established. Eggs are round or slightly oval (31 to 43 µm in diameter) and yellow-brown with a thick striated shell containing a six-hooked oncosphere. Diagnosis is based on the recovery of eggs or proglottids in stool or from the perianal area. T. solium and T. saginata cannot be differentiated on the basis of egg morphology. Speciation requires the examination of gravid proglottids or the scolices. T. solium gravid proglottids are longer than wide (19 × 17 mm) and may be distinguished from T. saginata according to the number of uterine branches. T. solium contains 7 to 13 lateral uterine branches along the proglottid (Figure 3), whereas T. saginata contains more than 13 branches. Uterine branches may be visualized by staining the proglottids with India ink. The scolex contains a neck region that is typically short and half the width of the scolex and differs from that of T. saginata by the presence of four suckers with hooks in a double row (Figure 4). The adult worm is usually 3 to 5 m long. Extreme care should be taken when handling infectious stool, since T. solium proglottids and eggs are extremely infectious. Additional laboratory findings may include a low-grade eosinophilia, increased serum IgE level, and the presence of atypical lymphocytes in the cerebrospinal fluid.
Fig2. A, Taenia spp. egg. B, Diphyllobothrium latum egg. C, Hymenolepis diminuta egg. D, Hymenolepis nana egg. E, Dipylidium caninum egg packet.
Fig3. Gravid proglottids. A, Taenia saginata. B, Taenia solium. C, Diphyllobothrium latum. D, Dipylidium caninum. (From Garcia LS: Diagnostic medical parasitology, ed 5, Washington, DC, 2007, ASM Press.)
Fig4. T. saginata scolex with suckers. (Courtesy Dr. Henry Travers, Sioux Falls, S.D.)
ANTIPARASITIC SUSCEPTIBILITY TESTING AND THERAPY
Adult worms can be eradicated with praziquantel or niclosamide. Expulsion of the scolex must be assured to assume satisfactory treatment.
PREVENTION
Good hygiene and immediate treatment are essential for the prevention of autoinfection. Pork should be cooked or frozen thoroughly. Cysticerci do not survive temperatures below −10° C or above 50° C. Educational programs concerning the hazards associated with living near human sewage and contaminated drinking water are important in populations at risk. When traveling in countries where food is likely to be contaminated, wash, peel, or cook all raw vegetables and fruits with clean water before eating.
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