Zoology 2015 Nematoda Phylum Nematoda - PowerPoint Presentation

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Zoology2015

Nematoda

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Phylum Nematoda

Adaptive Benefits of a Pseudocoelom - a space between the guts and the

body wall

It is not lined with a peritoneum therefore is termed a false cavityIt is an improvement over the acoelom of the platyhelminthes but not as advanced as the eucoelom / it lacks mesenteries

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Phylum Nematoda

It does offer

adaptation potential

– Greater freedom of movementSpace for development and differentiation of digestive, excretory and reproductive organsStorage for waste productsSimple means for distribution and circulation of materials

Hydrostatic support for the body

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Phylum Nematoda

General features of this phylum –

Very diverse phylum, about

25,000 species have been catalogued but estimate that there are 500,000 In good topsoil there are billions per acre of ground.

They live in all habitats, from mountains to the deep oceans, from the

polar ice

to the

tropics

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Phylum Nematoda

Free-living nematodes feed on

yeast

, bacteria and algaePredatory nematodes feed on other invertebrates and protozoansNematode worms are important food for mites,

insects and fungiAlmost all animals and most plant species have nematode parasites

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Phylum Nematoda

Form & Function of body systems –

Bilateral

symmetryComplete digestive system with both a mouth and an anus

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Phylum Nematoda

Form & Function of body systems –

Nematodes all have a

cylindrical shapeMuscles in body wall only run longitudinallyNematodes express Eutely which means they all show a set number of cells

Examples – C. elegans Researchers use this worm

Females have 1057 cells

Males have 959 cells

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Phylum Nematoda

Form & Function of body systems –

Dorsal

and ventral cords bear nerves while lateral cords bear excretory ducts

Longitudinal muscles run in four bands – between the nerve

and excretory cords

The digestive system

consists of

mouth

,

pharnyx

,

intestin

e,

rectum

and

anus

.

This is considered a

complete digestive system.

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Phylum Nematoda

Form & Function of body systems –

Senses include

papillae (sensory hairs) at the head and tail and amphids on the head. Parasitic nematodes also have phasmids (chemo-receptors) at the tail endNematodes are

dioecious and the males are smaller

than the females and

fertilization is

internal

.

Males bear a pair of

copulatory spicules

.

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Phylum Nematoda

Form & Function of body systems –

Nematodes have a non-cellular

cuticle that is shed between each of four juvenile stages (no larval stage) this is called moltingSkeletal system is hydrostatic

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Nematode Parasites

Ascaris

lumbricoides – large intestinal roundworms of humans More than 1.2 billion people affected worldwideSoutheastern US more than 64% of people affected

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Nematode Parasites

They feed on

intestinal contents

and a large infestation may block or perforate the intestines. They may cause a serious anemia in childrenFemales may be 50 cm – 20 inches) long and males 30 cm - (12 inches)

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Nematode Parasites

Ascaris

Life CycleA female roundworm lays 200,000 eggs a day which pass out in the host’s fecesEggs remain viable for long periods in the soil – (10-20 years)

When a host swallows the eggs, juveniles hatch and burrow through intestinal wall into the blood supply

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Nematode Parasites

Ascaris

Life Cycle (con’t)4. Carried through the heart to the lungs, they break into the alveoli and crawl upward into the trachea where they are coughed up and then swallowed with saliva

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Nematode Parasites

Ascaris

Life Cycle (con’t)5. They mature in the intestine where they feed on the intestinal contents. They sometimes cause allergic reactions or perforation of the intestine which results in

peritonitis. Wandering worms may occasionally emerge from the throat or anus

and have even been known to appear wriggling out of the

ears, mouth or nose if there is a heavy infestation

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Nematode Parasites

Ascaris

Life Cycle

Also seePage 311

Fig. 15-7

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Nematode Parasites

Hookworm

Necator

americanus – the hookworm – name means “American Killer”These are small worms, only 11 mm and their anterior end has a dorsal curving hook (male)

Large sharp cutting plates in their mouth cut into the intestinal mucosa

and they attach and

suck

the host’s blood

(see page 310, figure 15-6)

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Nematode Parasites

Hookworm

Hookworms become

blood pumps because they pump much more blood than they can digest, pumping the blood through their intestines, partially digesting it and absorbing the nutrients. They suck much more blood than they need for food and heavy infestations can cause anemia.Children with hookworms may experience retarded mental and

physical growth.

