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Wednesday, 12 December 2018

Parasitic Nematodes

These include Ascaris, hookworms, and filarial worms. They are roundworms with cylindrical unsegmented bodies, pointed at both ends. They have a mouth at one end, an anus at the other , and s simple straight , digestive tube with a muscular pharynx for sucking food. Their nervous and excretory systems are simple. They do not have a circulatory system. The sexes are separate with the male being smaller. The reproductive system is well developed. A female may lay 200,000 or more eggs per day.

Roundworms and hookworms : Ascaris lumbricoides, the  common round worm, and Ancylostoma diodenale , the hookworm, live in the intestines of humans. Their eggs are passed out in the faeces of an infested person.

     Ascaris infection is spread when people eat food which is contaminated with roundworms eggs. In the intestines, the eggs develop into young which bore through the intestinal wall in the blood. They grow in the bloodstream. Eventually, they make their way back to the intestines via the lings, oesophagus and stomach.

    Hookworm eggs hatch into free living larvae in the soil in which the faeces was deposited. The larvae feed on organic material and moult twice. at this stage, they become contact. The larvae take a complicated route in the hosts body and finally enter the intestine where they  mature after Moulting a further two times.

    Both worm infestations cause poor health and anaemia. Hookworm infestation is a more serious condition because the worm attached itself to the intestinal wall and sucks blood. KT produces a chemical to prevent blood from clotting. As a result, the wound bleeds even after the worm moves to another site. This causes a great loss of blood.

Filarial worms : the filarial worm, Wuchereria bancrofti, causes elephantiasis. the worms are spread from an infected person to a healthy person by mosquitoes. They live in the lymphatic vessels of humans and block them as they grow. This leads to abnormal large swollen of the infested part (usually the limbs). The adult female worm gives birth to tiny embryoes, called microfilariae (singular: microfilaria), which circulate in the blood stream. They are picked up by the mosquito when it bites an infested person and passed onto healthy people.

    Other filarial worms, found mainly in tropical Africa, include onchocerca and Loa Loa.

     Onchocerca causes river blindness or onchocerciasis. The worms are transmitted through the bites of the blackfly, simulium, that breeds near rivers and streams. In humans, the adult worms live below the skin forming lumps or nodules in the affected body areas. Their microfilariae, however, migrate to all parts of the body. Some reach the eye, causing the cornea to become inflamed. If untreated , this leads to blindness.

    Loa loa also causes a similar but less serious disease in humans. These worms are transmitted through the bites of the large chrysops fly that lives in forests.

Control : this employs the same basic methods as those for the tapeworms and flukes.
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