Allergic dermatitis in horses is likely to be deeper than the skin – review


A horse diagnosed with environmental and insect allergies. The itching in this patient was intense and resulted in significant self-trauma. Photo:

What first appears as allergic dermatitis in horses is likely to be part of deeper issues with the body’s immune response.

“It is now recognized that atopic dermatitis is not a single disease but a multifaceted clinical syndrome with different pathways in various subgroups of patients,” writes Rosanna Marsella in the journal. Veterinary sciences.

“Appreciating this complexity is clinically relevant as we are developing more targeted treatments that may work well in some patients but not in others. “

Marsella, a professor at the College of Veterinary Medicine at the University of Florida, conducted a review of the current understanding of atopic syndrome in domestic animals, highlighting possibilities for further study in the future.

She says sustainability and safety are essential for the long-term management of the disease, with the desired strategy being re-education of the immune system and reducing the need for rescue medications.

Atopic dermatitis is a clinical syndrome that affects both humans and animals. Dogs closely mimic the complexity of human skin disease, and much progress has been made in recent years in understanding the role of skin damage and identifying new treatments.

Horses and cats also develop atopic syndromes which include both skin and respiratory signs, but studies on these species are lagging behind, she says.

In humans, dermatitis is usually the first manifestation of an allergic disease and can be followed by respiratory disease later in life as part of what is called “atopic walking,” she writes.

Caring for horses, Marsella says allergy-related issues can manifest as respiratory or skin-related illnesses. Respiratory disease has been recognized to be similar to human asthma.

“Our understanding of atopic dermatitis in horses is very limited,” she says.

“It is commonly believed that this disease is the result of genetic and environmental factors, and it is common to see horses raised in colder climates not manifest the disease until later in life when they are moved to a warmer climate. hot with more pressure from insects and the environment. “

Many allergic horses are sensitized to a range of allergens and exhibit hypersensitivity to insects and various pollens.

Very little is known about the skin barrier and atopic disease in horses. A study in allergic horses showed abnormalities on electron microscopy compared to normal horses, but it is not known whether this is the result of inflammation or may suggest primary skin involvement that could facilitate absorption of the allergen. and increase the risk of sensitization.

The results of a recently published study suggest that the deterioration of the skin is a factor in horses allergic to insects.

“It is possible that some of these allergic horses are also atopic. Obviously, more work is needed before any conclusion can be drawn about the existence of primary skin involvement and pathogenetic relevance to equine disease.

Atopic dermatitis in horses presents as a recurrent itchy inflammatory disease that usually affects the face, ears, and hairless areas. Some horses may also have a history of lifting. Many atopic horses are also allergic to insects.

Controlling all of the itch triggers is crucial to the success of therapy, she says.

As in other species, the diagnosis of atopic dermatitis is a clinical diagnosis based on a suggestive history, compatible clinical signs and the exclusion of other diseases. More accurate serologic tests help make a diagnosis, she says.

Treatment still primarily involves the use of glucocorticoids and antihistamines, but no controlled studies have been performed to assess the effectiveness of these treatments in a controlled manner.

“The reports of these treatments are retrospective, uncontrolled studies where owners report the beneficial effects of these strategies.

“The same limitations apply to reports examining allergen-specific immunotherapy, which is recommended for atopic horses with a long allergy season. “

The reported success rate of allergen-specific immunotherapy in atopic horses ranges from 64% to 84%, with most of the improvement usually visible after the first year.

“Some horses can be maintained with allergen-specific immunotherapy alone, while others still need other drugs, although the amounts of drugs needed to make them comfortable may be reduced.”

Marsella has walked through several other potential pathways for relieving symptoms such as itching, but cautioned that our understanding of atopic dermatitis in horses is still rudimentary.

“Much work remains to be done to understand the role of the skin barrier and immune dysregulation in horses, and how this relates to other species.

“Based on what we know, it is reasonable to hypothesize that an alteration of the skin barrier may exist in horses.

“Identifying specific targets to decrease glucocorticoid use would be of immense benefit.”

Interleukin-31, an inflammatory cytokine that can trigger severe itching, appears to be a suitable therapeutic target, she says, describing it as a key player in several species.

In summary, Marsella says that atopic dermatitis affects animals in the same way as human disease.

“For animals such as dogs that have adopted lifestyle changes similar to humans (for example, increased exposure to clean indoor environments and increased consumption of processed foods), these changes have increased the risk to develop an allergic disease.

“It remains to be seen whether increased allergies also develop in horses and cats due to the fact that animals are dewormed more frequently and are therefore less exposed to parasites than in the past.

“Our approach to atopic dermatitis has changed over time to become more holistic and more focused on restoring rather than suppressing the immune system.

“Sustainability and safety are essential for long-term management,” she says.

“Regardless of the species, allergen-specific immunotherapy remains the most desirable long-term option with the goal of re-educating the immune system and reducing the need for rescue medication.”

Marsella, R. Atopic dermatitis in domestic animals: what is our current understanding and how it applies to clinical practice. Veterinary. Sci. 2021, 8, 124.

The study, published under a Creative Commons License, can be read here.

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