parasites 1

• parasitism is the intimate relationship between 2 organism , where one organism ( the parasite ) lives at the expense of the other.
• Subclinical diseases is a condition where there is no symptoms or very few symptoms of infection and only identified in labs
• Parasites may cause: 

  • Death • Overt clinical disease 

  • Sub-clinical disease 

  • Less than optimum productivity (farm animal production)

  → only a small percentage cause the death of their host.
• Less than optimum productivity (LOP)* caused by parasites 

  → Animals aren't putting on weight as quickly as they might

  → This is where animals are not reaching their genetic potential in terms of their productivity, the weight gain
• Commensalism → 2 species living together but no metabolic dependence ( egg hermit crab and sea anemone .
• Symbiosis → two species living together, each dependent on other ( egg ruminants  and ruminal floral)
• Major parasite groups

   Helminths (worms)

   Arthropods and Protozoa
• Helminths (worms)

   • Nematodes (roundworms)

   • Cestodes (tapeworms) 

  • Trematodes (flukes)
•  Arthropods 

  • Insects (fleas, lice, flies) 

  • Acarina (mites, ticks)

  Mites  and ticks are not killed by insecticides, but by acaricides.
•  Protozoa

   • Single celled organisms
• The relationship involves: 

  • nutritional dependence 

  • immunological defence 

  • integration of life-cycles
• Nematodes Morphological features → (roundworms)

  • Long (mm to >50cm long)

   • Tough elastic cuticle 

  • Muscular pharynx 

  • Nerve ring around pharynx and four longitudinal nerves

   • Separate sexes

   • Female worms (blunt, pointed tail) 

  • Male worms (spicules ± ‘bursa’ – expansion of cuticle
• Nematodes (cont.)

   Feeding behaviour

   • Some swallow gut ingesta and/or host secretions

   • Others suck a plug of mucosa into their buccal cavity (or mouth; plug feeders), leaving a circular ulcer 

  • Others bury their heads deep into the mucosa and suck blood
• Nematodes


  A type of worm with a very simple basic life cycle
• Stages of nematode life cycle

  • Egg
  • L1
  • L2
  • L3
  • L4
  • Adult worm (or L5)
• L3 stage


  • Infective stage that can infect another host
• Nematode life cycle


  1. Egg

  2. L1

  3. L2

  4. L3

  5. L4

  6. Adult worm (or L5)
• Toxocara canis


  • Eggs in the feces
  • Ingested by another dog
  • Infective larva has developed inside the egg
  • Larva is released and migrates around the body
  • Ends up in the small intestine of the next host where it matures
• Cestodes - TAPE WORDS 

  Morphological features 

  • Chain (strobila) of progressively-maturing independent reproductive units (segments or proglottids) 

  • Anchored to intestinal wall by hold-fast organ (scolex, head-end)
•  Pseudophyllidean tapeworms – scolex has 4 longitudinal ‘grooves’
•  Cyclophyllidean tapeworms – scolex often has hooks
• Cestodes Morphological features (cont.)

  → First important point to mention is that tapeworms are hermaphrodites

   • Each segment – male and female reproductive organs 
•  Mature (gravid) segment >100,000 eggs 

  segments grow from the head and oldest at the tail . tail has the eggs and drops off
• cestodes eggs have embryo with hooks and are infective
• Cestodes Feeding behaviour 

  • No alimentary tract

   • Absorb nutrients across body surface covered by a tegument (many minute projections, microthreces, increase the surface area)

  → Just like we lie in a mammalian gut, all increase the area of the surface of the segment for the absorption of nutrients.
• example of cestodes is echinococcus
• cestodes lifecycle is indirect and goes from infected dog with adult tapeworm to egg in feces and intermediate host sheep inhected and has a metacestode stage .
• Cestodes (cont.)

   Examples of epidemiological relationships

   • Predator-prey (e.g. cat eating infected mouse) 

  The adult tapeworm is found in the cat's intestine. And the mouse would be the intermediate host with the cyst like stages

  • Accidental (e.g. horse eating infected pasture mites) 

  horses can get tapeworms/ 

  the tapeworm in the horse little pasture mites

  • Irritation (e.g. infected flea – swallowed during grooming)

  occasionally fleas can act as an intermediate host for tapeworms.
• Types of metacestode Vary in the number of developing scolices they carry:

   • Cysticercus (one scolex) 

  • Coenurus (many scolices)

   • Hydatid cyst (thousands of scolices)
• Cestodes Feeding behaviour 

  • No alimentary tract

   • Absorb nutrients across body surface covered by a tegument (many minute projections, microthreces, increase the surface area)

  → Just like we lie in a mammalian gut, all increase the area of the surface of the segment for the absorption of nutrients.
• Trematodes- flukes 

  Trematodes Morphological features 

  • Typically flat, leaf-like worms (few mms to several cms long)

   • Oral and ventral suckers 

  • Mouth leads from oral sucker to blind ending caecae

   • Most species hermaphrodite, but individuals cross-fertilize 

  • Flukes covered by a metabolically, highlyactive tegument – important role in evasion of host immune response
• example of trematodes is schistosoma
• Trematodes Feeding behaviour

   • Suck blood/ingest tissue debris (pumped into caecae)

  liver
• life cycle of trematodes is indirect. Host is sheep > poos egg in feaces and > egg has miracidium > find intermediate host snail > metacercariae stage development > back into grass > back to sheep>
• Arthropods

   Morphological features 

  • Great diversity, e.g. insects & acarines

   • Separate sexes

   • Insects (3 body divisions, compound eyes, 3 pairs of legs, may have wings) 

  • Acarines (2 body divisions, simple eyes, 4 pairs of legs, no wings, small size)
• Arthropods

   Feeding behaviour 

  Mouthparts show a variety of adaptations:

   • Sucking up liquefied food 

  • Sucking blood

   • Chewing skin debris 

  • Not feeding at all
• Arthropods Life cycle (insects)

   • Simple metamorphosis: egg – nymph – adult (e.g. lice) 

  • Complex metamorphosis: egg – larva – pupa – adult (e.g. fleas, flies)
• Arthropods Life cycle (acarines) → ticks and mites 

  • Same for mites and ticks: Egg – larva – nymph – adult
• Protozoa 

  Morphological features

   • Protozoa are motile, unicellular organisms with a nucleus, endoplasmic reticulum, mitochondria, Golgi body and lysosomes

   • Great diversity, e.g. Trypanosoma and Toxoplasma
• Protozoa Feeding behaviour

   • Pinocytosis (liquid droplets or small particles) 

  → or phagocytosis (larger particles)