Ask Dr Iain-Allergies
Dear Dr. Iain….
Dear Dr.Iain, I think my dog has eczema, or it might be dermatitis? Are there many types of allergies in dogs and how does a vet work out what my dog could be allergic to? Jacki Gauci
Allergies result in unhappy itchy dogs, whether it’s their ears, feet, tummy, rump or all over, which unsurprisingly we call a generalised allergy or dermatitis or eczema. Sometimes dogs can have gastrointestinal symptoms due to a dietary allergy or even more rarely a respiratory complaint due to an allergen they are inhaling, but overwhelmingly it is the itchy skin and its consequences that they will suffer.
The first consultation. Sometimes an itchy dog doesn’t have an allergy but something else like mange, or hormonal disease or one of many types of skin infections (pyoderma). A complication is where allergies and other conditions can also create a pyoderma where the dog can also become seborrhoeic (where the inflamed skin will become greasy and flaky which encourages yeast and bacterial infections). So don’t be surprised if your vet wants to trial a product for sarcoptic mange if your dog visits bushland where they might encounter a wombat burrow or dead fox from which this very contagious mite could be caught. This mite is rarely detected on microscopic examination of skin scrapings and so we often will just treat for it when we see a dog that has visited the ‘country’ and is very red and itchy around the muzzle and lower legs. Demodectic mite is usually easily seen on scrapings that your vet might take. Sometimes looking at your dog in a darkroom with an ultraviolet lamp (Woods lamp) can detect ringworm fungal growth but unfortunately many ringworm infections won’t glow under Woods lamp exam and so we might then pluck some hair for fungal culture and take a sample from the skin with sticky tape and look at that under the microscope to look for evidence of ringworm or yeast and bacterial infections. We might take blood samples to diagnose hormonal diseases like hypothyroidism and Cushing’s disease. Finally, especially in recurrent cases where infections are involved we might suggest a swab for bacterial culture and antibiotic sensitivity test or even a biopsy if there seems to be a skin growth or abnormal pattern of colouration or depigmentation associated with the skin lesions and we are concerned there might be a cancer or autoimmune type disease (such as pemphigus or lupus) involved.
Otherwise, possibly after running some of tests already mentioned, we might suggest your dog is more typical of having an underlying skin allergy.
What are the main types of skin allergies? An important concept to understand is that many dogs can have multiple allergies which can be a combination of two or more of the common allergies we see, namely,
Flea Bite Allergy (a.k.a. flea bite dermatitis, summer eczema)
Contact Allergy (a.k.a. contact dermatitis)
Food Allergy (a.k.a. food hypersensitivity)
Inhalant Allergy (a.k.a. atopy)
There are some others like those triggered by a drug, or mosquito bite sensitivities where the dog might have red itchy spots occurring on their head and ears and those where they have become allergic to yeast (Malassezia species) that are proliferating in their ears and skin as a result of usually having one or more of the above allergies in the first place!
I explain the concept of multiple allergies by pointing to the floor and saying that floor level represents a dog with no allergies and no itchiness at all. Then I’ll gradually raise my hand while saying we now have a dog who is developing an allergy or allergies until we reach a point (usually I’ll stop at chest level) which is the itch threshold where they are now actually clinically inflamed and itchy. Now, you might have a dog whose flea allergy (or food allergy or contact allergy) takes us to knee or even stomach level but it isn’t until they develop an inhalant allergy that they reach the itch threshold and all the trouble begins. You might also have a dog where one single allergy alone is sufficient to reach the threshold and you can’t always tell which type is the cause at first glance, although with flea and contact allergies you can usually tell that they are probably involved.
So sometimes we can treat only one or two potential causes of an allergic condition to bring the dog back below that itch threshold and control the problem. This is why many vets follow a stepwise approach which might mean a few revisits but reaches a satisfactory result more quickly than expecting a cure in one consultation and then starting again at another clinic some months later. What is usually my first step you might ask?
Step one: flea and contact allergies and symptomatic treatment (but Doc, I’ve already used flea treatments before?!)
Fleas? After eliminating other causes of the skin problem I’ll usually recommend starting a first class flea product and will be confident that this will be effective especially for those dogs that have weepy itchy hotspots and possibly chronic inflammatory changes such as alopecia, darkened and thickened, leathery skin changes at their tail base or rump. However, dogs can be itchy and inflamed elsewhere with flea bite allergies which are by far the most common skin disease seen by vets.
