External Parasites INAG 120 – Equine Health Management November 21, 2011.
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Transcript of External Parasites INAG 120 – Equine Health Management November 21, 2011.
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
Horseflies & Deerflies
Tabanid species 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, largerthan horn flies
Feed on mucoussecretions aroundeyes, nose, mouth
Lay eggs in freshmanure
Can transmit eyeproblems
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
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
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
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
SPRING SUMMER
WINTER FALL
EGGS LARVAE MEAL 1•
Mouse
• Bird
Larvae moltinto nymph
stage
Nymphs dormant
NYMPHS
Nymphs moltinto adults
ADULTS
Meal 3• Person• Deer• Horse
Meal 3 (for adults thatdidn’t feed
in fall)• Person• Deer• Horse
Eggs laidadults die
MEAL 2Peak 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
bacteria1. History of tick exposure (or endemic area)2. Veterinary clinical exam suggestive of Lyme
disease3. Elimination of other possible diagnoses
(lameness exams, x-rays, blood work for other diseases, etc.)
4. 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 TICK CONTROL!! 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
Winterspring 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”
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
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