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🦠 CESTODES (TAPEWORMS) & NEMATODES

MUHS 2nd MBBS Microbiology - Exam-Oriented Notes (Apurb Shastri Pattern)

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PART A: CESTODES (TAPEWORMS)

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LAQ 1: CESTODES - CLASSIFICATION

Classification of Cestodes (Tapeworms) Infecting Man

CESTODES
│
├── INTESTINAL CESTODES (Adult in human intestine)
│   ├── Taenia saginata (Beef tapeworm)
│   ├── Taenia solium (Pork tapeworm) ← Also tissue cestode
│   ├── Diphyllobothrium latum (Fish tapeworm)
│   ├── Hymenolepis nana (Dwarf tapeworm) ← Direct life cycle
│   └── Hymenolepis diminuta (Rat tapeworm)
│
└── TISSUE CESTODES (Larval stage in human tissues)
    ├── Echinococcus granulosus → Hydatid cyst (Cystic echinococcosis)
    ├── Echinococcus multilocularis → Alveolar hydatid disease
    ├── Taenia solium (larval) → CYSTICERCOSIS
    └── Multiceps multiceps → Coenurosis (rare)

MUHS Exam Point: Taenia solium is BOTH an intestinal AND tissue cestode - only cestode that causes both adult worm infection (taeniasis) AND larval infection (cysticercosis) in humans.

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SN 1: HYDATID CYST ⭐⭐ (High Yield)

Causative Agent

• Echinococcus granulosus (Cystic Hydatid Disease)
• Echinococcus multilocularis (Alveolar Hydatid Disease - more invasive)

Sites Affected (Order of Frequency)

MUHS Mnemonic: "Liver Lungs Brain Bones" = L L B B

Cross-Section Structure of Hydatid Cyst ⭐⭐

        ┌─────────────────────────────────────────┐
        │          HOST TISSUE LAYER               │
        │     (Pericyst - fibrous, calcified)      │
        ├─────────────────────────────────────────┤
        │      ECTOCYST (Outer Laminated Layer)    │
        │   - Acellular, laminated, white          │
        │   - Like egg-shell membrane               │
        ├─────────────────────────────────────────┤
        │      ENDOCYST (Inner Germinal Layer)     │
        │   - Nucleated, single cell layer         │
        │   - Gives rise to all internal structures│
        │                                           │
        │   ┌──────────────────────────────┐       │
        │   │  BROOD CAPSULES              │       │
        │   │  (contain protoscolices)     │       │
        │   └──────────────────────────────┘       │
        │                                           │
        │   ┌──────────────────────────────┐       │
        │   │  DAUGHTER CYSTS              │       │
        │   │  (secondary cysts inside)    │       │
        │   └──────────────────────────────┘       │
        │                                           │
        │   HYDATID SAND (bottom)                  │
        │   = degenerated protoscolices             │
        │   + free hooklets + germinal cells        │
        │                                           │
        │         HYDATID FLUID (main)             │
        │   (clear, antigenic, anaphylactic)        │
        └─────────────────────────────────────────┘

1. Pericyst - Host-derived fibrous tissue (calcifies with age)
2. Ectocyst (Laminated membrane) - Acellular, white, pearly - parasite-derived
3. Endocyst (Germinal epithelium) - Inner nucleated layer, produces everything

• Hydatid fluid (under pressure, highly antigenic)
• Brood capsules (contain protoscolices/daughter scolices)
• Daughter cysts
• Hydatid sand = scolices + hooklets + granular debris

Clinical Features

• Silent period: 5-20 years (slow growth ~1 cm/year)
• Liver cysts: Right upper quadrant pain, hepatomegaly, jaundice if bile duct compressed
• Lung cysts: Hemoptysis, chest pain, cough
• Rupture → Anaphylactic shock (most dangerous complication), secondary echinococcosis
• Casoni's skin test - intradermal hypersensitivity test (historical)

Laboratory Diagnosis

1. Imaging: USG, CT scan - cyst with daughter cysts ("rosette pattern")
2. Serology: ELISA, IHA, Casoni test - detect antibodies
3. Microscopy: Hydatid sand in aspirated fluid (protoscolices, hooklets, germinal layer fragments)
4. Eosinophilia - mild to moderate
5. NEVER aspirate blindly - risk of anaphylaxis and seeding

