Worms

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Worms

• and Worming

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? Strongyles-

• most prevalent type of worm
• ? 56 known species
• ? Can be in large or small form
• ? large strongyles are also known as bloodworms
• ? small strongyles feed on intestinal mucosa
• ? Strongyles-known as S. vulgaris, S.edantus and
  S. equinnus

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? The horse and the worm a long history

• Horses and worms have coexisted ever since
  eohippus, predecessor to the modern horse, first
  walked on the plains of the North America, Asia,
  Europe, and Africa.

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• Worms, in their various forms, relied on
  differing strategies of survival in order to
  survive the various environmental challenges
  which present themselves throughout these
  climates.

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• Without going into detail as to theses various
  life cycles, let me point out that basically all
  of these bugs only present a problem when they
  are present inside of the horse.

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• How they get there and how to avoid them in a
  modern management system is important, but for
  now let us just concentrate on the fact that
  these bugs, if present in the environment, will
  infest the horse, and multiply to infest others,
  just as they have for eons.

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• That is natural, and is not a problem, provided
  the odds are not stacked too greatly in favor of
  the worm.

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Large strongyles

• ?are laid in large intestine and are passed out
  with the feces
• ? Eggs hatch in dung pile

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• ? Develop there into 2nd and 3rd stage larvae
• ? Take 5-10 days
• ? 3rd stage larvae migrate to blades of grass,
  ingested by horse
• ? Migrate to cecum and colon--encapsulate and
  undergo a molt

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• ? 8 days later become 4th stage--migrate to
  mesenteric artery via arterioles
• ? Thrombus and or emboli can form causing death
  or aneurysm to intestine or arterial wall
• ? return to intestine as 6th stage larvae, mature
  sexually, reproduce
• ? Benzimidazoles and avermectins effective
  against

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Small strongyles

• ? are not as devastating to animal as are large
  strongyles, yet nevertheless cause unthriftiness,
  weight loss, ulcers in digestive tract.
• ? Small strongyles may encapsulate- taking years
  to become active-wormers ineffective when
  encapsulated.

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Pinworms

• ? Oxycuris equi
• ? not as critical a problem as are strongyles
• ? cause a great deal of discomfort
• ? rubbing, hair loss are typical clues to
  infection
• ? Mature females-ceveral cm. long) migrate down
  intestine to lay eggs outside anus
• ? In 4-5 days eggs fall off and are re-ingested.

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Ascarids

• ? Roundworms or Parascarus equorum
• ? rarely seen in adults
• ? found in feces of young horses at 10-12 weeks
• ? after 12 to 18 months numbers decrease, rarely
  found in older horses
• ? when ingested migrate to liver, lungs, causing
  pneumonia and other problems
• ? causes unthriftiness and may cause gut rupture
• ? worms can be 15 or more inches in length

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Strongyloides

• ? S. westeri
• ? develop immunity with age
• ? ran over 6 months
• ? free living and parasitic forms exist
• ? can infect horse through mouth or oral mucous
  membrane. Once swallowed migrate to intestine.
• ? Or can pass through mares milk

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Strongyloides

• ? S. westeri
• ? develop immunity with age
• ? ran over 6 months
• ? free living and parasitic forms exist
• ? can infect horse through mouth or oral mucous
  membrane. Once swallowed migrate to intestine.
• ? Or can pass through mares milk

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Bots

• ? Gastrophilicus intestinalis
• ? yellow colored eggs
• ? five day incubation
• ? burrow into tongue
• ? three weeks, 6-7 mm long
• ? attach to tongue, then are swallowed
• ? remain in stomach for 9 months, develop into
  3rd stage larvae
• ? larvae pass out, then pupate
• ? live for only 5 days or so but may lay
  thousands of eggs in that time

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Tapeworms

• ? 3 species of Anacephala
• ? do not float in EPG tests and are therefore
  harder to detect
• ? require intermediate host-oribatid mite- before
  becoming infectious
• ? Horse eats mite and becomes infected
• ? can cause enteritis, unthriftiness, poor growth

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Dewormers

• ? Should be careful to use effective drug
• ? should start foals at one to two months of age
• ? rotation is good idea

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• ? Can rotate monthly or yearly or by strategy
• ? rotate all horses at same time
• ? new arrivals should be isolated

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• ? EPG's should be used to determine type of
  parasite present
• ? pasture should be rested if possible
• ? avoid overcrowding
• ? Do not spread fresh manure on pastures being
  used
• ? follow label directions
• ? make sure to give full dose