Lung

• Paragonimus westermani


  Common name: Oriental Lung Fluke
• Definitive host


  • Humans
  • Carnivores
• First intermediate host


  • Snail
  • Antemelania asperata
  • Antemelania dactylus
• For trematodes, the snail is the first intermediate host
• Snail as intermediate host is species-specific; must be specific on the scientific name
• Second intermediate host


  • Crabs
  • Crayfishes
  • Crustaceans
  • Sundathelphusa philippina (Mountain crablets)
• Adult Paragonimus westermani


  • Reddish-brown
  • 7 – 12 mm by 4 – 6 mm by 3.5 – 5 mm
  • Resembles coffee bean
  • Rounded anteriorly, slightly tapered posteriorly
  • Tegument is covered with single-spaced spines
  • Excretory bladder is large and at the center dividing the worm into 2 equal parts
  • Intestine is unbranched
  • Two testes, deeply lobed, opposite to each other, located midway between ventral sucker and posterior border of the body
  • Ovary is anterior to the testes, posterior to the ventral sucker, with 6 unbranched lobes
  • Testes and ovary are both lobulated
  • Uterus is adjacent to the ovary
  • Vitellaria (particle-like located on the side) are extensively branched up to the tail
• Cercaria


  • Ellipsoidal body, small tail (Microcercous cercaria)
  • Covered with spines
• Ova


  • Yellowish-brown
  • Unembryonated
  • Operculated, with thickened posterior end (abopercular end)
  • Operculum if there is a line-like structure
  • Thickened abopercular area indicates Paragonimus westermani
  • Seen in sputum and feces
• Life Cycle of Paragonimus westermani

  1. Raw or undercooked crablets is eaten by humans

  2. Humans ingest metacercaria from the second intermediate host. The encysted metacercaria from the tissue of the ingested second intermediate host excyst in the duodenum of the definitive host

  3. Metacercaria migrates to the lungs, becomes adults, and lay eggs

  4. Eggs can be expectorated through the sputum, or excreted in the feces

  5. Eggs are released to external environment, becomes embryonated, and eventually releases miracidium

  6. Miracidium infects the first intermediate host (snail), where once it penetrates the skin, it loses its cilia and becomes a sporocyst

  7. Sporocyst undergo asexual reproduction, becomes redia

  8. Redia bursts, releasing cercaria into the environment

  9. Free-swimming cercaria infects second intermediate host where it encyst in the tissues to become metacercaria

  10. Humans (definitive host) ingest infected secondary intermediate host and metacercaria excysts in the duodenum, migrates in the body and matures into an adult and the cycle continues

  
• Classical presentation


  • Chronic cough with thick brownish red (rusty colored) sputum due to adult worm and ova
  • Fever, myalgia
  • Hemoptysis mistaken as TB
  • Pleural effusion, pneumothorax due to damage caused by the worm

  
• The pneumothorax will burst and the air that is being inhaled will be released into the pleural cavity
• Teguments of P. westermani

  • Has spines that can irritate or rupture the lung resulting in pneumothorax
  • The irritation will elicit inflammatory response resulting to pleural effusions (fluid in pleural cavity)
• Fibrotic Capsule in the Lungs

  • Allows the egg to escape respiratory tract where they are moved up and out by ciliary epithelium along with lung exudates
  • It is released because of the ciliary clearance of the respiratory epithelium
  • It is released because of the proliferation and completion of the life cycle

  
• Extrapulmonary symptoms


  • Due to granuloma formation or cyst/abscess formation
  • Muscle, abdominal organs like liver, genitals, brain, hear, lymph nodes