Treatment

• PAIR procedure: Puncture - Aspiration - Injection (hypertonic saline/ethanol) - Reaspiration
• Surgery: Total pericystectomy
• Drug: Albendazole (before/after surgery)

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SN 2: ECHINOCOCCUS GRANULOSUS - LIFE CYCLE ⭐

DEFINITIVE HOST (Dog/Wolf/Canidae)
        │
        │ Adult worm in small intestine
        │ (tiny - 5 mm, 3 proglottids only)
        │
        ↓
   EGGS passed in feces
        │
        ↓ Ingested by
INTERMEDIATE HOST (Sheep/Cattle/Humans)
        │
        │ Egg hatches → Oncosphere (hexacanth embryo)
        │
        ↓ Penetrates intestinal mucosa
        │
        ↓ Portal blood → LIVER (trapped) → trapped or passes to...
        │
        ↓ LUNG → Systemic circulation → Brain, Bone, Kidney
        │
        │ Survives → Forms HYDATID CYST
        │ (grows slowly over years)
        │
        ↓ When intermediate host is killed
   Viscera with cysts eaten by dogs
        │
        ↓ Protoscolices → Adult worms in dog intestine
        │
    CYCLE COMPLETE

• Definitive host: Dog (adult worm lives 12 months)
• Intermediate hosts: Sheep, cattle, humans
• Adult worm: Only 5 mm long, 3 proglottids (immature + mature + gravid)
• Scolex: 4 suckers + double row of hooklets (armed tapeworm)
• Human infection: Hand-to-mouth after handling infected dogs (eggs in dog fur)
• Eggs appear identical to Taenia eggs microscopically

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SN 3 / LAQ 2: TAENIA SAGINATA vs TAENIA SOLIUM - FOUR DIFFERENCES ⭐⭐

Differences Table (Most Exam-Tested)

Why Is Differentiation Necessary? ⭐

1. Public health implications: T. solium can cause cysticercosis (tissue invasion) in humans who ingest eggs - T. saginata cannot. This is a serious neurological disease (neurocysticercosis).
2. Treatment urgency: T. solium infection requires careful management because anthelmintic drugs that kill the worm cause proglottid rupture and egg release, risking autoinfection/cysticercosis.
3. Prognosis: T. saginata is a benign intestinal infection; T. solium can be life-threatening (neurocysticercosis, seizures, raised ICP).
4. Food safety regulations: Different livestock inspection standards for beef vs. pork.
5. Contact tracing: Family members of T. solium patients need to be screened for cysticercosis.

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Taenia solium - Tissue Cyst (Cysticercus cellulosae) ⭐

Structure:

┌────────────────────────────────────┐
│    CYSTICERCUS CELLULOSAE          │
│                                    │
│   Outer: Bladder wall (fibrous)    │
│   Inner: Germinal epithelium       │
│                                    │
│   ┌─────────────────┐              │
│   │  Fluid-filled   │              │
│   │  bladder        │              │
│   │    ┌───────┐    │              │
│   │    │Scolex │    │ ← invaginated│
│   │    │(armed)│    │              │
│   │    └───────┘    │              │
│   └─────────────────┘              │
│                                    │
│  Size: ~pea (~1 cm)               │
└────────────────────────────────────┘

• Brain (Neurocysticercosis) - Most dangerous
• Subcutaneous tissue (palpable nodules)
• Eye (ophthalmocysticercosis)
• Muscle
• Liver, kidney, heart

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LAQ 1b: CYSTICERCOSIS - PATHOGENESIS ⭐⭐

How Cysticercosis Occurs

1. Exogenous: Ingesting T. solium eggs from contaminated food/water/hands of a tapeworm carrier
2. Autoinfection (Endogenous): Retrograde peristalsis brings gravid proglottids to stomach → eggs hatch → self-infection (in same person carrying adult T. solium)
3. External autoinfection: Eggs from own feces to hands to mouth (fecal-oral)

Pathogenesis Steps:

