nematodes general features have elongated, cylindrical, smooth, unsegmented, flesh- colored bodies....
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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