Allergic diseases are a significant cause of morbidity in small animals; in particular, they are commonly seen in dogs and cats. Canine and feline atopic dermatitis, recurrent otitis externa and chronic respiratory issues are major contributors to these issues.
Treatment on the front line often involves medications such as corticosteroids and antihistamines. These focus on relieving the clinical signs but frequently do not address the underlying cause of the allergy. In recent years, allergen-specific immunotherapy (ASIT) has been implemented in general practice. This method aims to modify the immune system’s response to these allergens and achieve long-term disease control.
Understanding allergic diseases in small animals
Allergies occur when the immune system misidentifies innocuous substances known as allergens and perceives them as harmful. (These allergens can be environmental components such as pollen, dust mites, parasites and certain foods.) When an animal encounters an allergen, their immune system creates a specific memory profile. Subsequent exposures trigger an exaggerated response to this allergen, leading to self-inflicted harm.
This response manifests as clinical signs such as inflammation, pruritus and erythema. Histamine is a potent chemical released by immune cells when they come into contact with allergens. Histamine triggers inflammation in surrounding tissues, resulting in the observed clinical signs.
Commonly seen allergens in small animals include:
- Flea allergens (animals usually react to the saliva from flea bites)
- Food allergens such as beef, chicken, dairy, wheat and soy
- Inhalant allergens such as dust mites, pollens, moulds and storage mites
Diagnosis of allergies
Diagnosing allergies in small animals can be challenging. It will often involve a combination of clinical signs, history and exclusion trials, as well as specific tests. There are three main types of allergy tests used:
- Intradermal skin test (IDST): injecting small amounts of different allergens into the skin. If the animal has an allergy, a raised bump appears at the injection site for that specific allergen. This test can sometimes require sedation due to the number of injections involved
- Blood test: a blood test identifies antibodies in the animal’s blood that react to specific allergens. The blood test is quick and convenient. However, blood tests can sometimes have lower accuracy compared to IDST
- Food elimination trial: feeding a special hypoallergenic diet for a set period of time to analyse clinical signs and assess if they improve. If clinical signs resolve, systematically reintroducing different ingredients can help identify the food allergen
How does ASIT work?
ASIT involves gradually injecting the animal with increasing doses of specific allergens. Over time, this controlled exposure retrains their immune system, fostering immunological tolerance. The immune system eventually becomes less sensitive to the allergens and stops overreacting. This desensitisation of the body to allergens means the body’s immune system is trained to stop attacking allergens and to tolerate their presence as a non-allergic animal would.
Veterinary practitioners should formulate a unique batch of the injection specific to the individual animal that is being treated. The liquid is usually injected under the skin, exactly like a vaccine. A loading dose is usually required in the first 12 weeks. This starts with a small dose and increases gradually every two to four weeks to reach 1ml; this is the maintenance dose. After the initial 12-week period, a maintenance dose of 1ml is given every four weeks until the bottle is finished. When the bottle is finished, a new bottle can be ordered if the vet deems this necessary.
There are a few different types of ASIT available in veterinary practice:
- Subcutaneous immunotherapy (SCIT): injections containing the allergens are administered under the skin
- Sublingual immunotherapy (SLIT): drops or tablets containing the allergens are placed under the pet’s tongue for absorption. This is a more recent development and is useful for animals that struggle with injections
What are the benefits of ASIT?
The advantages of ASIT include:
- Long-term relief from allergies: if successful, allergen-specific immunotherapy provides long-term relief from clinical signs of allergies
- Reducing the need for medication: animals that respond well will not require symptom-relieving medication such as steroids
- Better quality of life: if symptoms such as itchiness are controlled, the animal will be more comfortable and have a much better quality of life
- Safe with minimal side effects: compared to alternative treatments, such as corticosteroids, the side effects of ASIT are less of a concern, and the treatment offers a safer alternative for controlling the symptoms
- Prevention of complications: if allergies are left untreated, it can lead to secondary skin infections and other distressing complications. ASIT can help prevent these from occurring by controlling allergies
How is ASIT implemented in general practice?
Diagnosis and identification of allergens
First, a diagnosis must be made, and potential allergens identified using one of the methods mentioned above. A thorough work-up must be carried out. It is vital to rule out other causes of skin disease, such as parasite infestations and infections.
Frank discussion with client about treatment options
It is very important to discuss all treatment options with the client to ensure they are able to make an informed decision. Owners must be educated about the pros and cons of all options and any potential side effects that may occur. It is also important to consider the temperament of the animal and how likely they are to tolerate the administration of medicines. If ASIT is chosen, the route of administration must be discussed, as some pets will not tolerate one method or the other.
Treatment protocol
The treatment protocol must be determined. This includes the starting dose, the frequency of the injections and the ongoing monitoring. Each protocol will be unique to the individual pet.
Long-term management
Going forward, regular monitoring and adjustments to the ASIT protocol may be necessary throughout the treatment course.
Considerations for and potential limitations of ASIT
Despite the fact there are many benefits and advantages of ASIT, owners must be made aware of potential downsides to the treatment. These include cost, whether they are able to commit to treatment in the long term and the various side effects and responses to ASIT.
Cost
ASIT can be an expensive treatment option for owners. The cost will vary depending on the chosen method of administration, the number of allergens involved and the duration of treatment.
Long-term commitment
ASIT is not in any way a quick fix. It requires a long-term commitment: typically months or years of owner compliance and consistent administration.
Not a cure
ASIT is not a cure for allergies. The aim is to modify the immune response and provide the animal with long-term relief.
Side effects
As with all drugs and medications, there are side effects. In general, ASIT is very safe; however, there are still mild side effects reported, such as local reactions at the site of the injection or transient allergic flare-ups.
Varied response
The majority of animals will have an excellent response to the therapy, while some others will have no response at all.
Final thoughts
Allergen-specific immunotherapy (ASIT) is a valuable treatment option for combating allergies in dogs and cats. ASIT allows for a targeted approach that addresses the underlying cause of the allergic reactions that wreak so much havoc on our patients. Although not a true cure, ASIT provides a long-term solution for allergies while improving patient quality of life and comfort at the same time.
ASIT is a successful way of enabling owners to actively manage their pet’s allergies and witness a significant transformation in their quality of life and general well-being. It is fast becoming a widely recognised and recommended treatment option, now used frequently by vets and dermatologists when addressing allergies in small animals.