Ingestion of T. solium EGGS
          ↓
Gastric acid digests outer coat
          ↓
Oncosphere released in small intestine
          ↓
Hexacanth embryo penetrates intestinal wall
          ↓
Portal circulation → Liver, Lung, Systemic
          ↓
Embryo lodges in various tissues
          ↓
Forms CYSTICERCUS CELLULOSAE (bladder larva)
(encapsulated by host fibrous tissue)
          ↓
LIVING CYST → minimal inflammation (immune evasion)
          ↓
DYING CYST → intense inflammation + calcification
          ↓
In BRAIN → NEUROCYSTICERCOSIS

NEUROCYSTICERCOSIS - Clinical Features:

• Seizures (most common presentation - new onset epilepsy in young adult in endemic area)
• Raised intracranial pressure: Headache, vomiting, papilloedema
• Hydrocephalus (cysts in ventricles/subarachnoid space)
• Focal neurological deficits
• Mental disturbances

CT Scan Findings in Neurocysticercosis:

• Multiple small cystic lesions with scolex visible ("dot sign")
• Ring-enhancing lesions (dying cyst with inflammation)
• Punctate calcifications (dead calcified cysts)

Laboratory Diagnosis of Cysticercosis:

1. CT/MRI brain - imaging of choice
2. Serology: ELISA (anti-cysticercal antibodies) - most useful
3. CSF: Elevated cells, eosinophils, low glucose
4. Biopsy: Subcutaneous nodule - germinal layer + scolex
5. Fundoscopy: Ophthalmocysticercosis

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LAQ 2: TAENIA SOLIUM - Full Coverage

Morphology of T. solium

SCOLEX                    NECK               STROBILA (Chain of proglottids)
(head)                    │
┌─────────────┐           │
│  Rostellum  │           │  ← Immature proglottids (narrow)
│  (armed -   │           │
│  hooklets)  │           │  ← Mature proglottids (square)
│             │           │    (contain both male & female organs)
│  4 Suckers  │           │
│             │           │  ← Gravid proglottids (long)
└─────────────┘           │    (uterus: 7-12 branches/side)
                               │
                               ↓ Terminal gravid segments detach

Life Cycle of Taenia solium ⭐⭐

                    DEFINITIVE HOST = HUMAN
                           ↑
                           │
              Adult worm in small intestine
                           │
                    Eggs passed in feces
                           │
           ┌───────────────┴────────────────┐
           │                                │
           ↓ (Normal route)                 ↓ (Abnormal route)
    Ingested by PIG               Ingested by HUMAN
    (intermediate host)           (auto/heteroinfection)
           │                                │
    Oncosphere released                Oncosphere released
           │                                │
    Penetrates intestine               Penetrates intestine
           │                                │
    Portal blood                       Portal blood
           │                                │
    Settles in muscles/                Settles in tissues
    tissues of pig                     (brain, eye, muscle)
           │                                │
    CYSTICERCUS CELLULOSAE              CYSTICERCOSIS
    in pig muscle ("measly pork")       in HUMAN
           │
           ↓ Human eats undercooked pork
           │
    Scolex evaginates from
    cysticercus in human intestine
           │
    Attaches to small intestinal wall
           │
    Develops into ADULT WORM
    (takes ~2-3 months)
           │
    CYCLE COMPLETE (TAENIASIS)

Pathogenesis of T. solium

• Usually asymptomatic
• Mild: nausea, vague abdominal pain, weight loss, passage of proglottids in stools

Laboratory Diagnosis of T. solium

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PART B: NEMATODES

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LAQ 3: NEMATODES - CLASSIFICATION ⭐

NEMATODES (Roundworms) Infecting Man
│
├── A. INTESTINAL NEMATODES
│   ├── Ascaris lumbricoides (Roundworm)
│   ├── Ancylostoma duodenale (Hookworm - Old World)
│   ├── Necator americanus (Hookworm - New World)
│   ├── Enterobius vermicularis (Pinworm/Threadworm)
│   ├── Trichuris trichiura (Whipworm)
│   ├── Strongyloides stercoralis (Threadworm)
│   └── Trichinella spiralis (intestinal + tissue)
│
└── B. TISSUE/BLOOD NEMATODES
    ├── FILARIAL WORMS:
    │   ├── Wuchereria bancrofti → Lymphatic filariasis
    │   ├── Brugia malayi → Lymphatic filariasis
    │   ├── Brugia timori → Lymphatic filariasis
    │   ├── Loa loa → Loiasis
    │   └── Onchocerca volvulus → River blindness
    ├── SUBCUTANEOUS:
    │   └── Dracunculus medinensis (Guinea worm)
    └── TISSUE:
        └── Toxocara canis/cati → Visceral Larva Migrans

