Treatment and management of seasonal allergy problems in dogs

Many dogs affected with atopic dermatitis suffer from clinical disease at particular times of the year.

Dogs with reactions to allergens in the home environment, such as house dust mites, are usually uncomfortable during the autumn and winter months; those with reactions to pollens manifest a seasonal pattern that mirrors their pollen profile.

Atopic dermatitis is a diagnosis of exclusion and allergy testing is not necessary to confirm a diagnosis, but allergy testing, whether it is with in vivo intradermal allergy tests or in vitro serology, is useful in the author’s experience to help in the management of canine atopic dermatitis (CAD). The problem with many of the dogs that present with pollen allergy is when they first show clinical signs at the beginning of the pollen season they are so pruritic they need immediate symptomatic therapy.

Although, at this stage, an in-depth investigation and allergy testing are often not appropriate, basic diagnostic tests should still be undertaken.

Even if the dog’s clinical signs exactly match the rise in pollen count it is still important to ensure good flea control is in place and other ectoparasites, such as Sarcoptes and Cheyletiella, are eliminated. The institution of a hypoallergenic diet and therapy of concurrent infection is also useful and will usually reduce the dog’s need for specific anti-
inflammatory therapy. Symptomatic control of pruritus in such cases may include antihistamines, glucocorticoids, Janus kinase (JAK) inhibitors or ciclosporin. Antihistamines that may be suitable are listed in Table 1 (not licensed for veterinary use in the UK).

Antihistamine therapy can provide relief to some dogs, but many animals derive no benefit from treatment. In general, antihistamines should be used with care in dogs with hepatic disease or pregnant or lactating animals. The data sheets of each antihistamine should be checked for specific contraindications.

Glucocorticoids used appropriately provide excellent and immediate relief of pruritus in CAD where other factors are already controlled. Many dermatologists would suggest where a dog’s pruritus has been shown to be seasonal, and lasts less than three months, glucocorticoids are the drugs of choice. Short-acting oral drugs should be used either in the form of methylprednisolone or prednisolone. An oral anti-allergy dose of prednisolone for a dog, which can be divided, is 0.5mg/kg to 1mg/kg po daily.

Once remission is achieved, which should normally take three to five days, the dose should be reduced to the lowest possible alternate day regime. Where prednisolone produces unacceptable side effects of polyuria, polydipsia and polyphagia, methylprednisolone may be used following a similar regime, but with a starting dose orally of 0.8mg/kg to 1mg/kg po daily.

JAK inhibitors, although not yet widely available, will be exceptionally useful drugs in the management of seasonal CAD. They have a rapid onset of action and are well tolerated by most dogs – not producing the changes in thirst or appetite seen with glucocorticoids. These drugs work by inhibiting the formation of pruritogenic and pro-inflammatory cytokines by blocking interleukin 31 (IL31).

In CAD, IL31 has been shown to bind to the cell membrane on nerve cells to activate the JAK pathway causing itching. By selectively blocking IL31, drugs such as oclacitinib (the only licensed drug in this class for dogs) can produce very specific control of atopic pruritus. Although oclacitinib principally affects the JAK1 and JAK3 pathways responsible for itch, in rare cases it can affect the JAK2 pathways, which are involved in haematopoiesis, so manufacturers’ recommendations are that all dogs prescribed this drug should be monitored with blood samples, even if therapy is only to be used for a short period.

Ciclosporins are also effective in the control of CAD, but lack the rapid onset of action of glucocorticoids and JAK inhibitors. Ciclosporins can produce gastrointestinal signs in some dogs; however, they are tolerated best, and side effects are minimised, when they are introduced slowly over three to five days. With the introduction of liquid formulations, slow build-up of the drug is easier – especially in small breeds, which are often more susceptible to gastrointestinal upsets.

Ciclosporins have the advantage over both glucocorticoids and antihistamines of not interfering with in vivo allergy testing when used to control acute disease. They are the author’s drug of choice in cases where further investigation is deemed necessary, due to the ongoing cost of such drugs as ciclosporins or JAK inhibitors or where dogs are manifesting unacceptable side effects from treatment.

Where drug therapy provides control of pruritus, but cost or side effects are a concern for an owner, allergy testing, and the use of allergen-specific immunotherapy, offers an alternative. This sort of therapy is usually not possible in the first pollen season, and actually not sensible.

Even if a rapid induction protocol is used for a vaccine, it will take several weeks to be prepared and several more, as a minimum, for benefits to be seen. This means many dogs are starting to become comfortable due to the seasonality of their problem before the vaccine is able to produce amelioration of their clinical signs. The author will generally undertake allergy testing during, or within three months, of the end of the pollen season to establish an appropriate profile and then monitor the patient to the end of the pollen season using symptomatic therapy.

It is useful during this time to ask the owner to keep an allergy diary to check the dog’s most pruritic periods match the allergens that have been identified on allergy testing. This means when a vaccine is to be formulated it can be matched closely to the dog’s pruritus profile. There are many great resources available that allow both veterinary surgeons and their pet-owning clients to monitor the pollen counts – allowing them to be able to manage their dog’s allergies more effectively. Table 2 is a basic pollen calendar that can be used to help guide clients on the times of the year they can expect their pet to be most unstable with the different pollination periods.

Once the seasonal pattern and the causative allergens have been identified and matched to the dog’s clinical signs, vaccines can be prepared for the following season. The author will generally start dogs on pollen-based vaccines immediately after Christmas and then check them as the dog’s specific allergenic insults peak.

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  Some treatments in this article are not licensed for veterinary use in the UK.