Diphylobothrium latum was introduced to North America by immigrants from Scandinavia and has been spread greatly by domestic dogs that are fed raw fish. A severe broad tapeworm infection in humans is known to cause anemia due to the lack of vitamin B-12, which the tapeworm absorbs through the lining of the gut. The parasite can be avoided by thoroughly cooking fish and taking care when working with fish flesh.
Cestodes in general have sensory organs in the scolex, which are attached to longitudinal nerves extending down the body. The nerves are attached to organs and the cestodes can detect tactile stimulation.
Communication Channels: tactile
Perception Channels: tactile
Because of their potential harm to humans, efforts are being taken to prevent the spread of these worms.
CITES: no special status
The adults are hermaphroditic and capable of self- fertilization. Some are known to develop a second set of reproductive organs. Adults living in mammalian hosts produce eggs, which exit the host in fecal matter. Eggs may survive up to three years until conditions are right for development. The eggs are typically washed into freshwater lakes and streams where they are eaten by a copepod (Pappas, 1999). The coracidium larva, which hatches from the egg, is ciliated and bears six terminal hooks. The coracidium sheds its epithelium and furthur develops into the procercoid inside a copepod, the first intermediate host. Transformation into the fully infective procercoid takes several weeks to be completed (Roberts and Janovy, 2000). From there, the procercoid transfers hosts to a fish (such as trout) via ingestion of the copepod intermediate host. There it migrates to the flesh of the fish and further develops into the plerocercoid. The plerocercoid is characterized by a ribbon-like body with an undivided scolex. The plerocercoid may pass through other paratenic hosts until finally consumed by a mammalian definitive host (Roberts & Janovy, 2000). Mammals such as bears, dogs, and humans eat those fish and aquire the worms, which grow and reproduce in the host's intestines.
Diphyllobothrium latum has no positive effects on humans, but can be very harmful. Infestation (diphyllobothriasis) in humans can lead to anemia, due to depletion of vitamin B-12. Treatment for the anemia may be as simple as taking vitamin supplements. The worm must be irradicated medically, however, by the use of a drug called praziquantel (USFDA, 2001).
Negative Impacts: injures humans (causes disease in humans )
Ecosystem Impact: parasite
Species Used as Host:
This parasitic organism feeds on the contents of the host mammals' intestines through absorption. It has no gut or mouth, thus does not contain a complete digestive system. This tapeworm especially depletes the host of vitamin B-12, cleaving and sequestering almost all of the host's B-12. The worm may also interfere with the host's ability to take up the vitamin, thus supplements are needed to combat the deficiency (Roberts and Janovy, 2000; USFDA, 2001).
Animal Foods: body fluids
Primary Diet: carnivore (Eats body fluids)
This tapeworm is found in Palearctic and Nearctic areas: in the freshwater lakes and streams of North America and the Great Lakes, as well as the Mediterranean and Baltic Seas.
Biogeographic Regions: nearctic (Introduced ); palearctic
Diphyllobothrium latum is found in and around freshwater lakes and streams. Each stage inhabits a different habitat. The eggs inhabit fecal matter from the definitive host, the larvae live first in a copepod and then in the flesh of fish, and the adults inhabit mammalian intestines.
Habitat Regions: temperate ; freshwater
Terrestrial Biomes: forest
Aquatic Biomes: lakes and ponds; rivers and streams
Other Habitat Features: agricultural ; riparian
The adult Diphyllobothrium latum may reach up to 12 meters, increasing throughout its life. These whitish/yellow worms are dorso-ventrally flattened, and much more narrow than they are long. They have no oral opening, thus feeding through absorption. The finger-shaped scolex has no hooks, and narrow weakly-muscular grooves (bothria) run longitudinally along the body (scolex) (Roberts and Janovy, 2000).
