Intestinal & Tissue Nematodes

General Characteristics of Intestinal & Tissue Nematodes

• Shape: Elongated, cylindrical, pointed, and unsegmented.
• Size: Variable, ranging from <5 mm (Strongyloides) to 1m (Dracunculus). Female worms are generally longer than male worms.
• Symmetry: Bilaterally symmetrical.

Body Wall

• Outer Layer: Hyaline, noncellular cuticle.
• Inner Layer: Longitudinal muscles.
• Locomotion: Achieved through contraction of the longitudinal muscles.

Alimentary Canal

• Well-developed, consisting of:
  • Mouth (anterior end)
  • Muscular and Glandular Esophagus
  • Intestine
  • Rectum
  • Anus (posterior end)

Body Cavity (Pseudocoelom)

• Space between the body wall and the alimentary canal.
• Filled with fluids secreted from the intestine and genital organs.

Composition

• Body covering (from ectoderm).
• Muscle layer (from mesoderm).
• Digestive tract (from endoderm).
• Pseudocoelom.

Sexes

• Diecious (male & female). May exhibit parthenogenesis.
• Male: Smaller, curved posterior with spicule.
• Female: Larger, pointed posterior, no spicule.

Reproductive Systems

• Male: Consists of a long convoluted tube differentiated into testes, vas deferens, seminal vesicle, and ejaculatory duct.
• Female: Consists of one or two convoluted tubes differentiated into ovary, oviduct, seminal receptacle, and uterus.

Oviparity

• Oviparous: Lay immature/unembryonated/unsegmented eggs.
  • Examples: Hookworm, Ascaris lumbricoides, Trichuris trichiura (HAT).
• Oviviparous/Ovoviviparous: Lay mature/embryonated/segmented eggs.
  • Examples: Enterobius vermicularis, Strongyloides stercoralis (ES).
• Viviparous/Larviparous: Lay larva, not eggs.
  • All tissue nematodes.

Egg Structure

• Three layers:
  • Outer layer: Embryo membrane.
  • Middle layer: Chitinous layer.
  • Inner layer: Lipid layer/ascaroside.

Life Cycle

• Egg stage → Larval stage → Adult stage.

Classification of Nematodes

Based on Phasmids

• APHASMIDS: Lack phasmids or caudal chemoreceptors.
  • Parasitize the small intestine: Trichinella spiralis, Capillaria philippinensis.
  • Parasitize the large intestine: Trichuris trichiura.
• PHASMIDS: Possess phasmids.
  • Parasitize the small intestine: Hookworms, Strongyloides stercoralis.
  • Parasitize the large intestine: Wuchereria bancrofti, Brugia malayi.

Based on Habitat

• Small Intestine (Duodenum, Jejunum, Ileum): "CASHT" - Capillaria philippinensis, Ascaris lumbricoides, Strongyloides stercoralis, Hookworms, Trichinella spiralis (adult).
• Large Intestine: "ET" - Enterobius vermicularis, Trichuris trichiura.
• Tissue Nematodes:
  • Lymphatic: Wuchereria bancrofti, Brugia malayi
  • Subcutaneous: Loa loa, Onchocerca volvulus, Dracunculus medinensis
  • Eyes and Meninges: Parastrongylus cantonensis
  • Muscles: Trichinella spiralis (larva)

Heart to Lung Migration

• Ascaris lumbricoides, Strongyloides stercoralis, Hookworm ("ASH")
• Soil Transmitted Helminths: Hookworm, Ascaris lumbricoides, Trichuris trichiura ("HAT")

Based on Mode of Infection

• Ingestion of Eggs ("EAT"): Enterobius vermicularis, Ascaris lumbricoides, Trichiuris trichiura.
• Ingestion of Larvae (IH): Dracunculus medinensis
• Skin Penetration ("SAN"): Strongyloides stercoralis, Ancylostoma duodenale, Necator americanus.
• Blood Sucking Insect ("BOWL"): Brugia malayi, Onchocerca volvulus, Wuchereria bancrofti, Loa loa.
• Inhalation of Dust: Ascaris lumbricoides, Enterobius vermicularis.

