DERMATOLOGY
employed allergy tests (allergy serology, intradermal
skin testing) and it is suspected that false negative
and false positive results do occur. Allergy testing is
also unable to detect dogs with atopic like dermatitis,
which is a condition clinically identical to canine
atopy, but in which an IgE response to environmental
or other allergens cannot be demonstrated.
Allergen prescription formulation
Selection of allergens for inclusion in an allergen
specific
immunotherapy
vaccine
involves
interpretation of the medical records of the particular
dog, especially as regards seasonality and animal’s
habitat (i.e. presence of specific allergens in the
animals environment) in conjunction with IgE levels
of individual allergens achieved with allergy serology.
•
•
•
Non-seasonal – environmental allergens, indoor
moulds.
Seasonal – spring (trees/ectoparasites), summer
(grasses/outdoor moulds/ectoparasites), autumn
(weeds/outdoor moulds)
Seasonally non-seasonal – seasonal and non-
seasonal
allergens
involved
concurrently.
(Seasonal atopy complicating adverse food
reaction/Ectoparasites
complicating
non-
seasonal atopy).
Mould extracts should not be mixed in the same
vials as pollen extracts, as the pollen allergens will
be degraded by the mould proteases during storage.
Therefore, mould extracts should be in a separate vial
and administered as a separate injection.
Allergen Specific Immunotherapy (ASIT)
Although numerous treatments exist for atopic
dermatitis, many have significant side effects and
drawbacks and not all are universally effective. Allergen
specific immunotherapy (ASIT) is the only proven
treatment for atopic dermatitis that works through
reversing the underlying immunopathogenesis of the
disease with the added advantages of being virtually
free of serious adverse effects, even with prolonged
use, offering substantial, long-lasting relief in many
patients.
ASIT vaccines are available in two forms namely an
injectable form given by subcutaneous injection every
2-4 weeks (SCIT) and a sub-lingual immunotherapy
(SLIT) vaccine, which is applied orally under the
tongue on a daily basis.
ASIT has emerged as an important and useful tool in
the long-term management of skin disease in atopic
patients. Allergen avoidance, prevention of allergen
contact, antimicrobial therapy, pharmacotherapy
and/immunotherapy are crucial in the therapeutic
management of atopic patients. Pharmacotherapy
is frequently needed when a rapid and short-term
response is required or when allergen avoidance
is difficult or impossible to implement, while ASIT
is utilised as a long-term therapy that reduces or
eliminates the need for pharmacotherapy.
Mechanisms of action of ASIT demonstrated in humans
include early reduction in effective cell (eosinophils,
basophils, mast cells) activity, followed by a long-
term immunological shift from a lymphoid T helper
2 (Th2) cell to a T helper 1 (Th1) cell response and
the development of immunological tolerance. These
changes are accompanied by increases in immune
regulator cells and certain cytokines. This all results in
an increase in allergen specific IgG (especially IgG4)
which impairs the effector functions of IgE and with
extended application initiates a decrease in allergen
specific IgE.
In canine atopic patients a shift from Th2 to Th1 cell
response, increases in immune regulator cells and
certain cytokines plus increases in IgG levels, have all
been demonstrated and suggests that mechanism of
action in dogs is similar to that in humans.
Subcutaneous immunotherapy (SCIT) is available
as two methods based on availability and regulatory
approvals in North America versus Europe. SCIT
vaccines produced in North America are aqueous,
saline phenol preserved extracts. The protocol begins
with frequent injections of dilute extract, progressing
to less frequent injections of concentrated extract as
a maintenance therapy. In Europe alum precipitated
allergen extracts are utilised, with absorption of
the allergen molecules to an aluminum hydroxide
adjuvant, which provides a slower release product
which has the advantage of less frequent injections.
Time to efficacy with SCIT varies from up to 8 months
with aqueous allergens and 9 months with alum-
precipitated allergens. Those dogs which have not
responded by this time are unlikely to.
These sublingual immunotherapy (SLIT) vaccines
have an excellent safety record due to the unique
nature of antigen capture at this sublingual site. This
oral immune site comprises various antigen presenting
cells (Langerhans cells, myeloid and plasmacytoid
dendritic cells) with a distinct location in the mucosa
and sub-epithelial lamina propria. These dendritic
cells are tolerogenic being key in the induction of
immune tolerance, resulting in induction of peripheral
(skin, respiratory tract) tolerance to allergens. The
oral mucosa also contains limited numbers of mast
cells and eosinophils mainly located in the deep
submucosa explaining the good safety profile (lack of
adverse reactions) of SLIT.
SLIT shows a far more rapid clinical response with
some dogs showing significant improvement in 3
months, while many have substantial improvement by
6 months.
Issue 04 | SEPTEMBER 2018 | 17