Helminthology : Structure, Classification, Growth, and Development

Helminthology, which is the study of parasitic worms, is an important topic in microbiology. Helminth infections are prevalent in many parts of the world, particularly in tropical and subtropical regions. Many helminth infections can cause serious illnesses and even death. As a medical professional, you must be able to diagnose and treat these infections appropriately to prevent severe outcomes.

Let’s learn more about this important microbiology topic for NEET PG exam preparation.

CESTODES

Diphyllobothrium latum (Fish Tapeworm)

• Infective form → plerocercoid larvae 
• Operculated egg (Lid)
• A/w megaloblastic anaemia

H. Nana (Dwarf Tapeworm)

• Infective form -Egg
• Egg has polar filaments, polar thickening with central hooklet
• Non-bile-stained egg
• Autoinfection - present 
• DOC -Praziquantel

H. diminuta (Rat Tape worm)

• Autoinfection - Absent
• Egg lacks polar filaments

Echinococcus granulosus

• Infective form – Eggs with contaminated food and water
• MC site – Liver (Hydatid cyst) >Lungs >Brain

Hydatid Cyst

• Most active layer – Endocyst (Germinal epithelium)
• It leads to formation of brood capsules, protoscolices and hydatid fluid. 
• This can be detected by Casoni’s test (Type 1 HS reaction)
• Best treatment is surgical removal.
• PAIR therapy

Echinococcus Multilocularis 

• Malignant Hydatid Disease

Tinea

T. Solium	T. Saginata
	Longer
Armed (Rostellum with Hooklets)	Unarmed tapeworm as it lacks Rostellum and Hooklets
Larval form A/K/a Cysticercus cellulosae	Larval form A/K/a Cysticercus bovis
Eating Uncooked pork leads to taeniasis (diarrhoea)	Eating uncooked beef leads to taeniasis (diarrhoea)
Infection form - Eggs majority of cases of Cysticercosis  Also, for Neuro- cysticercosis MC site - Subarachnoid Present with Atypical Seizures IOC - CT / MRI (If calcified-CT) DOC - Albendazole	No infection with eggs of taenia saginata

TREMATODES (LEAF LIKE FLUKES)

Monoecious

• 2 intermediate host
  • 1^st → Snail
  • 2^nd → Aquatic vegetation / Fish / Crab
• Infective form - Metacercariae (Cyst like structure)
• Operculated egg (lid) except Schistosomes

Schistosomes

• Dioecious
• IH → Snail
• Infective form → Cercariae
• Non operculated egg

• S. Haematobium
  • Resides in vesical plexus
  • SCC of urinary bladder
  • Terminal haematuria
  • Egg has a Terminal spine
• S. Mansoni
  • Resides in the inferior Mesenteric Plexus
  • Katayama fever
  • Swimmer’s itch (Cercarial dermatitis)
  • Egg has a Lateral spine

• S. Japonicum
  • Resides in Superior Mesenteric Plexus
  • Katayama fever
  • Eosinophilic Diarrhoea
  • Egg has a Lateral knob / rudimentary spine

Fasciola Hepatica (Sheep Liver Fluke)

• Infection form – metacercariae
• 1^st IH – Snail
• 2^nd IH – aquatic vegetation. (Metacercariae) → (Man eats aquatic vegetation & develops infection)
• In bile duct, larvae mature to adult forms → Eggs are passed in faeces.

Clonorchis Sinensis (Oriental / Chinese Liver Fluke)

• 1st IH → Snail
• 2nd IH → Fresh water fish. (Metacercariae)
  • Larvae matures in bile ducts to adult forms
  • Constant irritation & inflammation of Bile duct → Carcinoma bile duct

Paragonimus Westermani (Lung Fluke)

• 1st IH → Snail
• 2nd IH → Crab / cray water fish (Metacercaria) → Rt lung → Erosions → Red brown sputum (Endemic haemoptysis)

Fasciolopsis Buski (Intestinal Fluke)

• Largest intestinal trematode

NEMATODES

Infective Form

• By Eating Eggs
  • E → Enterobius vermicularis
  • A → Ascaris
  • T → Trichuris trichiura
• By penetration of filariform larvae in sole of foot
  • A → Ancylostoma duodenale
  • N → Necator americanus
  • S → Strongyloides stercoralis
• Go to lungs for maturation
  • A → Ascaris
  • A → Ancylostoma duodenale
  • N → Necator americanus
  • S → S. stercoralis

Large Intestinal Worms

• T. Trichiura (Whipworm)

• Barrel shaped (dumbbell shaped) egg with mucus plugs.
• Bile stained (yellow)
• Rectal prolapse in children (coconut cake like rectum)
• Growth retardation
• A/W iron deficiency anaemia

• Enterobius Vermicularis (Pin / Seat / Thread Worm Or Oxyuriasis)

• Perianal pruritus in children (MC)
• Autoinfection
• Egg - D shaped
• Has tadpole like larvae
• Plano convex egg
• Non bile stained
• NIH (National institute health) swab used
• Autoinfection
  • Capillaria philippinensis, cryptosporidium parvum
  • H. Nana
  • E. Vermicularis
  • S. Stercoralis
  • Taenia Solium

Small Intestinal Worms

• Ancylostoma Duodenale (HookWorm)

