Parasites
- a parasite is any living thing that lives on or in, and
taking food from, another living thing, called the host,
and usually causing harm to the host
- endoparasites are internal parasites
- ectoparasites are external parasites
- the helpful bacteria within the horse's large intestines
are not parasites, since both the bacteria and the horse
benefit from their relationship
- an obligate parasite cannot survive at all without the
host
- partial parasites obtain some nutrients, but not all
nutrients, from the host
The Major Internal Parasites
- PARASCARIS EQUORUM (ASCARIDS):
- ascarids are commonly called the large roundworm
- ascarids are usually only found in younger horses, older
horses build a resistance
- Lifecycle of the Ascarid:
- eggs passed with feces develop on the ground, and are
later ingested
- when eggs are ingested, they hatch in the intestines and
migrate through the intestinal wall and through the blood
to the liver, and then the lungs
- reaching the lungs, ascarids crawl up the trachea, are
coughed up, and are swallowed
- adult ascarids lay eggs in the intestines
- an ascarid egg can survive for several years and still be
infective
- ascarids can cause respiratory and liver damage,
coughing, and occasionally a blocked intestine
- GASTROPHILUS (BOTS):
- the most common species of bot is Gastrophilus
intestinalis, others are Gastrophilus nasalis and
Gastrophilus hemorrhoidalis
- Lifecycle of the Bot:
- the female bot fly lays yellow eggs on the hairs of the
forelegs, shoulders, neck, and mane
- when the horse licks his legs, the warmth and moisture of
the tongue stimulate the eggs to hatch
- freshly hatched larvae burrow into the tongue and migrate
to the stomach
- after nine months in the stomach, the bots release their
hold and pass out of the horse in manure
- bots burrow into the ground, and after a month, the adult
bot fly emerges to mate and lay eggs on the horse's legs
- bots are not especially harmful, comparatively, although in large
quantities they can create an ulcer
- OXYURIS EQUI (PINWORMS):
- female pinworms are larger than male pinworms
- pinworm infections are more common in stabled horses
- Lifecycle of the pinworm:
- adult pinworms live in the large intestine, and when the
female is ready to lay eggs, it crawls out the anus and
lays the eggs on the skin, causing itching
- eggs fall off and are ingested, and the pinworms mature
in the large intestine
- pinworms cause itching and tail rubbing
- HABRONEMA (STOMACH WORMS):
- the three species of habronema are habronema muscae,
habronema majus, and habronema megastoma
- Lifecycle of the stomach worm:
- eggs are passed out of the horse in manure
- the larval stages of the stomach worm are eaten by the
larval stages of the house fly and stable fly, which are
growing in manure
- the stomach worm moves to the mouth parts of the adult
fly
- when the adult fly is feeding on wounds, or near the
eyes, the stomach worm infect the wound; when flies are
feeding near the mouth, the stomach worm can be swallowed
and grow in the stomach
- stomach worms cause summer sores and conjunctivitis
- STRONGYLUS VULGARIS (LARGE STRONGYLES):
- strongylus vulgaris is commonly called the bloodworm
- Lifecycle of the Strongyle:
- eggs are passed out of the horse in manure
- larvae hatch in manure and crawl up pieces of grass,
where they are ingested
- immature stages migrate extensively throughout the body
- stronglus vulgaris migrates through the mesentary
artery, then to the aorta, and can cause colic
- after migrating to the aorta, strongyles remain for three
to four months before migrating back to the intestine
- mature strongyles return to the intestine to lay eggs as
adults
- OTHER STRONGYLES:
- also called bloodworms are strongylus edentatus and
strongylus equinus
- these strongyles have a life cycle similar to stronglus
vulgaris
- TRIDONTOPHORUS (SMALL STRONGYLES):
- tridontophorus tenuicollis, or the small strongyle, can
cause diarrhea and constipation
- the small strongyle has a three week long life cycle and
migrates to the intestine; they are not as destructive
as the large strongyle
- STRONGYLOIDES (INTESTINAL THREADWORM):
- strongyloides westeri affect foals up to six months of
age, and is passed from mare to foal through the mare's
milk
External Parasites
- MICROSPORUM TRICHOPHYTON (RINGWORM):
- ringworm is a fungus, not a worm, and is the most serious
fungal infection found in the horse
- ringworm is caused by the fungus microsporum trichophyton
- ringworm is highly contagious to other horses, people,
and other animals
- symptoms of ringworm include:
- small, round lesions which spread
in circular patterns and have the
appearance of cigarette burns
- dermatitis and hair loss
- intense itching
- treatment includes washing the affected area with mild
soap and removing the crusts, then treating the area with
herbicide or iodine
- vinegar will also kill ringworm, and can be used to soak equipment possibly exposed
- PHYCOMYCOSIS (WEST COAST FUNGUS):
- west coast fungus is a fungal condition caused by either
Hyphomyces destruens or Entomophthora coronata
- lesions are hard, yellow-gray "leeches" of dead tissue
which may spread into tendons and ligaments
- surgical excision followed by daily application of DMSO
and amphotericin B for thirty days
- SPOROTRICHUM SCHENCKII:
- sporotrichum schenckii is a saprophytic fungus (one that
grows on decaying tissue) that causes sporotrichosis
- sporotrichum schenckii is usually introduced by a thorny
plant
- symptoms of sporotrichosis include:
- subcutaneous (beneath the skin)
hard nodules on the medial (inner)
surfaces of the limbs
- nodules ulcerate and produce pus
- weight loss may also occur
- TICKS:
- the tick burrows its head under the skin, and sucks blood
- the deer tick carries lyme disease, and may infect
horses, people, dogs, and other animals
- the lone star tick and spinose ear tick may also infect
the horse (ear ticks cause head shaking)
- to remove a tick, soak a cotton ball in rubbing alcohol
and hold it over the tick, this will suffocate it, since
ticks breath through air holes on their body, and the
tick will die and let go of the skin; if a live tick is
pulled out, the head could be left behind to cause
infection
- LICE:
- the singular for lice is louse
- the two species of lice that infect horses are Bovicola
equi (biting lice) and Hematopinus asini (sucking lice)
- a person may not become infected with the same species of
lice that infects the horse
- symptoms of lice infestation include:
- itching and hair loss
- tail rubbing
- two or three applications of louse dust or insecticide
sprays will eliminate lice
- MITES:
- mange mites are microscopic parasites that cause mange
- mange mites have six legs upon hatching, then eight legs
in later life, and have a life cycle of about two weeks
- chorioptes equi is the species of mite that causes leg
mange, which is found mainly on the fetlocks and pasterns
- psarcoptes scabiei is the species of mite that causes
sarcoptic mange (scabies), a severe condition since this
type of mite burrows tunnels in the skin
- psoroptes cuniculi and psoroptes equi cause psoroptic
mange, which may be confined to the ears or spread over
the entire body
- ear mites (psoroptes equi) cause excessive production of
ear wax as well as the characteristic lesions
- BITING FLIES include:
- house flies
- stable flies
- horn flies
- horse flies
- deer flies
- buffalo flies
- black flies (buffalo gnats)
- mosquitoes
Prevention of Parasites
- a regular deworming program (treatment with anthelmintic
drugs every eight weeks)
- regular stall cleaning
- proper manure disposal, which includes not piling manure
near barns, but spreading it so it may dry, killing eggs
(manure should not be spread on pastures, but on crop
fields if possible)
- pasture rotation, so that eggs don't build up in one
pasture
- use of insecticides and repellents
- avoidance of turn out during hot days
- fly masks
