External Parasites INAG 120 – Equine Health Management
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External Parasites INAG 120 – Equine Health Management






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  • Though horses have been experimentally infected none have developed clinical symptoms from the infection. On necropsy of experimentally infected horses mild lesions have been found in the skin, muscle, connective tissue, and around nerves and blood vessels, particularly those close to joints. Further epidemiological studies where the history of disease from both sero-positive and sero-negative horses is compared there has not been any clear indication that the sero-positive horses have had an increase incidence of disease. This throws the whole question of whether B. burgdorferi causes disease in horses or not.
  • Gold Standard - The horse had some other problem that would have gotten well without treatment; The tetracycline treated some other infection beside B. burgdorferi; Tetracycline has some non-specific anti-inflammatory action that relieve symptoms from another cause. IV tetracycline at 6.6 mg/kg every 24 hours (divided into a twice daily treatment) for 10 days followed by 30 days of oral doxycycline at 10 mg.kg every 12 hours for at least a month and continued until titers begin to fall has worked in many cases. Side effect – some horses show toxicosis to the dead bacteria  worsening of symptoms, reluctance to move  CAN LEAD TO LAMINITIS!!!! Watch horse for signs of laminitis during first week of treatment
  • There is a vaccine for humans – Lymerix  Though experiments have shown only mild reactions with the human vaccine some people feel that their symptoms have significantly worsened up following vaccination and it is felt that carrying a titer to Lyme disease may increase the chance of autoimmune reactions. This vaccine has been used in horses DEET has been used extensively in horses and they appear to tolerate it very well.
  • Horses can get lice from poultry (so if you have a horse with lice, get rid of the birds) BUT not from cattle and horse lice can’t be transmitted to people
  • Transmission of mites is by contact; horse with mites should be isolated; dispose of infested bedding
  • Horse with psoroptic mange

External Parasites INAG 120 – Equine Health Management External Parasites INAG 120 – Equine Health Management Presentation Transcript

  • 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
    • 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 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
    • Four major phases of life:
      • Egg
      • Larva
      • Pupa
      • Adult
    • Lifecycles vary in timing and duration depending on species
  • 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
  • Flies
    • Horseflies
    • Deer flies
    • Stable flies
    • Horn flies
    • Face flies
    • Bot flies
  • 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 & 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
    • 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 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
    • Non-biters
    • Closely resemble house flies, larger than horn flies
    • Feed on mucous secretions around eyes, nose, mouth
    • Lay eggs in fresh manure
    • Can transmit eye problems
  • 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
  • Bots
  • 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
  • Ticks
    • Lyme disease
    • Rocky Mountain Spotted Fever
  • 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
  • Borrelia burgdorferi
  • 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
    • MEAL 1
    • Mouse
    • Bird
    Larvae molt into nymph stage Nymphs dormant NYMPHS Nymphs molt into adults ADULTS
    • Meal 3
    • Person
    • Deer
    • Horse
    • Meal 3 (for adults that didn’t feed in fall)
    • Person
    • Deer
    • Horse
    Eggs laid adults die MEAL 2 Peak Feeding in people, horses, mice
  • 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 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
    • 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 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
    • 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
    • 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
  • Mosquitoes
    • May be encountered day and night
    • Many different species
    • Attracted to incandescent light but not to fluorescent light!
  • Lice
    • 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
  • Lice
    • 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
  • Mites
    • 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”
  • Psoroptic Mange…
  • Fly Control
  • More Fly 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