The term 'summer eczema' already encapsulates the entire problem of this allergic condition: The term 'eczema' denotes a non-infectious inflammatory reaction of the skin.
The eczema that occurs in horses is medically termed “local seasonal allergic dermatitis,“ meaning: “a localised skin inflammation triggered by an allergy.“.
As this condition is an allergy, it is not contagious.
This allergy is caused by the saliva of *Culicoides* midges. The visible symptoms are caused by the allergic itching.
Allergen: Culicoides or midges
Culicoides are a particular type of small midge.
The larvae are aquatic organisms, so they are found predominantly near bodies of water, with a preference for still water. After hatching, the adult insects do not stray further than several hundred metres from their breeding or hatching site. The main activity of biting midges occurs in low light intensity, high humidity, and calm winds. Female biting midges are particularly keen to bite, especially at dusk and during the night.
In horses, gnats primarily infest the mane and the dock of the tail, which is why the symptoms are mainly confined to these areas of the horse's body.
Symptoms
The visible symptoms of summer eczema manifest as typical itching symptoms:
- broken hair and
- (in later stages) open sores.
The diagnosis of summer eczema is then made based on the typical localisation of the symptoms on the mane and tail, as well as the period of occurrence between mid-April and early October.
In other conditions that cause itching, other symptoms are predominant: with lice infestation, itching and hair loss all over the body are the main features. The diagnosis can also be made by detecting the parasites in the coat.
In the case of real mange, it is an infestation with mites that burrow into the skin of the affected animal. The infected horses react with nodules all over their bodies and only a mild itch, with the mane and tail not being affected by this disease.
It is also important in this context that infestations with so-called ectoparasites – that is, parasites found outside the body – spread relatively quickly within a population. This is therefore not an individual animal disease, as is the case with summer eczema. Horses suffering from worm infestations occasionally show rubbing spots on their tail, while the mane remains completely unaffected by these symptoms.
The stages of sweet itch can be divided into 3 consecutive disease patterns:
- Pinhead-sized to three-centimetre swellings that cause itching. This symptom is very common. The horses have a thickened crest and their mane and tail resemble scrubber brushes. The animals react by rubbing, which leads to Condition 2:
- Hair loss and skin abrasions. Further rubbing then creates increasingly deeper wounds. As the skin's natural protective layer has been lost, bacteria can settle into the resulting wounds, leading to disease state 3:
- Suppurating wound infections and very deep open wounds.
Affected horses
The affected horses are primarily Icelandic horses, but also Shetland ponies, Friesians, Tinkers, Dülmener, and warmbloods. One has the impression that the disease is occurring more frequently in recent years, but this could also be related to a general change in keeping conditions.
The occurrence of summer eczema in Icelandic horses has already been the subject of investigations on numerous occasions. This breed is likely affected so frequently because no Culicoides species are native to Iceland. Consequently, the animals cannot be exposed to this allergen from the beginning of their lives and therefore develop immunity.
The horses most commonly affected appear to be imported Icelandic horses for this reason, with symptoms usually occurring in the year of import or up to 3 years after import. The age of the animals is irrelevant. It is questionable whether there is a genetic component or a dependency of the disease on colour and sex. In animals native to Germany, symptoms usually do not appear before the age of 4. However, the severity of the symptoms worsens with increasing age.
Diagnose
The diagnosis is made by excluding other parasitic infestations, taking into account the season and location, without the use of further tests. Confirmation of the diagnosis can be achieved through the so-called CAST (Cellular-Antigen-Stimulation-Test).
This testing method is used to test histamine-releasing cells for sensitisation. It can also be carried out outside of allergy season, as histamine-releasing cells are permanently sensitised. It is important to note that with all tests for this condition, circulating antibodies in the blood are not tested for. These merely indicate that the horse has come into contact with this antigen, in this case the midge. This should be the case for all horses living in Germany, which is why the informative value of this test is not particularly high.
When interpreting the test results, it is also important to know that sensitised horses do not necessarily become ill, and that the test also cannot predict which healthy horses will later develop sweet itch.
Therapeutic approach
The treatment of summer eczema must be built on two pillars: avoiding contact with Culicoides and treating the symptoms.
Allergen avoidance
The understanding of the habits of midges is important in this approach. Therefore, horses should be kept in pastures that are as dry as possible and where there is constant air movement. Shelters or open stables are not recommended as protection from the insects, as they are often wide open and offer good wind protection, which the insects appreciate very much.
If you want to protect horses spatially from insects, they should only be allowed out to pasture during daylight hours and brought into a as closed as possible stable, equipped with fine-meshed insect screens, before dusk begins. Of course, applying insect repellent can also bring some success, but the success is unfortunately usually not long-lasting.
Otherwise, the eczema rugs available commercially have proven very effective. However, it is absolutely essential to ensure that they fit well and completely cover the mane and tail area. The rugs should be checked daily for their fit. It is recommended to put the rugs on before the first symptoms appear (if the horse is known to suffer from sweet itch), as horses can otherwise quickly destroy the expensive rugs in their fight against itching.
Symptom relief
Of course, it's important to care for the already affected skin so that the symptoms don't worsen and bacterial infections don't occur, which are very common in weeping, inflamed skin. When it comes to this treatment, there are no limits to the owner's imagination.
- Some owners swear by skin oil,
- others on Ballistol,
- There is eczema care oil in equestrian shops and at the vet's.
In more severe cases, the vet will first prescribe a cortisone-based cream or lotion, and for very stubborn cases, an injection of a cortisone preparation. This will break the vicious cycle of itching, subsequent skin damage, and further itching, at least in the short term. Unfortunately, other therapeutic approaches with Baypamun®, Insol®, as well as hyposensitisation have not yet shown the expected success. Fidavet Cavalesse Kit® offers a new therapeutic approach. This therapeutic agent is a combination of an ointment applied to the affected body regions and a solution administered via food. This is intended to act directly on the histamine-releasing cells and influence them not to release histamine in the first place.
It is important to note with all possible therapies that there is still no cure for horses suffering from summer eczema! The affected horses recover during the fly-free period but require special attention and care every summer!
