The skin is the largest organ in the body and is the most common organ to show signs of allergy. It is very visible, touchable and accessible to sampling.
However case management of the itchy dog can be very frustrating and pruritus (the medical term for itchiness) can severely effect the quality of life of both your pet and you the owner. A detailed history is paramount to obtaining a diagnosis for your pet.
Do I have an Itchy Dog?
Below are a few questions that are asked as part of our dermatological consultation, if you answer yes to any of them you may have an allergic dog and this is the article for you.
Most common causes of itchiness in our dogs is ectoparasite infestation especially fleas. Flea allergic dermatitis is the most common skin disease of dogs and cats throughout the world! It is imperative that infestations of fleas on our pet is ruled out before embarking on further investigations.
Below is an example of a flea history that your vet may ask you:
- Which flea product is being used? - It is the correct dose?
- How often is the product been applied?
- Have any fleas been seen? - When and on which animals in the house?
- How many animals live in the house?
- Are the pets shampooed on a regular basis?
- What environmental control is being used? and how often?
The cat flea (C. Felis) is the primary flea causing the disease and below is a diagram of the life cycle of the flea, as you can see it involves both your pet and the environment, which is why we often advocate not just treating the pets in a household but also an environmental spray when trying to eliminate fleas.
It is also worth mentioning at this stage, that the cat flea can act as an intermediate host for the common tape worm (Dipyldium Caninum) and it is also important that effective tapeworm treatment is administrated if there is a suspicion of fleas.
It is the fleas saliva which contains the allergens that cause the reaction on your pets skin. Diagnosis involves a detailed history been taken, observation of clinical signs and trial treatment of flea control product.
Flea allergic dermatitis can occur in pets of any age but classically the signs are first noted in young adulthood. In the dog classical clinical signs are severe itching frequently effecting the tail base and back end of the the dog. Most of the lesions on the animal are a result of self trauma, these include redness of the skin, hair loss, secondary skin infections, thickening and darkening of the skin and sometimes open weeping skin.
Many flea allergic dogs exhibit a behaviour of jumping up suddenly and biting themselves, although because of the dogs efficient grooming style, as owners its often difficult to spot any fleas. When you come to the vet we will examine for fleas, close inspection of the animal is paramount and sometimes a flea comb may be used to demonstrate presence of fleas or flea dirt which is almost exclusivily made up of blood and when pressed on a tissue will be red.
Often if the vet has a strong suspicion of flea allergic dermatitis but can't find any fleas, which is common, they will still treat the pet to ensure it is eliminated from the work-up before moving on to any further more exhaustive testing.
Mites such as Sarcoptes Scabei (scabies), Demodex Canis, Cheylietella (also know as wondering dandruff) and Otodectes Cyamotis (ear mites) can all cause our dogs to itch and especially Sarcoptes Scabei (Sarcoptic mange) can be a complicating factor in allergic disease.
Sarcoptes Scabei (Sarcoptic mange)
Sarcoptic mange also known as scabies, is a non-seasonal, intensely itchy skin condition caused by infestations of the burrowing mite Sarcoptes Scabei. It has been demonstrated that mites applied to the skin can penetrate within 30 minutes. Following infestation the mites mate, and the fertilized females burrow, forming tunnels and laying eggs as they zig zag through the epidermis.
The feeding and the deposition of faeces within the skin expose our dogs to allergens which in dogs triggers an immunological response and most will develop moderate to intensely itchy skin initially affecting the outer ears, elbows, hocks and undercarriage of your dog. The skin becomes very red, hair is lost and the dogs skin becomes excoriated due to the intense itching. Secondary skin infections can develop and sometimes cause heavy scaling.
Canine Sarcoptic Mange is highly contagious, the majority of mites been transmitted by direct contact with infected dogs or foxes. It is also zoonosis which means it can cross the species and that means it can infect humans, also causing the condition Scabies.
Diagnosis again involves a concise history and examination of the pet. If we suspect Sarcoptic Mange we may wish to take skin scrapes so we can look under the microscope to visualize the presence of mites and/or eggs. Skin scrapes are taken from areas that show skin lesions, this is usually a quick process and can be performed in the consultation room. However some pets lesions may be too sore to sample and a light sedation may be suggested to retrieve the skin scrapings.
If no mites are retrieved on skin scrapes, which can happen, and the index of suspicion still remains high your vet may suggest either a blood sample, which can be sent to the laboratory, to look for circulating antibodies to Sarcoptes infection or your vet may suggest skin biopsies which will involve an anaesthetic to demonstrate the mite is present in your dogs skin.
