Cestodes and Trematodes Chapter Notes | Microbiology - NEET PG PDF Download

Properties

Cestodes

• Intestinal Cestodes — Humans are Definitive Host

  • Taenia saginata and T. solium
  • Diphyllobothrium
  • Hymenolepis nana
  • Dipylidium caninum

• Tissue Cestodes —Humans are Intermediate Host

  • Echinococcus: Causing hydatid disease (liver)
  • Taenia solium: Causing cysticercosis (CNS)
  • Taenia multiceps: Causing coenurosis (CNS)
  • Spirometra: Sparganosis (muscle)

Cestodes Exist in three Morphological Forms

• Adult (tapeworm): Divided to head (scolex), neck and segments called as proglottids or strobila
• Some adults bear hooklets in scolex and called as armed tapeworm, e.g. T. solium, Echinococcus, H. nana
• Eggs: All cestodes eggs have an egg shell and three pair of hooklets except D. latum eggs (operculated)
• Larva: Eggs develop to larva which are called as:
  • Cysticercus: Larval stage of Taenia [T. saginata-Cysticercus bovis, T. solium- C. cellulosae]
  • Sparganum: Larval stage of Spirometra
  • Hydatid cyst: Larval stage of Echinococcus
  • Coenurus: Larval stage of Multiceps
  • Cysticercoid: Larval stage of Hymenolepis, Dipyllidium
  • Diphyllobothrium: has 3 larva stages, L1-Coracidium, L2-Procercoid, L3-Plerocercoid larva

Taenia

Differences between Taenia saginata and Taenia solium:

Proglottids:

Cysticercosis

• Potentially dangerous systemic disease.
• Definitive host: Man, Intermediate host: Man
• Transmission: (i) Ingestion of food/water contaminated with eggs, (ii) autoinfection
• Eggs develop to larva (Cysticercus cellulosae) in human intestine
• Larvae penetrate the intestine and get deposited in-MC sites- CNS (60-90%) followed by Eye and muscle.

Neurocysticercosis (NCC)

• NCC: MC parasitic CNS infection of man and MC cause of adult onset epilepsy in world.
• MC site: Sub-arachnoid space followed by parenchyma.
• Seizure: MC manifestation (70% of cases). NCC accounts for 50% cases of late onset epilepsy.
• Hydrocephalus, intracranial hypertension and psychiatric disturbances.
• Four morphological stages: Vesicular, necrotic, nodular, calcified stages.
• Clinical feature depends on: (i) No. of cyst, (ii) Location-parenchymal or extraparenchymal, (iii) Size (small cyst-C. cellulosae, big cyst-C. racemosus), (iv) Morphological stage and (v) Host immune response.
• Lab diagnosis:
  • Antibody detection by ELISA or Western blot (specific)
  • Detection of the cyst by CT/MRI
  • CT scan is superior to detect calcified cysts (appears as hyperdense dots).
  • MRI is superior to CT scan to detect the Extra parenchymal cysts in ventricle and cisterns, inflammatory changes, vesicular, necrotic lesions and noncystic lesions.
  • Del Brutto’s criteria used for neurocysticercosis.
• Treatment: Albendazole, Praziquantel, Surgery (for ocular and spinal and ventricular lesions).

Taenia Multiceps

• Definitive host: Dog, fox and wolf
• Intermediate host: herbivorous animals like sheep (or man)
• Transmission: Ingestion of food/water contaminated with eggs
• Eggs develop to larva (Coenurus) which is a unilocular cyst with multiple scolices.
• Larva penetrate the intestine and get deposited in CNS (Coenurosis)
• Man space occupying lesions in CNS (headache, vomiting, paralysis, seizure, etc.)
• In animals, it causes gid (CNS lesion)
• Epidemiology: African countries (like Uganda, Kenya).

Echinococcus Granulosus

Life Cycle

• Definitive host: Dog and wild carnivores.
• Intermediate hosts: Man and other herbivorous animals.
• Man is an accidental host (dead end).
• Eggs: Infective stage of the parasite.
• Eggs transform to larva (hydatid cyst) that penetrate GIT and migrates to various organs like liver.

