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External Parasites. INAG 120 – Equine Health Management November 26, 2008. Ectoparasites. = parasites that attack skin and body openings Flies Black Flies/Midges Ticks Mosquitoes Lice Mites. Mechanism of blood feeding. Females: Blood = Protein

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external parasites

External Parasites

INAG 120 – Equine Health Management

November 26, 2008

  • = parasites that attack skin and body openings
  • Flies
  • Black Flies/Midges
  • Ticks
  • Mosquitoes
  • Lice
  • Mites
mechanism of blood feeding
Mechanism of blood feeding
  • Females: Blood = Protein
  • Males generally subsist on sugars from nectar, etc.
  • EXCEPT: stable flies and horn flies
    • Both sexes feed on blood
  • Flies can detect and follow an “odor plume” at great distances
mechanism of blood feeding4
Mechanism of blood feeding
  • Most flies can detect Carbon Dioxide
  • Flies are also sensitive to heat and moisture
  • Mouth-parts differ between species
    • Blade- or sword-like with serrated edges
  • Once blood starts flowing, fly secretes saliva that prevents coagulation
    • Saliva is allergenic and causes swelling and irritation
life cycles
Life cycles
  • Four major phases of life:
    • Egg
    • Larva
    • Pupa
    • Adult
  • Lifecycles vary in timing and duration depending on species
disease transmission
Disease transmission
  • Insects that transmit diseases = vectors
  • Two types of transmission:
    • Mechanical
    • Biological
  • Deerflies, horseflies, stable flies are thought to be able to transmit anthrax on their mouthparts
  • Mosquitoes and ticks serve as biological reservoirs for other diseases
  • Horseflies
  • Deer flies
  • Stable flies
  • Horn flies
  • Face flies
  • Bot flies
horseflies deerflies
Horseflies & Deerflies
  • Breed in boggy areas
  • Active only during the day in warm weather
  • Deerflies have patterned wings and are smaller
  • Horseflies have transparent wings
horseflies deerflies9
Horseflies & Deerflies
  • Larvae overwinter in the soil
  • Prefer wet mud near or under ponds, marshes, or streams
  • One cow can lose one quarter liter of blood per day in heavily infested areas!
stable flies and horn flies
Stable Flies and Horn Flies
  • Introduced from Europe
  • Spend almost entire adult lives on their host (horses and cattle)
  • Stable flies look like house flies
  • Bite ankles of people, legs of horses
stable flies and horn flies11
Stable Flies and Horn Flies
  • Mouth parts are jabbed into skin like a needle
  • Curved spines at the tip move back and forth making hole deeper and wider
  • Larvae develop in manure and decaying vegetation
face flies
Face Flies
  • Non-biters
  • Closely resemble house flies, largerthan horn flies
  • Feed on mucoussecretions aroundeyes, nose, mouth
  • Lay eggs in freshmanure
  • Can transmit eyeproblems
bot flies
Bot Flies
  • Lay their eggs on legs and chests of horses
  • Horses lick that area ingest eggs
  • Eggs hatch in intestines
  • Internal/External parasites!
  • Deworming program to control bots
black flies midges onchocerca
Black Flies/Midges - Onchocerca
  • Spread a parasitic roundworm, Onchocerca, which causes bumps to form in skin, can also be found in the eye!

Onchocerciasis in the eye of a horse. By permission from Knottenbelt DC, Pascoe RR, Diseases and Disorders of the Horse, Saunders, 2003

  • Lyme disease
  • Rocky Mountain Spotted Fever
lyme disease
Lyme Disease
  • Spirochetal (corkscrew-shaped) bacteria – Borrelia burgdorferi
  • Transmitted through the bite of a deer or black-legged tick
  • Endemic areas for Lyme disease:
    • Northeast
    • Mid-Atlantic
    • Northern Midwest states
    • Northern California
lyme disease transmission
Lyme Disease Transmission
  • Larval deer ticks can become infected with bacteria if they take a blood meal from a rodent already infected
  • Transmit disease with subsequent blood meals
  • Ticks have 3 developmental stages:
    • Larvae, nymph, adult
    • Must have a blood meal before they can molt to next stage
two year life cycle of deer tick
Two-Year Life Cycle of Deer Tick


