Ecdysozoa

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Ecdysozoa

• Protostomes are divided into two large groups the
  Lophotrochozoa and the Ecdysozoa.
• The Ecdysozoa includes two major groups the
  Nematoda and the Arthropoda.

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Ecdysozoa

• Members of the Ecdysozoa are characterized by the
  fact that they shed their cuticle as they grow.

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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.

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1 mm long nematode
http//www.ucmp.berkeley.edu/phyla/ecdysozoa/nemat
oda.html
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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.

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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.

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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.

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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.

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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.

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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.

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Free-living nematode http//kentsimmons.uwinnipeg.
ca/16cm05/16labman05/lb5pg8.htm
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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.

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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
  worlds cash crops annually.

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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.

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Ascaris lumbricoides large roundworm of humans

• Its estimated that worldwide as many as 1.4
  billion people are infected with Ascaris
  lumbricoides which lives in the small intestine.
• 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.

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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.

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Ascaris lumbricoides large roundworm of humans

• In the intestines the worms cause abdominal
  symptoms and allergic reactions and may produce
  an intestinal blockage.

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9.8
Male (top) and female Ascaris lumbricoides
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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.

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http//www.virginmedia.com/images/hookworm.jpg
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Hookworms

• Large plates in the hookworms 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.

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9.9
Section through hookworm attached to dog
intestine
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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.

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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.

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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.

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Hookworm life cycle
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Guinea worms

• Guinea worm infections (also referred to as
  Dracunculiasis) are now confined to sub-Saharan
  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.

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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.

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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.

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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.

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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.
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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.

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Guinea worms

• Since the mid 1980s 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 and by 2006 to
  11,000.

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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.

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Guinea worms

• The Carter Center and the fight against Guinea
  worms. (4 minutes)
• http//www.youtube.com/watch?vu4kQWvUv_Ns

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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.

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http//en.wikipedia.org/wiki/FileFilariasis_01.pn
g
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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.

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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.

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Elephantiasis of leg caused by filarial worms
9.12
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Filarial worms

• Lymphatic filariasis (elephantiasis) 4.5 minutes.
• http//www.youtube.com/watch?vpw7TSYLRrmQ

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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.

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Diriofilaria immitis Dog heartworm
9.13
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http//www.plymouthmosquito.com/dog_heartworm.htm
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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.

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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.

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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.

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River blindness

• Carter Center River blindness (9 minutes)
• http//www.youtube.com/watch?vpRvwEUNGlqI

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Trichina worms
http//en.wikipedia.org/wiki/FileTrichinella_larv
1_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.

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Trichina worms

• Trichinella when it hatches from an ingested cyst
  in its hosts 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.

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Trichina worms

• Trichinella, just as a virus does, manipulates
  the host cells 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.

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Trichinella life cycle in humans
http//www.trichinella.org/bio_lifecycle.htm
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Trichina worms

• Adults usually do not persist long in the gut
  before being expelled by the hosts 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.

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http//www.foodsafetyindia.nic.in/images/Trichinel
la_LifeCycle.gif
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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.