Treatment is usually very effective at eliminating infection and there is rapid resolution of the pruritus and malaise in these patients. This is why a therapeutic trial can be used also as a diagnostic aid. It is often lovely to see a mite under the microscope to confirm diagnosis but as an attending vet I feel, trial Sarcoidal treatment is justified for any pruritic dog presenting with historical and clinical features suggestive of Sarcoptic Mange. It is important to remember that the mite can live off the body for a limited period, so all dogs known to be in contact with affected animals should be treated. Grooming equipment, bedding and the domestic environment should be treated with an appropriate spray. Attempts should be made to limit socialization with other dogs and foxes during treatment and persistently infected humans should consult their doctor.
This is caused by a mite called Cheyletiella, which lives on the skins surface. They live in little tunnels formed by the scale generated in response to their activity hence the name they are more commonly known as 'wondering dandruff'. This mite is not host specific so can transmit to other pets and humans often causing paticularly uncomfortable rashes. They can live off the body for up to 10 days so it is important to treat incontact pet mammals and the environment if diagnosis is established. Typically a dog will present with dandruff down their back, there may be mild redness of the skin itching is vanable, young animals often exhibit more obvious clinical signs than adults. In some dogs infection can cause traumatic dermatitis known as hot spots. Animals presenting with repeated hot spots should be investigated for Cheyletiella.
Diagnosis involves either skin scrapes or applying adhesive acetate tape (cellotape) to areas of the animals coat and examining these under the microscope. To the right is a picture of a cheyletiella mite under the microscope.
Atopy and Adverse Food Reactions
The second part of this article will focus on Allergic causes of itchiness in our dog's. We have touched on flea allergic dermatitis and are now going to look at Atopic dermatitis and adverse food reaction.
The definition of Atopic dermatitis is an allergic skin condition associated with an allergy to environmental allergens. While adverse food reaction is a clinically abnormal response to a dietary constituent. Adverse food reactions cannot be distinguished clinically from atopic dermatitis and the former needs to be ruled out before embarking on serum blood testing for environmental allergens.
Adverse Food Reactions
Adverse food reactions (Afr) can develop in dogs of any age, although in the majority of dogs clinical signs become evident as puppies or young adults before 3 years of age. Labrador Retrievers and West highland Terriers seem to be at increased risk. There is no gender predisposition.
The predominant presenting clinical sign of Afr in the dog is a non-seasonal itch. These dogs often have recurrent skin infections. The itch can involve any body region but is often identical to that of Atopic Dermatitis.
Recurrent ear infection is also common and may present in 56%-80% of cases with dogs with Adverse food reactions. Gastrointestinal signs have been recognised as a symptom of Afr. Intermittent vomiting, diarrhea, colitis and rumbling bowel sounds have all been noted in cases of Afr.
The current gold standard method is a dietary trial on a strict novel protein diet for 4-6 weeks, sometimes up to 8-10weeks. The selected diet should be based on a protein to which the dog has little or no exposure to . For the normal healthy adult dog, an unsupplemented single protein and carbohydrate diet can be fed without complications for the duration of the trial but MUST be balanced for long term feeding. Food trials can very difficult to implement correctly but can be very rewarding if the primary and only reason for your dog's itch is food allergen-related. If you feel your dog could possibly be suffering from Afr please speak to your vet.
As defined this is an allergic reaction to environmental allergens. these can be divided into indoor allergens such as house dust mites and storage mites and outdoor allergens such as grass pollens. Historically the allergens were presumed to be inhaled but it is more likely that the allergens are absorbed across the skin barrier. The presenting sign is itchiness with recurrent skin infections. Signs are typically seen in young adulthood between 1 and 3 years old, although atopic dermatitis can occur as young as 3 months or as old as 12 years.
Certain breeds seem to be predisposed to atopic dermatitis. A list can be seen below:
- Boston Terrier
- Bull Terrier
- Cairn Terrier
- French Bulldog
- German Shephard
- Golden Retriever
- Jack Russell Terrier
- Labrador Retriever
- Lhasa Apso
- Scottish Terrier
- Shar Pei
- Shih Tzu
- West Highland White Terrier
Dogs with Atopic dermatitis often show a partial or complete resolution of their symptoms on steroids. However, long-term use of steroids can cause clinical problems.
On exam, Atopic individuals have salivary staining over their body, they have loss of hair, the skin can be greasy or scaly and often ear infections are present. Atopic Rhinitis (snotty nose) and conjunctivitis can be present. The skin is often very red and sometimes thickened. Atopic individuals can have recurrent skin infections which can act as a complicating factor in their Atopy.
This can be difficult as you can see distribution and clinical signs are very similar to other skin conditions. The diagnosis is based on the history given, physical examination and ruling out all other differential diagnosis which may involve skin scraping, sellotape strips, trial treatments and food trials. Allergy testing is available in the form of a blood test at Taylors, please speak to your vet further about this.
If you feel your pet is suffering from Atopy, please come along for a consultation to discuss further diagnosis and management strategies.
So that was a whistle stop tour of the itchy dog. I hope it gave you an insight into common causes of the itchy dog and if any of the article resonates with you please don't suffer in silence with an itchy pet.