CYLINDRICAL WORLD

BY hasan askari BDS RDS MS Lecturer /demonstrator at Muhammad bin qasim

medical and dental college

Phylum Nematoda

Tissue nematodes

Filarial wormsFilarial worms are thread-like nematodes of

which there are at least 8 species for which humans, especially in tropical regions, are the definitive host.

Approximately 250 million people worldwide are infected with these worms which are spread by mosquitoes.

Different species inhabit different locations in the body. Some live in the lymphatic system, others subcutaneously and others in the abdominal cavity.

Filarial wormsFemales can be 10cm long and they release live young

microfilariae into the blood and lymphatic system.

The microfilariae are picked up by mosquitoes where they develop, become infective and can infect another person.

Filarial wormsIn some people exposed to persistent infections

with filarial parasites that live in the lymphatic system, elephantiasis may develop.

This is caused by blockage of lymphatic ducts and inflammation. There may be excessive growth of connective tissue and enormous swelling of infected parts including legs, arms and scrotum.

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Figure 15.12

Diriofilaria immitis Dog heartworm

Filarial wormsThe most common filarial worm in the U.S.

Dirofilaria immitis is the cause of heartworm in dogs.

Adult worms may be as long as 40cm and they live in the dog's heart and lungs.

Because they damage the heart, infection is often fatal, and killing adult worms is difficult and dangerous to the dog.

Prevention of infection by regular dosing of a dog with drugs that kill circulating larvae is a better strategy.

River blindnessRiver blindness is also caused by filarial worms

that live subcutaneously.

In this case the insect that transmits the disease is a blackfly.

18- 30 million people are infected worldwide (mainly central Africa and parts of South America) and more than 300,000 have been made blind.

River blindnessWhen a black fly becomes infected, the worm

larvae spread to its salivary glands. When it bites someone the larvae pass into the skin.

The larvae develop into adults and form nodules under the skin. The adults breed and produce thousands of larvae, which spread all over the body - including the eyes.

River blindnessThe worst problem is caused when the parasites die.

The immune system produces a severe inflammation, which if it occurs in the eye can cause blindness.

People infected at birth with river blindness commonly become blind by their 40s.