External Parasites

INAG 120 – Equine Health ManagementNovember 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

Flies

Horseflies Deer flies Stable flies Horn flies Face flies Bot flies

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

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

Not generally a problem in horses

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

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

ADULTSMeal 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”

Mange…

Chorioptic Mange

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

Fly Parasites

Gnat-sized parasitic wasp Female wasp lays eggs in larvae of

stable/house flies Eggs hatch feed on developing larvae

Release more fly parasites every 3-4 weeks to keep up with flies

Effective, but depends on neighbors!