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Kingdom - Animalia
Subkingdom - Metazoa (multicellular organisms) 
  1. Phylum – Nemathelminthes
  2. Class Nematodes: round worms, round in cross section; separate sexes; complete digestive tract; 500,000 species only a few parasitic to man; e.g. hookworm., filarial.
  3. Phylum - Platyhelminthes: flat worms; incomplete or absent digestive tract; no body cavity; mostly hermaphrodite.
  4. Class Trematoda: flukes; leaf shaped unsegmented body, incomplete GIT often complex life cycle; e.g. lung  fluke.
  5. Class Cestoidea: tapeworms; segmented bodies each segment containing complete set of male and female reproductive organs; no alimentary tract, nutrition by absorption through body wall. e.g. beef tape worm.
  1. Also called round worms
  2. They have a body cavity
  3. They have a complete GIT
  4. They have separate sexes
  5. Non segmented body
  6. Whip worm- T. trichiura
  7. Pin / thread/seat worm- E. vermicularis
  8. Hook worm- Ancylostoma
  9. Round worm- Ascaris
  10. Serpent worm-Dracunculus
1.  Classification based on location/habitat of adult worm
  1. Intestinal
i. Small intestine
  1. Ascaris lumbricoides           
  2. Ancylostoma duodenale
  3. Necator americanus            
  4. Trichinella spiralis               
  5. Strongyloides stercoralis
ii. Large intestine
  1. Trichuris trichiura       
  2. Enterobius vermicularis
b.  Somatic
i. Lymphatic system
  1. W. bancrofti               
  2. B. malayi
ii. Subcutaneous tissue
  1. Loa loa                       
  2. Onchocerca volvulus
iii. Mesentery
  1. perstans                                
  2. Mansonella ozzardi
  3. Drancunculus medinensis   
  4. Conjunctiva                        
  5. Loa loa
2.  Classification based on mode of infection 
a.  Ingestion
  1. A.   Lumbricoides
  2. T.   trichiura
  3. E.   vermicularis
  4. D.   medinensis
  5. T.   spiralis
b.  Cutaneous penetration
  1. Ancylostoma duodenale
  2. Necator americanus
  3. S. stercoralis
c.  Insect
  1. W. bancrofti
  2. B.  malayi
  3. Loa loa
  4. O.  volvulus
Nematodes laying eggs/ larvae
a.  Oviparous
i. Unsegmented ovum
  • Lumbricoides
  • T. Trichiura
ii. Segmented ovum
  • Doudenale
  • N. americanus
b.  Egg containing larvae
i. Enterobius vermicularis

