Chapter 9 Vasculitis Flashcards
What is an allergic reaction?
An overreaction of the immune system to a normally harmless substance called an allergen.
What are IgE-mediated allergies also known as?
Type I hypersensitivities.
What characterizes IgE-mediated allergies?
Immediate onset after exposure to an allergen, production of allergen-specific IgE, binding of IgE to tissue mast cells, and release of inflammatory mediators.
What are common IgE-mediated allergies in horses?
Culicoides hypersensitivity and urticaria (hives).
What is Culicoides hypersensitivity?
A seasonal, recurrent allergic dermatitis in horses caused by salivary allergens from Culicoides midges.
What are the clinical signs of Culicoides hypersensitivity?
Pruritus, alopecia, excoriations, secondary bacterial infections, and lesions on various parts of the body such as the mane, neck, tail, face, ears, chest, and belly.
What factors influence the prevalence of Culicoides hypersensitivity?
Environmental exposure, genetic predisposition, age of the horse, and housing style.
What are the immunologic mechanisms involved in Culicoides hypersensitivity?
Production of allergen-specific IgE, mast cell sensitization, degranulation, and release of inflammatory mediators like histamine, leukotrienes, prostaglandins, and cytokines.
What is mast cell sensitization?
The process by which IgE antibodies bind to high-affinity IgE receptors on tissue mast cells.
What is the Prausnitz-Küstner reaction?
A method to transfer allergic reactions from affected to healthy horses via IgE obtained from allergic horses.
What role do Th2 cells and regulatory T cells play in Culicoides hypersensitivity?
Increased Th2 cell responses and reduced regulatory T cell functions contribute to the development of clinical allergy.
What diagnostic techniques are used for detecting allergen-specific IgE in horses?
Intradermal allergy testing and serological assays like enzyme-linked immunosorbent assays (ELISAs).
What is intradermal allergy testing?
A method where small doses of allergens are injected into the skin to observe immediate inflammatory reactions at the injection site.
What is the main goal of allergy testing?
To identify the causing allergen(s) for developing a management plan toward allergen avoidance and hyposensitization.
What are the limitations of serological allergy testing in horses?
Poor performance due to numerous positive reactions, many of which are likely false positives.
What treatments are available for IgE-mediated allergies in horses?
Symptomatic treatments like steroids, anti-histamines, allergen avoidance, fly control measures, and supportive care for skin lesions.
What preventive measures can be taken for horses with Culicoides hypersensitivity?
Managing turn-out times, using fly sprays, fly masks, whole body blankets, and providing smooth surfaces or brushes for rubbing.
What is urticaria in horses?
A condition characterized by lesions on the skin that can be round or have various shapes, and may or may not be associated with pruritus.
What are common causes of urticaria in horses?
Food allergens, insect bites, environmental allergens, drug or vaccine administration, and blood transfusion.
What histopathological findings are associated with urticaria?
Dermal edema with eosinophilic and/or lymphocytic perivascular infiltrates and increased numbers of mast cells, eosinophils, and macrophages in skin lesions.
What is recurrent airway obstruction (RAO) in horses?
A condition suspected to be mediated by hypersensitivity type I, characterized by mucus production, neutrophil accumulation, bronchial hyperreactivity, and bronchospasm.
What triggers RAO in susceptible horses?
Inhaled molds and organic dusts that induce inflammatory airway responses.
What is the controversy regarding IgE’s role in RAO?
Studies show conflicting results, and evidence for a causal role of IgE in RAO pathogenesis is still unclear.
What is the prognosis for horses with IgE-mediated allergies?
No cure exists, and allergies typically recur with allergen exposure. Clinical outcomes depend on allergen pressure and environmental conditions.
