Talking Horses Equestrian Issue 19 2010 Queensland Itch – the Old Menace Moves South T he allergic intense itchiness caused by biting midges, gnats and sandflies has been dubbed ‘Queensland Itch’ because historically, it predominately affected horses in northern Australia and the tropical and subtropical areas of Queensland.
The syndrome is known as ‘Sweet Itch’, ‘Summer Itch’, ‘Summer Eczema’ and ‘Summer Seasonal Recurrent Dermatitis’ (SSRD) in the UK, Canada, USA and South America – and ‘Kasen Disease’ in Japan and ‘Equine Dhobi Itch’ in the Philippines.
All breeds and types of horses can be affected, irrespective of age, coat colour and condition.
Some authorities believe that grey horses attract more midges, as they do have a different skin odour, but this association has not been proven.
Donkeys and fine coated animals, such as goats, can also be affected.
Over the last 20 years, the ‘itch’ has spread to more central and southern coastal areas of the eastern coastline, with some areas having a high incidence over the summer months.
More widespread outbreaks follow a pattern of summer rainfall as the climate changes, making a habitat of wet marshes, decaying forest matter and high humidity suitable for breeding and harbouring biting midges and sandflies. Symptoms The symptoms are easily recognised in a sensitised horse as small localised juicy lumps on the skin surface over the target areas.
The hair becomes erect and the skin begins to itch.
The horses start to rub and then self-traumatise the skin, attracting more insects to feed and increasing the allergic reaction.
This results in weeping of serum and shedding of skin surface cells which mats the already thinning and abraded hair over the affected area.
Secondary bacterial and even fungal lesions (similar to ‘rain scald) can occur over areas of broken and irritated skin.
In chronic annual sufferers, the skin becomes bald and thickened and develops ridges (called ‘rugae’) along the withers and lower rump and tailhead.
Severely sensitive horses can become active and gallop around during a midge attack and run into fences in an effort to escape the irritation.
In some cases, where the itching has led to self-mutilation, a course of antibiotics may be necessary to control the skin infection so as to help the skin to heal.
Consult your vet for advice. Primary Cause The management to reduce the risk of Queensland Itch includes shielding The primary skin reaction is due to an allergic reaction or hypersensitivity to the sensitive or hyper-allergic horses from the swarming insects, combined with bites and insect saliva from small biting Culicoides brevitarsus (previously known topical repellents and lotions to ease the discomfort and itching.
Robertsii) insects – a common sandfly or midge (juvenile gnat) endemic in tropical and subtropical areas.
The midges breed in humid, scrubby and bushy Rugging to Cover Target Areas – In endemic areas, it is a good idea to localities along the coastal fringe and inland in tropical areas with summer rainfall, apply a protective sheet or light rug to cover the topline from head to tail.
A or northern areas with monsoonal rains.
The small 2-3 mm long insects swarm full body rug and neck combo is helpful and in very sensitive, chronically in a feeding frenzy just prior to nightfall and in the pre-dawn period under warm, affected horses, a covering over the ears and a fine fly mesh over the forehead humid conditions.
They fly quickly and do not make a noise (sometimes they is recommended.
It is important to apply the covering from around 4pm are referred to as ‘no-see-ums’ in the UK) and bite target areas on the topline in the evening to 8am the following morning to grazing horses and also from the forehead and ears, over the withers, rump and tail-butt.
Mosquito to sensitised horses stabled overnight in endemic areas.
Bites are also a possible trigger for midge attack if the skin is abraded or oozing serum from itching, rubbing and self-mutilation on trees or posts.
Reports Purchase an Under-Belly Protective Rug indicate that each swarming midge can bite a horse up to 100 times per hour, each time injecting minute amounts of highly sensitising saliva into A special rug designed with under-belly covering the skin surface layers to create the allergic reaction.
In southern areas, to virtually seal and protect the under-body areas from midges biting highly sensitised horses is available in the UK.
It is called a Boett Rug®..They can be cold, frosty weather causes the insect attacks to reduce over winter and purchased on the Internet or from distributors in Australia.
When combined with the symptoms may subside until the next midge season. Management Handy Hint 4 Did You Know That… The hypersensitivity reaction is caused by allergens in the type of saliva common to a large variety of biting midges and sandflies.
These allergens trigger an intense immune mediated IgE antibody sensitisation with cytokine and histamine release.
This creates a severe immune response, making the horse’s skin inflamed, itchy and even more sensitised from repeated midge attacks.
Certain horses appear to have a much lower tolerance to the effects of the allergens.
Once sensitised, the increased IgE antibody levels specific to the allergens increase the risk of chronic, recurring lesions from season to season and eventually become subclinical over the cooler season when midges are not prevalent. Some Horses Become Chronic Sufferers The risk of a chronic recurring annual reaction is exacerbated when potentially ‘sensitive’ horses from inland or southern areas with no previous exposure, are moved into endemic areas for breeding, showing and competition and especially after sale or relocation.
Some individual horses appear to be more sensitive than others, with often one or two horses in a group suffering from the ‘itch’ at around the same time each year.
Older horses which have been previously affected generally show increasing allergic symptoms and chronic thickening of the skin as they endure repeated hypersensitivity reactions each year.
In some cases, the itch barely cleans up in the cooler months of the year before the intense skin reaction develops again.
It is important to identify these horses before the sandfly season starts from November to May and take steps to minimise their exposure. stabling overnight and windows and doors fitted with fine mesh fly wire, the risk is greatly reduced.
This is recommended as a barrier protection for older, highly sensitised horses.
