Allergic manifestations in the horse

Allergic manifestations in horses open a very varied and complex chapter in the field of diseases of this species. Allergic manifestations involve the skin area, the respiratory system and the digestive system. Environmental, hygienic and food conditions can be decisive for the development of the disease. In addition, there are various predisposing factors such as infections or flu-viruses, advancing age and a genetic predisposition.

Respiratory diseases on an allergic basis

It is known that the horse is the most sensitive among the animals to these allergic forms thanks to the complex structure of its respiratory system. It is currently agreed that in the pathogenesis of COPD (Chronic obstructive pulmonary disease) there may be a Type I hypersensitivity to allergens present in the dust which contains mostly pollen and especially mold spores widely present in the stable (hay, bedding, environment).

COPD has a chronic evolutionary course characterized by persistent and intermittent cough, dicrotic breathing up to dyspnea, dilation of the nostrils, nasal discharge and wheezing, decreased tolerance to work and often poor physical conditions. It ranges from minimal initial involvement to emphysema and irreversible lung compromise. COPD is more frequent in subjects housed in stables than in those living outdoors and is found more frequently in subjects of a certain age than in young subjects.
A horse with mild allergy-based bronchitis that is promptly diagnosed and treated could avoid chronic problems in the future.
The diagnosis of COPD on an allergic basis is not easy to achieve, requires an accurate medical history of the patient (environmental conditions in which he lives, diet, previous infections), a thorough general clinical examination, specialist instrumental analyzes and finally research of specific allergens, if the allergic nature has been established.

Relapsing Summer Dermatitis (RSD)

The “Relapsing Summer Dermatitis (RSD)” is a more or less serious disease that afflicts horses, ponies and donkeys. It is a manifestation of Type I hypersensitivity to insect allergens, of which the main responsible belong to the genera: Culicoids, Black flies, Tabanids and Culicides. There are different opinions on a possible breed predisposition: a notable predisposition has been documented in all pony breeds, on the other hand it seems that do not exist predispositions related to sex or coat color and the age of greatest appearance is between 2 and 4 years.

In general, the animals most affected are those that live constantly outdoors or those housed in boxes with openings without protection.
In “summer dermatitis” the main and most evident symptoms are: itching, appearance of papules that raise the hair and erythema at the injection site. Due to the severe itching the animal scratches with insistence causing damage to the coat and skin resulting in scabs, scales, erosions, alopecia and lichenification located mostly at the base of the tail, on the back, the mane and the ears up to affect the whole body. The disease is purely seasonal: the symptoms initially appear in spring and slowly regress in autumn, but being relapsing, the symptoms recur every year mostly in an aggravated form until, in the most exacerbated cases, they persist throughout the year.

The diagnosis of RSD is easy, but it cannot be separated from an accurate anamnesis, from the clinical visit and from the differential diagnosis with other parasites that can give similar symptoms (Sarcoptes, Sporoptes, Helminthiasis, Oncocerca etc.); moreover, atopic dermatitis caused by pollen or mites can give the same symptoms.