Cestodes And Trematodes Notes

Cestodes And Trematodes

Read And Learn More: Micro Biology And Immunology Notes

Cestodes

• Cestodes or tapeworms are segmented worms.

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 eggshell 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, and L3-Plerocercoid larva.

Taenia

Cysticercosis

• Potentially dangerous systemic disease.
• Definitive host: Man, Intermediate host: Man
• Transmission: (1) Ingestion of food/water contaminated with eggs, (2) 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 subcutaneous tissue, skeletal muscle, and eyes.

Neurocysticercosis (NCC)

• NCC: MC parasitic CNS infection of man and MC cause of adult-onset (commonly affects 30–50 years) 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.
• Other features include: Hydrocephalus (Its presence carries bad prognosis), increased intracranial pressure and hypertension (presented as headache, vomiting, and vertigo), Chronic meningitis,
• Focal neurological deficits, Psychological disorders and dementia.
• Four morphological stages: Vesicular, necrotic, nodular, calcified stages.
  Clinical feature depends on: (1) No. of cyst, (2) Location-parenchymal or extra-parenchymal,(3) Size (small cyst-C. cellulosae, big cyst-C. racemosus), (4) Morphological stage and (5) Host immune response.
• Lab diagnosis:
  • Radiodiagnosis -CT scan and MRI (useful for detecting number, location, size of the cysticerci and the stage of the disease)
  • Antibody detection in serum or CSF—by ELISA (using crude extract of cysticerci) and Western blot (using 13 kDa LLGP Ag)
  • Antigen detection in serum or CSF by ELISA Lymphocyte transformation test when subjected to T. solium cyst fluid antigens
  • Histopathology of muscles, eyes, subcutaneous tissues or brain biopsies—can detect cysticerci
  • FNAC of the cyst and then staining with Giemsa- Microscopically, it can differentiate between viable, necrotic and calcified cysticerci through their morphological pattern
  • Fundoscopy of eye -detects larvae
  • Modified Del Brutto diagnostic criteria is used for the diagnosis of neurocysticercosis in endemic countries.
• 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 other canine animals.
• Intermediate hosts: Man and other herbivorous animals.
• Man is an accidental host (dead end).
• Eggs: Infective stage of the parasite. Man acquires the infection by ingestion of food contaminated with dog’s feces containing E. granulosus eggs.
• 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).
• The rapid invasion is due to a surface protein 14-3-3 found on germinal layer. Cysts spread by direct extension or via blood or lymphatics.
• 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 demonstrates cyst wall and attached brood capsules
• Casoni’s skin test: Example of immediate hypersensitivity reaction.
• Antibody: Indicates past infection, used for seroepidemiology:
  • Screening: IHA, CIEP, ELISA (using B2t antigen), DIGFA (dot immunogold filtration assay)
  • Confirm: Western Blot against antigen B fragment and h-HCF-IB (human hydatid cyst fluid-immunoblot).
• 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
• Viability of the parasite can be assessed by:
  • USG (differentiating the cyst into active or inactive)
  • Histopathology (evaluating the intact parasite-derived cyst wall including germinal layer)
    Vital stain (e.g. eosin stain)—evaluate the protoscolices for flame cell activity and morphological integrity
  • Metabolic viability assessment using high-field MRS (magnetic resonance spectroscopy) of cyst content
  • Real-time PCR targeting several constitutively expressed genes of E. granulosus that determine viability

Treatment

• Therapy for cystic echinococcosis is based on viability, size and location of the cyst; guided by USG and overall health of the patient.

PAIR (puncture, aspiration, injection and re-aspiration):

• Alternate method instead of surgery.
• It claims higher cure rate, less recurrence rate, less complications and hospitalization compared to surgery.
• It is recommended for single hepatic cyst (CE1 lesion and uncomplicated CE3 lesion).