Diphyllobothrium latum is hermaphroditic, carrying both sets of sex organs (Vergeer, 1932). In each proglottid, testes and vitelline follicles are found (Roberts and Janovy, 2000). The uterus is a bilobed structure that loops, extending from the ovary to the uterine pore on the midventral surface of the segment, through which the mature proglottids (the term for a complete set of sex organs) release the eggs. The eggs are continually produced (Swiderski, 2000). This species is anapolytic, meaning that they shed their proglottids after usage. The eggs are unembryonated and have a lid-like operculum (USFDA, 2001).
Range length: 12 (high) m.
Other Physical Features: ectothermic ; bilateral symmetry
The adults are hermaphroditic and capable of self- fertilization. Some are known to develop a second set of reproductive organs. Adults living in mammalian hosts grow and reproduce in the host's intestinges. The eggs exit the host in fecal matter.
Key Reproductive Features: simultaneous hermaphrodite; sexual
Parental Investment: no parental involvement
The cestode (tapeworm) Diphyllobothrium latum (Broad Tapeworm or Fish Tapeworm) is the largest human tapeworm, sometimes exceeding 10 m in length. In the human intestine, it may live for over two decades. Transmission to humans occurs via the consumption of infected fish. Several other Diphyllobothrium tapeworms have been reported to infect humans, but less frequently (these include D. pacificum, D. cordatum, D. ursi, D. dendriticum, D. lanceolatum, D. dallliae, and D. yonagoensis). The familiar pork and beef tapeworms are in a different genus, Taenia (Taenia solium and Taenia saginata, respectively).
Immature eggs of D. latum are passed in feces from the definitive host (i.e., the host harboring adults, or "final" host). Under appropriate conditions, the eggs mature (after approximately 18 to 20 days) and yield oncospheres (first stage larvae), which develop into coracidia (swimming larvae that attract potential first intermediate hosts). After ingestion by a suitable freshwater crustacean (the copepod first intermediate host), the coracidium develop into procercoid larvae. Following ingestion of the copepod by a suitable second intermediate host, typically a minnow or other small freshwater (or, possibly, anadromous or marine fish), the procercoid larvae are released from the crustacean and migrate into the fish flesh, where they develop into plerocercoid larvae (spargana). The plerocercoid larvae are the infective stage for humans. Because humans do not generally eat undercooked minnows or similar freshwater fish, these do not represent an important source of infection. However, these small second intermediate hosts can be eaten by larger predator species such as trout, perch, and walleyed pike. In this case, the plerocercoid can migrate to the musculature of the larger predator fish and humans can acquire the disease by eating these later intermediate infected host fish raw or undercooked. After ingestion of the infected fish, the plerocercoids develop into immature adults and then into mature adult tapeworms, which will reside in the human host's small intestine. The adults of D. latum attach to the intestinal mucosa by means of the two bilateral grooves (bothria) of the scolex (the anterior part of the tapeworm that is specialized for attachment to the gut wall of the host). The adult tapeworms can exceed 10 m in length, with more than 3,000 proglottids (the bisexual reproductive units strung along the length of the body, which in most cestodes each represent a single worm segment). Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) and are passed in the feces. Eggs appear in the feces 5 to 6 weeks after infection. In addition to humans, many other mammals can also serve as definitive hosts for D. latum. Most Diphyllobothrium species exhibit fairly low host specificity as adults, suggesting that the natural hosts of this parasite could be carnivorous mammals or even fish-eating birds.
Infection by D. latum is known from the Northern Hemisphere (Europe, states of the former Soviet Union, North America, Asia) and Uganda and Chile. Freshwater fish infected with Diphyllobothrium larvae may be transported to and consumed in geographic areas where active transmission does not occur, resulting in human diphyllobothriasis. For example, cases of D. latum infection associated with consumption of imported fish have been reported in Brazil.
(Centers for Disease Control Parasites and Health Website; Scholz et al. 2009 and references therein)
In the early 1970s, diphyllobothriosis was estimated to affect 9 million people globally in Europe, Asia, and North America. A more recent estimate indicated that 20 million people are infected worldwide, although infection appears to have declined in some regions and increased in others. Scholz et al. (2009) provide a recent broad review of the biology and epidemiology of D. latum. (Scholz et al. 2009 and references therein)
