Study Notes on Heterophyiasis (Heterophyes heterophyes)

Heterophyiasis

Overview of Heterophyiasis

  • Parasite: Intestinal fluke, specifically Heterophyes heterophyes.
  • Phylum: Platyhelminthes
  • Class: Trematoda
  • Genus: Heterophyes

Habitat

  • Primarily resides in the small intestine of:
    • Humans
    • Cats
    • Dogs
    • Fish-eating birds (known as reservoir hosts)

Morphology

  • Shape: Pear-shaped
  • Suckers: Three total (oral, ventral, and genital)
  • Reproductive Organs: Ovary positioned anterior to testis
  • Size: Approximately 2 mm
  • Appearance: Can be identified stained from a dog’s small intestine containing:
    • Oral sucker
    • Eggs in the uterus
    • Testes

Life Cycle and Method of Infection

  • Diagnostic Stage: Eggs are oval, light brown, operculated, mature with a knob on the shell.
  • Process of Infection:
    1. Stool to Water: Eggs are released into brackish water (a mix of fresh and saltwater).
    2. First Intermediate Host: Inhabit Pirenella conica (a right-handed snail):
    • Eggs are ingested by snails, where:
      • Miracidia emerge and penetrate the snail’s intestine.
      • Sporocysts develop in snail tissue.
      • Two generations of rediae are produced.
      • Cercariae are formed and released from the snail.
    1. Type of Cercariae:
    • The specific developmental form is known as pleurolophocercus, which swims away.
    1. Second Intermediate Host: Fish species, such as:
    • Mugil cephalus (Boury)
    • Tilapia nilotica (Bolty)
    • Cercariae penetrate the skin of fish and encyst as metacercariae (infective stage).
    1. Mode of Infection: Humans become infected by consuming undercooked or improperly salted fish (e.g., sweet fessikh: fish salted for less than seven days).
    2. In the Intestinal Tract:
    • Upon ingestion, metacercariae are liberated from their cyst walls and attach to the villi of the small intestine using their suckers.

Pathogenesis and Pathology

  • Two principal factors cause disease symptoms:
    1. Mechanical Irritation:
    • Caused by the movement of worms leading to harmful effects on the mucosa of the small intestine.
    1. Chemical Substances:
    • Excretory-secretory proteins (ESP) that include antigens and toxins having impacts on host health.
  • Symptoms at Site of Attachment:
    • Catarrhal inflammation, superficial ulcers, mucosal necrosis.
    • Malabsorption leading to poor nutrient absorption.
    • Increased permeability of intestinal mucosa, resulting in watery diarrhea.
    • Decreased enzyme activity influencing nutrient absorption.

Clinical Picture

  • Intestinal Manifestations:

    • Most cases are asymptomatic.
    • Potential symptoms may include:
    • Mucous diarrhea.
    • Colicky pain.
    • Lethargy.

  • Ectopic Manifestations:

    • Eggs may travel via lymphatics to the heart leading to myocarditis and potential heart failure symptoms, which include:
    • Cardiomegaly
    • Cough
    • Dyspnea

  • Neurological Involvement:

    • Parasite may deposit antigens or immune complexes affecting:
    • Brain (causing neurological disease)
    • Spinal cord (resulting in transverse myelitis).
    • Symptoms may include loss of sensory and motor function.

  • Kidney Effects:

    • Antigens to the brain and kidney may cause additional complications.

Diagnosis

  • Diagnosis is primarily achieved through identifying eggs in feces.

Treatment

  • Medications: Praziquantel is the drug of choice; typically administered as a single oral dose.

Prevention and Control Strategies

  1. Proper disposal of human excreta is essential to prevent contamination.
  2. Avoid consumption of undercooked or improperly prepared fish to mitigate infection risk.