The larger mosquito nylon mesh may still allow small midges to get through, so use a fine aluminium fly mesh if it is available, as the midges cannot distort the strands of the mesh to gain entry to the stable area.
Block off all other openings, including the edges of sliding doors. — Handy Hint 5 Handy Hint 6 Move Sensitive Horses to a Dry Area during the Midge Season Handy Hint 7 Long acting corticosteroid injections and oral Prednisolone granules, as prescribed by your vet, are helpful in reducing the intensity of the itching and rubbing associated with Queensland Itch.
Although draining of water away from ponds and lagoons is helpful in However, you must avoid administering any form of corticosteroid to heavily pregnant mares, as reducing midge and mosquito numbers in the immediate area, these insects can cortisone is the natural hormone which triggers the birthing cascade.
Also avoid use in obese seek out horses on flight and return after rain.
If a horse is highly sensitised and is or over-weight horses and ponies suffering from laminitis and those bordering on EMS or Insulin self-mutilating itself by rubbing, despite rugging and insecticidal treatments, then Resistance.
Cortisones can modify the control of glucose and intensify the effects of circulating the only logical alternative is to move the horse away from the endemic area insulin and impede blood flow to the lamellae.
Do not administer ‘left-overs’ of these preparations, during the midge and sandfly season to a dry, southern locality or which may have been prescribed for another condition or horse/pony, without seeking advice away from the coastal fringe and the humid climate.
From your vet, as you may trigger an acute laminitic reaction. Onchocerca Skin Lesions Horses grazing in northern areas of Australia can also be affected by intense irritation and allergic reaction caused by the collection of microfilaria of the Onchocerca spp worms.
The most common is Onchocerca cervicalis, a long filarial worm which develops within the ligaments of the neck.
The incidence is highest in Western Australia, Central Australia and Northern Queensland, but it has been carried south by infected horses and isolated cases are reported each summer.
The microscopic larvae or ‘microfilaria’ produced by this worm circulate in the blood stream and congregate within the skin layers of the upper neck, head, chest and under-belly.
They are ingested by biting insects, including mosquitoes and Culicoides spp, which cause a secondary intense itching and localised symptoms similar to Queensland Itch.
The congregation of allergic microfilaria result in the development of small discreet raised lumps about the size between a pea and a marble.
Itching causes rubbing and thinning of the hair, breaking the skin resulting in serum matting and scab formation on the skin and the hair.
This attracts more insects and flies.
Often the mane is rubbed off.
In severe cases, the damage to the hair follicles under the lesions results in bald patches over thickened fibrous nodules on the neck under the mane and in strips along the under-belly.
The diagnosis of Onchocerca spp infection can be confirmed by biopsy of one or more of the skin ‘lumps’ to identify that microfilaria are present. Control of Onchocerca Itching and Lesions SEASONAL WARNING: Stringhalt There have already been reports of Stringhalt developing in horses following recent summer rains in Victoria and New South Wales where Flatweed and Dandelion are endemic.
The moisture facilitates rapid emergence of these common weeds from the taproot crown, before any other pasture seed can germinate and take root.
Horses hungry for a green pick will graze on these weeds which grow in poor soils and grazed out pasture, especially under trees, in gateways and hollows in a paddock.
The toxin ingested affects the long sciatic nerves in the hind limbs of tall breeds of horses, especially draft horses and their crosses, Thoroughbreds and Warmbloods.
It does not affect ponies or miniatures.
In severe cases, the long recurrent laryngeal nerves in the neck may be affected, resulting in ‘roaring’ in some horses. Move Horses to A comprehensive Fact Sheet providing information a Flatweed-Free Pasture on Stringhalt and its management can Immediately be obtained by emailing Gary at If you notice that Flatweed or firstname.lastname@example.org Dandelion has sprouted in your This Fact Sheet has also been pastures after summer rainfall or an uploaded onto the website early autumn break in the season, move www.kohnkesown.com under the all horses onto a pasture free of these Fact Sheet section.
Weeds and if necessary, supplement with Handy Hint 9 Handy Hint 8 The parent worm, which develops in the neck ligaments 4-5 months following contamination with infective microfilaria introduced by biting insects, cannot be controlled effectively within its protective environment deep within the neck ligament.
Once a horse becomes infected, it will have repeated seasonal recurrence of microfilaria-induced itching.
The circulating and congregated microfilaria can be controlled by ‘mectin’ worming compounds administered when the lesions are active and itchy.
Consult your vet for advice.
However, there is often a severe itching reaction triggered by the immune system by the dying microfilaria within the skin lesions, causing self-mutilation by rubbing.
This reaction normally occurs in heavily infected horses within 24-36 hours after worming with a ‘mectin’ wormer.
In cases where the itching is so intense as to cause severe skin damage, an injection of corticosteroid may be recommended to relieve the itch.
In this case, the precautions as outlined in Handy Hint 7 above, must be strictly observed. lucerne hay.
In horses showing early signs of Stringhalt with a sudden uplifting hind limb gait, move them from the pasture immediately to a secluded yard or small weed free paddock to keep them as calm as possible.
Provide lucerne hay and a daily supplement of an organic magnesium and Vitamin E product to correct low or inadequate levels from the predominately Flatweed diet, such as Kohnkes Own Mag-E™.
Mag-E should be given at double doses for 10-14 days in a chaff feed and then at a maintenance dose until symptoms subside. Left: Flatweed growing on the edge of a dressage arena.
Read more about Bald : In chronic annual sufferers the skin becomes bald and thickened….: