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Tapeworm

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Tapeworm
Extremly long tapeworm.jpg
Scientific Classification
Orders

Subclass: Cestodaria

Subclass: Eucestoda

Tapeworms are any of the species of parasitic flatworms that belong to the taxonomic class Cestoda. They are soft-bodied, legless invertebrates that can reach 6m or 20 ft. in length. The tapeworms have a primitive nervous system but have the characteristic of cephalization (having all the sensory organs concentrated in the anterior or head region). They develop from three cell layers (from outside to inside): epidermis, mesoderm, and the gastroderm, with a thick tegument protecting them from the host's digestive juices. Also, tapeworms spend their entire adult life inside the small intestine of a vertebrate. They live in the small intestine because they have no digestive system of their own and thus must rely on absorption of already digested nutrients.(Porch, pg455) Tapeworms can cause infections in many vertebrates including fish, dogs, cats and humans.[1]

Anatomy

A Taenia solium tapeworm scolex with its four suckers, and two rows of hooks
The tapeworm is a long (6m or 20 ft.), soft-bodied, legless invertebrate with bilateral symmetry.[2] They are made up of a knob-like head or scolex (where most of the sensory organs are located-cephalization), a short, unsegmented neck following the scolex, and multiple flat, rectangular body segments or proglottids forms the strobila. On the external surface of the scolex there are hooks or suckers that allow the tapeworm to latch onto the inside of a host's intestines where it lives for most of its adult life.[3] Adult tapeworms have no external cilia or flagellum. The worm's body covering consists of a thick tegument which protects it from the digestive juices of its host.(Porch, p458)

Almost all of the tapeworm's metabolism is dedicated to reproduction; inside the proglottid is a complete set of male and female reproductive organs. There are hardly any sensory organs in an adult tapeworm, the nerve center of a tapeworm is its scolex as well as a nerve cord running the length of the body even through the proglottids (they stop working upon detachment). They also have an excretory canal which is the only digestive system associated organ. The tapeworm has no organs for respiration or circulation and achieves this on a cellular level.[4] Each proglottid fertilizes and stores hundreds of eggs, the more mature proglottids are at the posterior end of the tapeworm. Proglottids that break off are called terminal proglottids.(Porch, p458)

Reproduction

Immature proglottids from the tapeworm, Mesocestoides variabilis
A tapeworm's life cycle starts as an egg (once contained in a proglottid) that has been excreted in a host's feces. Once eaten by the intermediate host the egg travels to the intestine where it hatches. The newly hatched larvae (in most species it has a fully developed scolex) than burrows into and through the intestine wall into an organ or the body cavity.[5] The larvae stays in an organ (for example; the muscles, eyes, brain or almost any other organ of the body) of the intermediate host (which can be almost any vertebrate) until it is consumed by the final host, though some species have multiple intermediate hosts.(Porch, p458) Once it is eaten by the intermediate host it goes through the digestive system to the small intestine where the scolices of larvae attach. After attachment to the inside of the intestine the tapeworm starts producing proglottids and the strobila (the bulk of the tapeworm's body) forms. After more development the proglottids start producing eggs.[6] When fully matured a proglottid breaks off (a terminal proglottid) it is excreted in the host's feces.[7]

Each proglottid contains one set of male reproductive organs and one set of female reproductive organs. In most species the male reproductive organs develop first, though there are some species in which the female reproductive organs develop first.[8]

Ecology

Tapeworm life cycle.jpg
Tapeworms are parasitic flatworms meaning they spend their adult life inside of a host.[9] As an egg it stays on the ground or in the feces of the parent's host until consumed by the intermediate host. The egg passes through most of the digestive system, thus at that short stage of life their environment is the digestive tract of the intermediate host. Once they reach the small intestine they hatch and the larvae burrows through the intestine wall. The second environment which they stay in is an organ (the brain, muscles, eyes and nearly any other organ) in their intermediate host. The tapeworm's final environment is its final host where it stays in the small intestine.(Porch, p458)

The tapeworm stays in the small intestine of its host for its entire adult life protected by a thick tegument. It must live there due to the fact that it has no digestive tract of its own thus it must absorb the nutrients where most of the digestive work has been done.[10]

The tapeworm does not have any natural enemies, its only enemies are good hygiene and anthelmintic agents. Humans can avoid becoming a host it by thorough cooking meats (to a temperature of 57° C or 135° F), keeping drinking water separate from sewage and feces, deworming pets, and freezing meats for a long period of time. If a human or pet becomes a host there are effective anthelmintic agents that basically wash out the tapeworm.[11]

Tapeworm Infection

Tapeworms can be caught by eating uncooked or undercooked pork, beef, or freshwater fish containing cysts. Because of this the Old Testament dietary laws forbade the eating of pork to prevent such infections.(Porch, p461) Humans can catch them as well as pets and almost any other mammal.[12] A human can become either the final, or even intermediate host.(Porch, p458)

Symptoms and Diagnosis

The symptoms, if any (some people do not get any), for the tapeworm infection are; nausea, weakness, abdominal pain, loss of appetite, diarrhea, weight loss and inadequate absorption of vitamins and nutrients (though these symptoms may vary depending on what species of tapeworm you may have and are for an intestinal infection). For an invasive infection or one in which the tapeworm leaves the intestine and forms cysts in tissues the common symptoms are; bacterial infections, neurological symptoms or seizures, fever, cystic masses or lumps, and allergic reactions to the larvae (these symptoms also differ between species). If someone thinks they have an intestinal infection, there are tests they can take to determine whether or not they really have it or not such as taking a stool test or the "scotch tape test". If they have have invasive infection a doctor may test their blood for antibodies their body may have produced to fight the tapeworm infection.[13]

Prevention and Treatment

To avoid catching the tapeworm infection you should thoroughly cook meats and freshwater fish at a temperature of 135° F or 57° C, prolonged freezing also works, finally, careful evaluation of meat and fish will help avoid eating any of the contaminated meat. The treatments for the intestinal tapeworm infection include a single dose of praziquantel, drugs such as albendazole or praziquantel (antiparasitic drugs) and corticosteroids are used for an invasive infection. Though these drugs depend on the location of the cysts though none of these drugs are used for infections in the eyes or spinal cord because they can damage nearby tissue. [14]

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References

External Links