There is no point arguing with the vet that because you never see fleas or have never been bitten by a flea yourself that it can’t be flea allergy. It can be! It just takes one flea bite every several days in a highly allergic dog to cause them to start biting and scratching. After a feed of blood from your dog or cat, a female flea then proceeds to lay several hundred eggs that fall straight out of the pets coat into their bedding, garden beds, carpet as if they were a little mobile salt shaker but dispensing flea eggs instead of salt of course!
You must treat all the dogs and cats in the household with a reputable product forever. Commonly owners only treat the dog or cat that has the allergic hotspot which if flea products killed fleas instantly before they can even land a bite would be adequate, but they don’t. You must treat all the pets,there is no point treating one pet while the fleas are populating freely on the others. Owners also often give up flea treatment after only a few months because the ‘product doesn’t work’ as the dog is itchy again and they’ve seen a flea. Remember that you might have thousands of flea eggs in the environment that will gradually hatch over the next several months if it is warm and the flea pupae detect the vibrations of your dog’s presence nearby. The flea you have seen has only just recently jumped onto your pet and will be killed. It can take several months of treatment even with a reputable topical product such as activyl, advantage, frontline or the new monthly flea tablet, comfortis, nexguard or even the 3 monthly bravecto before you will be exhausting the numbers of fleas in the environment and might be able to relax any antinflammatory treatment. Other good topically applied products which will kill fleas, protect against sarcoptic mange for those dogs in rural environments and are also monthly heartworm preventatives are revolution and advocate. For those living in tick areas thennthe topical monthly products frontline or advantix, or the monthly oral product nexguard or 3 monthly bravecto are great choices. If you have breeding animals then care is needed when choosing a product as not all have been thoroughly tested on pregnant and lactating bitches, however, frontline and revolution for example are safe for these cases and pups over eight and six weeks of age respectively. Of course, vacuuming, washing bedding and possibly in some cases, judicious use of environmental flea sprays or bombs can be helpful to reduce the environmental flea population which accounts for virtually all the flea population.
Ned says, "Mmmmm. This must be Comfortis. It is the only edible one here."
Contact Allergy? We suspect this where relatively hairless areas like the tummy, under the front legs (axillae) and sometimes around the lips and eyes are involved. Contact allergies only occur where the allergen can come into direct contact with the skin and as you might suspect it is things like grass, ground cover plants or weeds, carpets, rugs and bedding that can responsible. We will recommend keeping the lawn mowed short and avoiding walks through long grass, pulling out any Wandering Jew or similar ground cover varieties that are notorious for causing contact allergies, providing cotton or linen bedding rather than synthetic or woollen bedding and avoiding plastic food bowls.
Antibiotics, shampoos, supplements? Your vet might also dispense antibiotics to treat any secondary skin infection which might be tablets, an injection, ear drops or lotion. We’ll often recommend using gentle hypoallergenic soothing shampoos and conditioners unless there is fairly chronic and extensive greasy seborrhoea and/or infection in which case we might recommend a antibacterial, antifungal and antiseborrhoeic shampoo such as Malaseb or Mediderm.
Some vets will recommend starting an essential fatty acid supplement to add to your dog’s diet such as EFA-Z or Megaderm, while some are available as topical products such as Essential 6. Essential fatty acid supplementation can help modulate an inappropriately overactive immune system which is essentially what an allergy is.
Cortisone is still the most effective treatment to quickly settle any skin inflammation and itchiness and will stop the dog aggravating themselves while you are eliminating potential underlying causes. Side effects such as excessive drinking and appetite are at the very least a nuisance but in some cases in especially older animals with cardiac, endocrine and other chronic diseases can be quite problematic. Another complication is that animals already on non-steriodal anti-inflammatory drugs (NSAID’s) for problems such as arthritis cannot also take cortisone without running the risk of gastrointestinal ulcers and bleeding. In these cases we might rely on a anti-histamine medication.
We generally will use a cortisone lotion for small hotspots, or a cortisone spray such as cortavance which especially reduces the amount of cortisone absorbed into the body yet still has the anti-inflammatory effects on the skin that we need. However, if the affected areas are just too extensive then a systemic dose of cortisone is needed whether as an injection, some of which can be effective for up to a few weeks or more preferably in a short acting tablet such as prednisolone where we try to quickly reduce the dose to as low as possible every second or more days. Sometimes we might add an anti-histamine tablet which can help reduce the dose of cortisone needed but rarely is as effective as cortisone if given alone.
