MICROBIOLOGY

• E. granulosus sensu lato complex
  • Composed of a complex of 10 specific genotypes, G1–10, that has been divided into species: E. granulosus sensu stricto (G1–G3), E. equinus (G4), E. ortleppi (G5), E. intermedius (G6–G7), and E. canadensis (G8–G10)
• Additional Echinococcus spp. include E. shiquicus, E. vogeli, E. felidis, E. oligarthra, and E. multilocularis.
• Zoonotic cestode parasite: two major forms for human clinical disease.
  
  • Echinococcus granulosus: a most common cause of cystic echinococcosis (CE).
    • Intermediate hosts: sheep, cattle, pigs, camels, goats
    • Definitive hosts: dogs and other canids that eat internal organs of the intermediate host [Fig 1].
      
      • Humans are indirectly infected by ingesting eggs from canid feces via environmental contamination of food/water.
  • E. multilocularis: less common, cause of alveolar (tumor-like) echinococcosis (AE).
    • Intermediate hosts: rodents, domestic pigs, wild boars, dogs and monkeys
    • Definitive hosts: foxes, dogs, cats
    • Most cases are described in Europe and Asia. Rare cases are described in North America.
  • Other:
    • Echinococcus vogeli (very rare): rodents intermediate hosts, while bush dogs are the definitive host in South and Central America.
    • E. oligarthus (rare)
• Larval forms (metacestodes) are infectious to humans.
  • Organism growth in the host is extremely slow, hence often asymptomatic x many years.