Adaptations to a way of life

Parasites

• Parasites (endo-) or (ecto-) feed on living organisms (host) while causing harm
• They gain benefits from them (e.g. unlimited supply of nutrients, H2O, constant temp)
• Can be bacteria, protoctists, viruses, fungi, arthropods, platyhelminthes

Adaptations

• Modification of mouthparts and digestive enzymes
  • Allow attachment to host
  • Allow use of host's food supply, blood or tissues
• Reduction of unnecessary sensory organs and locomotory organs in adult stage
  • Not required as they live in protected, optimum conditions
• Specialised reproductive strategies
  • May have male and female reproductive systems
  • May reproduce asexually
  • May produce large amounts of eggs/larvae
• Resist attack by immune system
  • Inaccessible to immune system (gut)
  • Adapt antigens from host (host recognizes parasite as own tissue)
  • Change its own antigens
• Infect two hosts
  • Asexual reproduction in secondary host
  • Use secondary host to infect primary host
  • Can survive if one host is unavailable
  • Can spread through different environments (water, land)

Toxocara

• Roundworms that live in the small intestine of dogs
• Lifecycle
  • Dogs accidentally swallows worm eggs from contaminated soil
    • Eggs hatch into larvae and cross intestinal wall
    • Distributed in body tissues but remain dormant (inactive)
    • Larvae are reactivated in pregnant female dogs
    • Cross placenta or mammary glands → infect offspring
  • Larvae stay in puppies’ intestine and become mature worms
    • Produce eggs and are excreted in faeces
    • Some larvae spread to lungs, are coughed up, and swallowed back to small intestine
    • This way, puppies can infect humans by licking their face
• In humans, larvae migrate to body organs but cannot reproduce
  • Often they only cause constitutional symptoms
  • Severe or repeated infections may cause swelling of organs or CNS
  • May enter eye and cause reduced vision or blindness
• Adaptations
  • Sticky eggs increase infection
  • Attaches to intestine by hooks
  • Lacks unnecessary organs (locomotory, nervous system)
  • Produces large amount of eggs to increase infection
  • Anaerobic respiration allows survival in intestine
  • Produces enzymes that prevent degradation by host's digestive enzymes
  • Larvae form cysts around them which allows them to hide from immune system