Surgery

• Though surgery is the definitive method of treatment, it should be reserved for:
  • Cases where PAIR is contraindicated or refractory
  • Secondary bacterial infection
  • Advanced disease
• Disadvantages of surgery are high recurrence rate (2–25%) and postoperative complications (10–25%)
• Preoperative use of albendazole is effective in reducing size and to prevent recurrence.

Antiparasitic agents

• Albendazole is the drug of choice, given to prevent recurrence and to reduce the size of the cyst before surgery or PAIR.
• Complicated and multivesicular cysts may require longer duration.
• Pulmonary cyst, preoperative albendazole should be avoided; praziquantel is given alternatively
• Percutaneous thermal ablation
  It is a non-invasive method, involves percutaneous radiofrequency ablation of the germinal layer of the cysts.

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 plerocercoid)
• Causes Megaloblastic anemia (adult worm absorbs B12)
  Diagnostic form: Operculated eggs in stool. Embryonated egg contains a hexacanth oncosphere lined by a ciliated membrane and Proglottids may be discharged in the stool (released in chain of segments of few cm to 0.5 meter long and they are wider than long).
  Treatment: Praziquantel (drug of choice) or Niclosamide is given alternatively and parenteral
  vitamin B12 (if deficiency).

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.

Aberrant sparganosis: Caused by spirometra proliferum. It is a rare tapeworm larva that grows by budding and continuous branching. It is fatal in all reported cases.

• In India, sparganosis is extremely rare. A case of cerebral sparganosis was reported from Hyderabad in 2003 and a case of sparganosis of kidney was reported from UP in 2011.
• Diagnosis is made by surgical removal of the nodules and demonstration of the elongated worm like sparganum larva.
• Treatment: Surgical removal pf the nodule, however, praziquantel or triclabendazole is recommended.

Hymenolepis Nana

• Hymenolepis refers to a thin membrane covering the eggs (Hymen-membrane, lepis-covering,and nana-small size). 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, non-bile stained and has polar filament: Diagnostic form.

Treatment: Praziquantel (treatment of choice since it acts against both the adult worms and the cysticercoid larvae in the intestinal villi) or Nitazoxanide or Niclosamide can also be given.

H. Diminuta

• Rat tapeworm
• Mode: Ratflea infected with cystecercoid larva
• Diagnosed by the detection of eggs in the stool: Eggs larger than H.nana eggs, bile stained 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 like indigestion, loss of appetite, diarrhea, pruritus ani, abdominal pain may be reported. Children are affected commonly.
• Diagnostic form:
  • Eggs in packets (group of 15)
  • Proglottid has two common genital pore
  • Barrel shaped Proglottid (looks like cucumber seeds).
• Praziquantel is the DOC.
• Treatment of Cestodes
• Praziquantel is the DOC of all cestodes followed by Niclosamide except. Hydatid disease and neurocysticercosis: Albendazole.

Trematodes

General Features

• Agents:
• Blood flukes: Schistosoma haematobium (resides in vesical venous plexus), Schistosoma mansoni (reside in rectal venous plexus) and S. japonicum (reside in venous plexus draining ileocaecal region).
• Hepatic flukes: Fasciola hepatica and Fasciola gigantica (both reside in liver),
  Clonorchis species and Opisthorchis species (both reside in the bile duct)
• Intestinal fluke:
  • Small intestine: Fasciolopsis buski, Heterophyes species, Metagonimus species,
    Watsonius species
  • Large intestine: Gastrodiscoides species
    Lung flukes: Paragonimus westermani.
• 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)
• 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:
  • Urinary Schistosomiasis/Bilharziasis
  • Hematuria, hydroureter and hydronephrosis
  • Bladder Carcinoma: Sqamous cell Ca (in high worm burden) > transitional cell Ca (low worm burden)
• Predisposing factors are-Diet containing nitroso compounds (cheese, fava beans, raw salted fish) and Secondary bacterial infections (cystitis) and genetic factors (H-ras, inactivation of p53 and retinoblastoma genes).
• Epidemiology: S. haematobium infection is endemic in Middle East, the African continent
  (across Nile river valley) and the Indian Ocean islands (Madagascar, Zanzibar and Pemba).
  In India, Schistosomiasis is extremely rare in India. A confirmed endemic focus of urinary schistosomiasis was demonstrated in Gimvi village of Ratnagiri district, Maharashtra;transmitted by snail of genus Ferrissia.
• Urine microscopy and Histopathology of bladder mucosal biopsy—detects terminal spined eggs.
• 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 by ELISA or dip stick assay:
  • 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 (Symmers pipestem fibrosis),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.
• Hatching test: This involves hatching of motile miracidia when the eggs are diluted in water and perpendicular beam of light is passed through the water at the top; It confirms the viability of the parasite.

