Taeniasis (Taenia Infection)
Taeniasis (Taenia Infection)
Disease History, Characteristics, and Transmission
Introduction
Taenia infection, or taeniasis, is an infection of the digestive tract caused by parasitic flatworms generally called cestodes, or tapeworms. It is specifically caused by only the species within the Taenia genus, those that infect carnivores (flesh eating animals). Taeniasis is acquired when humans (definitive hosts) eat raw or undercooked meat from infected animals (intermediate hosts).
For instance, cows (and other ruminants) carry the tapeworm species Taenia saginata and pigs (and dogs, cats, and sheep) harbor the species Taenia solium. When humans acquire taeniasis from cows the tapeworm is commonly called beef tapeworm and when it is from pigs the tapeworm is called pig tapeworm. In addition, Taenia multiceps infect hares, rabbits, and squirrels, while only rarely infecting humans.
Disease History, Characteristics, and Transmission
When humans eat infected meat from an intermediate host, tapeworm larvae hatch and develop inside the intestines. T. saginata matures to a length of 13 to 26 feet (4 to 8 meters). T. solium reaches adulthood at a length of 3 to 7 feet (1 to 2 meters). Both tapeworms can be found as an adult in the human intestines and as larvae in muscles and other tissues of cattle (and other ruminants) and pigs (and dogs, cats, and sheep), respectively. Adult tapeworms can stay inside their hosts for many years. The eggs are passed into the soil from human feces where they are eaten by intermediate hosts. Then, the eggs hatch and larvae enter tissues of the animal host where they enclose themselves in cysts (this is called encysts). When humans eat infected animal flesh, they also eat the cysts.
Tapeworms are long, segmented worms with each segment able to produce eggs. Each segment can detach from the worm and pass out through the feces or they can also crawl on their own through the anus. The worms do not have an intestinal tract, so must obtain their nourishment through their outer covering (integument). The structure of an adult consists of a head, neck, and segmented body that contain both male and female reproductive features. The head attaches to the mucous lining of the intestine.
Humans infected with T. solium can become infected again when eggs are ingested from human hands after coming in contact with the anal area. These infected individuals can infect other humans through improper food handling and other unsanitary means. These humans are considered intermediate hosts. The larvae will travel to various tissues of organs within the human host. Thus, T. solium are tapeworms that can infect humans as intermediate and definitive hosts.
Taenia infection does not usually cause any symptoms. However, sometimes there can be minor gastrointestinal pain, weight loss, and persistent ill feelings. The infection is usually recognized when the infected person passes tapeworm segments in the stool, especially if the segment is moving.
Scope and Distribution
Taenia infection is found worldwide, but only rarely in the United States. In the United States, T. saginatait is found in less than 1% of cattle because cattle are thoroughly treated for tapeworms. T. solium is also rare in the United States, but it is becoming more frequent as immigrants come in increasing numbers from areas infected with the parasite.
T. saginatait is found most often in Latin America, central Asia, Africa, and the Middle East. It is also found somewhat in Europe, southern Asia, Japan, and the Philippines. T. solium is found mostly in Latin America, Africa, the Slavic countries of central and southern Europe, southeast Asia, India, and China.
According to the Division of Parasitic Diseases (DPD), of the U.S. Centers for Disease Control and Prevention (CDC), T. solium is found more than T. saginatait in underdeveloped areas because people live very close to pigs and often eat undercooked pork.
WORDS TO KNOW
CHEMOTHERAPY: Chemotherapy is the treatment of a disease, infection, or condition with chemicals that have a specific effect on its cause, such as a microorganism or cancer cell. The first modern therapeutic chemical was derived from a synthetic dye. The sulfonamide drugs developed in the 1930s, penicillin and other antibiotics of the 1940s, hormones in the 1950s, and more recent drugs that interfere with cancer cell metabolism and reproduction have all been part of the chemotherapeutic arsenal.
ERADICATION: The process of destroying or eliminating a microorganism or disease.
HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.
PARASITE: An organism that lives in or on a host organism and that gets its nourishment from that host. The parasite usually gains all the benefits of this relationship, while the host may suffer from various diseases and discomforts, or show no signs of the infection. The life cycle of a typical parasite usually includes several developmental stages and morphological changes as the parasite lives and moves through the environment and one or more hosts. Parasites that remain on a host's body surface to feed are called ectoparasites, while those that live inside a host's body are called endoparasites. Parasitism is a highly successful biological adaptation. There are more known parasitic species than non-parasitic ones, and parasites affect just about every form of life, including most all animals, plants, and even bacteria.