c.  Viviparous
  1. T. spiralis,       
  2. W. bancrofti,  
  3. B. malayi,        
  4. D. medinensis
d.  Ovo-viviparous
  1. S. stercoralis
B. Trichuris trichiura/Whip worm
  1. Habitat: large intestine, caecum, appendix
  2. Egg: barrel shaped, bile stained, mucus plugs at each pole, unsegmented ovum
  3. Life cycle: Egg? develop in moist soil (2 weeks) ? embryonated egg? ingested? larvae released? migrate to caecum? develop into adult worm? fertilization? egg
  4. Clinical features: Abdominal pain, weight loss, anaemia, acute appendicitis
  5. Laboratory diagnosis
    1. Stool examination
    2. Sigmoidoscopy: “coconut cake rectum”
C.  Trichinella spiralis
  1. Habitat: Adult worm found in small intestine of pig, rat, man
  2. Morphology
    1. Adult worm: smallest nematode infecting humans, 1-3mm in length
    2. Larva: 100x6µm
  3. Life cycle: Man is a dead end host, pig is a reservoir host. Ingestion of infected meat (pig)? larvae released in duodenum? adult worm? mating? larvae? penetrate intestinal wall? lymphatic vessel? blood stream? skeletal muscles (diaphragm, intercostals muscles, pectoral muscles)
  4. Clinical features:
  5. Intestinal invasion phase: first week, nausea, vomiting, and diarrhea
  6. Muscle invasion phase: second week, orbital edema, chemosis, photophobia; death due to myocarditis, neurological complications
  7. Laboratory diagnosis:
  8. X ray: calcified cysts
  9. Increased muscle enzymes
  10. Muscle biopsy
  11. Skin test: Brachman’s antigen
  12. Serological test: main stay, CFT, IFAT
D. Strongyloides stercoralis
  1. Morphology: Adults worm, egg, larvae
    1. Adult: female parthenogenetic
    2. Egg: embryonated, hatch in mucosal epithelium
    3. Larvae: rhabditiform larvae? filariform larvae
    4. Internal reinfection
    5. External reinfection  
2.  Life cycle:
  1. Direct phase: filariform larvae? penetrate skin? venous circulation? right heart? lungs? leave pulmonary capillaries? alveoli? bronchi? trachea? larynx? swallowed? intestinal tract? develop into adults in duodenum/ jejunum? mating? eggs? immediately hatched into rhabditiform larvae? filariform larvae
  2. Free living phase (heterogenetic development) : rhabditiform larvae? soil? free living males & females? mating in soil? rhabditiform larvae? filariform larvae  
3.  Clinical features:
  1. Larva currens (intra dermal migration of the filariform larvae)
  2. Diarrhea, nausea, vomiting, loeffler’s syndrome, infection of brain, meninges
    Hyperinfection syndrome: Immunocompromised (HIV/ AIDS), massive larval invasion of the lungs, other organs  
4.  Laboratory diagnosis:
a.  Stool examination:
  1. only larvae are seen
  2. Concentration: bearmann’s method
  3. Stool culture: Harada mori technique
b.  Enterotest
  1. Disseminated: sputum, urine, CSF etc.
  2. Serological test: ELISA, IFAT  
E.  Ascaris lumbricoides-Round worm
  1. Habitat: adult worm in jejunum/ upper ileum
  2. Life cycle: fertilized egg containing unsegmented ovum? develop in soil (3 weeks)? egg containing second stage rhabditiform larva (first moulting) ? ingestion? larva released? penetrate the wall of small intestine? portal circulation? liver? venous circulation ? right heart? pulmonary circulation (moult twice 2nd ,3rd )? penetrate capillary wall? alveoli? bronchi? trachea? larynx? pharynx? swallowed? localize in upper part of small intestine (fourth moulting)? develop into adult worms? mating? egg
1.  Clinical features:
  1. Asymptomatic,
  2. malnutrition,
  3. intussusceptions,
  4. intestinal obstruction,
  5. perforation,
  6. appendicitis,
  7. obstructive jaundice,
  8. pancreatitis,
  9. loeffler’s syndrome   
2.  Laboratory diagnosis:
  1. Adult worm: stool, vomitus
  2. Egg: bile stained, unsegmented ovum; stool
  3. Larvae: sputum

Malabsorption syndrome is caused by all except: (AIIMS May 09)
A. Ascaris               
B. Giardia                
C. Strongyloides              
D. Capillaria philippinensis


Ans. A. Ascaris

F.  Ancylostoma doudenale/ necator americanus- Hook worm
  1. Habitat: jejunum
  2. Life cycle: egg containing segmented ovum? develop in soil? first stage rhabditiform larva? (1st moult) second stage rhabditiform larva ? (2nd moult) filariform larva? penetrate skin? venous circulation? right heart? lungs? leave pulmonary capillaries? alveoli? bronchi? trachea? larynx? swallowed? intestinal tract (3rd moult, third stage larva)? (4th moult) develop into adults in jejunum? mating? eggs
  3. Clinical features:  Nausea, vomiting, diarrhea, epigastric pain, microcytic hypochromic anaemia, wakana disease (seen in japan), rash

