Five common things that make your dog itch!

Rusty Muse DVM, Diplomate ACVD, Animal Dermatology Clinic-Perth (WA)

#1  Atopic dermatitis

What is atopic dermatitis (atopy)?

Atopic dermatitis is a reaction by an individual animal to environmental pollens from grasses, weeds, trees, mould spores and house dust mite. A dog with atopic dermatitis is exposed to airborne allergens through the sparsely haired, thin skinned anatomic regions and thus the common areas of involvement include the undersides of the feet, armpits, tummy and groin as well as the face and ears.  Dogs can also be exposed to airborne allergens through aerosol exposure and ingestion of allergens through licking. Most dogs develop atopicdermatitis as young adults, i.e. between one and three years of age.

What are the signs of atopy?

The most common clinical sign is itching, usually involving the muzzle, around the eyes, ear flaps, armpits, groin and paws. Some dogs may have recurrent ear infections. As a result of chewing, licking, rubbing and scratching the skin becomes inflamed and is prone to secondary infections with bacteria and yeast. In dogs with chronic disease there is hair loss and the skin often becomes thickened, scaly and black. The hair coat may feel greasy and be associated with an offensive odour.

How do we diagnose atopy?

In order to define the most accurate allergy profile for dogs, we generally perform skin and blood testing in our atopic patients. An intradermal allergy test or allergy skin test involves clipping a patch of hair from the side of the flank and pricking the skin with a tiny amount of purified allergen extract. A positive reaction is a raised red swelling observed thirty minutes after injection. The skin test can be affected by a number of drugs including antihistamines and corticosteroids.  Blood allergy testing can also be performed. A blood test detects allergen specific IgE and while not all laboratories are the same and have the same reliable results, the current laboratory that we use has a very specific and accurate test.

How do we approach management of atopy?

We usually manage atopic dogs using a combination of allergen specific immunotherapy (allergy vaccine) and medical therapy. We combine the results of the skin and the blood test to develop an allergy profile and then we select the most appropriate allergens to make the allergy vaccine. We usually administer the induction phase of the vaccine in hospital under medical supervision (see Rush Immunotherapy) and then the maintenance phase of the allergy vaccine is either given at home or administered by your referring veterinarian. It is important to remember that the vaccine is successful in approximately 70% of dogs and cats and takes approximately six months to take effect. In order to alleviate discomfort we design an individual medical program to be administered for at least the first six months to give your pet relief from scratching and itching. A successful outcome with allergy vaccine is usually measured by a reduction in the required medication to control itch as well as a marked improvement in the skin and hair coat. If the allergy vaccine is successful in achieving this then it is generally continued for a period of approximately three years. In some cases we can reduce the frequency of the vaccine administration in the second and third year.

#2 Food allergy dermatitis

What Is a Food Allergy?

Food allergy is one type of adverse immunologic reaction to a substance in the diet (the “allergen”).  In most cases, a protein, such as chicken, lamb, beef or fish is the culprit, though any carbohydrate, fat or dietary supplement may contain an allergen.  It is NOT a reaction to a specific brand of food, or a result of switching diets.  Most commercial and home-cooked diets, treats, and raw-foods share ingredients that may be allergens, no matter how high quality they are.  The pet may have been fed the offending allergen for over two years before developing signs of a food allergy. Food allergy can occur at any age, in any breed or gender, and patients may react to one or two items or several.

What Does Food Allergy Look Like?

Most food allergic pets are itchy continuously.  They will scratch, chew, lick or rub at their skin. Often the head, ears, underarms, groin and paws are affected; however, any area of the body can be involved.  Pets will often lose hair or develop infections because of the scratching and inflamed skin. This will result in bad odor, scaly skin, rashes, moist waxy skin, or ear infections.  Between 25%-50% of animals will have intestinal problems such as large or excessive numbers of bowel movements, mucus in stools, and flatulence.

How is Food Allergy Diagnosed?

There is no accurate blood or skin test to determine if a pet has a food allergy.  Simply switching from one commercial brand food to another is usually not sufficient, as these diets have many shared ingredients. The only reliable method of diagnosing a food allergy is undergoing an “elimination diet trial” and then performing challenges. This means feeding dogs will be fed a special diet that is either a home-cooked or prescription diet containing a single new animal or vegetable protein, such as rabbit or beans; and a single new carbohydrate, such as yams or green peas.  Some of the commercial elimination diets contain common proteins that have been altered (hydrolyzed i.e. made smaller) so the body doesn’t recognize them as allergens.  Regardless of the diet chosen, it needs to be fed exclusively for at least 8 weeks to see improvement.  No other treats, supplements or foods can be fed or even mistakenly ingested during this period.  Your goal is to prevent your pet from ingesting anything other than what you have been instructed to feed and water. During the diet trial skin infections or other sources of itch and discomfort will be addressed by the veterinarian. It is imperative that your pet be examined by the veterinarian prior to ending an elimination diet, even if you believe your dog is cured or not at all helped by the diet.

