Endoparasites & Ectoparasites

• Parasitology


  The study of organisms that live in or on another organism, from which they derive their nourishment
• Parasitology


  • Requires: Mode of entry
  • Availability of susceptible host
  • Accommodating location and environment
  • Mode of exit from host
• Vector (carrier of parasite)


  Can be mechanical or biological
• Life Cycle


  A period of time spent in a host organism and can be divided into phases of growth, reproduction and transmission
• Direct life cycle


  A life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species
• Indirect life cycle


  A type of a life cycle wherein a parasite is transmitted from one host to another by using a vector or by an intermediate host of another species. A parasite with an indirect life cycle would therefore require more than one type of host species to complete their life cycle
• Kingdom Protista


  Subkingdom Protozoa
• Protozoans


  • Single-cell organism with nuclei containing DNA
• Protozoan life cycle


  1. Asexual: binary fission, schizogony, budding (separation of a body into 2 new bodies)

  2. Sexual: syngamy, conjugation (fusion of 2 cells in reproduction)
• Trophozoite


  Vegetative form can feed, move, and reproduce; fragile
• Cyst


  Transmission form; walled, sturdier (resting or dormant stage of microorganism)
• Parasitology Classification: Phylum Platyhelminthes

  • Cestodes (tapeworms)
  • Trematodes (flukes)
• Cestodes (Tapeworms)


  • Multicellular with no body cavity
  • Parenchyma
  • Head (scolex) with suckers (bothria) and maybe a snout (rostellum)
  • Body (strobila) composed of segments (proglottids)
  • Proglottids near head are immature
  • Proglottids toward the tail become progressively more sexually mature
• Gravid proglottids


  • Contain developed embryo with six hooks in three pairs (hexacanth embryo or oncosphere)
  • Contain zygote that develops into ciliated embryo (coracidium)
• Cestode Life Cycle


  1. Always indirect

  2. One or two intermediate hosts

  3. Domestic animals: definitive or intermediate host

  4. Transmission: Ingestion of larval stages

  5. Transmission: Ingestion of cestode egg
• Cestode Eggs

  • Dipylidium Caninum
  • CORACIDIUM is the oncosphere of a tapeworm at about the time of hatching while still surrounded by the embryophore
• Trematodes (Flukes)


  • Flatworm with no body cavity
  • Unsegmented; leaf-shaped
  • Anterior and posterior suckers
  • Outer wall or cuticle
  • Simple digestive tract
  • Mostly pathogenic; some are not
• Trematode Life Cycle


  1. Multiplication: One or more intermediate hosts

  2. Sexual multiplication in definitive host

  3. Asexual reproduction in intermediate host

  4. Eggs: operculated

  5. Larval stages: Miracidium, sporocyst, redia, cercaria, metacercaria

  6. Transmission: Ingestion or skin penetration
• Nematode Anatomy


  • Cylindrical body with body wall cuticle
  • Hypodermis
  • Longitudinal muscle layer
  • Body cavity with digestive tract and reproductive organs
  • Nervous system and excretory system
  • No respiratory system
  • Separate sexes
• Nematode Life Cycle

  1. Standard life cycle

  2. Developmental stages

  3. Infective stage

  4. Direct life cycle

  5. Indirect life cycle

  6. Transmission

  7. Migration

  8. Final site of infection
• Nematodes of Veterinary Significance


  • Ascaroidea (Roundworms)
  • Strongyloidea (Hookworms)
  • Trichostrongyloidea (Roundworms)
  • Metastrongyloidea (Lung Worms)
  • Oxyuroidea (Pinworms)
  • Trichuroidea (Whipworm)
  • Filaroidea (HeartWorm)
  • Rhabditoidea (parasite that lives in the soil)
  • Spiruroidea (GI Parasite)
  • Dracunculoidea (Round Worm in the skin tissues)
  • Dioctophymoidea (Kidney Worm)
• Phylum Acanthocephala


  Thorny-Headed Worms
• Acanthocephala Life Cycle


  1. Adults in small intestine; eggs passed in feces

  2. Eggs: embryonated, surrounded by three to four envelopes

  3. Indirect life cycle

  4. Transmission: ingestion of intermediate host
• Acanthocephala are rarely seen
• Ectoparasite


  A parasite that resides on the outside surface of the body
• Host


  Provides nutrition and possibly protection for the parasite, can be periodic or definitive
• Intermediate host


  Harbors the larval, immature, or asexual stages of a parasite
• Insect


  • 3 distinct body parts (head, thorax and abdomen), have 6 legs (3 pairs) and antenna or suckers present
• Insect class includes


  • Fleas and lice
• Arachnid


  • 2 distinct body parts (head and abdomen), have 8 legs (4 pairs)
• Arachnid class includes


  • Ticks and mites
• Nematoda


  • No distinct body parts, resemble worms, includes leeches
• Orders within Insect class

  • Siphonaptera (fleas)
• Siphonaptera (fleas)


  • No wings, powerful hind legs for jumping, siphon mouthpart for sucking blood, not common on horses or ruminants
• Flea


  Intermediate host for roundworms and tapeworms, large enough to be seen by the naked eye, most animals and humans are allergic to fleas
• Flea Dirt


  Feces on their hosts
• Flea species


  • Ctenocephalides canis, Ctenocephalides felis
• Orders within Diptera (fly) class


  • Diptera (very large order of insects in which the adults feed on blood, saliva, tears, and mucous, the larva can develop inside an organ or just under the skin of its host)
• Bot fly (Cuterebra)


  Bots - the larva and pupal stage of many common flies, normally found on livestock, sometimes on small animals, most closely related to maggots
• Bot fly (Cuterebra)


  Burrow into the mucous membranes of a host and migrate to the stomach and intestines, later pass in feces and mature into adult flies