Clinical Features

• Hydatid disease: Hepatomegaly (60—70% of cases), then lungs
• E. multilocularis:
  • Causes Alveolar Hydatid disease because cyst has multiple locules but has no fluid/free brood capsule
  • 90% liver involvement, rapidly metastasizes (mimic malignant tumor)
• E. oligarthrus and E. vogeli: Causes Polycystic Hydatid disease.

Diagnosis

• Hydatid fluid microscopy:
  • Wet mount examination to demonstrates protoscolices and brood capsule
  • Acid fast staining of centrifuged deposit
  • Histological examination
• Casoni’s skin test: Example of immediate hypersensitivity reaction
• Antibody: Indicates past infection, used for seroepidemiology:
  • Screening: IHA, CIEP, ELISA
  • Confirm: Western Blot (against antigen B fragment )
• Detection of antigen: Indicates Recent infection
• Imaging methods like USG, MRI and X-ray: Demonstrates size, exact location and extension of the cysts
• Water lily sign in USG: Due to collapsed cyst (floating membrane) floating in the abdomen
• Tests to monitor the response to treatment: Imaging methods and Antigen detection methods.

Treatment

• Treatment of choice: Surgery
• DOC: Albendazole and mebendazole
• Commonly preferred method: Percutaneous Aspiration Injection Reaspiration (PAIR) of the cyst.

Diphyllobothrium Latum

• Largest tapeworm in human GIT: Adult is >10 meters with long > 3000 proglottids
• Scolex bears two longitudinal groove called bothria
• Also k/a-fish tapeworm or human broad tapeworm
• Definitive host: Man
• Intermediate host:
  • 1st intermediate host: Cyclops/diaptomus
  • 2nd intermediate host: Fresh water fish
• There are three larval stages: L1 (coracidium), L2 (procercoid) and L3 (plerocercoid)
• Infective form- Plerocercoid: (L3 stage larva)
• Mode: Ingestion of raw fish
• Life cycle: Ingestion of Plerocercoid (L3) in fish → develop to Adult → Eggs released in feces → Eggs transform to coracidium (L1) in feces → Cyclops (forms Procercoid) → ingested by fish (forms pleurocercoid)
• Causes Megaloblastic anemia (adult worm absorbs B12)
• Diagnostic form: Operculated eggs in stool.

Sparganosis

• Caused by Spirometra and other nonhuman Diphyllobothrium tapeworms
• Definitive hosts: Dogs and cats (rarely man), 1st intermediate host: Cyclops and 2nd intermediate host: Frog, snakes and birds.
• Sparganosis: Sparganum or plerocercoid (L3) larva get deposited in SC tissues, muscles, eyes, lymphatics and visceral organs like brain.

Hymenolepis Nana

• Also called as Dwarf tapeworm
• Egg is infectious to man
• Only one host involved
• Autoinfection seen
• Armed scolex
• Larva form called Cystecercoid larva
• Egg smaller, bile non stained and has polar filament: Diagnostic form.

H. diminuta

• Rat tapeworm
• Mode: Ratflea infected with cystecercoid larva
• Diagnosed by the detection of eggs in the stool: Egg larger and lack polar filament.

Dipylidium Caninum (Double Pored Tapeworm)

• Host: Definitive host—dogs and cats (rarely man), intermediate host—insects (flies)
• Man acquires infection by ingestion of flea containing cysticercoid larva
• GIT symptoms
• Diagnostic form:
  • Eggs in packets
  • Proglottid has two common genital pore
  • Barrel shaped Proglottid.

Treatment of Cestodes
Praziquantel is the DOC of all cestodes followed by Niclosamide except. Hydatid disease and neurocysticercosis: Albendazole.