Scientific and Common Names

• Ascaris lumbricoides: Giant Intestinal roundworm, Lumbricus teres
• Enterobius vermicularis: Oxyuris vermicularis, Pinworm, Seatworm, Social/Society worm
• Trichiuris trichiura: Whipworm
• Capillaria philippinensis: Pudoc worm, Mystery worm
• Necator americanus: New World Hookworm, American hookworm, American murderer
• Ancylostoma duodenale: Old World Hookworm
• Ancylostoma braziliense: Cat hookworm
• Ancylostoma caninum: Dog hookworm
• Strongyloides stercoralis: Threadworm, Military worm

Intestinal Nematodes

Ascaris lumbricoides

• Common Name: Giant Intestinal Roundworm
• Largest intestinal nematode.
• Most common nematode in humans.
• Habitat: Small Intestine
• Final Host: Human
• Diagnostic Stage: Fertilized/Unfertilized Egg
• Infective Stage: Embryonated Egg
• Mode of Transmission: Ingestion of Embryonated egg (fecal-oral)

Morphology

• Adult:
  • Shape: Cylindrical, fusiform body
  • Color: Pink (alive), White (dead)
  • Length: Male 10-31 cm, Female: 22-35 cm
  • Special structure: Trilobate lips, Paired cross veins and lateral lines.
  • Tail: Curled with pair sickle like copulatory spines (males).

Egg

• Become infective 2-6 weeks after deposition.
• Survive harsh environments (dry/freezing temperatures).
• Three kinds of eggs:
  • Fertilized
  • Unfertilized
  • Decorticated

Fertilized Eggs

• Size: $45-75 \,\text{x} \, 35-50 \,\mu\text{m}$
• Shape: Elliptic
• Color: Brown
• Shell: Thick protein membrane
• Content: One embryo cell
• Three Layers:
  • Inner: Lipoidal vitelline membrane
  • Middle: Transparent glycogen layer
  • Outer: Coarsely mamillated albuminous layer
  • Undeveloped unicellular embryo.
  • Coarse mammillated albuminous covering.
  • Thick, yellow-brown chitin shell.

Unfertilized Eggs

• Size: $88-94 \, \text{x} \, 39-44 \,\mu\text{m}$
• Shape: Longer and slender than fertilized egg
• Color: Brown
• Shell: Thin protein membrane
• Content: Mass of refractile lecithin granules, no glycogen membrane
  • Heavy albuminous coating.
  • Thin shell.
  • Amorphous mass of protoplasm.
  • Protein granules.

Decorticated Eggs

• Size: $45-75 \, \text{x} \, 35-50 \,\mu\text{m}$
• Shape: Broadly ovoid
• Color: Transparent
• Shell: Absent albuminous coat
• Content: Contains a mass of organized yolk cells

Embryonated Eggs

• Shape: Broadly ovoid
• Color: Brownish-yellow
• Content: Contains a coiled larva inside

Life Cycle

1. Adult lives in the small intestine.
2. Undeveloped eggs in feces, embryonates in warm, moist soil.
3. Embryonated egg ingested by human.
4. Larvae hatch in small intestine and begin larval migration:
   • Intestine wall → Blood vessels → Liver → Blood vessels → Lungs → Alveoli → Bronchioles → Pharynx → Small intestine (adult)

Symptoms and Pathology

1. Asymptomatic
2. Pneumonia, cough, fever, eosinophilia (during larval migration)
3. Vomiting and abdominal pain
4. Intestinal perforation
5. Moderate infections:
   • Lactose intolerance
   • Vitamin A malabsorption
6. Heavy infections:
   • Bowel obstruction (due to bolus formation)
   • Volvulus

• Ascariasis "sandbox infection"
• Larva: Heart-Lung Migration (ASH)
• Loeffler's Syndrome
  • pneumonitis + eosinophilia
• Ascaris pneumonitis
  • pneumonia-like symptoms
• Pneumonitis

Laboratory Diagnosis

1. Direct microscopy. If negative, consider:
   • No infection
   • Early infection (no eggs laid yet)
   • All male worm infection

• Charcot-Leyden crystals: Eosinophil degradation products

Treatment

• Albendazole
• Mebendazole
• Pyrantel Pamoate

Prevention and Control

• Avoid contact with soil contaminated with human feces
• Do not grow food in night soil
• Improve hygiene and sanitation practices
• Proper food preparation
• Regular deworming

Enterobius vermicularis

• Common Names: Pinworm, Seatworm, Social Worm, Society Worm
• Habitat: Large Intestine
• Final Host: Human
• Diagnostic Stage: Embryonated Egg
• Infective Stage: Embryonated Egg
• Mode of Transmission: Ingestion, Inhalation, Autoinfection, Retroinfection

