VM1032 - Endoparasites

• What is an endoparasite?

  A parasite living within a host's body
• What are the two types of endoparasites?

  • Extracellular: live on/within host tissue
  • Intracellular: live inside host cells
• What are the two subdivisions of endoparasites?

  Flatworms and roundworms
• What is the prepatent period?

  Time from infection to life cycle stages appearing
• What defines a patent infection?

  Oocysts, eggs, or larvae are shed into the environment
• What are the characteristics of flatworms?

  • Flattened body with suckers
  • Most are hermaphrodites
  • Metabolically active body surface
• What are the two major groups of flatworms?

  • Cestodes: tapeworms
  • Trematodes: flukes
• What is the body structure of cestodes?

  Segmented and ribbon-like
• How do cestodes absorb nutrients?

  Through their body surface
• What is the primary location of adult cestodes in the host?

  Small intestine
• What are proglottids in cestodes?

  Independently maturing reproductive segments
• What is the scolex in cestodes?

  An attachment organ at the anterior end
• How are proglottids produced in cestodes?

  • Produced at the base of the scolex
  • Push older proglottids back
• Why is faecal examination unreliable for detecting cestodes?

  Whole proglottids are shed, not eggs
• What are the four main cestode families of veterinary species?

  • Taeniidae
  • Anoplocephalidae
  • Dipylidium
  • Davainea
• Describe the life cycle of a cestode.

  1. Gravid proglottid reaches end of tapeworm
  2. Proglottid separates and releases eggs
  3. Eggs hatch in intermediate host
  4. Embryo migrates and becomes metacestode
  5. Metacestode waits to be ingested by final host
  6. Adults develop in final host
• What are metacestodes in cestodes?

  • Thin-walled fluid-filled cysts
  • Protoscolices grow from cyst wall
  • Develop into adults when ingested
• What is the shape of Taenia gravid segments?

  Rectangular and longer than broad
• How can Taenia eggs be distinguished?

  They cannot be distinguished from echinococcus eggs
• What are the characteristics of T. saginata?

  • Beef tapeworm
  • Humans infected by undercooked beef
  • Metacestodes settle in muscle
• What are the characteristics of T. solium?

  • Pork tapeworm
  • Metacestodes can infect human brain
  • Significant health problem globally
• What is the health impact of T. solium?

  Causes 30% of epilepsy cases in endemic areas
• What are the main Taenia species affecting dogs?

  • Taenia ovis
  • Taenia hydatigena
  • Taenia multiceps
• What is the prepatent period for Taenia species in dogs?

  6-8 weeks
• What is the significance of Taenia hydatigena?

  Commonest in the UK, affects sheep
• What are the characteristics of Echinococcus?

  • Smaller than Taenia
  • Scolex embeds in mucosal villi
  • Shed few proglottids
• What are the two major species of Echinococcus?

  • E. granulosus: hydatid cyst metacestode
  • E. multilocularis: alveolar cyst metacestode
• What is hydatid disease?

  • Caused by E. granulosus
  • Space-occupying cysts in tissues
  • Common in humans and livestock
• What is alveolar hydatid disease?

  • Caused by E. multilocularis
  • Rapidly growing invasive cysts
  • Lethal zoonosis
• What are the main trematodes of veterinary interest?

  • Fasciola
  • Dicrocoelium
  • Paramphistomum
  • Schistosoma
• Describe the lifecycle of Fasciola.

  1. Egg passed in faeces
  2. Miracidium hatches in water
  3. Miracidium penetrates snail
  4. Asexual reproduction produces cercariae
  5. Cercariae leave snail
  6. Metacercaria form on vegetation
  7. Metacercaria eaten by final host
  8. Fluke matures in liver
• What is Fasciola hepatica?

  Liver fluke affecting various mammals
• What is the intermediate host for Fasciola hepatica?

  Galba trunculata, a snail
• What is the significance of the temperature for Fasciola hepatica eggs?

  Hatch only in temperatures >10˚C
• What are the disease forms caused by Fasciola hepatica?

  • Acute disease: fatal liver damage
  • Subacute disease: weight loss and anaemia
  • Chronic disease: liver fibrosis and production loss
• Describe the basic life cycle of nematodes.

  1. Females produce eggs in faeces
  2. Four larval stages (L1-L4)
  3. Moulting occurs at each stage
  4. Immature adults mature and lay eggs
• What are the four bursate nematode superfamilies?

  • Trichostrongyloidea
  • Strongyloidea
  • Ancylostomatoidea
  • Metastrongyloidea
• What is the general pattern of the strongyle lifecycle?

  1. Strongyle egg passed in faeces
  2. L1 develops and hatches
  3. L3 climbs onto grass
  4. Infective L3 is swallowed by host
  5. L3 reaches predilection site and moults
  6. Maturation to adult and egg production
• What factors influence strongyle epidemiology in the UK?

  • Ambient temperature
  • Rainfall
  • Seasonal patterns of pasture contamination
• What are type 1 and type 2 diseases in nematodes?

  • Type 1: Active lifecycle in summer-autumn
  • Type 2: Mass emergence from hypobiotic state in late winter-spring