• Strongyloides Stercoralis
  • Infection form – Filariform larvae
  • Ovo – Viviparous
  • A/W HIV +ve
  • Parthenogenetic development →Female lays eggs without male.
  • Autoinfection (Hyper infection syndrome in HIV +ve patients CNS and viscera are involved)
  • Cutaneous larvae migrans (Larvae currens)
• Ascaris
  • Infection form → Fertile Egg  
  • Lungs for maturation (2^nd& 3^rd moulting of larvae)
  • A/W Intussusception
  • Can l/t Intestinal obstruction
  • Loffler’s syndrome (Massive eosinophilia)
  • Female → Egg (Unfertilized egg)

Fertile Egg                   Infertile Egg

• Eggs that Float on saturated salt solution
  • Fertilised egg of ascaris
  • A. Duodenale
  • T. Trichiura 
  • E. Vermicularis
  • H. Nana infertile Egg

Also Read:

TISSUE NEMATODES

W. Bancrofti

• Infective form – L₃ filariform larvae
• Vector → Culex
• Viviparous (Microfilariae) 
• Nocturnal periodicity (Come in blood at night)
• Sheathed (No nuclei in tail tip)
• Acute Filariasis
  • Fever
  • Lymphadenitis
  • Lymphangitis  
• Chronic Filariasis
  • LN sclerosed and blocked so leads to 
    • Elephantiasis
    • Hydrocele
    • Chyluria
    • Albuminuria
• Granuloma Breast in females

• Lab Diagnosis
  • Day time testing 
    • DEC given which irritates the larvae to come in blood at daytime 
• Blood smear examination done 
  • Sheathed microfilariae of W. bancrofti with no nuclei in tail tip seen 
  • Differentiated from Brugia malayi microfilariae is sheathed but has terminal 2 nuclei in the tail tip.
• IOC
  • PCR for W. Bancrofti (Even picograms of DNA can be detected)

Subcutaneous Site Filariae

Trichinella Spiralis/ Muscle Worm

• Infective form → Larvae in uncooked pork
• Viviparous

Dracunculus Medinensis (Guinea Worm Disease)

• Eradicated in India (last case in Rajasthan)

Previous year Questions

Q. A child with 10 days abdominal pain presented to OPD. Stool microscopy was done which showed the given findings. What is the DOC for the disease caused by the given organism?      

(AIIMS - May- 2018)

A.  Albendazole

B.  Mebendazole

C.  Praziquantel

D.  Pyrantel Pamoate

Q. Slow growing alveolar like tumour in liver?      

(AIIMS - Nov - 2019)

A.  E. Granulosus

B.  E. Multilocularis

C.  Cysticercus cellulosae

D.  Amoebic liver abscess

Q. Which is correct about larval stage of Taenia solium?      

(FMGE - June - 2019)

A.  Larva currens

B.  Cysticercosis Cellulose

C.  Cutaneous Larvae Migrans

D.  Visceral Larvae Migrans

Q. Which parasite lives in bladder plexus?     

(FMGE - Nov - 2017)

A.  Schistosoma

B.  Fasciola

C.  Ascaris 

D.  Echinococcus

Q. A 35-year-old man presented with dry cough & rusty coloured sputum. He has history of eating in Chinese restaurant very often with consumption of crabs often; what is the causative agent in this condition?

(NEET - Jan - 2019)

A.  Diphyllobothrium latum

B.  Pneumocystis jirovecii

C.  Paragonimus Westermanii

D.  Strongyloides stercoralis

Q. Identify the egg shown in image?

(FMGE - Aug - 2020)

A.  Ascaris Lumbricoidoes

B.  Enterobius Vermicularis

C.  Trichuris Trichiura

D.  H. Nana

Q. A 5-year-old child presented to OPD with complaints of rectal prolapse; on examination stunting & growth retardation was documented. What is parasitological cause for this clinical feature?

(NEET–Jan - 2019)

A.  Trichuris Trichiura

B.  Trichinella Spiralis 

C.  Giardia Lamblia

D.  Enterobius vermicularis

Q. Identify the egg shown in image?

(FMGE - Dec - 2020)

A.  Trichuris Trichiura

B.  Enterobius Vermicularis

C.  Ankylostoma

D.  Ascaris

Q. Cutaneous larvae migrans caused by which organism?

(NEET–Jan - 2018)

A.  Anisakiasis Simplex

B.  Toxocara Species

C.  Ancyclostoma braziliensis

D.  Necator americanus

Q. Patients with history of kidney transplantation presenting with diarrhoea. The motility of the worms is given. Correct statement is?

(AIIMS - Nov - 2018)

A.  Monoecious & the organism related with pathogenesis

B.  Transmitted by intake contaminated food & water 

C.  Loffler’s pneumonia is not caused by same organism

D.  Body gets this infection through filiform larvae

Q. Image shown here is?

(INICET - Nov - 2020)

A.  Ascaris

B.  Ancylostoma duodenale

C.  Enterobius vermicularis

D.  Strongyloides Stercoralis

Q. Pulmonary eosinophilia is seen d/t which of following infection?

(FMGE - Nov - 2017)

A.  Ancyclostoma

B.  Trichinella

C.  Filaria

D.  Roundworm

Q. A person working in which of the following profession can have the problem shown in the image?

(AIIMS–May - 2019)

A.  Person is working in the butcher house

B.  Life guard in swimming pool

C.  Kennel worker

D.  Poultry farm worker

To study this high-yield microbiology topic in detail, download the PrepLadder app and find in-depth video lectures, study notes and MCQs covering the entire topic comprehensively.