Morphology

• Adult

  • Shape: Round
  • Color: Whitish or Brownish
  • Length: Male 2-5 mm long, Female: 8-13 mm long
  • Special structure: Anterior end (cervical alae) found in both Male and Female
  • Posterior end: Male: Curved; Female: Tapered

• Egg

  • Shape: Elongated, flattened on one side “D shaped”
  • Color: Colorless
  • Length: $50-60 \, \text{x} \, 20-30 \,\mu\text{m}$
  • Shell: Thick, Double layered
  • Contents: Immature: Single cell, Mature: Larva

Life Cycle

1. Eggs on perianal folds
2. Embryonated eggs ingested by human - Larvae inside the eggs mature within 4 to 6 hours.
3. Larvae hatch in small intestine
4. Adults in lumen of cecum
5. Gravid female migrates to perianal region at night to lay eggs

Symptoms and Pathology

1. Pruritus ani/Nocturnal Pruritus ani
2. Hemorrhagic colitis
3. Extraintestinal enterobiasis: Vagina, Uterus, Fallopian tube

Laboratory Diagnosis

1. 5% survival in stool
2. Perianal swab
3. Scotch Tape Swab

Treatment

• Albendazole
• Mebendazole

Prevention and Control

• Personal cleanliness and personal hygiene are essential
• Infected persons should sleep alone until adequately treated
• Vacuum cleaning

Trichuris trichiura

• Common Name: Whipworm
• Habitat: Large Intestine
• Final Host: Human
• Diagnostic Stage: Ova in stool
• Infective Stage: Embryonated Egg
• Mode of Transmission: Ingestion of embryonated egg (fecal-oral)

Adult Morphology

• Shape: Round
• Color: Pinkish gray
• Length: Male 35-50 mm long, Female: 30-45 mm long
• Special structure: Anterior is attenuated and slender resembling a whip. Anterior 3/5 portion is traversed by a narrow esophagus resembling “string of beads”.

Egg Morphology

• Shape: Lemon shaped
• Color: Brown
• Length: $50-54 \,\mu\text{m}$
• Special structure: With prominent bipolar plugs, barrel/football/Japanese lantern

Life Cycle

1. Unembryonated eggs are passed in feces.
2. 2-cell stage
3. Advanced cleavage
4. Embryonated eggs are ingested.
5. Larvae hatch in small intestine.
6. Adults in cecum.

Symptoms and Pathology

• People with light infection:
  • Asymptomatic
• People with heavy infection:
  • Frequent defecation
  • Painful passage of stool
  • Stool appearance: Mixture of mucus and blood (dysentery)
  • Clinical feature: Amoebic dysentery
• Complications:
  • Colonic obstruction (tangle of worms)
  • Ulceration of large intestine → Blood loss
  • Iron deficiency anemia
  • Rectal prolapse

Laboratory Diagnosis

• Specimen: Stool
• Technique:
  • Direct Wet Examination (heavy infection)
  • Concentration technique

Treatment

• Albendazole
• Mebendazole

Prevention and Control

• Prevent contamination of soil with human feces
• Wash hands before eating (children, soil worker)
• Wash vegetable and fruits
• Do not use night soil as fertilizer

Capillaria philippinensis

• Common Names: Pudoc worm/Mystery worm
• Habitat: Small Intestine
• Final Host: Human
• True Definitive host: Migratory birds
• Intermediate host: Freshwater fish/Brackish water fish, Birot, Guppy Ipon (Hypseleotris bipartita, Bagsang, Bagtu, Biyang bato)
• Diagnostic Stage: Larva/Ova found in stool
• Infective Stage: Filariform larva (L3)
• Mode of Transmission: Ingestion of raw/undercooked fish/seafood bearing infective larva

Morphology

• Adult:
  • Delicate, tiny worms
  • Male: with chitinized spicule
  • Female: usually have eggs in utero
• EGGS
  • With flattened bipolar mucus plugs, striated
  • Guitar, peanut-shaped
  • smaller than Trichuris trichiura egg

TYPICAL EGG

• Immature eggs
• Unembryonated eggs
• Will go to stool

ATYPICAL EGG

• Will go to fresh water ( embryonation occur)
• Eaten by fish
• Segmented egg
• Embryonated egg
• Hatch inside the small intestine
• Responsible for autoinfection

Life Cycle

1. Unembryonated, thick-shelled eggs passed in feces.
2. Eggs become embryonated in water.
3. Infective larvae develop in tissue of intermediate host.
4. Ingestion of raw or undercooked infected fish.
5. Adults in small intestinal mucosa
6. Females may produce two types of eggs: unembryonated eggs (passed in feces) and embryonated eggs lacking shells (hatch inside defintive host).
7. Larvae re-invade small intestinal mucosa in autoinfective cycle.

