1. INAG 120 – Equine Health Management November 21, 2011
External Parasites
INAG 120 – Equine Health Management
November 21, 2011

2. Ectoparasites = parasites that attack skin and body openings Flies
Black Flies/Midges
Ticks
Mosquitoes
Lice
Mites

3. 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

4. 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

5. Life cycles Four major phases of life:
Egg
Larva
Pupa
Adult
Lifecycles vary in timing and duration depending on species

6. 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

7. Flies Horseflies Deer flies Stable flies Horn flies Face flies
Bot flies
Photo is of Fly Island lab – not somewhere I’d want to live…

8. 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

9. 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!

10. 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

11. 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

12. 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

13. 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

14. Bots

15. 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

17. Ticks Lyme disease Rocky Mountain Spotted Fever
Not generally a problem in horses

18. 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

20. Borrelia burgdorferi

21. 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

22. Two-Year Life Cycle of Deer Tick
LARVAE
MEAL 1
Mouse
Bird
EGGS
NYMPHS
Eggs laid adults die
MEAL 2 Peak Feeding in people, horses, mice
Nymphs molt into adults
Meal 3 (for adults that didn’t feed in fall)
Person
Deer
Horse
Larvae molt into nymph stage
SPRING
SUMMER
WINTER
FALL
ADULTS
Animated – clicking advances development.
Meal 3
Person
Deer
Horse
Nymphs dormant

23. Lyme Disease Transmission
Ticks live for 2 years
Must attach to animal host and feed for 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

24. 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

25. 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

26. 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
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.

27. 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!
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

28. 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
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 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.
Keeping pastures mowed decreases the environment for ticks and lessens tick bites.

29. Mosquitoes May be encountered day and night Many different species
Attracted to incandescent light but not to fluorescent light!
Can breed in less than 1 inch water.
Carriers for several important diseases (ask class which ones)
Keep standing water to a minimum
Fans may help
Most active at dusk and dawn.

30. Lice Most common of external parasites Two varieties: Horse with lice:
Chewing/Biting – feed on skin cells
Sucking – feed on blood
Horse with lice:
Heavy dandruff
Greasy skin
Bald spots
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

31. 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

32. 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”
Transmission of mites is by contact; horse with mites should be isolated; dispose of infested bedding
Treatment:
Organophosphate insecticides or lime-sulfur solution can be used by spraying, sponging, or dipping. repeated at 12- to 14-day intervals at least 3-4 times. OR: oral administration of ivermectin or moxidectin at 200 µg/kg - several treatments are required 2-3 wk apart.
Treat all contact animals.

33. Horse with psoroptic mange – actually very rare in horses

34. Mange…
 Psoroptic Mange
Chorioptic Mange 

35. Fly Control Reduce standing water (mosquitoes)
Remove and/or compost manure (stable flies)
Mow pastures and clear brush (ticks)
Sheets and masks – check horse daily for sores, weeping eyes, etc.
Fly sprays have very short effectiveness – especially if horse sweats or gets bathed.
Spot-on treatments? Not sure if studied. Erin has used them and likes them but feels they only work for about a week.

36. More Fly Control
Tabanid trap – works for horse flies and deer flies. Liquid fly traps don’t work for tabanids. Placement: in wide open for horse flies, near woodline for deer flies.
Fly paper, etc. – watch placement (near ground for stable flies)

37. 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

38. 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!
Flies can travel great distances, so if your neighbor doesn’t practice good fly control, you will still have a fly problem.