All horses are affected by parasites. Some parasites, such as flies, are just a nuisance. Others cause severe impairment of well being or even fatal diseases. The greatest threat comes from endoparasites: mainly worms and fly larvae.


Worms (internal parasites)

General signs of a severe worm problem include illthrift, poor condition, rough coat, pot belly (foals), depression, persistent diarrhoea, colic, anaemia, lowered performance, sudden death.

Harmful and even deadly worm burdens can build up where the number of horses per hectare (stocking rate) is high, as often occurs in near-city horse paddocks, particularly those with more dung than grass. Poor hygiene and crowding in stable and yard areas contributes and horses low in condition have less resistance to worms.



Signs: illthrift, poor appetite, a pot belly, sometimes diarrhoea and a cough.

Mainly a problem in foals through to yearlings.

The adult worms are very long, a foot (30 cms) or more in length and as thick as a pencil, though they are not usually seen except in the dung of a recently wormed foal.

It is the roundworm eggs that pass out in the foals’ manure, they are very resistant and can remain in the environment for well over a year . They only hatch once eaten by another foal.


Large redworms (bloodworms, strongyles)

Signs: illthrift, poor condition, lowered performance, anaemia, repeated attacks of colic, diarrhoea, sudden death from a ruptured blood vessel, even hind leg lameness.

The adult worms suck blood and the larval worms cause blockages in blood vessels.

The eggs of the adults pass out in the dung, hatch into larvae and climb up grass blades waiting to be eaten by another horse.

Depending on the severity of the infestation, some or a lot of redworms will be seen coating the balls of dung the day after a horse is wormed. They are thread to string-size in diameter, one to four centimetres long and off-white or red, depending on whether they contain blood.


Small redworms

Signs: persistent diarrhoea, illthrift, anaemia and poor performance.

These worms can be a major cause of ill health because the larvae are able to lie dormant within the horse for long periods in which state they are resistant to wormicides.



Signs: illthrift and colic, sometimes sudden death.

Tapeworms are not killed by the 'mectin' group of chemicals, so wormicides that will kill them need to be used twice yearly. Equest Plus Tape is one product that will control all the internal worms including tapes.



Signs: illthrift, colic and occasionally death if in large numbers, but they rarely cause trouble and are easily controlled by commonly used wormicides.

The bot fly has a bee-like appearance and drives some horses crazy buzzing about them laying eggs particularly on the forelegs. Horses lick and chew at these eggs which hatch in the mouth and end up as bots (larvae) attached to the stomach wall. Bot eggs can be removed physically with a bot egg knife.


Stomach worms (Habronema)

Signs: summer sores.

The larvae of stomach worms are passed out in the dung, ingested by flies which deposit them into wounds on the horse’s skin and in moist areas, e.g. around the eyes. The tumour-like nodules (summer sores) that form can become very large. The avermectin wormicides have markedly reduced the incidence of summer sores.


Pin worms

Signs: tail itching, mainly stabled horses.

Not usually a major problem.


Neck threadworm (Onchocerca)

Signs: itching and rubbing of skin lumps and/or open sores mainly on the head, neck and belly; hair loss along the mane due to rubbing.

The itchiness is an allergic response to the migrating larvae produced by the female worms which live in the major neck ligaments, apparently without harm.

Onchocerca was once confined to northern Australia but is spreading south.

The larvae are killed by ‘mectin’ wormers.


External parasites

General signs of all external parasites usually include itchiness and hair loss.

Queensland itch 

Signs: intense itchiness. Manes and tails become non-existent from the constant rubbing, fences and other structures can be damaged.

Qld itch is an allergic response to the bite of the sandfly (midge). It mostly disappears during the winter, though older horses will still show evidence of it by thickened skin and a sparse mane and tail.

Treatment: firstly, eliminate the breeding places of the midges, e.g. containers of stagnant water. Keep insect repellant on susceptible horses. Confining horses from pre-dusk until after dawn in gauzed-in stables helps, also a very lightweight polyester rug and face mask have been developed for Qld itch sufferers. In most parts of Australia, heavy rugs should not be used on horses in summer, even at night.


Rain scald (dermatophilus)

Signs: Areas of matted, lumpy hair along topline of horse and down the sides, following the water run-off pattern. Usually begins on the rump. The coat feels hot and rough and the horse will flinch when touched. The hair lifts off in crusty scabs.

The cause is bacteria (Dermatophilus sp) which are spread from horse to horse by flies. Prolonged rain slightly damages the horse’s skin, allowing the bacteria to enter.

Rain scald can be confined just to the muzzle and lower face, particularly on white markings. The cause is grazing in long wet grass which has the same effect as constant rain in weakening the skin’s defences.

Treatment: antiseptic sprays and creams can be used, although the condition will clear up itself once the rain stops. Protection from constant wetting is an obvious prevention, but not with a heavy rug during summer. Horses with scalded backs should not be ridden or have any tack put on them, the condition is quite painful while active.


Greasy heel

Signs: crusty, greasy scabs on the lower legs, coronet region, heel area or the front of the hind cannons, particularly where there are white markings. Cracks may develop in the heels, causing lameness.

The cause is continual wetting of the lower leg and heel area, which allows dermatophilus and other bacteria to enter. It is associated with frequent hosing, or grazing or working in long wet grass, or sweat constantly running down the legs. Working on cinders or sand predisposes, the bacteria gaining entry through tiny abrasions.

Treatment: veterinary in severe cases, antibacterial ointments and creams for milder cases. Prevention is by keeping the lower legs dry. The heels should always be dried off thoroughly after hosing or work.


Ringworm (girth itch)

Signs: small, circular, scaly, hairless areas, often beginning in the girth region but can be on the head and elsewhere. They may coalesce to form larger areas. The condition is irritable rather than itchy.

Caused by several different microscopic fungi, it is mainly a disease of young horses and is highly contagious, spreading quickly where tack and grooming gear is shared, or on riders’ boots.

Treatment: individuals can be treated with antifungal washes and ointments. Fumigation of gear may be needed if the problem persists.



Signs: itchiness. Small, active blue-grey critters with six legs. Eggs are greyish.

Typically a winter problem, lice can spread rapidly through stabled, yarded or paddocked horses. They disappear with shedding of the winter coat but heavy infestations may need insecticidal treatment, also of gear and equipment.



Signs: itchiness, skin irritation and lumps, paralysis and death (scrub ticks only). Adult ticks have eight legs and are dark brown to blue-grey and the size of a pea when fully engorged.


In coastal southeast Queensland cattle ticks, bush ticks and scrub tick can all get on horses. Bush and cattle ticks sometimes cause local swellings and skin irritation. The scrub tick (paralysis tick, Ixodes) is the one to worry about, particularly in young foals. It is carried by bandicoots which live in bushy areas. It readily attaches to other animals and engorges with blood before injecting a paralyzing poison and dropping off to lay eggs. In scrub tick areas, young foals should be caught and checked every second day, same as for cats and dogs.


Buffalo flies

Signs: skin irritation and sores on cattle mainly, but can be a problem for horses. Small flies with long flat wings, may be in clouds and completely covering the backline of cattle.


Buffalo flies rapidly build up resistance to chemicals. Consequently a variety of sprays, pour-ons, walk-through dusts, insecticide-impregnated ear tags, insect growth regulators in the feed have been developed to control them. Some of these products can be used on horses and will also control Qld itch – but always check the label.

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