Transcript Nematodes

Ecdysozoa
Protostomes are divided into two large
groups the Lophotrochozoa and the
Ecdysozoa.
The Ecdysozoa includes two major groups
the Nematoda and the Arthropoda.
Ecdysozoa
Members of the Ecdysozoa are
characterized by the fact that they shed
their cuticle as they grow.
Phylum Nematoda
Nematodes (from Greek nema a thread)
are long, thin often threadlike “worms” with
a thick cuticle.
The head is small and possesses only
small sense organs and the overall
appearance is of an organism that narrows
at both ends.
1 mm long nematode
http://www.ucmp.berkeley.edu/phyla/ecdys
ozoa/nematoda.html
Phylum Nematoda
The nematodes are quite species diverse
(about 15,000 species although this is
probably a huge underestimate) and the
many parasitic forms have a significant
impact on humans.
Most nematodes are under 5cm and many
are microscopic. However, some parasitic
forms can be over a meter in length.
Phylum Nematoda
Nematodes use their pseudocoelom as a
hydrostatic skeleton.
A pseudocoelom is a fluid-filled body cavity in
which mesoderm lines only the outer edge of the
developing blastocoel. No peritoneal lining
develops.
The body has a thick cuticle (made primarily of
collagen) secreted by the underlying epidermis,
which resists the high hydrostatic pressure
exerted by the fluid in the pseudocoelom.
Phylum Nematoda
Beneath the epidermis is a layer of longitudinal muscles.
Muscles in nematodes are not arranged in antagonistic
pairs, the antagonistic role is played by the cuticle.
Contraction of a longitudinal muscle on one side is
transmitted through the hydrostatic skeleton and
stretches the cuticle on the opposite side of the body.
When the muscle relaxes, the cuticle contracts and the
body returns to its resting position.
Phylum Nematoda
Nematodes have a complete gut with a mouth,
muscular pharynx, intestine, rectum, and anus.
Most nematodes are dioecious and males are
smaller than females.
Fertilization is internal and juveniles go through
several developmental stages, each time
molting or shedding their cuticle.
Free-living nematodes
Free-living nematodes live in the sea, in fresh
water, and in the soil. They occur worldwide in
all environments and most live in the interstitial
spaces of sediments and soils.
Vast numbers of nematodes occur. One square
meter of sea bottom mud has been estimated to
hold 4.4 million nematodes and 90,000 were
counted on a single decomposing apple.
Free-living nematodes
The slender, tapered body of nematodes
equips them to live in interstitial spaces.
Most free-living nematodes are less than
2.5mm in length and often are
microscopic. The largest soil dwelling
nematodes may be 7mm long and the
largest marine forms a whopping 5cm.
Free-living nematode
http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb5pg8.htm
Free-living nematodes
Most free-living nematodes are
carnivorous.
However, some feed on algae and fungi
and some are detritivores. Others feed on
plants, especially the roots.
Free-living nematodes
Many root feeding nematodes are major
agricultural pests. These species pierce
root cells and suck out their contents.
Nematodes are estimated to destroy 12%
of the world’s cash crops annually.
Parasitic nematodes
There are a great many species of
parasitic nematodes and they attack
virtually all groups of animals and plants.
Parasitic forms include ascarids,
hookworms, Guinea worms, trichina
worms, pinworms, and filarial worms.
Ascaris lumbricoides: large
roundworm of humans
It’s estimated that worldwide as many as 1.4
billion people are infected with Ascaris
lumbricoides which lives in the small intestine.
Roundworms removed from a person’s gut
http://roundworms.net/p/17/roundworms-in-humans/picture-17
Ascaris lumbricoides: large
roundworm of humans
Females may be a foot long and produce
200,000 eggs a day.
Infection occurs when parasite eggs are
eaten with uncooked food or when soiled
fingers are put into the mouth.
Ascaris lumbricoides: large
roundworm of humans
The larvae penetrate the intestinal wall
and travel through the blood stream to the
lungs where they break out of the alveoli
(often causing pneumonia).
Then they make their way up the trachea
where they are swallowed and eventually
settle in the small intestine.
Ascaris lumbricoides: large
roundworm of humans
In the intestines the worms cause
abdominal symptoms and allergic
reactions and may produce an intestinal
blockage.
Figure 15.05a
Male (top) and 9.8
female Ascaris lumbricoides
Roundworms in cats and dogs
https://www.youtube.com/watch?v=kskGJwLODA
Hookworms
Hookworms are named for the dorsal
curve in their anterior end.
Hookworms are quite small, the
commonest species Necator americanus
is only 11mm long. However, because
they feed on blood a heavy infection can
produce severe anemia.
http://www.virginmedia.com/images/hookworm.jpg
Hookworms
Large plates in the hookworm’s mouth are used
to cut the intestinal lining of the host.
The parasite then pumps blood through its gut,
partially digesting it before excreting it.
Because hookworms suck more blood than they
use, they can cause debilitating anemia. In
children a hookworm infection can stunt growth
and cause a general lack of energy.