MUHS Exam - Enumerate Intestinal Nematodes: "All Naughty English Teachers Smack Them" = Ascaris, Necator, Enterobius, Trichuris, Strongyloides, Trichinella

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LAQ 1: ASCARIS LUMBRICOIDES ⭐⭐⭐ (Most Important)

Morphology ⭐⭐

• Three "lips" around mouth opening (trilobate lips)
• No suckers or hooks
• Body covered by tough cuticle

• Fertilized: Round/oval, 60-70 μm, thick shell with outer mammillated (bumpy albuminous) coat, bile-stained brown. Contains unsegmented ovum initially.
• Unfertilized: Elongated, thin shell, irregular mamillations (less diagnostic value)
• Infective stage: Egg containing second-stage larva (takes 2-3 weeks in soil)

Ascaris Egg (Fertilized) - DIAGRAM:

  ┌───────────────────────────────┐
  │  ≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈    │  ← Mammillated (bumpy) outer coat
  │  ┌─────────────────────┐  ≈  │  ← Shell (thick, brown)
  │  │                     │  ≈  │
  │  │  Unsegmented ovum   │     │
  │  │  (or developed      │     │
  │  │   larva if infect.) │     │
  │  └─────────────────────┘     │
  └───────────────────────────────┘
         60-70 μm

Life Cycle of Ascaris lumbricoides ⭐⭐

HUMAN (only definitive host)
        │
   Adult worms in small intestine
   (Jejunum - ileum)
        │
   Eggs passed in feces
        │
   In SOIL (2-3 weeks)
        │
   Egg contains infective L2 larva
   (Embryonated egg = infective stage)
        │
        ↓  ORAL INGESTION (contaminated food/water/hands)
        │
   Egg hatches in small intestine
        │
   L2 larva released
        │
   Penetrates intestinal mucosa
        │
   Portal blood → LIVER
        │
   Heart (right side) → Lungs (pulmonary capillaries)
        │
   Breaks into alveoli
        │
   LÖFFLER'S SYNDROME stage
   (2nd infection → eosinophilia, pneumonitis)
        │
   Larva ascends bronchial tree → Trachea → Pharynx
        │
   SWALLOWED (2nd time)
        │
   Small intestine → Molts → Adult worm
        │
   PREPATENT PERIOD: ~60-75 days from ingestion to egg in stool

Pathogenicity / Pathogenesis ⭐

• Löffler's Syndrome: Transient eosinophilia + pulmonary infiltrates + cough/wheeze
• More severe on re-infection (immune-mediated)

• Light infection: Asymptomatic
• Heavy infection: Vague abdominal pain, nausea, diarrhea, malnutrition
• Complications (ECTOPIC ASCARIASIS):
  1. Intestinal obstruction - Worm bolus in small intestine (most common surgical complication)
  2. Biliary ascariasis - Worm enters bile duct → biliary colic, obstructive jaundice, cholangitis
  3. Pancreatic ascariasis - Worm enters pancreatic duct → pancreatitis
  4. Appendicular ascariasis - Worm in appendix → appendicitis
  5. Hepatic ascariasis - Liver abscess
  6. Peritonitis - Perforation of bowel
  7. Migration - Triggered by fever, anesthesia, anthelmintics like piperazine → worm vomiting, nasal expulsion

SN 5: ECTOPIC ASCARIASIS ⭐

• Worms migrate from their normal habitat (small intestine) to other sites
• Triggers: Fever, illness, anesthesia, piperazine, steroids
• Sites: Bile duct (most common), appendix, pancreatic duct, liver, stomach, peritoneum, fallopian tubes, lung
• Biliary Ascariasis: Colicky RUQ pain, jaundice, cholangitis, liver abscess
• Diagnosis: USG (worm in biliary tract - "bull's eye sign"), ERCP
• Treatment: Endoscopic removal, mebendazole/albendazole