#3 Bacterial infections

What are bacteria?

Bacterial are organisms that cause infections in dogs and there are numerous species that can create these problems.  Among these in dogs are Staphylococcus pseudintermedius, S intermedius, S schleiferi, S hyicus and rarely S aureus.  However S. pseudintermedius is by far the most common of these organisms creating disease in the dog.  Bacterial infections can be manifested as pustular eruptions but also can present as papular lesions or crusting and scaling with red colour change to the skin.  Epidermal collarettes with a central area of darkening and pigmentation with a ring of scale is also typical of bacterial infections.  The normal intact epidermal barrier of the skin provides protection from colonization by normal resident bacterial organisms but in cases of underlying disease in which that barrier becomes compromised or an altered host immune response develops (commonly atopic dermatitis) secondary bacterial pyoderma can become a factor that requires veterinary management.

What do they mean and how do we test for bacteria?

Basic diagnostic testing, such as skin scrapings, fungal cultures, biopsies, food elimination diets, allergy testing, and thyroid and adrenal function testing, should all be considered to determine the underlying cause in cases of recurrent pyoderma.  Almost all cases of bacterial pyoderma are a secondary issue and thorough evaluation of primary disease becomes critical in resolving infection and preventing relapses.  If an underlying cause cannot be identified, the likelihood of chronic relapsing infections will be high.  Cytological evaluation of surface exudate or pustular contents is the most rapid test to assess the presence of pyoderma or bacterial overgrowth.  This can be easily done in the clinic setting with routine Dif-Quik stains. There is no substitute for cytology in clinical assessment of dermatology cases and this is best practice for your veterinarian to perform.  Culture and sensitivity testing is indicated in cases that have not responded to appropriate therapy based on cytology, in cases of suspected resistant infections, and in cases of severe immune suppression.

How are bacterial infections treated?

Topical therapy should be used in all cases of pyoderma.  It can be of particular value in treating and controlling chronic recurrent cases. It decreases bacteria counts and reduces surface colonisation, helping to prevent recurrences. There are many topical antimicrobial vehicles: shampoos, whirlpools, soaks, rinses, sprays, lotions, gels, creams, and ointments. Shampoos are the most practical and effective tool in clinical practice. Whirlpools and soaks are more labour-intensive and require additional equipment. For localised lesions, sprays, lotions, gels, creams, and ointments can be used.  When selecting systemic antibiotic therapy for pyoderma, there are important considerations. These include an appropriate choice of antibiotic implemented at the optimal dose and correct duration of therapy. Antibiotics are usually initially selected empirically or based on the results of skin cytology. In more chronic, refractory cases, or when gram-negative bacteria are seen on cytology; antibiotic selection should be based on culture and sensitivity.  It is very important to follow the minimum recommended dose regimen to achieve optimum results. There is also a wide range of dose regimens, depending on the severity, chronicity, and scarring of the pyoderma.  Antibiotic therapy needs to be continued until the pyoderma resolves and then 1 week beyond clinical cure for superficial pyodermas and 3 to 4 weeks beyond for deep pyodermas. This usually requires 3 to 6 weeks for superficial and 6 to 12 weeks or longer for deep pyodermas.

#4 Malassezia (yeast) infections

What are yeast infections?

Yeast infections on the skin of dogs are most commonly caused by the yeast Malassezia pachydermatis. This is an organism that normally inhabits the skin and the ear canal of dogs, and does not usually cause a problem. However, when conditions are right, the organism will overgrow and cause significant skin and/or ear disease, discomfort and itch. Some breeds are more prone to yeast overgrowth including the Basset hound, West Highland white terrier, poodles (ear) and others.  Dogs that develop a yeast infection can present with different clinical signs. Some dogs have only ear infections, while others will present with any combination of hair-loss, redness, darkening of the skin, thickening of the skin, flakiness, greasiness, and/or skin odour. At times, the skin or ears maybe itchy and flaky without the obvious redness and odour.

What causes the yeast to overgrow?

Generally, abnormal growth of yeast on the skin occurs when the skin is compromised in some way. Allergies, immune suppression, seborrhea (excessive skin dryness or greasiness), and other skin barrier defects can all contribute to yeast overgrowth. Dogs will then develop an allergic reaction to these organisms resulting in itch. This also means that even very low numbers of organisms can result is severe irritation and itch.

How do we diagnose this condition?

Cytology is the most common method that yeast infections are diagnosed. Ear cytology involves putting a Q-tip down the ear and collecting debris. That debris is spread on a slide and then stained with special stains and evaluated with a microscopic exam. Skin cytology is similar, except that the sample is collected by gently rubbing a glass microscope slide or a piece of clear tape directly on the affected skin. Cytology is used both to diagnose the condition as well as repeated with subsequent visits to evaluate response to therapy.