Figure 15.06
9.9
Section through hookworm
attached to dog intestine
Hookworms
Hookworms do not permanently attach in
one spot, but move around the gut and
reattach when they are ready to feed.
Hookworms have evolved sophisticated
anti-clotting factors that keep platelets
from clumping and forming a clot while the
hookworm is feeding.
Hookworms
When the hookworm releases, a clot forms
and the tissue can recover.
By using this approach instead of
producing a crude blood thinner to ensure
blood flow, hookworms prevent hemophilia
developing in their hosts, which would be
fatal for the hookworm.
Hookworms
The life cycle of hookworms is similar to
that of ascarids.
Infection occurs after a larva hatches from
an egg and penetrates the skin of a
person. It then makes its way to the lungs
where eventually it is coughed up and
swallowed and travels to the intestines.
Hookworm life cycle
Guinea worms
Guinea worm infections (also referred to as
Dracunculiasis) are now confined to subSaharan Africa. Adults are threadlike nematode
worms that can grow to 1 meter in length.
The adult lives in humans and the intermediate
host is tiny crustaceans.
Humans become infected when they drink water
containing the crustaceans.
Guinea worms
The immature worm penetrates the gut
wall and wanders through the body,
maturing and growing.
After about a year the female makes her
way to the surface of the skin (usually in
the legs) causing very painful blistering.
Guinea worms
To ease the pain, sufferers immerse their
feet in water. This bursts the blisters and
the female worm then protrudes from the
sore and lays her eggs, thus continuing
the life cycle.
Guinea worms
There is no cure for Guinea worms and
the only way to remove one is to slowly
over the course of weeks wind the worm
out on a stick.
If the worm breaks,
a serious bacterial
infection results.
Interestingly, the traditional symbols for medicine
and healing the staff of Asclepias (showing a
snake entwined around a staff) and the caduceus
(which shows two snakes entwined about
a winged staff) very likely are derived from the
Guinea worm removal technique.
Guinea worms
Guinea worm infection is avoidable with
relatively simple precautions such as
preventing people walking in drinking
water sources and boiling or filtering water
before drinking it.
Guinea worms
Since the mid 1980’s a campaign to
eradicate Guinea worms coordinated by
the U.N. and the Carter Center has had
tremendous success.
In 1986, an estimated 3.5 million people
were infected, but by 2000 the number of
cases had been reduced to about 75,000.
Guinea worms
Guinea worms have been eliminated from
Pakistan, India, and Iran and infections
greatly reduced over much of sub-Saharan
Africa.
The major barrier to elimination at this
point is the ongoing conflict in southern
Sudan where the majority of cases now
occur.
Guinea worms
The Carter Center and the fight against
Guinea worms. (4 minutes)
http://www.youtube.com/watch?v=u4kQW
vUv_Ns
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.
http://en.wikipedia.org/wiki/File:Filariasis_01.png
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.
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.
Figure 15.11
Elephantiasis of leg
caused by filarial worms
9.12
Filarial worms
Lymphatic filariasis (elephantiasis) 4.5
minutes.
http://www.youtube.com/watch?v=pw7TS
YLRrmQ
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.
http://www.plymouthmosquito.com/dog_heartworm.htm
Figure 15.12
Diriofilaria immitis
Dog heartworm
9.13
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.
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.
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.
River blindness
Carter Center – River blindness (9
minutes)
http://www.youtube.com/watch?v=pRvwE
UNGlqI
Trichina worms
http://en.wikipedia.org/wiki/File:Trichinella_larv1_DPDx.JPG
Trichinella spiralis is a tiny nematode that
causes the potentially fatal disease
trichinosis.
Humans typically become infected by
eating undercooked pork. Trichinella lives
in cysts formed in individual muscle cells
of the host.
Trichina worms
Trichinella when it hatches from an ingested cyst
in its host’s gut drills through the wall of the gut
where females produce living young.
These juveniles travels in the circulatory system
to a muscle.
The juvenile penetrates an individual muscle cell
and breaks the cell down so it can be remade.
Trichina worms
Trichinella, just as a virus does, manipulates the
host cell’s DNA. It causes the cell to recruit a
blood supply to supply food to the cell and also
produce collagen to form a cyst around the cell.
The Trichinella juvenile awaits ingestion by
another host. When ingested it emerges from its
cysts enters the mucosal lining of gut, develops
into an adult and continues the life cycle.
Trichinella life cycle in humans
http://www.trichinella.org/bio_lifecycle.htm
Trichina worms
Adults usually do not persist long in the gut
before being expelled by the host’s immune
system.
Trichinella occurs commonly in wild animals
such as foxes, wolves and bears. Smaller
mammals such as skunks, raccoons and rats,
which commonly associate with people, are the
main sources of domestic pig infections.
http://www.foodsafetyindia.nic.in/images/Trichinella_LifeCycle.gif
Trichina worms
Pigs may become infected by eating fecal matter
or the bodies of animals infected with the
parasite. Humans are an inadvertent host of
Trichinella.
In humans, infection with a few Trichinella
parasites may cause no symptoms, but heavy
infections can cause intense muscle pain and in
some cases death.