Trematodes

General Features

• Agents:
  • Schistosoma (blood fluke)
  • Fasciola hepatica (liver fluke), Fasciolopsis buski (intestinal fluke)
  • Paragonimus westermani (lung fluke)
  • Clonorchis, Opisthorchis
• Infective form: Metacercaria larva for all except: (Cercaria larva for Schistosoma)
• Definite host: Man
• Intermediate host:
  • 1st – Snail
  • 2nd–Aquatic plants (F. hepatica and F. buski) Cray fish/crab Fish (Paragonimus, Clonorchis, Opisthorchis)
• Mode of transmission:
  • For all: Ingestion of 2nd intermediate host containing Metacercaria larva
  • Schistosoma: Skin penetration by cercaria larva present in contaminated water
• All trematodes are Oviparous (lays eggs)
• Diagnostic form:
  • For all: Demonstration of operculated Eggs
  • Schistosoma: Demonstration of nonoperculated Eggs
• All trematodes are hermaphrodite (except Schistosoma: sexes are separate)
• DOC: Praziquantel is DOC of all trematodes except F. hepatica (Triclabendazole).

Schistosoma Hematobium – (Blood Fluke)

• Resides in: Vesical and pelvic venous plexus
• Associated with:
  • Hematuria
  • Hydroureter and hydronephrosis
  • Bladder Carcinoma: Sqamous cell Ca (in high worm burden) > transitional cell Ca (low worm burden)
• Egg has terminal spine
• Antibody detection:
  • HAMA-FAST: ELISA (Falcon assay screening test ELISA) using S. haematobium adult worm microsomal antigen (HAMA).
  • HAMA Western blot: Specific
  • Other methods: Cercarial Huller reaction, IFA, IHA
• Antigen detection:
  • Circulating cathodic antigen (CCA) in urine and circulating anodic antigen (CAA) in serum.
  • It indicates recent infection and can be used for monitoring the treatment.

S. Mansoni

• Common in Africa including Caribbean Islands (West Indies), South America
• Resides in mesenteric veins draining sigmoido-rectal region.
• Clinical manifestation:
  • Swimmer’s itch (cercarial dermatitis): Type 1 hypersensitivity reaction
  • Dysentery and Eosinophilic diarrhea
  • Acute schistosomiasis (Katayama fever) Serum sickness like illness: Type III hypersensitivity
  • Chronic schistosomiasis: due to fibrosis and granuloma formation as a result of egg deposition in various sites like intestinal wall, liver, spleen and lungs.
  • Secondary bacterial infection especially with Salmonella spp.
• Diagnostic form: Egg has lateral spine (feces), eggs of S. mansoni are acid fast.
• Quantitations of eggs in stool by Kato Katz thick smear technique.

S. Japonicum

• Resides in mesenteric veins draining the ileocecal region.
• Clinical feature: Similar to S. mansoni but it is more severe due to higher egg production and smaller size of the eggs (easy dissemination).
• Diagnostic form: Eggs in stool (has rudimentary lateral spine).

Fasciola Hepatica - Sheep Liver Fluke

• Definitive host: Sheep or man, Intermediate host- 1st -Snail and 2nd -Water cress
• Mode of transmission: Ingestion of aquatic plant contaminated with encysted metacercaria.
• Clinical manifestation:
  • Hepatomegaly
  • Halzoin (laryngeal edema): d/t eating sheep liver
  • Bile duct obstruction
• Diagnostic form: Operculated eggs in feces.

Fasciolopsis Buski

• Intestinal fluke → Largest fluke
• Definite host: Man/pig
• Mode of transmission: Ingestion of aquatic plant contaminated with encysted metacercaria
• GIT symptoms
• Diagnostic form: Operculated eggs in feces.

Paragonimus Westermani: (Lung Fluke)

• Definitive: host man; Intermediate host- 1st –snail, 2nd - Cray/Crab fish
• Mode of transmission: Ingestion of crab/crey fish contaminated with encysted metacercaria
• Cyst in Right lung (granuloma formation due to egg deposition)
• Cerebral and cutaneous paragonimiasis
• Golden brown sputum
• Causes endemic hemoptysis
• Diagnostic form: Operculated eggs in early morning, deeply coughed sputum
• Endemic in Manipur.

Clonorchis Sinensis

• Oriental/Chinese liver fluke
• Definitive: host man; Intermediate host: 1st –snail, 2nd - Cray/crab fish
• Mode of transmission: Ingestion of crab/crey fish contaminated with encysted metacercaria
• Causes:
  • Cholangitis, dilatation of the bile duct and ductal epithelial hyperplasia and fibrosis
  • ​Cholangiocarcinoma
• Diagnostic form: Flask shaped operculated egg in stool.a