Help for Scratching Animals

By Dr. Ed Mapes

Stonebridge Animal Hospital
McKinney, Tx

Scratching is one of the most common complaints pet owners bring up during veterinary visits. We have enjoyed a respite from the number of cases seen during the winter months, but as the temperatures and length of daylight increase, so has the caseload of scratching pets.
This begins a series of articles designed to inform pet owners of the multitude of causes for itching (pruritus) in their pets, how allergic reactions occur, diagnostic measures at our disposal, and treatment options available. Today we’ll discuss some of the most common causes of itching.

External parasites are usually easily diagnosed and relatively simple to treat. Fleas are the most common offenders, but we also look for lice and ticks and lesions from biting flies. Fleas and ticks cause itching directly by the bite wound they inflict (injecting saliva into the wound to prevent blood from clotting), but some animals also develop an allergic reaction to the bite that heightens the itch produced. This is called flea allergy dermatitis (FAD). Sometimes we find very few fleas on an animal that presents with a severe itch — that’s the allergy at work.
Mange is the term used to describe infestation with microscopic organisms (mites) that are most closely related to spiders. They burrow into the skin, digesting dead cells and debris while laying eggs to reproduce. Two of these mites are seen most commonly; Demodex folliculorum and Sarcoptes scabiei.
Demodex is diagnosed most often, seen typically iin young pit bulls, bulldogs, and boxers; but it can arise in any breed. Demodex cases can be localized or generalized, depending on the extent of infestation and the dog’s immune response to the organisms. Simple cases appear ass small hairless areas on the ears, elbows, top of the head, or trunk. They typically do not cause a great deal of scratching unless bacterial infection occurs secondarily.
Sarcoptic mange causes small reddened sores and very severe pruritus and is often complicated by infections of the lesions, with abrasions from scratching and biting at the skin. Sarcoptes is far more likely to be transmitted to humans than is Demodex, so prompt diagnosis is important.
Ringworm is a dermatolica problem caused by the presence of fungal organisms-this is known as dermatophytosis. Some fungal species (microsporum canis and species of Trichophyton) are the main culprits. Ringworm produces circular grey, crusted, hairless skin lesions that causes relatively little itch unless secondarily infected.
Another type of fungus affects the skin in a less dramatic fashion; these are yeast organisms that can only be identified by microscopic examination. Malassezia is a dermatological yeast that can also produce scratching. Malassezia often occupy the ear canals, chin, lips, perivaginal, and rectal areas. The yeast infections are usually seen in moist, inflamed areas of the skin and are often malodorous.
Allergic reaction (hypersensitivity) to substances in the environment is behind a great deal of the skin disease we treat. This is call allergic dermatitis, and our task is to determine the nature of the problem and best mode of therapy to alleviate the discomfort. Any foreign substance entering the body (called allergens when the animal is hypersensitive to them) is recognized by the immune system, which attempts to eliminate it. Allergies result when these protective measures become overzealous, producing abnormal and heightened responses – thus the term immune hypersensitivity.
Virtually any protein an animal touches, tastes, or breathes can cause hypersensitivity; usually manifest as itchy skin on the feet, face, and torso, watery eyes and nose, loose stools, and infected ears. A more severe form of allergy response is known as anaphylaxis, in which overwhelming reaction occurs and causes shock, severe swelling of airways, pulmonary congestion, and even death.
Another form of allergy is referred to as contact allergies – reactions against substances the animal touches – like new carpeting or a plastic food bowl. Also known as delayed hypersensitivity or cell-mediated immune reactions, these usually manifest as the feet, belly area, or face.
The most common form of allergic dermatitis is the result of reaction to substances in the environment; pollen, dust mites, house dust, mold spores, feathers, and even other animals. These reactions occur when the allergen lands on the skin or is breathed by the animal. As you can imagine, the list of possible allergens is a long one.
Once it has entered the body, the allergen comes into contact with components of the immune system known as immunoglobulins, which stimulate release of substances from mast cells or lymphocytes that create the allergy reaction. The most important of these substances include serotonin and histamine.
This type of allergy can occur seasonally or on a year-round basis, depending when the offending allergens are present. Symptoms are seen only during the time of exposure to that allergen, though animals commonly react to more than one substance. Spring and fall – when plants are pollinating the most heavily-are the worst times of year for seasonally sensitive patients.
Year-round symptoms cause more serious problems for the animal, which never has a respite from the itch. Many patients fall into this category; they’re either allergic to multiple substances or to those within the home or react to elements of their food.
Food allergies account for about 5 percent of skin cases and are among the most serious of the year-round allergies. Animals develop immune sensitivities to proteins in their food and react throughout the year. These patients often have a history of chronic dermatitis, skin infections, intermittent vomiting and diarrhea, and severely itchy skin. Symptoms usually begin at the ages of two to four years, but can also arise in older animals.
A new test has become available that uses saliva to detect sensitivity to the 24 most immunogenic foodstuffs. This has made diagnosis of food allergy/sensitivity much more reliable.
As you can imagine, diagnosing the cause(s) of skin ailments can be challenging. We strive to become partners with pet owners, working together toward a resolution of these sometimes challenging cases.

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