NematodesGeneral Features

• Have elongated, cylindrical, smooth, unsegmented, flesh-colored bodies.

• Body is usually tapered to a pointed posterior end, and to a rounded anterior end

• The body is covered by a noncellular, 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.

• They are classified into 2 main categories according to their primary location:

– Intestinal nematodes

– Tissue nematodes (filariae)

Main features of Nematodes

Intestinal NematodesTissue Nematodes

ShapeLarge size, CylindricalElongated, Slender (slim)

Habitat Most adult worms live in the intestinal tract

Inhabit either lymph vessels; or skin and subcutaneous tissues

Diseases Diseases are diagnosed by identifying their characteristic eggs in stool

Diseases are diagnosed by demonstrating microfilariae in blood, in tissue or tissue fluids

Medically important Nematodes.

Intestinal Nematodes Tissue (Filarial worms)

1. Enterobius vermicularisI. Lymphatic filariae:

1. Wuchereria bancrofti

2. Burgia malayi

2. Ascaris lumbricoides

3. Hookworms

*Ancylostoma duodenale

*Necator americanus

II. Cutaneous filariae:

1. Dracunculus medinensis

2. Loa loa

3. Onchocerca volvulus 4. Trichuris trichiuria

5. Trichinella spiralis

Comparison between

1. Enterobius vermicularis

and

2. Ascaris lumbricoides

I. Intestinal Nematodes

Female

Male

Enterobius vermicularis

Enterobius vermicularis eggs

Enterobius vermicularis egg

Ascaris fertilized egg.

Ascaris egg containing a larva, which will be

infective if ingested.

Ascaris unfertilized egg.

Female

Male

Ascaris lumbricoides

Enterobius vermicularisAscaris lumbricoides

Name Pinworm, seat wormAscariasis, round worm

Size Female 8-13 , male 2-5 mm Female 20-35, male 15-30 cm

Disease Enterobiasis (oxyuriasis) Ascariasis

Geographica

l distribution

Worldwide, most common in temperate regions and in crowded places

Worldwide; high prevalence in tropical and subtropical areas with inadequate sanitation, and where human feces are used as fertilizer

Infective stage

Embryonated eggEmbryonated egg

Mode of

infection

Ingestion; or autoinfection via nails scratching the perianus

Ingestion of eggs in food contaminated with human feces

Infection siteLarge intestineSmall intestine, lung

Enterobius vermicularisAscaris lumbricoides

Symptoms Perianal Pruritis, especially at night, appendicitis, abdominal pain, *invasion of girls’ genital tract cause vaginitis, pelvic or peritoneal granulomas

Migrating worms cause occlusion of biliary tract or oral expulsion in lung it causes inflammation with pulmonary symptoms, e.g. cough, hemoptysis

Identification

Characteristic eggs collected mornings from perianal area using transparent adhesive tape adult worm may be found in perianal area or during vaginal examination

Characteristic eggs in feces, larvae identified in sputum or gastric aspirate adult worm may pass in stool.

Treatment Pyrantel pamoateAlbendazole, Mebendazole, Pyrantel pamoate

Enterobius vermicularis

Ascaris lumbricoides

3. HookwormsAncylostoma duodenale Old World hookworm Necator americanus New world hookworm

Geographical distribution

Worldwide, in areas with warm, moist climate

Ancylostoma duodnale: Middle East, North Africa

Necator americanus: America

DiseaseHookworm infection

Infective stageFilariform larva

Mode of transmission

Filariform larvae in moist soil penetrate skin through bare feet

Site of infectionSmall intestine, heart, lung

Diagnostic stageEgg in feces; oval, colorless, thin- shelled, segmented

Clinical findingsIron deficiency: Anemia due to loss of blood at site attachment in intestine

*cardiac problems

*local skin manifestations “ground itch”

*respiratory symptoms during larval pulmonary attack

Hookworms

Laboratory diagnosis:

Microscopic examination of characteristic egg in stool

Treatment

Albendazole, Mebendazole, Pyrantel pamoate

Hookworm larva

Egg of hook worm:

oval or ellipsoidal shape

with thin shell

4. Trichuris trichiuria

Trichuris trichiura: a macroscopic view of a tangled mass of adults

Trichuris trichiura adults in gut

(preserved post mortem specimen)

Trichuris trichiuria egg a typical barrel shape with two polar plugs, that are unstained

Common nameWhipworm

Length of adult wormFemale 20-35, male 15-30 mm

Geographical distribution

Worldwide; high prevalence in tropical and subtropical areas with inadequate sanitation, and where human feces are used as fertilizer as Ascaris

DiseaseTrichuriasis, trichocephaliasis

Infective stageEmbryonated egg

Mode of transmissionIngestion of eggs in food contaminated with human feces

Site of infectionLarge intestine (cecum)

Diagnostic stageEgg in feces; are brown, barrel-shaped with a plug at each pole ; contains a fertilized unsegmented ovum.