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Nematode Parasites

Hookworm

Necator

life cycle –similar to that of the AscarisEggs pass in feces, but if soil conditions are warm and moist the eggs hatch and the juveniles live in the soil, eating bacteria

.When juvenile worms come into contact with bare skin, they

burrow

into the blood vessels and then they follow the same path as

Ascaris

to get to the intestine. Penetration usually occurs through soles of the feet. Southern US population had a

55%

infection rate at the turn of the century but because of the practice of

wearing shoes

the infection rate is now

5-10%

.

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Nematode Parasites

Necator

americanus life cycle –

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Nematode Parasites

Trichinella

spiralis – trichina wormCauses the potentially lethal disease trichinosisAbout 2.4% of the US population is infectedAdult worms are tiny, about

1.5 – 3 mm long

Colour

SEM of

Trichinella

spiralis

roundworms

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Nematode Parasites

Trichinella

spiralis – trichina worm (con’t)Infection occurs when meat containing live encysted juveniles is eaten, adults burrow into intestinal mucosa and females give birth to live young

Muscle tissue with encysted larval trichina

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Nematode Parasites

Trichinella

spiralis – trichina worm (con’t)E. Trichina worms infect hogs, rats, cats, and dogs . . . People usually become infected by eating undercooked pork.Hogs become infected by eating infected meat scraps or infected rats

.

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Nematode Parasites

Trichinella

spiralis life cycleIn an infected host, living juvenile worms are born in the intestineJuveniles penetrate blood vessels and circulate through the body invading all organs, tissues

and intestinal spaces

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Nematode Parasites

Trichinella

spiralis life cycleWhen they invade skeletal muscles, they redirect genes and muscle looses its striations and becomes a nurse cell of the parasite. This this encysted meat is eaten, it cause the infection.

While the juveniles are wandering in the body, they can cause death if large numbers invade the heart or the brain

.

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Nematode Parasites

Trichinella

spiralis life cycle

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Nematode Parasites

Enterobius

vermicularis – the pinwormThis is the most common worm parasite in the US but it causes little disease (just irritation)Adults live in the large intestine

They attain a body length of 12 mm

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Nematode Parasites

Enterobius

vermicularis – the pinworm30% of US children are infectedUp to 75% of college students who live in dorms are infectedThere are several oral drugs that are effective against this infection but

all people living in the household must be treated because they are very infectious

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Nematode Parasites

Enterobius

vermicularis – pinwormExhibit haplodiploidyMales are haploid – come from unfertilized eggsFemales are diploid – come from fertilized eggs

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Nematode Parasites

Enterobius

vermicularis – the pinwormDiagnosed by scotch tape test or flashlight test

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Nematode Parasites

Enterobius

life cycle – Adults live off of intestinal contents in the large intestineFemales detach from the intestinal lining and migrate to the anus at night to lay eggs on the external surface

. This causes intense itching.Scratching the itch contaminates

hands and bed clothes

Eggs develop rapidly and can become infective in

just 6 hours

at

body temperature

Contaminated hands put eggs into

mouth

and

airborne

–eggs hatch in the

duodenum

and mature in the large intestines.

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Nematode Parasites

Enterobius

life cycle –

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Nematode Parasites

Filarial Worms – “Elephantiasis”

Wucheria

bancrofti and Brugia malayi250 million people in the tropics are infected

Worms live in the lymph system and obstruct the ducts

Worms may grow to

100 mm

Females release live young called

microfilariae

which circulate in the blood stream

Wucheria

bancrofti

Brugia

malayi

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Nematode Parasites

Filarial Worms – “Elephantiasis”

Elephantiasis is a disease caused by repeated exposure. Blockage and swelling of

lymph ducts causes gross enlargement of certain body parts

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Nematode Parasites

Filarial Worms – “Elephantiasis”

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Nematode Parasites

Filarial Worms –

River blindness

- another filarial worm disease

Microfilarial

worm infestation of eye tissue

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Nematode Parasites

Filarial Worms –

Dog heartworm

is the most common filarial worm disease in the US. It reaches a 60% infection rate in the south and eastern seaboard states and can infect dogs, cats, otters and occasionally humans

.

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Nematode Parasites

Dog Heartworm Life Cycle

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Nematode Parasites

Filarial Worms Life Cycle –

Adult worms live in the

lymph ductsFemales bear live tiny juveniles called microfilariaeAt night, microfilariae congregate in vessels near the surface of skin

Mosquitoes transmit disease when they ingest the microfilariae as they feedThe microfilariae develop into the infective stage in the mosquito, considered the

intermediate host

and then they infect a new

definitive

host by moving into a bite wound through the

proboscis

of the mosquito.