Symptoms and Pathology

1. Malabsorption
2. Steatorrhea
   • Borborygmi: peculiar abnormal gurgling sound
   • LBM alternating with constipation (abdominal pain and diarrhea)

Laboratory Diagnosis

• Specimen: Stool
• Technique:
  • Direct Wet Examination
  • Concentration technique

Treatment

• Albendazole
• Mebendazole

Hookworms

• Common Name
  • Ancylostoma duodenale: Old World Hookworm, Germ of Laziness
  • Necator americanus: New World Hookworm, American Hookworm, American Murderer
  • Ancylostoma braziliense: Cat Hookworm
  • Ancylostoma caninum: Dog Hookworm
• Habitat: Small Intestine
• Final Host: Human
• Diagnostic Stage: Ova/Larva
• Infective Stage: L3/Filariform larva (sheathed)
• Mode of Transmission: Skin penetration (unprotected feet)

Morphology

• Adult
  • Shape
    • Ancylostoma duodenale: C-shaped
    • Necator americanus: S-shaped
  • Buccal cavity
    • Ancylostoma duodenale: 2 pairs of teeth
    • Necator americanus: Semilunar cutting plate
  • Copulatory burse
    • Ancylostoma duodenale: Tripartite (3 digits), Simple, not barbed
    • Necator americanus: Bipartite (2 digits), Barbed/Bristle like
  • Dorsal rays
    • Ancylostoma duodenale: splits at tip
    • Necator americanus: splits from base
  • Spicules
    • Ancylostoma duodenale: free
    • Necator americanus: Two spicules fused

Difference between Adult Male and Female

• EGG
  • Shape: Oval shaped
  • Size: $65 \,\mu \text{m}$
  • Color: Colorless (non-bile stained)
  • Shell: Thin
  • Contents: Contains segmented ovum with four (4) blastomeres “Morula ball” formation
• LARVA
  • L2 Rhabditiform larva
    • 1st stage larva
    • Short and Stout
    • Open mouth: Feeding stage
    • Long buccal cavity
    • Short/Small Genital Primodium
  • L3 Filariform larva
    • 3rd stage larva
    • Long and slender
    • Closed mouth: Nonfeeding stage
    • Sheathed, Pointed tail

Life Cycle

Development to filariform larva in enviornment
Rhabditiform larva hatches
Filariform larva penetrates skin
Larvae exit circulation in the lungs; they are then coughed up and swallowed.
Adults in small intestine
Ancylostoma spp. larvae can become developmentally arrested and dormant in tissues.
Re-activated larvae may enter the small intestine.
Eggs in feces

Symptoms and Pathology

• LARVAL PENETRATION
  • Human Hookworm Allergic Reaction:
    • Ground itch/Dew itch/Water sore/Mazza Mora
    • Severe itching at the site of larval penetration of skin
    • Erythematous popular rash
• Animal Hookworm
  • A. braziliense and A. caninum:
    • Creeping Eruption
    • Cutaneous Larva Migrans (CLM)
• LARVAL MIGRATION
  • Heart-to-lung migration (ASH): Pneumonitis
    • Wakana Disease: Pulmonary lesions and hemorrhage
    • Pneumonia and alveolar hemorrhage, bloody sputum
• ADULT
  • Tissue damage at the site of attachment
  • Enteritis and pain; blood loss and anemia
    • Necator americanus: 0.03 mL blood/day
    • Ancylostoma duodenale: 0.26 mL blood/day
  • Chronic blood lost → Iron Deficiency Anemia
    • Microcytic, Hypochromic Anemia
  • Acute gastrointestinal phase
    • demonstrates increased eosinophilia

