NEMATODES

Instructor: Almonther I. Alhamedi

The Islamic University of GazaDepartment of Biology

E-mail : . .mhamedi@iugaza edu psWeb page: http:// . . . /site iugaza edu ps mhamedi

GENERAL FEATURESo Nematodes, more commonly known as round-worms, have three basic

body characteristics.o unsegmented: not divided into segments.o bilaterally symmetric: body is identical on each side.o triploblastic: consists of three primary germ layers the ectoderm,

mesoderm and endoderm. o posses fluid-filled body cavity called a “Pseudo-coelom

GENERAL FEATURES

Have elongated, cylindrical, smooth, flesh-colored bodies. The body is covered by a non-chitineus, highly resistant coating

“the cuticle” They have complete digestive system with mouth, oesophagus,

midgut and anus. All are separate sexes; the female is usually larger than the male. Eggs may be embryonated unembryonated, meaning that they

may not yet be developed. Parasitic forms include ascarids, hookworms, trichina worms,

pinworms, and filarial worms.

GENERAL FEATURES Roundworms are also characterized by a complete

digestive system. Their digestive system can be divided into three parts, the

stomodeum, intestine, and proctodeum.

o The stomodeum consists of the “mouth and lips”, buccal cavity, and the pharynx (esophagus).

o The intestine functions by digesting, absorbing water and nutrients, and eliminating the residues of digestion.

o The proctodeum serves as the anus and is where waste is excreted.

o The cuticle functions as a barrier, it provides protection. And As a hydrostatic skeleton it acts as an antagonist to longitudinal muscles.

GENERAL FEATURES

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.

Large 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.

Marine nematodes have a large role in decomposition and recycling. As a result of this they tend to be extremely sensitive to pollution, which drastically changes their environment.

Most free-living nematodes are less than 2.5mm in length and often are microscopic.

Most free-living nematodes are carnivorous. However, some feed on algae and fungi and some are detritivores. Others feed on plants, especially the roots.

ASCARIS LUMBRICOIDES the order Ascaridida are relatively large nematodes found in

a wide variety of aquatic and terrestrial vertebrates, mostly in Tropical and Subtropical Regions.

Ascaris lumbricoides lives in the small intestine. Ascaris is the largest intestinal nematode. 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. The larvae penetrate the intestinal wall and travel through

the blood stream to the lungs where they break out of the alveoli . Then they make their way up the trachea where they are swallowed and eventually settle in the small intestine.

The egg has an outer shell membrane which is heavily mamillated. This layer is sometimes rubbed off in passage down the fecal stream. Infertile eggs often appear longer, and thinner shelled.

Ascaris unfertilized egg.

Ascaris fertilized egg

ANCYLOSTOMA DUODNALE HOOKWORMS

Hookworms are quite small,

because they feed on blood a heavy infection can produce severe anemia. In children a hookworm infection can stunt growth and cause a general lack of energy.

ANCYLOSTOMA DUODNALEHOOKWORMS

Infective stage : Filariform larva Mode of transmission : Filariform larvae

in moist soil penetrate skin through bare feet

Hookworm rhabditiform larva

Hookworm filariform larva

 ENTEROBIUS VERMICULARIS Pin worm Female 8-13 larger than male 2-5 mm. The infective stage is embryonated egg. It is a group infection especially common among children. Very often

associated with low sanitation and hygiene. Mode of infection: by ingestion or autoinfection via nails scratching

the perianus. Infection site: Large intestine.

 ENTEROBIUS VERMICULARIS

•Adult pinworms live in the large intestines of their host;

After copulation the males die. When the female is ready to lay eggs she crawls out تزحفof the anus and deposits the eggs on the perianal skin.

A single female can produce more than 10,000 eggs. After laying her eggs, the female also dies.When ingested by another person the eggs hatch inthe small intestine, and the juvenile worms grow into adult, sexually mature worms in about a month.

STRONGYLOIDES STERCORALIS - THE THREADWORM

Life cycle: (very complex) Infective third stage filariform larvae

penetrate skin, enter the lymphatics or bloodstream.

Larvae migrate to the lungs, break out of lung capillaries into alveoli.

After maturation, larvae travel to the pharynx, are swallowed, and return to the intestine.

Larvae mature to adults and attach to the

mucosa of the small intestine.

Strongyloides stercoralis rhabditiform larva

Strongyloides stercoralis filariform larva

STRONGYLOIDES STERCORALIS – THE THREADWORM

Life cycle: (Continued) Parthogenetic Females only - no parasitic

males. Females are capable of unisexual reproduction, no fertilization required. Produce viable eggs.

Eggs hatch in mucosa. Larvae: Are passed in feces, live in the soil,

mature into a free-living adult males and females, which produce eggs; Rhabditiform larvae feed in soil and develop into infective stage larvae which penetrate the skin; First stage larvae develop into infective stage larvae in the intestine (autoinfection).

Strongyloides stercoralis rhabditiform larva

Strongyloides stercoralis filariform larva

STRONGYLOIDES STERCORALIS - THE THREADWORM

Morphology: Rhabditiform larvae - short buccal cavity;

large, prominent genital primordium. Filariform larvae - tail has a notch in it, in

contrast with the filariform larva of hookworms.

