This document discusses various filarial worms that infect humans. It notes that approximately 250 million people worldwide are infected with filarial worms, which are spread by mosquitoes. Different species of filarial worms inhabit different locations in the body, such as the lymphatic system, subcutaneously, or abdominal cavity. In some cases of persistent infection of filarial worms in the lymphatic system, elephantiasis can develop due to blockage and inflammation of lymphatic ducts. River blindness is also discussed, which is caused by filarial worms transmitted by blackflies, infecting up to 30 million people worldwide and blinding over 300,000.

1. CYLINDRICAL WORLD
BY hasan askari
BDS RDS MS
Lecturer /demonstrator at Muhammad bin qasim
medical and dental college

2. Phylum Nematoda
Tissue nematodes

3. Filarial worms
Filarial 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.

4. Filarial worms
Females 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.

5. Filarial worms
In 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.

7. 9.13
Figure 15.12
Diriofilaria immitis
Dog heartworm

8. Filarial worms
The 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.

10. River blindness
River 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.

11. River blindness
When 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.

12. River blindness
The 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.