Ectoparasites and their control

• Ectoparasites seen on cats, dogs, rabbits, cattle, sheep and horses

  • Sarcoptes Scabiei
  • Sarcoptic mange
  • Psoroptes ovis
  • Chorioptes bovis
  • Demodicosis
  • Cheyletiellidae
  • Hard ticks - Ixodidae
  • Lice - pediculosis
  • Myiasis
• Sarcoptes Scabiei


  • Intense itching, inflammation, hair loss, self-trauma
  • Egg - adult = 17-21 days (3 weeks)
  • Survive 2-3 weeks off host
  • ZOONOTIC
• Sarcoptic mange


  • Site of infestation: Dog - pinnae and elbows and ventrum, Pigs - external ear canals and dorsum
  • Can be asymptomatic
  • ZOONOTIC
• Psoroptes ovis lifecycle


  1. Egg -> larvae -> protonymph -> tritonymph -> adult

  2. 2-3 days between each stage

  3. Adult lifespan = 20 days (3 weeks)

  4. Off-host = survive up to 16-18 days
• Chorioptes bovis


  • Survival off host = 3 weeks
  • Life cycle = 3 weeks
  • Can have 20 eggs
  • Less severe pathogenic effects on host than Psoroptes mites
• Chorioptes vs Psoroptes


  • Psoroptes - funnel-shaped sucker
  • Chorioptes - cup-shaped sucker
• Demodicosis


  • Life cycle = 18-24 days
  • Obligate parasite
  • Deep in dermis and difficult to find
  • Passed from dam to young with suckling
  • Demodex canis and Demodex injai
• Cheyletiellidae


  • Can survive up to 10 days off host
  • Mild but highly contagious dermatitis
  • ZOONOTIC
• Hard ticks - Ixodidae

  • Life cycle up to 3 years
  • Larvae feed on small mammals
  • Nymphs and adults feed on larger hosts
• Ixodes Ricinus


  Most common tick in the UK
• Lice - pediculosis lifecycle

  Egg -> 1st nymph -> 2nd nymph -> 3rd nymph -> adult
• Lice


  • Outdoor pigs
  • Obligate, host specific parasites
  • Variable pruritis, alopecia, excoriation
  • Anaemia (calves)
• Myiasis lifecycle


  1. Egg -> feeding larvae -> wandering larvae -> pupae -> adult

  2. Eggs hatch after 12-24 hours and the larvae feed for about 3 days before dispersing
• Ideal agents for controlling parasites

  • Destroy all parasites at all stages of their lifecycle
  • Are rapid in action
  • Are non-toxic to the host
  • Provide a minimum residue in the host and are rapidly detoxified in the environment
  • Resistance in parasites should be slow to develop
• Classification of Ectoparasiticides


  • Drugs which act upon the insect nervous system: Ach neurotransmission (organophosphates, carbamates, imidacloprid), Axonal sodium (Na+) channels (pyrethroids), Octopamine system (amidines), Cl- channels (avermectins, fipronil, isoxazolines)
  • Drugs which act as insect growth regulators
• Factors that influence the successful control of parasites

  • Practice policy
  • Cost
  • Ease of application
  • Duration of activity
  • Adverse effects: Animal, owner, environment
  • Resistance
  • Treating more than 1 parasite
  • Prophylaxis
  • Meat, milk withdrawal
  • Life cycle: Mites, lice, fleas ~3 weeks
  • Obligate parasite
  • Host immunity and health
  • Environmental survival of various life cycle stages
  • Zoonotic potential
  • Vector borne disease (risk to host and zoonotic risk)
• Fleas - lifecycle and treatment

  • Prevent infective stage from reaching definitive host
  • Prevent immature parasite stages from reaching the environment or intermediate host/vector
  • Modify the within-host environment to make it harder for parasites to survive and propagate
  • Modify the external environment to make it harder for free-living or within-vector stages
• Fleas - treatment and control

  • Treatment of environment is key as much of the life cycle is spent off the host
  • Basic control: thorough vacuuming, apply insecticide/insect growth inhibitor
  • Hypersensitive animals can react to very few fleas and their bites
  • Treat all susceptible animals in the home
  • House is easily re-infested
• Formulations and their effect on efficacy for eliminating adult flea (and lice) burdens

  • Dips, shampoos, collars, powders, sprays
  • Spot-on preparations and tablets
• Factors affecting efficacy and duration of action

  • Hair coat length
  • Bathing, swimming and shampooing
  • Body weight an dose
• Insect Growth and Development Inhibiors (IGIs)

  • Do not kill adult fleas
  • Decrease the viability of eggs and/or interfere with the development of larvae and pupae
  • Chitin synthesis inhibition - lufenuron
  • Methoprene and pyriproxidfen - Minimal mammalian toxicity
• Insect growth and development inhibitors

  • IGIs do not interrupt the pupal stage, Pupae and pre-emerged adults unaffected and viable for long periods
  • Apply IGIs to the environment
  • Topically administered IGIs may be distributed through the animal's bedding or nesting places of direct contact
• Ticks - life cycle and treatment

  • Prevent infective stages from reaching the definitive host
  • Prevent immature parasite stages from reaching the environment or intermediate host/vector
  • Modify the within-host environment to make it harder for parasites to survive and propagate
  • Modify the external environment to make it harder for free-living or within-vector stages
• As little as 2% of tick life cycle spent on the host, making them difficult to control
• Livestock tick control


  • Generally, for most sheep flocks in high-risk areas, acaricides are the main form of control
  • Diazinon (OP) is the active ingredient contained in plunge dips licensed for use in the UK, with deltamethrin, alpha-cypermethrin and cypermethrin available as pour-on applications
• Tick control in dogs and cats

  • Tablet
  • Collar
  • Spot-on
  • Combination products
• Tick control in dogs and cats

  • Duration of activity or repellent effects: Weeks to months
  • Speed of kill: 12-48 hours
  • Which ticks are covered?
  • Data on insects? Leishmaniosis
  • Minimum age and weight
  • Pregnancy
  • Product ingredients: Fipronil, Permethrins, Ixoxazolines
  • Cost: Over-the-counter or prescription
• Routine sheep scab (Psoroptes) control

  • Dips - organophosphate - diazinon
  • Injectable - macrocyclic lactones
  • Assume all arrives are infected and treat them
  • Treat away-wintered lambs before departure
  • Check fences and gates - unplanned mixing!
  • Co-ordinate with neighbours
  • Treat all sheep on farm in autumn/winter
  • Reportable in Scotland
• Treatment of bovine mites

  MACROCYLIC LACTONES + Permethrin