Organisms Affecting Human Health Part 2
Some common parasitic worms are round worms, thread worms, liver fluke and tapeworms.
Roundworms (nematodes)
Ascaris is a common roundworm. It is 20-30 cm long and is pinkish white in colour.
These
worms live in the small intestine of man and move freely. The major
symptoms of the disease are abdominal pain, dyspepsia, anxiety, nausea,
and coughing. The eggs of ascaris are excreted in soil along with feces.
These eggs can enter another person, due to unhygienic conditions. When
these eggs reach small intestine, they develop into new worms and cause
disease.
This disease is more common in children as compared to adults and children are source of its spread.In this disease, as the worms feed on the food of the patient, that is why patient suffers from malnutrition.
Fig. 20.12
Thread worms
Thread
worms are very small only ½ inch long. Both male and female worms live
in the colon of human beings. At night the female descends the colon and
lays her eggs in the folds of skin about the anus. This causes intense
itching, if the anus is scratched, the eggs stick to the fingers and
thus transferred to the mouth or deposited on cutlery and household
utensils. The eggs also become attached to the clothing and the bedding.
When these articles are shaken, the eggs are dispersed in the air and
may be breathed in. the eggs pass to the stomach and to the large
intestine and develop into adult thread worms. Children are mainly
affected by these worms. Drugs can be given to get rid of worms.
Liver fluke (platyhelminthes)
The
fluke are flat worms. They are the parasites of both man and animal.
All flukes require at least two hosts to complete their life cycle. One
of the fluke is liver fluke. It lives in and feeds in the liver of the
human beings, where it causes much damage. The eggs of the fluke pass
out in the faeces of infected person and thus they may come to the
freshwater. Snails living in the freshwater eat the eggs. The eggs
develop and form larva in the snails. The larva develops into small
creature with a tail. At this stage they leave the snail and swim into
water and seek a fresh host.
Their
next host is freshwater fish. The embryos penetrate the skin and enter
the muscles of the fish. In the muscles the embryo forms a hard
protective layer and become cysts. These cysts are very hard and are
only destroyed by a thorough cooking of the fish. When partially cooked
fish is eaten by man, the cysts arrive in the stomach and there they
develop. From the stomach the parasites pass to the liver, where they
grow to adult flukes. The adult flukes are both male and female, they
come together and fertile eggs are produced and the cycle is repeated
(fig. 20.13).
Drugs for the treatment are available but the best way is to improve sanitation.
Fig. 20. 13 life cycle of liver fluke
Tapeworms (Taenia solium)
Flat
worms are largest organisms to parasitize human beings. They are called
flat worms because of their flattened bodies. All tapeworms are
parasites and require at least two hosts to complete their life cycle.
Tapeworms
have a small head on which suckers and sometimes hooks are present to
attach them to their host’s intestine. Their length varies from few
centimeters to 10 meters and their body is made of segments called
proglottids. They are hermaphrodite i.e. each proglottid has both sexes.
The
life cycle of tapeworm involves two hosts. Primary host is the one in
which the adult tapeworm lives and reproduces. And secondary host is an
animal, which is eaten by the primary host for example beef tape worm’s
primary host is humans and secondary host is cattle. If the sewage
disposal conditions are not proper, tape worm eggs may be eaten by a cow
while grazing. Because of the digestive juice of cow in the gut, larvae
come out of the eggs which then find their way into the muscular
tissues. There they remain unchanged for several years. If the partially
cooked cow meat of infested cow is eaten by humans the larvae are
activated by digestive juices, where they manage to attach the
intestinal wall with their suckers or hooks. There the larvae develop
into adult tapeworms. After fertilization sex organs disappear and are
replaced by thousands of microscopic proglottids. At this stage
proglottids drop from the tape worm and pass out of the host’s body with
faeces (fig 20.14).
Fig 20.14 life cycle of tapeworm
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