It is inflammatory reaction of epidermal cells to the substances to which these cells are sensitized. Such substances may be present either in the external or internal environment.
Etiology: Skin may come in contact of exogenous or endogenous allergens. The exogenous allergens may be ectoparasites or chemical substances present in antiseptic or disinfectants. Endogenous allergens are absorbed from the gut and they may be either ingested proteins or amino acid formed in gut. There are some factors which increase susceptibility of animals for eczema like inherited susceptibility, repeated wetting and dampness caused by continuous sweating, constant scratching due to presence of external parasites and long-term soiling and accumulation of skin debris.
Pathogenesis: Initially animals show erythema and edema of inter- and intra-cellular space. The vesicles are formed on the body surface and rupture to release fluid, and later on, scabs are formed.
Clinical signs: True cases of eczema are seen rarely in large animals but are more common in small animals. Initially patches of erythema appear followed by small vesicles formation. Due to rupture of these vesicles, fluid comes out leaving a moist surface. Later on scabs are formed. These lesions are present in small patches or diffused over a large area. There is excessive itching, irritation, scratching and rubbing. Alopecia is seen in affected area but there is no discontinuity of skin. In some cases, patchy dermatitis also develops.
Diagnosis: The cases can be detected by clinical symptoms and can be confirmed by testing of allergens. The haematological analysis usually reveals eosinophilia. Eczema should be differentiated from chronic dermatitis, which has lesions in deeper layers of skin and they develop irregularly while in eczema lesions are more regular and involve superficial skin layer.
Treatment: The sensitizing agents to which animal is allergic should be avoided. The affected animal should be given laxatives so as to remove consumed allergen quickly through faeces. Repeated doses of antihistaminics such as chlorpheniramine male ate or pheniramine maleate ar e helpful in checking allergic reactions. Corticosteroids are also of high value in early recovery. However, if the disease is caused by ectoparasites, specific treatment of the ectoparasites will be helpful in recovery of the case. Non-specific protein like milk iodine or iodinated protein can be given @10 ml intramuscularly in large animals once daily for 2-3 days. Lotion prepared from equal parts of alcohol and saturated sodium bicarbonate solution can be applied to prevent itching and rubbing. Cream can be prepared by mixing 10 parts icthymol, 250 parts zinc oxide and 10 parts salicylic acid in liquid paraffin for external application.