Milk Allergy
In some mares, a milk allergy develops when the pressure inside the mammary glands increases enough that some stored milk components (usually the protein casein) are forced into the mare's circulatory system. The mare's immune system reacts to these “foreign” proteins in her blood. This results in a hypersensitivity reaction that may be localized (hives and/or swelling involving only a small part of the mare's body) or generalized and severe (anaphylactic shock). Recovery is usually prompt once the mare's mammary gland is emptied.
Sweet Itch
Sweet itch is a skin allergy in horses that is usually seen in the warm summer months. It is associated with some insect bites, especially night feeding Cullicoides spp. These insects include midges (“no-see-ums”) and are a member of the black fly family. Sweet itch is characterized by intensely itchy patches that appear along the dorsal &/or ventral midline of the horse. Sweet itch is identified by skin tests. Treatment includes keeping the horse away from the biting insects and providing medication to control the itching and allergic reaction. Preventive measures include destroying the flies' breeding grounds, spraying stable areas with an approved pesticide, and using a fan to move the air around the horses.
Type II Reactions
Type II reactions can lead to several types of diseases in horses, including anemia, blood clotting problems, and skin and muscle disorders. They may be associated with other immune system disturbances, such as cancers of the lymphoreticular system, or triggered by a drug, vaccine, or infection. Most often, the triggering cause cannot be pinpointed. Also known as antibody mediated hypersensitivity, ________________or __________________ are involved and the complement system is often activated. Antibodies are produced against self antigens on body’s own cell. The antibody binds to the antigen and triggers the immune system to destroy it.
Immune-mediated Hemolytic Anemia
This type of anemia is a severe and life-threatening disease in which the immune system sees its own red blood cells as foreign invaders and produces antibodies to destroy them. Red blood cells are manufactured as usual in the bone marrow, but once released into the bloodstream, they are attacked and destroyed by antibodies. Signs of anemia may include fatigue, paleness of the lips and gums, and depression, along with jaundice in some cases. Other signs your veterinarian may find include an enlarged liver or spleen.
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