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Tuesday, 11 December 2018

Some Important Endoparasites of Humans

Tape worms

Tape worms are long parasitic flatworms which live in the gut of humans.  Several species of tape worms infects human, e.g. taenia solium, the pork tapeworm and taenia saginata, the beef tapeworm.

Structure : Each tapeworm has a knob like head known as a scolex and a large number of segments known as proglottides ( singular: proglottis) ,  arranged in a long row. 

    The scolex bears hooks and suckers, with which the worm clings to the wall of the host intestine. This prevents the worm from being carried away with the food.

    Internally, the tapeworm has become simplified as a result of adaptation to its parasitic way of life. It has no moth or alimentary canal. Hence, it absorbs food digested by its host over IRS whole body surface. It has no organs of respiration and circulation.

   As it leads a sedentary life, its muscles are poorly developed. Its nervous system consist of only a ring of nervous material in the head, joined to a pair of longitudinal nerve cords which pass down the whole length of the body. It excretory system consist of  a pair of tubes, the excretory ducts, which also pass down the whole length of  the body. 

   Each proglottis, when mature, has both male and female Reproductive parts, I.e. testes and ovaries in it. The tapeworm is, therefore a hermaprodite.

Mode of life : like most Endoparasites, tapeworms show adaptations to their parasitic mode of life. This is seen in the 

• Loss or poor development of unwanted organs such as digestive system, sense organs and muscles;

• Long flattened body that provides a large surface area for the absorption. Of nutrients;

• Presence of hooks and suckers for attachment;

• Ability to live in the absence of oxygen (anaerobic conditions);

• ability to produce large numbers of eggs and their hermaproditic nature  

Life cycle : the life cycle of the tapeworm involves two hosts: a human being who is regarded as the primary host and another animals, such as the cow or pig, which is known as the secondary host.

   The adult tapeworm is found in the intestine of the human. Mature proglottides of the worm, containing numerous fertilized eggs, break off from the rest of the worm and pass out with the faeces of the host. The fertilized eggs develop into embryos bearing six hooks and covered with protective shells.

    Further development takes place when the embryos are swallowed by a  secondary host. In the intestine of the secondary host, the digestive juices help to break down the protective shells around the embryos. On Being released, the embryos bore through the intestinal wall of the new host, with the help of their six hooks. They enter the blood stream and are carried by the blood to be deposited the muscle or in the brain. Each embryo then forms a thick covering, or cyst, and remains inactive till it reaches a new human host. The encysted embryo is known as a bladderworm.

    Of beef or pork containing live bladderworms is eaten by a human being, the bladder worms become active in the new host intestine and begin to grow into adult tapeworms. Thus, an uninfected person could get infected by eating the meat of an infected Animal. The latter acts as a vector.

   To get from the ground or grass on which faeces containing the tapeworm's eggs are deposited, the tapeworm makes use of an established food chain,

Grass --> Cow ---> Human

To get into its final host. At each stage where it waits to get into a host, it had evolved a resting form that can withstand unfavourable conditions

Economic importance : Tapeworms do not cause any severe diseases in humans, but because they feed in the digested food present in the intestines, they draw away much of the nutritive substances and cause anaemia. If the anaemia is severe, the infected person will be susceptible to many other disease as his resistance will be poor. Tapeworm will also irritate the wall of the intestine which results in pain and physical damage. In children and weak patients, tapeworm infection may give rise to more symptoms which indigestion, vomiting, loss of appetite and nervous disorders.

Control : infestation of humans by these worms can be prevented by having all meat for sale examined by health inspectors so as to ensure that bladderworms are absent. Further more, meat should be well cooked. Other preventive measures include 

• The implementation of proper sanitary conditions so that animals may not become infected by eating the faeces of infected persons; and 

• The treatment of infected persons with suitable drugs to kill the worms.

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