Laboratory Diagnosis of Ascaris ⭐

Complications Summary

• Löffler's syndrome (pulmonary phase)
• Intestinal obstruction
• Biliary colic/cholangitis
• Pancreatitis
• Appendicitis
• Malnutrition/growth retardation in children

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LAQ 2: ENTEROBIUS VERMICULARIS (Pinworm) ⭐

Morphology

• Female: 8-13 mm, thin, white, pointed tail (like a pin - hence "pinworm")
• Male: 2-5 mm, curved tail
• Egg: Asymmetric, oval, flattened on one side ("D-shaped"), 50-60 μm, colorless, thin shell

Enterobius Egg - DIAGRAM:
   ┌─────────────────────┐
   │  ─────────────────  │  ← Flat side
   │ (                   )│
   │  ──────────────────  │
   └─────────────────────┘
   D-shaped / slightly flattened on one side
   Contains coiled larva

Life Cycle of Enterobius vermicularis ⭐

HUMAN (only host)
        │
  Adult worms in caecum/appendix/large intestine
        │
  GRAVID FEMALE migrates at NIGHT to PERIANAL REGION
        │
  Deposits ~11,000 EGGS on perianal skin
        │
  Eggs embryonate within 6 hours (infective)
        │
  ┌─────────────────┬──────────────────────────┐
  │                 │                          │
  ↓                 ↓                          ↓
Scratching +    Retroinfection:           Airborne/
fingers→mouth   Larvae migrate back       Environmental
(Autoinfection) through anus → rectum     contamination
  │                 │                          │
  └────────────────┼──────────────────────────┘
                   ↓
           ORAL INGESTION OF EGGS
                   │
           Hatch in small intestine
                   │
           Larvae mature in large intestine
                   │
           Adult worms in caecum
           (Prepatent period: 2-6 weeks)

• Retroinfection: Larvae can migrate back through anus (unique)
• Transmission: Fecal-oral, fomites (bedding, clothing), occasionally airborne
• Children in schools/daycare most affected
• Ectopic migration into female genital tract → vulvovaginitis, salpingitis

Pathogenicity

• Perianal pruritus (most common symptom) - worse at night
• Sleep disturbance, restlessness in children
• Rarely: Appendicitis, ectopic migration to fallopian tubes (salpingitis, peritonitis)

Laboratory Diagnosis ⭐

• Apply tape to perianal skin early morning BEFORE bathing/defecation
• Stick tape to glass slide
• Examine under microscope for D-shaped eggs
• Repeat on 3-5 consecutive mornings (sensitivity increases)
• Stool examination is NOT useful (eggs rarely found in stool)

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LAQ 4 & 5: HOOKWORM - Ancylostoma duodenale ⭐⭐

Morphology of Ancylostoma duodenale ⭐

A. DUODENALE               NECATOR AMERICANUS
┌──────────────┐           ┌──────────────┐
│  ┌──┐  ┌──┐ │           │   ╔════╗     │
│  │  │  │  │ │  ← Teeth  │   ║Plate║    │ ← Cutting
│  └──┘  └──┘ │           │   ╚════╝     │    plates
└──────────────┘           └──────────────┘
  (2 pairs of teeth)        (cutting plates)

• Oval, 60 × 40 μm, thin shell, contain 4-8 blastomeres (partially segmented embryo inside)
• Both species: identical eggs

• Characteristic umbrella-like expansion at posterior end - used for classification

Life Cycle of Ancylostoma duodenale ⭐⭐

HUMAN (definitive host)
        │
  Adult worms in small intestine (duodenum/jejunum)
  - Attach to villi by teeth, suck blood
        │
  EGGS passed in feces
        │
  In SOIL (warm, moist, shaded)
        │
  Hatch within 24-48 hours → RHABDITIFORM (L1) larva
        │
  Feeds on bacteria in soil (free-living stage)
        │
  Molts → L2 (2nd stage rhabditiform)
        │
  Molts → L3 FILARIFORM larva (infective stage)
  (Does NOT feed, can survive in soil weeks)
        │
        ↓  SKIN PENETRATION (barefoot walking on contaminated soil)
        │  [Also: Oral ingestion in A. duodenale - "swallowed infection"]
        │
  GROUND ITCH (cutaneous larva migrans at entry site)
        │
  Subcutaneous tissues → Blood vessels → HEART → LUNGS
        │
  Alveoli → Bronchi → Trachea → Pharynx
        │
  SWALLOWED → Small intestine
        │
  L3 → L4 → Adult worm (5-9 weeks from skin penetration)
        │
  Attach by teeth to mucosa → BLOOD SUCKING
  (A. duodenale: 0.2 mL/worm/day; Necator: 0.03 mL/worm/day)