1.  Laboratory diagnosis:
  1. Demonstration of eggs in stool, duodenal aspirate; non-bile stained, segmented ovum
  2. Demonstration of adult in stool, duodenal aspirate
G. Enterobius vermicularis
Thread worm, pin worm, seat worm, oxyuriasis
  1. Life cycle: adult female emerges from anus at night? lay eggs? perianal pruritis? scratch? contaminated nails & finger tips? mouth? eggs hatch? develop into adult worms in small intestine? mating? female migrates to caecum & colon
  2. Mode of infection:
    i. Direct transfer of eggs from anus to mouth through contaminated fingers
    ii. Retroinfection/ Autoinfection: eggs hatch in the perianal area and larvae migrate back in the bowels
  3. Through contaminated night clothes, bed Lenin
  4. Clinical manifestation:
     i. Pruritis ani, nocturnal enuresis, anorexia, weight loss
    ii. Ectopic enterobiasis: salpingitis, omentitis, cervicitis, peritonitis
  5. Laboratory diagnosis
    i. Demonstration of adult worms: stool
    ii. Demonstration of eggs: stool examination not recommended, NIH swab, cellulose tape
H. Capillaria Philippinensis
  1. Infection endemic to the Philippines and parts of Thailand transmitted to humans upon ingestion of inadequately cooked or raw C. philippinensis-bearing fresh- or brackish-water fish
  2. *Two other species of Capillaria are C. hepatica and C. aerophila (which cause hepatic capillariasis and pulmonary capillariasis, respectively). These infections are primarily zoonotic, as fewer than 50 cases have been reported in humans worldwide
1.  Clinical infections-
  1. Asymptomatic or only mildly symptomatic.
  2. Early symptoms of intestinal capillariasis include abdominal pain, diarrhea, and borborygmus (gurgling noises in the gut).
  3. Nausea, vomiting, anorexia, hypotension, and weight loss (the symptoms which lend themselves to the infection's common name--Wasting Disease) are also commonly observed in infected patients.
Patients suffering from autoinfection (the development of a second generation of adult worms in the same human host) often suffer more severe symptoms such as malnourishment, hypoproteinemia, low electrolytes, generalized anasarca, visible paristaltic waves (traversing the abdomen) and secondary bacterial infections.
2.  Diagnosis:
  1. Specific diagnosis of C. hepatica infection is based on demonstrating the adult worms and/or eggs in liver tissue at biopsy or necropsy
Treatment; Mebendazole, which is administered as a twice daily dosage of 200 mg for 20 days. Mebendazole impairs glucose uptake by the larval and adult C. philippinensis

I.   Larva migrans

a.  Infection with helminth larvae not adapted to humans
b.  Cutaneous larva migrans (creeping eruption)

Ancylostoma brasiliense (commonest)
  1. caninum
  2. Uncineria stenocephala
  3. Gnathostoma spinigerum
  4. Bunostomum phlebotomum
  5. Visceral larva migrans
  6. Toxocara canis (commonest)
  7.  T. catis
  8. Angiostrongylus cantonensis
  9. A. Costaricensis
  10. Anisakine spp. 
1. Comparison of CML & VML
Tissue involved Skin Viscera (liver, lungs)
Infecting organism Zoophilic hook worm Zoophilic round worm
Route of infection Larvae penetrate the skin Ingestion of infected eggs
Eosinophilia Rare Present
Anti-A, anti-B agglutinins Not present Present
Serodiagnosis (ELISA) No role Well established
J. Filariasis- Lymphatic filariasis caused by W. bancrofti (90%), B. malayi (10%), B. timori 1.  W. bancrofti
  1. Habitat: adult worm in lymphatics, sheathed microfilaria in blood
  2. Definitive host: humans
  3. Intermediate host: mosquito (culex, aedes, anopheles), India: Culex pipens fatigans
  4. Adult worm in lymphatics? sheathed microfilaria in blood?  mosquito bite? exsheathing in stomach? penetrate stomach wall? migrate to thoracic muscles? first stage larva? second stage larva? third stage filariform larva (infective stage)? mosquito bites humans? larvae reach lymphatics? adult worm
  5. Extrinsic incubation period: 10-20 days
  6. Pre-patent period (biological incubation period): time taken for the third stage infective larvae to develop into adult worms? sexually mature? liberate microfilariae in the peripheral blood (patent period) 
  7. Clinical incubation period: 8-16 months
  8. Clinical features: Fever, lymphangitis, lymphadenitis, chylocele, chyluria, chylous ascites, chlythorax, lymphedema, elephantiasis, occult filariasis
2. Comparison of Classical & Occult filariasis
  Classical filariasis Occult filariasis
Cause Adult, developing worms Microfilariae
Organs involved Lymphatic vessels, lymph nodes Lymphatic vessels, lung, liver, spleen
Microfilariae Present in peripheral blood Absent
Lesion Lymphangitis, lymphadenitis Eosinophilic granuloma
Response to DEC No response Good response
3.  Laboratory diagnosis