Clinical findingsheavy infection, especially in children can cause gastro-intestinal problems (abdominal pain, diarrhea, rectal prolapsed), and possibly growth retardation

Laboratory diagnosismicroscopic examination of characteristic egg in stool adult worm may be identified upon examination of rectal mucosa by proctoscopy

TreatmentMebendazole; Albendazole as alternative

Trichuris trichiuria

5.Trichinella spiralis

Encysted larvae of Trichinella in pressed

muscle tissue. 

Larvae of Trichinella, freed from their cysts,

typically coiled.

Common nameTrichinosis

Length of adultMale 2.2, female 1.2 mm

Geog. distributionWorldwide

DiseaseTrichinillosis, trichinosis

Infective stageEncysted larva

Transmission modeLarvae in undercooked pork. Pigs are main reservoir

Site of infectionStriated muscles

Diagnostic stageLarvae in muscles and tissues

Clinical findingsLarvae migration in muscular tissues cause facial and periorbital oedema, rash, muscle pain, conjunctivitis

Laboratory diagnosisMuscle biopsy to identify larvae in striated muscles *indication of eosinophilia*serologic tests

TreatmentSteroid plus Mebendazole in severe infections *thiabendazole

II. Tissue (Filarial) Nematodes

a. Lymphatic Wuchereria bancrofti

Brugia malayi

b. CutaneousDracunculus medinensis

Loa loa

Onchocrca volvulus

Wuchereria bancroftiBancroft's filaria

Brugia malayi Elephantiasis

Geo. Dist.Worldwide in tropical areasLimited to Asia (Malaysia)

Disease Elephantiasis, Wuchereriasis Bancroftian filariasis, lymphatic filariasis

Malayan filariasis,lymphatic filariasis

Mode of transmn

Mosquito (Anopheles sp. or Culex sp.)

Mosquito (Mansonia sp., or Aedes sp.)

Inf. stageMotile microfilariaMotile microfilaria

Site of infection

Lymph nodes, lymphatic glands and vessels in legs, arms and genitalia (testes)

Lymph nodes, lymphatic glands and vessels in legs, arms but genitalia is not affected.

Clinical findings

Inflammation of vessels, rupture of lymphs, fibrosis, leading to obstruction. Thickening, hypertrophy of tissues, enlargement of tissues (especially extremities and genitalia)

Inflammation of vessels, rupture of lymphs, fibrosis, leading to obstruction. Thickening, hypertrophy of tissues, enlargement of tissues (especially extremities)but genitalia enlargement is not seen.

Life cycle of wuchereria bancrofti

Diagnosis: Demonstration of microfilaria in blood molecular diagnosis using PCR

Treatment: Diethylcarbamazine,

Surgery in elephantiasis

Wuchereria bancrofti Brugia

malayi

b. Cutaneous Nematodes

1. Dracunculus medinensis

2. Loa loa

3. Onchocrca volvulus

Dracunculus medinensisLoa loaOnchocerca volvulus

Guinea fire wormEye wormBlinding worm

Geog. distrib

Africa, Yemen, India, South America

Africa, Africa, Latin America, and Middle East

LengthFemale over 100 cm, male 2 cm F: 40-70mm, m: 30-34mmF: 33-50 cm, male 19-42 m

VectorCyclopeFly of genus Chrysops (deerfly or mango fly)

Fly of genus Simulium (black fly )

Site of infectio

Spread from intestinal walls to tissues and subcutaneous tissues

Subcutaneous tissues, and muscles

Nodules in subcutaneous tissues

DiseaseDracunculosis, Guinea worm dis.Loiasis, Calabar swellingOnchocerciasis, River blindness

Symptoms

Urticaria, skin ulcer (the worm emerges as whitish filament in the center of a painful ulcer), rupture of worm during surgical removal an anaphylactic reaction

Angioedema, swelling of various parts of body (Calabar swelling), conjunctivitis, irritation, oedema of eyelids, impaired vision

Pruritis, papule dermatitis with thickening, scaling and dryness of skin (lizard skin), fibrous onchocercoma subcutaneous nodules, ocular lesion blindness

Diagnosis

Demonstration in local lesion or fluid discharge of adult worm (head of worm) or rhabditiform larva seen under the skin

Demonstration of microfilaria in blood (since adult worm lives in subcutaneous tissue and microfilaria in blood)

Examination of nodule aspirate, histopathology of skin near nodule; adult lives in subcutaneous tissue, microfilaria in subcutaneous fluid

Treatment

Diethylcarbamazine, thiobenzadole, niridazole, surgery

Diethylcarbamazine for microfilaria and adult, soothing lotion for Calabar swelling

Ivermectin against microfilaria, Suramin (Bayer 205, antropyl) against adult, surgery

The female guinea worm (Dracunculus medinensis)

induces a painful blisterRuptured blister, the worm emerges as a whitish filament in the center of a painful ulcer which is often secondarily infected.

Rolling of the worm over a rod

1. Dracunculus medinensis

2. Loa loa

3. Onchocerca volvulus

Black flies of the genus Simulium.

Nodules containing Onchocerca volvulus on the head of a man in Guatemala

Dracunculus medinensis