Laboratory Diagnosis

1. Direct microscopy
2. Kato-katz method
3. Harada mori culture technique
4. Coproculture: Harada mori

Strongyloides stercoralis

• "Smallest nematode infecting man"
• Common Name: Threadworm
• Habitat: Small Intestine
• Final Host: Human
• Diagnostic Stage: Rhabditiform/Filariform larva Egg (heavy infection)
• Infective Stage: L3 larva/Filariform larva (unsheathed)
• Mode of Transmission:
  • Skin penetration
  • Internal Autoinfection (chronic and hyperinfection)

Morphology

• EGG
  • Shape: Oval shaped
  • Size: $55 \,\mu \text{m}$
  • Color: Colorless (non-bile stained)
  • Shell: Thin
  • Contents: Similar to hookworm but are smaller
• ADULT
  • Male
    • Parasitic/Free-living
    • Length: 0.7 mm
    • Posterior end: Curved ventrally with spicules
  • Female
    • Parasitic
      • Length: 2.2 mm
      • Posterior end: Straight
    • Free-living
      • Length: 1 mm
      • Posterior end: Straight
• LARVA
  • L2 Rhabditiform larva
    • a. Buccal Cavity Small/Inconspicuous
    • b. Genital Primodium Prominent/conspicuous
  • L3 Filariform Larva
    • a. Sheath Unsheathed
    • b. Tail Notched

Life Cycle

• Free-Living Cycle

1. Rhabditiform larvae hatch from embryonated eggs.
2. Development into free-living adult worms.
3. Eggs are produced by fertilized female worms.
4. Rhabditiform larvae develop into filariform (L3) larvae.

• Parasitic Cycle

1. Infective filariform larvae penetrate the intact skin of the definitive host.
2. The filariform larvae migrate by various pathways to the small intestine where they become adults.
3. Eggs deposited in intestinal mucosa.
4. Rhabditiform larvae hatch and migrate to intestinal lumen.
5. Rhabditiform larvae in the intestine are excreted in stool.
6. Autoinfection: Rhabditiform larvae in large intestine become filariform, penetrate intestinal mucosa (or perianal skin) and migrate to other organs.

Symptoms and Pathology

• LARVAL PENETRATION
  • Allergic reaction at the site
    • “larva currens” tracks under skin from worm migration
• LARVAL MIGRATION
  • Heart-Lung Migration → Pneumonia
    • signs and symptoms resembling bronchopneumonia)
• ADULT
  • Cochin China Diarrhea, Vietnam Diarrhea (Intermittent Diarrhea)
    • Honeycomb appearance of the intestinal mucosa
• AUTOINFECTION
  • Infective larva will penetrate the intestinal mucosa

Laboratory Diagnosis

1. Stool Exam
   • Diagnostic stage: Rhabditiform Larva o usually passed in the feces
2. Baermann Funnel Technique
3. Harada Mori Filter Paper Culture Technique
   • Recommended culture method

Tissue Nematodes

Trichinella spiralis

• Common Names: Muscle worm/Trichina worm/Garbage worm
• Habitat
  • Adult: Small Intestine
  • Larva: Encysted in striated muscle (skeletal muscle)
• Final Host: Pigs and other mammals (omnivores/carnivores)
• Accidental Host: Human
• Dead-end Host:
• Diagnostic Stage: Encysted larva
• Infective Stage: Encysted larva
• Mode of Transmission: Ingestion of undercooked raw meat with encysted larva

Morphology

• ADULT
  • Shape: Round
  • Color: White
  • Special structure
    • Male: with conical papillae (aid in copulation)
      • after copulation, male dies
    • Female: with club-shaped uterus
      • viviparous/larviparous
• LARVA
  • Become encysted in striated muscle fiber
    • Spiralis – larva in the cyst is coiled
• CYST Tissue reaction around encapsulated larvae

Life Cycle

Domestic Cycle
* Meat scraps/cannibalism
Sylvatic Cycle
* Predation/scavenging
Encysted larva in striated muscle
Larva released in small intestine
Larva deposited in mucosa
Circulation
Adults in small intestine
Encysted larva in striated muscle
Ingestion of undercooked meat

Symptoms and Pathology

• Trichinosis, Trichiniasis, Trichinellosis
  • Great Imitator: can mimic other diseases

1. Larva (Muscle)
   • Larval Migration: Fever, Facial Edema, Eosinophilia
   • Muscle pain at the site of encystations
   • Edema (eyelid edema)
   • Difficulty in swallowing and breathing
2. Adult (Small Intestine)
   • Diarrhea and abdominal pain