a.  Demonstration of microfilaria
  1. Direct film
  2. Concentration (Knott’s)
  3. DEC provocation: 2mg/kg, blood sample after one hour
b.  Demonstration of adult worm
  1. Biopsy of lymph node
c.   Immunodiagnosis
  1. Detection of antibody: ELISA, IHA, IFAT
  2. Detection of antigen: ELISA, immunochromatography
  B malayi-Vector: mosquito, mansonia annulifera (in India)   

K.  Onchocerca volvulus- Onchocerciases, river blindness
  1. Tropical Africa
  2. Habitat: Adult worm in subcutaneous tissue (onchocercomas); microfilariae found in skin
  3. Definitive host: man
  4. Intermediate host: female black flies (simulium spp./ buffalo gnats) breed in fast flowing rivers
    Bite of mosquito? ingests microfilaria? develop into third stage larva (infective stage)? bite? in humans develop into adults? microfilaria
1.  Clinical features:
  1. Adult worm relatively non-pathogenic (onchocercomas)
  2. Microfilariae main cause of disease: dermatitis, keratitis, iridocyclitis
2.  Laboratory diagnosis
  1. Adult worm: biopsy of subcutaneous nodules
  2. Microfilaria: skin snip (iliac crest); mazzotti reaction: 50mg DEC? pruritis, erythema  
L.  LOA LOA-Loaisis, calabar swellings, fugitive swelling
  1. West & central Africa
  2. Habitat: Adult worm in subcutaneous tissue ; microfilariae found in blood
  3. Definitive host: man
  4. Intermediate host: female chrysops (mango fly/ deer fly/ soft fly)
  5. Bite of mosquito? ingests microfilaria? develop into infective larva (infective stage)? bite? in humans develop into adults? microfilaria
  6. Clinical manifestations:
    1. Adult worm: migratory swellings (calabar/ fugitive swellings), glomerulonephritis, retinopathy, peripheral neuropathy, meningitis, jacksonian epilepsy
    2. Microfilariae: relatively non pathogenic
1.  Laboratory diagnosis
  1. Adult worm: biopsy
  2. Microfilaria: blood
M.  Dracunculus medinensis-Guinea worm, medina worm
  1. Habitat: adult female found in subcutaneous tissue
  2. Definitive host: humans
  3. Intermediate host: Cyclops
  4. Patient enters water? adult female worm emerges from blister/ ulcer? anterior end of worm ruptures? thousands of larvae released in water? ingested by cyclops? develops in coelomic cavity to third stage larva? human drink water (contaminated with Cyclops)? penetrate the gut wall? migrate to retroperitoneal connective tissue? mature into adult worms? mating? male dies? fertilized female migrates to subcutaneous tissue of the body? blister? blister/ ulcer on the skin
1. Clinical features: blister, ulcer, secondary bacterial infection, urticaria, nausea, calcified worm (arthritis, spinal cord compression)
2.  Laboratory diagnosis:
  1. Emerging adult worm
  2. Embryo: contact with water, larvae released in water, examined under microscope
  3. X-ray: calcified worm
  4. Serology: ELISA, IHA
Important Points
India achieved eradication of Guinea worm disease in 1999  
N. Classification of microfilaria
 1.  Unsheathed and nonperiodic microfilaria
  1.  Found in blood
    i.    Pointed tail tip with nuclei: M. perstans
    ii.    Pointed tail tip without nuclei: M. ozzardi
  2. Found in skin
  i.    Tail tip hooked, nuclei upto tip: M. streptocerca

ii.    Tail tip free of nuclei: O. volvulus

2.  Sheathed periodic microfilaria found in blood

a. Tail tip free of nuclei: W. bancrofti
b. Blunt tail with two terminal nuclei: B. malayi
c. Pointed tail tip with nuclei upto tail tip: Loa loa

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