Must be able to differentiate these from hookworm larvae.

Eggs hatch in the intestine (not usually passed in stool specimens). Eggs resemble

hookworm eggs, but are embryonated.

Buccal cavity of rhabditiform larva

Notch in tail of filariform larva

Strongyloides stercoralis - The Threadworm

TRICHINELLA SPIRALIS – TRICHINOSIS Trichinella spiralis is a tiny nematode that causes the

potentially fatal disease trichinosis. a parasite of carnivorous mammals. It is common in rats and in

swine fed uncooked garbage and slaughterhouse scraps. Human infections occur most often as a result of consumption

of raw or undercooked pork. Infective stage larvae are ingested in meat products. Tissue is digested, larvae are freed in the intestine. They mature

into adult males and females. Female in mucosa releases larvae. These disseminate throughout

the body via the bloodstream. Larvae encyst in striated muscle.

Encysted larvae of Trichinella in pressed muscle tissue. 

Encysted larvae of Trichinella in pressed

muscle tissue. 

Larvae of Trichinella, freed from their cysts,

typically coiled.

TRICHURIS TRICHIURA causes trichuriasis when it infects a human 

large intestine. It is commonly known as the whipworm which refers

to the shape of the worm; it looks like a whip with wider "handles" at the posterior end.

They attach to the host through their slender anterior end and feed on tissue secretions instead of blood.

Females are larger than males; approximately 35–50 mm long compared to 30–45 mm. The females have round posterior end compared to their male counterparts with a coiled posterior end. Their characteristic eggs are barrel-shaped and brown, and have bipolar protuberances حدبة.

II. TISSUE (FILARIAL) NEMATODES

a. Lymphatic Wuchereria bancrofti

Brugia malayi

b. CutaneousDracunculus medinensis

Loa loa

Onchocrca volvulus

The Filariae are long thread-like nematodes. Eight species inhabit portions of the human subcutaneous tissues and

lymphatic system. Adults of all species are parasites of vertebrate hosts. Female worms produce eggs. The eggs modify, becoming elongated and

worm-like in appearance and adapting to life within the vascular system. Microfilariae transform into infective larvae in the insect and are

deposited in the next host when the insect takes a blood meal. Human infection is acquired when infective larvae enter the skin at the

arthropod’s feeding site. Larval migration and development takes place in tissue. Adults are in various tissues (according to species). They mature and

produce microfilariae.

THE FILARIAL WORMS

“Bancroft's Filariasis.” A blood & lymphatic dweller. The infection often results in elephantiasis.

Vectors - Culex, Aedes, & Anopheles mosquitoes.

Diagnosis - Detection and identification of microfilaria in stained blood smears.

Wuchereria bancrofti microfilaria in blood smear

WUCHERERIA BANCROFT

Major pathology and symptoms – Swelling, due to allergic reaction occurring

around adult worms, produces obstruction & elephantiasis. Each individual reacts differently. Very few develop elephantiasis, but in some this is extensive.

WUCHERERIA BANCROFTI:

BRUGIA MALAYI“Malayan filariasis.” A blood & lymphatic dwellerقاطن.

The infection can cause elephantiasis, but is not as disfiguring or common as with Wuchereria bancrofti.

Vectors - Mansonia, Anopheles & Aedes mosquitoes.

Diagnosis - Detection and identification of microfilaria in stained blood smears.

Morphology - Microfilariae are sheathed, nuclear column extends to tip of tail with two nuclei near end of tail, one in a swelling just short of tail’s end, the other in the end of the tail.

Brugia malayi microfilariae in blood smear

LOA LOA The “eyeworm.” Infections involve the dermis

and subcutaneous tissues (Calabar swellings). Vector - Crysops (mango fly), a large fly with

biting mouthparts.

Major pathology and symptoms -

Infections cause a localized subcutaneous edema, particularly around the eye, because of larval migration and death in capillaries.

Brugia malayi

DRACUNCULUS MEDINENSIS – THE GUINEA WORM

An important parasite in the Middle East, central India and Pakistan. Also found in Africa in the Sudan and scattered through central equatorial regions, and on its west coast.

It is believed to no longer occur in the Western Hemisphere.

Sometimes classified with the filarial worms, but Dracunculus is not a true

filaria.

Blister containing Dracunculus medinensis

Adult Dracunculus emerging from broken blister

DRACUNCULUS MEDINENSIS – THE GUINEA WORM

Life cycle: Infective stage exists in a water flea (copepod –

the intermediate host). Humans become infected by drinking water

containing the infected copepod. Larvae penetrate the digestive tract to enter the

deep connective tissues where they mature in about 1 year.

Females migrate to the subcutaneous tissue (usually the skin of the extremities).

Females release larvae which leave the human through ruptured blisters on the skin.

The larvae enter the water and are ingested by copepods.

DRACUNCULUS MEDINENSIS – THE GUINEA WORM

Diagnosis - Visual observation of skin blister. The worm’s

serpentine presence beneath skin can be seen.

Induce release of larvae from the skin ulcer by

applying cold water.