RUMINANTS: Cud-chewing animals with a four-chambered stomachs and even-toed hooves.
SEIZURE: A seizure is a sudden disruption of the brain's normal electrical activity accompanied by altered consciousness and/or other neurological and behavioral abnormalities. Epilepsy is a condition characterized by recurrent seizures that may include repetitive muscle jerking called convulsions. Seizures are traditionally divided into two major categories: generalized seizures and focal seizures. Within each major category, however, there are many different types of seizures. Generalized seizures come about due to abnormal neuronal activity on both sides of the brain, while focal seizures, also named partial seizures, occur in only one part of the brain.
TAPEWORM: Tapeworms are parasitic flatworms of class Cestoidea, phylum Platyhelminthes, that live inside the intestine. Tapeworms have no digestive system, but absorb predigested nutrients directly from their surroundings.
Treatment and Prevention
Taenia infection is diagnosed with a stool sample. Tapeworm eggs can be found with a medical examination. Segments of worms can also be readily seen in feces after they are passed from the body. An infected person is treated with oral anti-parasitic worm medications. Usually one dose of niclosamide (Niclocide®) is used, and sometimes either praziquantel (Biltricide®) or albendazole (Albenza®, Eskazole®, or Zentel®) is given. After the treatment is complete, tapeworm infection is normally eliminated, but reinfection is possible if more cysts are ingested.
Any complications are usually from an infected person re-infecting themselves with tapeworm eggs. In rare cases, worms may cause blockage of the intestines and obstruct the bowels, resulting in a medical emergency.
Taenia infection is prevented in the United States and other industrial countries with strict federal law governing the feeding and inspection of domesticated animals slaughtered for food. According to the CDC's Division of Parasitic Diseases, taeniasis has been largely eliminated in the United States. In addition, fully cooking meat destroys any tapeworm larvae that may be present and any infection they may carry. Anyone infected with tapeworms can prevent infecting oneself again by practicing good hygiene, especially by thoroughly washing one's hands after using the toilet.
Impacts and Issues
T. saginatait infection can cause obstruction of the appendix (small outgrowth of intestines), pancreatic duct (carrier of pancreatic juices), and biliary duct (transporter of bile).
Infections involving T. solium can cause debilitating complications with regards to the central nervous system and the skeletal muscles. Under many conditions, a neurologic examination comes back normal, making it very difficult to diagnosis the infection. Other complications that can set in include meningitis (inflammation of the meninges), dementia (deterioration of memory functions), and hydrocephalus (increased fluid around the brain).
Larvae can also migrate from the intestines to other tissues of the body. If larvae migrate to the brain, they can cause neurological problems that are generally called cysticercosis. Seizure can occur when the brain is affected, along with earlier signs of vomiting, confusion, visual changes, and headaches.
Several international health organizations, including the World Health Organization (WHO), have identified taeniasis as potentially eradicable, meaning that health officials hope to eliminate the disease in humans. As of 2007, current efforts to eradicate taeniasis focus on hygiene education, improved sanitation, and preventative vaccinations for carrier animals. In South America and parts of Asia and Africa, efforts to control Taenia solium employ aggressive chemotherapy (using drugs or chemicals that are toxic to sources of diseases within the body) campaigns to reduce the number of human carriers.
See AlsoHelminth Disease; Parasitic Diseases; Tapeworm Infections.
BIBLIOGRAPHY
Books
Maule, Aaron G., and Nikki J. Marks, eds. Parasitic Flatworms: Molecular Biology, Biochemistry, Immunology and Physiology. Wallingford, UK: CABI Publishing, 2006.
Singh G., and S. Prabhakar, eds. Taenia Solium Cysticercosis: From Basic to Clinical Science. Chandigarh, India: CABI Publishing, 2002.
Periodicals
Beers, S., and T. Abramo. “Otitis externa review.” Pediatric Emergency Care. 20(4) (2004): 250–256. Verbrugge, L.M., et al. “Prospective study of swimmer's itch incidence and severity.” Journal of Parasitology. 90 (2004): 697–704.
Web Sites
Division of Parasitic Diseases, U.S. Centers for Disease Control and Prevention. “Taeniasis.” November 29, 2006 <http://www.dpd.cdc.gov/dpdx/Default.htm> (accessed March 27, 2007).