Internal Equine Parasites

Parasites• Small organisms that live on or in and derive their food from a

host organism, such as a horse• Be beneficial or detrimental • Primary management goal is to control harmful internal

parasites that can lower efficiency, performance, digestion and can even kill a horse

• Symptoms:• May develop slowly• Weakness• Unthrifty appearance• Emaciation• “potbelly” • Tucked up flanks• Rough hair coat• Slow growth

Parasites• Spend their life cycle in the host• Generally be classified as roundworms• Six groups of roundworms:

• Ascarids• Small Strongyle• Large Strongyle (Bloodworms)• Threadworms• Pinworms• Stomach Worms

• Ascarids, strongyle, and pinworms are major concern for the horse

• An insect that has an internal stage of development in the horse is the stomach bot

• To minimize that life cycle must be broken

Ascarids• AKA large roundworms• Largest parasites that live in the horse• Grow 30.5 to 38.1 cm (12 to 15 in) and are about

the diameter of a lead pencil• Primarily problem in young horse• Older horses develop immunity

Ascarids• Life Cycle:• Starts with mature female laying eggs in the SI• Eggs pass out in the feces• After they are outside the horse (~2wks), develop into the infective

stage• Eggs are swallowed when horse eats grass, feed and feces and

drinks water• Eggs then hatch into larvae stage• Larvae then burrow into the wall of the SI • Enter bloodstream from SI where that are carried to the liver and

heart• Migrate through the liver and heart, and veins that drain these

organs, and travel to the lungs• From the lungs they are coughed up and swallowed • Upon reentering the SI they mate, females produce eggs

Ascarids• Damage liver, heart, and lungs• Heavy infestations can block the SI causing colic• May rupture intestinal lining, causes peritonitis

and death• Eggs are resistant to environmental conditions

and can live for years before ingested• Control requires thorough cleaning of stalls before

foaling, preventing fecal contamination of feed and water buckets, frequent manure removal, frequent drug treatment

Strongyles• Most serious threat to horse’s health• Severe infestation is common in horses

permanently grazed on pastures• Symptoms (condition is called strongylosis):• Low appetite• Anemia• Emaciation• Rough hair coat• Sunken eyes• Digestive disturbances• “Tucked up” appearance

Strongyles• Life Cycle:

• Eggs are laid in intestines• Pass out in feces and continue to develop 1-2 days • After ~ week, larvae become infective, move up blades of grass,

horse ingests• Migrate through various body tissues causing extensive damage• After they return to the small intestine, they attach to the lining of

the gut where they mature• Cause arterial damage and the development of small

blood clots in the arteries• Aneurysms may develop and burst

• Horse will bleed internally and die• May break loose and become lodged in smaller arteries

blocking blood flow to certain tissues and organs

Strongyles• Management control involves removal of manure

at least 2x weekly• Infective larvae are not as resistant to the

environment as ascarid eggs and usually cannot live beyond one year

• Pasture rotation and resting the pasture for a year helps

• Routine deworming with appropriate drugs must be used to keep larvae numbers and damage at a minimum

• Grazing cattle and sheep help remove them

Pinworms• Do not cause must damage to the horse• Mature worms live in the colon of the LI• Can be 7.6 cm (3 in) long• Life Cycle:• Females lay eggs in the colon, pass out in the feces• Or females lay eggs on the skin around the anus

• Causes itchy sensation• Eggs are sticky and therefore stick on walls, feed

buckets, and other equipment contaminating the environment and increasing the chances for re-infestation

• Controlled by manure removal and medication

Stomach bots• Three species that affect horses• Adult bot fly resemble a honey bee• Bot flies are active from first part of summer to

first hard frost

Stomach Bots – Common Botflies• Gasterophilus intestinalis• Eggs are yellow and can easily be seen• Life Cycle:

• Laying eggs in the hairs of the horse’s legs, chest, belly, and neck• Eggs hatch after about 1-2 weeks, when exposed to moisture, warmth

and friction• Condition is met when the horse licks the area• Upon hatching, they enter the mouth where they enter the mouth and

burrow into the tongue and are eventually swallowed• Inside the stomach, attach to lining where they mature• Detach themselves and pass through the digestive tract• Develop in the pupae stage and pass out in feces• Outside they burrow in the ground, develop into the botfly and emerge

in warm weather• Takes about one year

Stomach Bots – Throat or Chin Botfly• Gasterophilus nasalis• Lay eggs around the chin and throat area• Eggs incubate in 4 – 6 days and hatch without

stimulation• Larvae crawl into mouth and enter gum tissue

around teeth• Leave mouth and enter stomach, attach to

stomach lining and mature• Rest is similar to Botfly

Stomach Bots – Nose Botfly• Gasterophilus hemorrhoidalis• Lay black eggs on the nostrils and lips• Hatch in 2 – 4 days without stimulation • Burrow into the inner lip membranes • After 5 – 6 weeks they enter stomach. • Rest is similar to Botfly

Stomach Bots• Cause stomach damage and rupture to stomach• Control or prevent heavy infestation, kill adult

flies, remove eggs and deworm• Once eggs are laid, they can be removed from the

hairs by scraping them with a knife or sandpaper• Should be treated with anthelmintic medication at

least 4x/year• First frost should kill them, no new larvae will

enter the horse