NEMATODES 3

• Tissue nematodes

  • Toxocara spp.
  • Dracunculus medinensis
  • Parastrongylus cantonensis
  • Anisakis
• Toxocara species

  Zoonotic disease from stray dogs and cats
• Toxocara life cycle

  1. Life cycle is completed in dogs or cats

  2. Encysted eggs may be reactivated and infects their puppies through transplacental or transmammary transmission
• Factors contributing to Toxocara infection

  • Common among children than adults
  • Tendency to play in soil
  • Exhibit geophagia or soil eating
  • Common in places where dogs and cats are not dewormed
• Toxocara Biology

  • Accidental Host: Humans
  • Paratenic Host: Rabbits and small mammals
  • Definitive Hosts: Dogs or cats
  • Infective Stage: Embryonated ova
  • Diagnostic Stage: Larvae encysted in tissues
• Infective Ova in Definitive Host

  1. Infective ova hatch to larva and penetrate the gut wall

  2. Young dogs: larvae undergo lung migration

  3. Older dogs: larval encystment in tissues is more common

  4. Female old dogs: encysted larvae reactivated during pregnancy
• Humans as Accidental Host

  1. Ingestion of embryonated ova or infected paratenic host (Food-borne) to penetrate intestinal wall

  2. Migration to liver, heart, lungs, brain, muscle, eyes
• Diagnosis of Toxocara:
• Infective Ova in Paratenic Hosts

  1. Ingest embryonated ova (generally Toxocara canis)

  2. Hatch to larvae and encyst in various tissues

  3. Eaten by dogs to become adult worms
• Embryonated Ova


  1. Ingested by the definitive hosts (dogs/cats)

  2. Ingested by paratenic host
• Pathogenesis and Clinical Manifestations of Toxocara

  1. Visceral Larva Migrans (VLM)

  2. CNS: Neurological Toxocariasis

  3. Lungs: pneumonia, respiratory failure

  4. Liver: hepatomegaly, necrosis

  5. Heart: Loeffler endomyocarditis

  6. Ocular Larva Migrans (OLM)

  7. Covert Toxocariasis (CoTOX)
• Common among children 5-10 years old


  • Unilateral visual impairment
  • Strabismus
• Retinal Invasion is the most serious consequence
• Definitive Hosts of Dracunculus medinensis

  • Humans
  • Wolves
  • Dogs
  • Horses
  • Cows
  • Leopards
  • Monkeys
  • Baboons
• Covert Toxocariasis (CoTOX) is less specific syndrome or may be asymptomatic
• Diagnosis


  1. Tissue Biopsy demonstrating larva

  2. ELISA test for IgG

  3. PCR

  4. Stool exam to demonstrate eggs has no role in the diagnosis of human toxocariasis
• Treatment

  1. Most patients recover without therapy

  2. If therapy is warranted: Albendazole or Mebendazole PLUS anti-inflammatory drug (Steroids)

  3. For those with CNS, cardiac, or lung complications

  4. More difficult for Ocular Toxocariasis to prevent progressive damage to the eye
• Intermediate Host of Dracunculus medinensis

  • Cyclops copepods
• Infective Stage of Dracunculus medinensis

  • Third Stage Larva (L3) within the Cyclops copepods
• Prevention and Control

  1. Control and capture of stray dogs and cats

  2. Cleaning up feces from soil and pavements

  3. Closing of potentially contaminated areas to animals and children

  4. Gardens should be fenced to prevent fecal contamination by dogs and cats

  5. Vegetables gathered from possible contaminated gardens should be washed thoroughly

  6. Avoidance of consumption of raw or undercooked meat of potentially infected animal

  7. Hand washing at all times

  8. Strategic antihelminthic treatment of dogs and cats

  9. Puppies: start 2-3 weeks of age, repeated every 2 weeks until 12 weeks age

  10. Adult: treated every 6 months

  11. Female: after each estrus cycle
• Dracunculus medinensis, also known as Guinea Worm, is the longest nematode known to cause human parasitism
• Dracunculus medinensis infection has been recorded as early as the 15th BC
• Diagnostic Stage of Dracunculus medinensis

  • Female adult worm in the subcutaneous tissue
  • Rhabditiform larvae
• Dracunculus medinensis Biology

  • Female length: 60cm up to 3 ft
  • Male length: 1.2-2.9cm
  • Larvae length: 500-700 um
• Dracunculus medinensis Pathogenesis and Clinical Manifestations

  1. Female adult worm emerges to the subcutaneous tissue, releasing toxic chemicals causing nausea, rash, diarrhea, dizziness, localized edema, reddish papule, blister, and itching

  2. If the worm fails to reach the skin, it may get calcified in the joint causing arthritis

  3. If the worm reaches the CNS, it may lead to paraplegia

  4. Abscess and swelling may occur when worms rupture

  5. Secondary bacterial infection may occur on blisters or ulcers

  6. Entry of tetanus spores with the retreating worm
• Dracunculus medinensis Treatment


  Manual Removal of Adult Female Worm by submerging the affected body part in water to coax the worm out, cleaning the site, applying slight pressure to pull the worm out slowly, stopping when resistance is met to avoid breaking the worm
• Dracunculus medinensis Diagnosis

  1. Recovery of adult worm from the blister

  2. Recovery of rhabditiform larvae

  3. Fluid discharged by the worm
• Worm extraction

  1. Coaxing the worm out with water

  2. Cleaning the site thoroughly

  3. Applying slight pressure and slowly pulling the worm out of the wound

  4. Stopping pulling when resistance is met to avoid breaking the worm

  5. Full extraction usually takes several days
• Anisakis infective species


  • Anisakis simplex
  • Pseudoterranova decipiens
• CT Scan findings

  • Cerebral edema
  • Hydrocephalus
  • Meningeal lesions
• Related species to Anisakis

  • Contracaecum sp
  • Hysterothylacium sp
• Elevated eosinophils in CSF


  • Similar with other CNS parasitism
• Definitive Hosts of Anisakis

  • Whales
  • Dolphins
  • Pospoises
  • Walruses
  • Seals
  • Sea lions
  • Other deep-marine mammals
• Paratenic Hosts of Anisakis

  • Squid
  • Fish
• Intermediate Host of Anisakis

  • Crustacean (L2 to L3)
• Common regions for Anisakis infection

  • Asia: Japan, Korea
  • Europe: Netherlands, France, Germany, Italy, Spain, UK
  • North and South America
• Anisakis infection is not very common
• Accidental Host of Anisakis

  • Humans
• Biology of Anisakis Larva

  1. First Stage Larva developed inside the ovum

  2. Second Stage Larva hatched from ova and released free-swimming L2, ingested by crustaceans

  3. Third Stage Larva in crustaceans (L2 to L3), harbored by paratenic hosts
• Anisakiasis/Anisakidosis is a larval infection in the stomach, not growing into adults in humans