How is a yeast infection of the skin treated?

When these infections are treated, both the infection, as well as the underlying condition, are addressed, often simultaneously.

Oral Medication: Most of these infections (unless it is mild and confined to the ears) are treated with oral antifungal medication. The duration of treatment can vary from a few weeks to several months. As the numbers of yeast organisms decrease, the skin condition will improve and the itch will subside. The infection can recur depending on control of the underlying disease, and sometimes longer term maintenance therapy will be recommended.

Topical therapy: There are numerous shampoos, rinses, conditioners, medicated ear drops and ear flushes that address both yeast and the inflammation and itch associated with yeast infections. The regimen chosen will be determined by your dog’s specific infection and underlying condition.

Treating the underlying condition: Diagnosing and addressing the primary disease that resulted in the yeast infection is imperative for long-term control of yeast infections. This can involve allergy testing and subsequent antigen-specific immunotherapy, an elimination diet trial or increased flea bite prevention or other diagnostics that evaluate your dog’s immune system.

Overall, yeast infections are often a result of conditions that do not have a cure, but rather can be controlled. Your dermatologist will work to determine what diagnostics and treatments are suited best for your dog.

#5 Flea allergy dermatitis

But my pet doesn’t have fleas!   It may seem confusing to you that your pet might have a flea allergy when you never see fleas! How can fleas be the cause of your pet’s severe itch and dermatitis if you never see fleas? Flea allergy dermatitis results from a true hypersensitivity to flea bites, not damage from heavy flea infestations. Infrequent or intermittent flea bites can perpetuate severe symptoms. Because flea allergic animals spend so much time chewing and grooming, they often remove fleas before you get the opportunity to see them. Once a flea has bitten your pet the itch that follows can last 14 days! Flea allergy is NOT the same as flea infestation. Heavily flea-infested pets often show little to no discomfort, while flea-allergic pets may not tolerate even a single flea bite. The diagnosis of flea allergy is made by observing where the pet itches, not by the perceived presence of absence of fleas.

What does flea allergy dermatitis look like?

Flea allergy dermatitis affects both dogs and cats. When the flea bites your pet, a small amount of saliva is injected into the skin. Dogs and cats develop an allergy to components of the flea’s saliva, which can result in severe and persistent itching and resultant bacterial skin infections. Dogs tend to show hair loss, skin thickening, and redness over the rump, inner and outer thighs, and the tail-head area. The abdomen may be affected. Flea bites are also the most common trigger for “hot spots”, rapid forming patches of intense itch, inflammation, and pus..

What is important about the flea life cycle?

To reduce flea exposure it is critical to understand the life cycle of the flea. Adult fleas feed, mate, and lay eggs on pets and local wildlife. These eggs then fall to the ground (indoors and outdoors) and depending on the temperature and humidity, they can hatch in 2-50 weeks! Therefore it is critical to treat the pet with topical flea control to kill adult fleas, and treat the yard and house to treat eggs, larvae, and pupae which will grow into biting adults.

How is flea allergy dermatitis treated?

The most important aspect of treatment is the PREVENTION of flea bites. This involves the use of products that effectively and rapidly kill adult fleas, preferably before they can lay eggs, and environmental treatment to prevent eggs and larvae from growing into adults. Since no product is 100% effective at preventing flea bites keeping pets in flea free environments is the best way to prevent flea bites. Unfortunately, allergen immunotherapy (allergen vaccines) has been unrewarding in the treatment of flea allergy dermatitis.

There are many different aspects and options to flea bite prevention and flea control:  Topical products for adult flea control are a mainstay of therapy.  While the manufacturers of these products recommend monthly application of these products for general flea bite prevention, dermatologists may recommend more frequent or combinations for the flea allergic pet.  Each product has different strengths and weaknesses that help to determine which one is most appropriate in your situation.

There are oral medications available as well. Some of them provide an immediate and long lasting kill of the adult flea while others are used to interrupt the flea life cycle and are used for flea population control.  Environmental controls and measures aimed at controlling all stages of the flea life cycle are numerous. These can be very important, as the majority of flea populations are in the immature stages and live in your pets surroundings (unlike the adult that resides on the pet).

How long will my pet be itchy?

The itching may take from days to weeks to subside, even after the fleas are gone. Therefore, some pets benefit from additional anti-inflammatory medications. If infection is present, treatment with antibiotics will be necessary, as well. Shampoos and conditioners can be soothing to inflamed skin; however, frequent bathing may decrease the activity of topical flea medications. Generally, avoid bathing your pet two days before or after application of a topical spot-on flea product.

Overall, the best prevention of flea allergy dermatitis is a year-round, comprehensive flea control program tailored for your pet by you and your veterinarian.