Pathogenesis ⭐

• Ground itch (cutaneous larva migrans): Pruritic erythematous papules at entry site

• Transient pneumonitis, cough, eosinophilia (less prominent than Ascaris)

• Adult worms attach by teeth, suck blood + cause anticoagulation
• Hypochromic microcytic iron deficiency anemia (hallmark)
• Abdominal pain, diarrhea
• Hypoproteinemia → edema
• Children: Growth retardation, mental development delay

Laboratory Diagnosis ⭐

Four Parasites Causing Anemia ⭐ (MUHS Specific)

1. Ancylostoma duodenale / Necator americanus - Iron deficiency anemia (blood sucking)
2. Diphyllobothrium latum (Fish tapeworm) - Megaloblastic anemia (B12/folate competition)
3. Plasmodium species (Malaria) - Hemolytic anemia
4. Trichuris trichiura - Iron deficiency anemia (heavy infection)

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SN 1: STRONGYLOIDES STERCORALIS - HYPERINFECTION ⭐

Normal Life Cycle (Brief)

• Adult female in small intestinal mucosa (only parasitic females, parthenogenetic)
• Eggs hatch in intestine → Rhabditiform larvae → passed in stool
• In soil: Can develop into free-living adult cycle OR filariform larvae
• Filariform larvae penetrate skin → lungs → swallowed → adult female

HYPERINFECTION SYNDROME ⭐ (Key Exam Topic)

Normal: Rhabditiform larvae → passed in feces
                │
Hyperinfection: Rhabditiform larvae in intestine
                ↓  (skip external development)
          Molt to FILARIFORM larvae IN the intestine
                ↓
          Penetrate intestinal wall / perianal skin
                ↓
          Re-enter circulation (AUTOINFECTION)
                ↓ ↓ ↓ (massive repeated cycles)
          HYPERINFECTION = exponential worm burden

• Corticosteroids (most common - even short courses)
• HIV/AIDS
• HTLV-1 infection
• Organ transplantation, immunosuppressive therapy
• Hematological malignancies

• Severe diarrhea, abdominal pain, GI bleeding
• Cough, wheezing, hemoptysis (pulmonary infiltrates)
• Skin: Larva currens - rapidly migrating urticarial rash (periumblical/trunk)
• Secondary gram-negative bacteremia/sepsis - larvae carry enteric bacteria through gut wall → gram-negative bacteremia/meningitis (leading cause of death)

• Stool: Rhabditiform AND filariform larvae (in hyperinfection)
• BAL (bronchoalveolar lavage): Larvae in sputum/BAL
• Serology: ELISA
• Eosinophilia may be absent in hyperinfection (due to immunosuppression)

MUHS Exam Point: Always screen for Strongyloides before giving immunosuppressive therapy (especially steroids) in patients from endemic areas.

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SN 2: DRACUNCULUS MEDINENSIS (GUINEA WORM) - LIFE CYCLE ⭐

Life Cycle

HUMAN (definitive host)
        │
  Adult female worm in subcutaneous/connective tissue
  (lower limbs usually - ankle/foot)
  Female: 60-100 cm long; Male: 1-4 cm (dies after mating)
        │
  Blister forms on skin (usually foot/ankle)
  (due to worm migrating to surface)
        │
  Host puts foot in water to relieve burning pain
        │
  Blister ruptures → Female worm protrudes
        │
  Female releases FIRST STAGE LARVAE (rhabditiform)
  into water - up to 1 million/day
        │
  Larvae ingested by CYCLOPS (water flea - copepod)
  (intermediate host)
        │
  Develop into L3 INFECTIVE LARVAE in Cyclops
  (2-3 weeks in cyclops)
        │
  ↓ HUMAN DRINKS unfiltered water containing infected Cyclops
        │
  Cyclops digested in stomach
        │
  L3 larvae released → penetrate intestinal wall
        │
  Migrate to retroperitoneum, connective tissue
        │
  Mature, mate (male dies, degenerates)
        │
  Gravid female migrates to lower limbs
  (takes ~1 year)
        │
  PREPATENT PERIOD: ~10-14 months
        │
  Cycle continues