Laboratory Diagnosis

1. Muscle Biopsy
2. Beck’s Xenodiagnosis (albino rats)
3. Serological tests
   • Bentonite flocculation
   • Bachman Intradermal test
4. Confirmatory test
   • Western blot
   • Latex agglutination

Dracunculus medinensis

• Common Names: Guinea Worm, Fiery Serpent of the Israelites, Medina Worm, Dragon Worm, Serpent Worm
• Longest nematode in human (1 meter)
• Habitat: Subcutaneous Tissue
• Intermediate Host: Aquatic Crustacean (Copepods)
• Definitive Host: Human
• Infective Stage: Filariform Larva (L3)
• Mode of Transmission: Ingestion of infected copepods (drinking unfiltered water containing the copepods)

Morphology

• ADULT
  • Male
    • Size: 21 x 0.4 mm
    • Special structure: Anterior End: Coils itself atleast once
  • Female
    • Size: 840 x 1.5 mm
    • Special structure: Anterior End: Rounded, Prominent blunt
• LARVA
  • Size
    • Length: 500-750 um
    • Diameter: 5-25 um
  • Special structure
    • Anterior End: Broad
    • Tail: Slender, Tapered

Life Cycle

Larvae undergoes two molts in the copepod and becomes a L3 larvae.
Infective copepods Ingested by fish.
Under/uncooked fish harboring/ infective larvae eaten by dogs or people.
L1 larvae consumed by a copepod.
Human drinks unfiltered water containing copepods with L3 larvae.
Larvae are released when copepods are digested. Larvae penetrate the host's stomach and intestinal wall. They mature and reproduce in subcutaneous tissues.
Fertilized female worm migrates to surface of skin, causes a blister, and discharges larvae.
L1 larvae released into water from the emerging female worm.
Female worm begins to emerge from skin one year after infection.
Old Third- stage larva
Released larva
Emerging worm
Water flea
First-stage larva

Symptoms and Pathology

• SYMPTOMS
  • Slight fever
  • Itchy rash
  • Nausea
  • Vomiting
  • Diarrhea
• CONDITIONS
  • Female worms emerges subcutaneous tissue
  • Secondary bacterial infections
    • Cellulitis
    • Abscesses
    • Sepsis

Laboratory Diagnosis

• X-ray image

Treatment and Prevention

• No treatment, removal only
• Worms are attached to a stick and slowly retracted from the host by gradual turning of the stick and removal of the worm
• TOTAL REMOVAL OF THE WORM

Soak blistered region in container of water daily to coax the worm out.
When worm starts to emerge, begin to gently retract its body.
CAREFUL not to break the worm's body!
Gently massage the area around the lesion to help free the worm. Continue traction until worm can no longer be advanced.
Wrap worm around a stick to maintain tension on its body.
Apply topical antibiotics to prevent secondary infections and cover the wound with clean dressings.
Repeat steps 1-4 daily until entire worm is removed. Worm may be up to a meter long and removal may last several weeks.

Eyes and Meninges

Parastrongylus cantonensis

• Common Name: Rat Lungworm
• Habitat: Small Intestine
• Larva: Encysted in striated muscle (skeletal muscle)
• Final Host: Human
• Definitive Host: Rats
• Intermediate Host: Molluscs, Slugs, and Snails [Pila luzonica (Kuhol); Brotia asperata (Suso)]
• Infective Stage: Filariform Larva (L3)
• Mode of Transmission: Ingestion of Intermediate Host by man containing infective larva
• Migrate to the brain and spinal cord causing Eosinophilic Meningoencephalitis

Morphology

• Adult Female worm
  • Barber's pole appearance
  • Looping of whitish uterus to the red digestive tract

Life Cycle

Larvae migrate to brain (occasionally eyes or lungs) in aberrant human host, and do not reach reproductive maturity.
Adults in pulmonary arteries
Accidental ingestion of gastropod or larvae (e.g. on contaminated produce)
Third-stage larvae are ingested by definitive host.
Eggs hatch in the lungs, and first-stage larvae are passed in rodent feces
Infective stage
First-stage larvae shed from definitive host are ingested by gastropod intermediate host.
Diagnostic stage
Larvae reach the infective (third) stage after two molts in the intermediate host.

Symptoms and Pathology

• Eosinophilia and Meningitis symptoms
• Laboratory Diagnosis:
  • Specimen: CSF (Increased WBCs, Eosinophil count)