If the client has already been practising excellent flea control or is revisiting after doing all these things and can’t seem to be able to wean their dog off the cortisone and other medications without their dog’s allergic symptoms recurring, then we move on to a hypoallergenic food trial in case a food allergy has been the reason that the dog remains above that ‘itch’ threshold.
Step two: Food allergies (but Doc, I’ve already been feeding some chicken and rice?!). Food allergies are usually due to a particular meat protein in the diet or sometimes due to grain products (wheat, rice amongst others). If a dog is allergic to beef then they will be affected whether the beef is in canned or dry dog food, fresh beef or bones, raw hide chews, dairy products or beef liver or other treats. Food allergies gradually develop after sometimes years of becoming hypersensitive to the food responsible, so it doesn’t matter if the dog had previously eaten the same food without having itchy skin. There is no simple blood test to diagnose food allergies so we will suggest putting the dog on a strict hypoallergenic diet for at least 8 to 12 weeks. It must be strict as one snack on food containing the allergen can make a dog itchy again for a few weeks. A hypoallergenic diet can be a food that we know contains a meat protein that the dog has never encountered before and so is unlikely to be allergic to. Examples include Eukanuba sensitive skin diet which is fish protein based or Hills d/d venison based diets. Alternatively we might try my favourite one, Hills z/d where the chicken based protein has been hydrolysed so that the dog’s immune system is unlikely to be sensitive to it even if they are allergic to chicken. Another excellent product is Hills Ideal Balance Chicken and Potato Grain free. We need to trial the food for at least 8 weeks because it takes several weeks for the effects of any previous diet to which we might have been allergic to leave the body. Also, over this time we may be gradually attempting to wean the dog off cortisone again while keeping up the flea control and other supportive treatments previously mentioned. If the allergy returns in spite of our efforts so far then we start to consider an inhalant allergy as the main problem on the next revisit.
"Daaad...this is sooo boring and I don’t even eat this stuff"
Step three: Inhalant Allergies (Atopy). If all else has failed yet the dog is comfortable on a low dose of cortisone tablets every second or third morning then many owners will validly continue this treatment and sometimes we find that we can stop the tablets over the winter months which is typical if a seasonal pollen is the cause of a inhalant allergy.
Dogs can be allergic to pollens, fungal spores, house dust mite amongst other inhaled particles just like we can be. However, while we tend to get hay fever, asthma and bronchitis problems, they will get skin and/or ear problems.
If the patient isn’t tolerating the side effects of cortisone or suffers from other chronic diseases or needs medications such as NSAID’s for arthritis that make cortisone undesirable or even dangerous to use then we can look at testing to find the allergens responsible.
Unfortunately, the patient needs to have stopped cortisone for several weeks before we can either run blood tests that are available to detect inhalant allergy antibodies to about 70 common allergens or even better, a veterinary dermatologist can carry out skin patch testing to test for even more allergens. These tests can lead to the dermatologist formulating injections containing minute amounts of the offending allergens, such as specific pollens or house dust mite, that are given regularly for several weeks or months in gradually increasing doses to desensitise the patient. Overall, these treatments have about a 70% success rate where success mightn’t mean a cure but at least a reduction in any cortisone or anti-histamine medication needed to provide adequate relief. This treatment is more successful where the dog is found to be reactive to only several allergens. Another treatment that is especially useful for those dogs that are reactive to dozens of potential allergens where desensitising injections are less likely to work is cyclosporine therapy. Cyclosporine (e.g. Atopica) is an immune suppressant that is highly effective against inhalant allergies without the side effects associated with cortisone. It can occasionally have its own side effects like gastrointestinal upsets but these are often managed by lowering the dose for a time. It has no effect in controlling other allergies. Many dogs can be stabilised by gradually reducing the dose to a capsule given every second or third day. Sometimes vets might offer this treatment without running atopy tests but it isn’t the recommended way where if the atopy test proves negative then we are better to then proceed to skin biopsies rather than using an expensive drug like cyclosporine unnecessarily.
Hopefully this overview of allergic skin disease is helpful in explaining why dogs sometimes do need to revisit and that there is no point rushing into atopy testing when adequate flea control and maybe a low allergy diet might adequately resolve the problem by getting the dog below that ‘itch threshold’. Fortunately, our Griffons don’t seem to be an allergy prone breed; however, it’s a different story if we’re dealing with one of those small white breeds!
Iain Mitchell B.V.Sc (Hons), M.A.C.V.Sc.
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