• Eradication campaign very successful - near elimination by 2022 (only ~13 human cases globally in 2022)
• Intermediate host: Cyclops (water flea/copepod) - ONLY intermediate host
• No drug treatment - mechanical removal only
• Traditional treatment: Slowly wind worm around a stick over days-weeks (don't break it - causes severe inflammation)
• Prevention: Drinking filtered/boiled water, ABATE (temephos) in water to kill Cyclops

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SN 3: OCCULT FILARIASIS ⭐

Mechanism:

• Occult filariasis = hypersensitivity reaction to filarial antigens from microfilariae
• Mf are rapidly cleared from bloodstream by the immune system (hyperimmune response)
• Instead, Mf trapped in lungs, lymph nodes → intense eosinophilic inflammatory reaction

Clinical Features of TPE:

• Paroxysmal nocturnal cough and wheeze (asthma-like)
• Fever, malaise, weight loss
• Bilateral pulmonary infiltrates on CXR
• Extreme eosinophilia (>3000/mm³, often >50,000)

Diagnosis of Occult Filariasis:

• Blood: No microfilariae found even at night (characteristic)
• Extreme eosinophilia (>3000 cells/μL)
• High IgE levels
• High antifilarial antibody titers (ELISA)
• CXR: Bilateral miliary/patchy infiltrates
• Bronchoalveolar lavage: Eosinophils + trapped Mf
• Good response to Diethylcarbamazine (DEC) - diagnostic/therapeutic

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SN 4: WUCHERERIA BANCROFTI - MORPHOLOGY & LAB DIAGNOSIS ⭐

Morphology of Wuchereria bancrofti

W. bancrofti Microfilaria - DIAGRAM:
┌────────────────────────────────────────────────────────────┐
│   ← Sheath (extends beyond body)                          │
│ ●────────────────────────────────────────────────── /      │
│   HEAD SPACE   NUCLEI (body)        TAIL = EMPTY (no nuc) │
└────────────────────────────────────────────────────────────┘
                        ↑ SHEATHED, TAIL TIP EMPTY

• Lymphatic filariasis (Bancroftian filariasis)
• Lymphedema → Elephantiasis (lower limbs, scrotum most common)
• Hydrocele, chyluria
• Acute dermatolymphangioadenitis (ADLA)
• Occult filariasis/TPE

Laboratory Diagnosis of W. bancrofti ⭐

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Summary Tables for Quick Revision

Cestodes Affecting Man - Quick Reference

Nematodes - Infective Stage & Route of Entry

Nematode Vectors/Intermediate Hosts

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High-Yield Points for MUHS Exam ⭐⭐⭐

1. T. solium - Only tapeworm where humans can be both definitive AND intermediate host
2. Hydatid cyst - Liver > Lungs; Never aspirate blindly (anaphylaxis risk); PAIR procedure
3. Ascaris - Largest intestinal nematode; Löffler's syndrome; Ectopic ascariasis (bile duct most common)
4. Hookworm - A. duodenale has teeth; N. americanus has cutting plates; IDA (microcytic anemia)
5. Enterobius - Perianal pruritus; Scotch tape test; Retroinfection
6. Strongyloides - Hyperinfection in immunosuppressed; Ivermectin treatment
7. W. bancrofti - Nocturnal periodicity (10 PM-2 AM); Sheathed Mf with EMPTY tail tip; Culex vector; ICT antigen test
8. Occult filariasis = no Mf in blood + TPE; Extreme eosinophilia
9. Guinea worm - Cyclops intermediate; No drug; Winding around stick; Near eradication
10. Four parasites causing anemia: Hookworm (IDA), D. latum (megaloblastic), Malaria (hemolytic), T. trichiura (IDA)
11. Cysticercosis vs Hydatid - T. solium larva vs E. granulosus larva; Both cause cysts in brain
12. Neurocysticercosis - Most common cause of secondary epilepsy in endemic countries; MRI + ELISA diagnosis

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