Immune-mediated Thrombocytopenia
Immune-mediated thrombocytopenia is caused by the destruction of Ig-G bound thrombocytes by the immune system in much the same manner as red blood cells are destroyed in immune- mediated hemolytic anemia. When an animal has thrombocytopenia, clotting does not occur correctly. Even minor injuries can cause uncontrollable bleeding, further decreasing the number of red blood cells. The most frequent signs are bleeding of the skin and mucous membranes.
Pemphigus foliaceus
Pemphigus foliaceus involves an autoimmune reaction to the collagen found in the skin. More about pemphigus foliaceus may be found in Section IV: Skin Diseases in this text.
Type III Reactions
Type III reactions or disorders are among the most common immune-mediated diseases. An immune complex is a combination of antigen & antibodies. The location in the body where the immune complexes are deposited determines the signs and the course of the disease. This usually involves inflammation. It also involves IgG or IgM as well as neutrophils. As seen prior, neutrophils lead to bystander injury resulting in greater inflammatory responses due to lysosomal enzymes.
Hypersensitivity Pneumonitis
This condition occurs when horses are exposed to substantial amounts of inhaled antigens, such as those found in dusty feeds or moldy hay. The lung tissues become inflamed, and signs of respiratory distress, such as difficulty breathing or rapid breathing, may be noticed about 4 to 6 hours after exposure to the antigen. The most effective treatment involves detecting and removing the source of the antigen. Your veterinarian may also recommend certain drugs, such as corticosteriods to help control the allergic reaction.
Vasculitis
Vasculitis caused by immune complexes occurs in horses. At first, abnormalities are seen as purplish red dots appearing on the skin. Depending on which blood vessels are involved, signs may appear on the legs, mouth, or lips. Drugs are a frequent cause of vasculitis. The disorder is diagnosed by performing tests on samples removed from the affected areas. Vasculitis is treated by stopping the offending drug (if implicated as the cause) or by giving drugs that suppress the immune system.
Purpura Hemorrhagica
Purpura hemorrhagica is an immune reaction characterized by swelling and abscesses. It is a serious complication of infection with Streptococcus equi bacteria. The bacteria can spread from one horse to another by inhalation or ingestion of infected fluids or cells. It can also spread
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