  • MEAL 1
  • Mouse
  • Bird



Eggs laidadults die

MEAL 2Peak Feeding inpeople, horses, mice

Nymphs moltinto adults

  • Meal 3 (for adults thatdidn’t feedin fall)
  • Person
  • Deer
  • Horse

Larvae moltinto nymphstage






  • Meal 3
  • Person
  • Deer
  • Horse

Nymphs dormant

lyme disease transmission23
Lyme Disease Transmission
  • Ticks live for 2 years
  • Must attach to animal host and feed for 12-24 hours before the bacteria can be transmitted to new host!
  • Natural host of larval ticks = white-footed mouse
  • Host of nymph ticks = humans, rodents, dogs, cats, birds, etc.
  • Host of adult = deer plus others
lyme disease24
Lyme Disease
  • Multisystem disease!
  • Clinical Signs:
    • Joints
    • Musculoskeletal system
    • Neurological system
    • Subclinical infection is common!
    • Development of clinical signs only occurs in 10% of infected animals!
lyme disease and horses
Lyme Disease and Horses
  • Spring and Fall  adult tick most active
  • Found commonly around head, throatlatch area, belly, under tail
  • Prompt removal of tick reduces risk of infection
  • Most common signs = behavioral changes and shifting lameness
lyme disease and horses26
Lyme Disease and Horses
  • Diagnosis is difficult – VERY political!
    • Blood test detects antibodies/exposure to bacteria
    • History of tick exposure (or endemic area)
    • Veterinary clinical exam suggestive of Lyme disease
    • Elimination of other possible diagnoses (lameness exams, x-rays, blood work for other diseases, etc.)
    • Positive blood tests for Lyme Disease
lyme disease treatment
Lyme Disease Treatment
  • Antibiotics –
    • “Gold Standard” = IV Tetracycline (6.6 mg/kg) for 10 days followed by oral doxycycline for 30 days
    • Oral doxycycline alone more common (10 mg/kg 2x per day)
    • Several weeks – with response to therapy within 2-5 days
    • Monitor titers
  • Anti-inflammatories
  • Pro-biotics to replenish gut microbes killed by antibiotics
  • Side Effects!
lyme disease prevention
Lyme Disease Prevention
  • No Vaccine licensed for horses
  • Daily grooming and removal of ticks
  • Tick repellents applied to head, neck, legs, belly and under tail
    • Permethrin or DEET are particularly effective
  • Keep pastures mown
  • Remove brush, woodpiles, etc. to decrease rodent nesting areas
  • May be encountered day and night
  • Many different species
  • Attracted to incandescent light but not to fluorescent light!
  • Most common of external parasites
  • Two varieties:
    • Chewing/Biting – feed on skin cells
    • Sucking – feed on blood
  • Horse with lice:
    • Heavy dandruff
    • Greasy skin
    • Bald spots
  • Can cause weight loss, general unthriftiness, anemia
  • Winterspring problem!
  • Lice are host-specific and spend their entire lives on the animal!
  • Transmitted by direct contact
  • Control with pesticide
  • Microscopic!
  • Can cause mange
    • Sarcoptic mites (head neck, shoulders, flanks, abdomen)
    • Psoroptic/scab mites – skin surface  gooey scabs and crusts
    • Chorioptic mites  most common, seen on skin, cause scaling on legs “Clydesdale itch”
premise control
Premise Control
  • Control standing water
  • Compost manure far away from animals
  • Chain-drag fields and paddocks
  • Feed pelleted feed vs. sweet feed
  • Stall fans
  • Spray barn with Permectrin or Buzz Off