External Parasites

1. 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

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, largerthan horn flies • Feed on mucoussecretions aroundeyes, nose, mouth • Lay eggs in freshmanure • Can transmit eyeproblems

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 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 SPRING SUMMER WINTER FALL ADULTS • Meal 3 • Person • Deer • Horse Nymphs dormant

23. 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

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

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!

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

29. Mosquitoes • May be encountered day and night • Many different species • Attracted to incandescent light but not to fluorescent light!

30. 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

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”

34. Mange…  Psoroptic Mange Chorioptic Mange 

35. Fly Control

36. More Fly Control

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!