Download Phylum Nematoda - southbutterfield

Phylum Nematoda
(nematodes, round worms,
threadworms, Aschelminths)
• Large, important phylum -at least 20,000
described species, many economically or
medically important
• Ranks #4 in species number after
Arthropoda,Mollusca, and Chordata, but
many are undescribed maybe a million
species in all.
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Most are very small, < 2mm
But some are nearly 1m long
Abundant (100’s in a cupful of soil)
Diverse
Flatworm vs. Roundworm
• Acelomate vs. pseudocoelomate
– No body cavity vs false cavity
• Don’t shed skin vs. Shed skin
• One hole digestive tract vs. two hole
digestive tract
Living & Eating Patterns
• Ecologically widespread: free-living
marine, freshwater, terrestrial (interstitial),
many parasitic on plants and animals.
• Herbivorous, carnivorous, saprphagous
Nematode body plan
• Usually small- most less than a millimeter,
a few pencil-sized.
• cylindrical body, tapered at both ends
• muscular pharynx to suck in liquid food
Nematode body plan
Nematode Movement
• Hydrostatic skeleton, longitudinal muscle
only
• longitudinal muscles only- characteristic
sinusoidal undulating motion
– More like a snake than an earthworm
• Longitudinal muscles that pull against that
pressure to provide a spiral lashing motion
– For burrowing and penetrating host tissues
Nematode Reproduction
• No asexual budding or fragmentation
• most are dioecious, use internal
fertilization
• Sexual dimorphism
• males have terminal cloaca and copulatory
spicules (Picture at right)
• female genital pore at midbody
Cuticle
• Syncitial epidermis secretes outer cuticle
of collagen which is tough and flexible.
• Cuticle is molted (shed), usually four times
during the life of a nematode as it grows,
before reaching the adult stage.
• No cilia
• A molted cuticle and lack of cilia are
features shared with arthropods
Importance of Nematoda
• Many are important parasites of humans
and domestic animals
• Others are important agricultural pests
• Some are used as biological control
agents
• One is widely used for research on
development and developmental genetics
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Some human-parasitic nematodes
Ascariasis: Ascaris lumbrioides
Pinworms: Enterobius vermicularis
Whipworms: Trichuris trichiura
Hookworms: Necator, Ancylostoma
Trichinosis: Trichinella spiralis
River blindness: Onchocerca volvulus
Guinea worm: Dracunculus medinensis
Heartworm: Dirofilaria immitis
Filarial worms: Wucheria, Loa, Brugia
Ascaris lumbricoides
• Most common nematode parasite
of humans
• 1 billion people infected world
wide (1/6 of all people on earth!).
• Most common in tropical and
subtropical regions, and areas
with inadequate sanitation.
Occurs in rural areas of the
southeastern United States.
Ascaris life cycle
• Adults (up to 30 cm long) live in human intestine.
• Each female produces approximately ~200,000
eggs per day – these pass in feces and are
transmitted by fecal contamination of water or
food.
• Eggs are very long-lived and persistent.
• When eggs are ingested the larvae (filariae)
penetrate the gut, enter blood vessels, migrate
via the circulatory system to the lungs, then are
coughed up and swallowed
Symptoms of Ascariasis:
• A few adult worms usually cause no
symptoms.
• Large numbers can cause abdominal pain
and intestinal obstruction.
• Migrating adult worms can occlude the bile
tract, causing jaundice and malnutrition.
• During the lung phase of larval migration,
lung damage can occur.
• Don’t eat the eggs.
Trichinella spiralis
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parasite of man and other mammals- causes trichinosis
Adults in the intestine- small size, not pathogenic.
Females give live birth to ~1500 larvae over 3-4 weeks
Each is about 0.1 mm long.
larvae cause disease – they penetrate lymphatics and
blood vessels, ride circulation to various tissues
• Larvae form coiled cysts in muscle, brain.
• Adults develop if the cyst is eatenthe cysts remain infective for
several years
• Common in pigs & rats- pigs eat rats rats eat pig
scraps from butchering poorly cooked venison or
pork sausage is usual cause of infection in North
America
• Also common in marine mammals. Eskimos are
a high risk group if they eat raw blubber.
• Trichinella infection was once common;
however, now it is relatively rare. Average of ~50
cases in the US per year reported to CDC.
• Transmitted by biting insects
• Adults live in tissues, blood vessels, or lymphatic
ducts of vertebrate host
• Produce live young (filariae) that invade tissues
and fluids
• Wucheria bancrofti rarely causes a condition
called elephantiasis by blocking lymphatic return
and causing chronic edema and fibrosis
• Onchocerca volvulus causes “river blindness”
affects 30 million people
• Dirofilaria- dog & cat heartworm