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).
• Both colorectal carcinoma and liver carcinoma (and cirrhosis) have been reported from people of China and Japan infected with S. japonicum.
• Chronic secondary infection with Salmonella species and hepatitis B virus have been associated with S. japonicum.
• 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, Liver and bile duct damage (by toxins produced by the larvae), multiple subcapsular liver abscesses (liver rot)
  • Halzoun or Marrara syndrome: In endemic areas (Lebanon or Marrara in Sudan),where uncooked goat and sheep livers may be eaten, the adult worms may attach to the pharyngeal wall; causing severe pharyngitis and laryngeal edema.
  • Bile duct obstruction.
• Diagnostic form: Operculated eggs in feces.

Fasciola Gigantica

• F. gigantica is closely related to F. hepatica.
• It is seen in tropics (Africa, Southern Europe, and some Pacific Islands)
• Human infection is also reported but rare
• In India, less than 10 cases have been reported (Assam, Arunachal Pradesh and West Bengal)
• First intermediate host is aquatic snail
• Clinical feature: Similar to that of F. hepatica
• Eggs are morphologically similar to that of F. hepatica and F. buski, but larger in size (160–190 μm × 70–90 μm).

Fasciolopsis Buski

• Giant intestinal fluke → Largest fluke
• Definite host: Man/pig
• Epidemiology: In India, most of the cases have been reported from Eastern Uttar Pradesh, Bihar, West Bengal and Assam and Maharashtra.
  • Sporadic cases were reported from Odisha, Manipur, Tamil Nadu and Karnataka
  • Phulwaria endemic foci: Endemic focus of fasciolopsiasis in Phulwaria village, Bihar;118 cases were detected during 2015
• Mode of transmission: Ingestion of aquatic plant contaminated with encysted metacercaria
• GIT symptoms
• Diagnostic form: Operculated eggs in feces. Operculated eggs of F. hepatica, Echinostoma and Gastrodiscoides are morphologically similar to that of F. buski

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
• Causes endemic hemoptysis (frank hemoptysis or brownish blood tinged rusty sputum) and in chronic cases bronchitis, bronchiectasis, pneumonia or lung abscess may be seen.
• Diagnostic form: Operculated eggs in early morning, deeply coughed sputum
  India: Paragonimiasis is endemic in Northeast states of India. Many cases are reported from
  Manipur with a prevalence of 6.7%. The first true case of, P.westermani infection in India was reported in 2015 from 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: Chronic irritation of the bile duct for long periods and Inhibition of tumor suppressor genes (P53) and release of cytokines such as IL-6 and TNF-α promotes carcinogenesis.
• Diagnostic form: Flask-shaped operculated egg, measuring 28–35 μm × 12–19 μm with a tiny knob. Eggs of C. sinensis are morphologically similar to that of Opisthorchis, Heterophyes,and Metagonimus.
• Antibody detection: ELISA using recombinant propeptide of cathepsin L proteinase (rCsCatLpropeptide) for detection of specific IgG4 antibodies.
• Antigen detection: ELISA for detection of circulating antigen in the serum; it indicates current infection.
• Molecular Methods: multiplex PCR (to detect Clonorchis and Opisthorchis simultaneously),Real-time PCR (detects mitochondrial NADH dehydrogenase subunit 2 (nad2) DNA elements.