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(5) Eczema: Eczematous Dermatoses:

It is an inflammatory reaction of the epidermal cell to exogenous or endogenous substances to which cells are sensitized. This occurs when the skin is in contact with allergens either applied on the skin and so called exogenous or arise from the blood stream and known as endogenous allergen.
Etiology
(A) Predisposing Factors
Nutritional deficiency, trauma and chemicals.
Genetic causes.
Prolonged soiling, dampness and accumulation of debris.
Constant scratching due to external parasites.
(B) Exogenous Allergens:
Using of chemicals as antiseptics and disinfectants.
Some Ectoparasites as flea-saliva in dog and cat, which cause hypersensitivity of skin.
(B) Endogenous Allergens:
These aresubstances, which are ingested and absorbed through the gut and introduced into the blood stream and affect on the skin indirectly ingestion proteins.
Pathogenesis
The primary lesion is erythema, Spongiosis due to in intra and intercellular edema forming vesicles which is characteristic for eczema, this leads to rupture of vesicles and causes weeping of skin with formation of scabs. This occurs in the acute stage of eczema and may disappear rapidly. Chronic form may persist accompanied with parakeratosis and pachydermia.
Clinical findings:
True eczema is rare in large animals.
In typical form
Erythema, papules and vesicles on the back of animal, weeping of the surface mainly in long haired dogs.
Itching, scratching and rubbing which aggravate the condition.
In chronic form
Alopecia in many areas of skin.
Scaling and hypertrophy of skin.
Pachydermia but no discontinuity of skin.


Diagnosis
The clinician must define the cause and exclude other disease ,but it is difficult.
Treatment
Improve environmental condition of the animal, change of bedding and diet, will be useful.
Treatment of internal and external parasites.
Sedatives in early stags.
Antihistaminies.
Corticosteroids as anti-inflammatory.
Local application of astringent on weeping area, In addition to local anesthetic agent.
(6) Alopecia
Alopecia is deficiency of hair or wool coat. It is a manifestation of many diseases as eczema, dermatitis, and mange.
Etiology
In most of species, hair loss occurs normally in the spring and autumn for the coat to be changed. However, hair loss may be due to failure of follicle to produce a fiber or it may due to damage hairs previously.

(A)Failure of follicle to produce hair fibers

Inherited hypotrichosis, symmetrical Alopecia. The skin in the affected area becomes completely bald.
Congenital hypothyroidism (goiter) due to deficiency of iodine in dam.
Congenital, after viral infection of dam as in Bovine Viral Diarrhea in cattle and sheep.
Infection of follicles or neurogenic due to damage of peripheral nerve.

Sertoli cell tumors in Male dog.

(B)Damage of producing fibers
It is mainly symptomatic Alopecia due to other diseases.
Dermatomycosis as ringworm, (dermatophytosis).
Poisoning of thallium or molybdenum.
Deficiency of copper and zinc and vit. A, vit. E.
Excessive palm - whale or soybean in milk replaces of calves usually result in weakness of hair fibers.
Traumatic as in sweat itch of horses.
In case of symptomatic alopecia it is a temporary case or condition that will be improved by removal of the original causes.

Pathogenesis

In many of metabolic alopecia there is weakness of fibers, which degenerated rapidly.
In congenital Alopecia, there is a failure in follicles to form fibers.
Damages of nerve ending and blood capillaries are impaired.
Chemical depilation may occur by cytotoxic agents , cytoplasmic degeneration in follicle of hair (chemotherapy).
Clinical findings
Stumps of breakageor new-formed fibers are seen.
Skin may be shiny and thinner than normal (this is true only when fibers fail to grow).
There are manifestations of primary disease.
Scratching or rubbing.
Treatment
Treatment of primary causes.
Improve the diet with balanced quantities.
Improvement of blood supply of skin.
In gonadal disorders, castration or administration of gonadal hormones might be useful in reactivation.

(7) Dermatitis

The term dermatitis include those conditions characterized by inflammation of the deeper layer of the skin, including the lymphatic with secondary involvement of epidermis.
Etiology
The causes and types of dermatitis in all animals classified into:
1- Bacterial dermatitis:
Due to invasion of bacteria as in udder impetigo in cattle.
Pyoderma due to Staph. aureus.
2- Mycotic dermatitis
Ringworm
Strawberry foot Rot, (dermatophilus pedis).
3-Viral dermatitis
Poxvirus infection.
Contagious pustular dermatitis.
Lumpy skin disease in cattle.
Foot & Mouth disease, vesicular exanthema.
Vesicular stomatitis , mucosal disease.
Blue tongue and bovine malignant catarrh.
4- Parasitic dermatitis
Mange and other mites.
Myiasis of hypoderma and others.
5- Nutritional dermatitis
Deficiency of vit. B. complex, vitamin, A, zinc, nicotinic acid, riboflavin, biotin, pantothenice acid.
6- Physical dermatitis
Sunburn and photosensitization.
7- Chemical dermatitis
Arsenical compound.
Potassium , mercuric , iodide.
8- Allergic dermatitis


Pathogenesis
Involvement of deeper layers including blood vessels, lymphatic and epidermis.
Black necrosis at the site of inflammation.
Erythema with other factors causes an increase in the thickness of the skin accompanied by edema.
Pain or itching.
Clinical findings
Erythema and hotness of the affected part of the skin.
Vesicular lesion and edema of skin.
Scab formation, necrosis or gangrene may occur.
Phlegmon may be developed, distinctive suppurative lesions.
Systemic reactions may occur ( such as toxemia, septicemia ).
Secondary bacterial infection may result in pus formation.
Treatment
Treatment of the primary cause.
Supportive treatment by local and systemic application.
Antihistaminic.
Antibiotic administration to prevent secondary complication.
Parentral fluid should be administered in case of shock.