Auto-Immune Disease - Hemolytic Anemia
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About Auto-Immune Hemolytic Anemia
The third and last ailment resulting from auto-immune syndrome is Auto-Immune Hemolytic Anemia (AIHA), a disease in which the body attacks its own red blood cells (RBC). A pet suffering with AIHA will have a lower-than-normal number of red blood cells within the blood. This is termed anemia.
The exact mechanisms which trigger the dog's immune system to attack and destroy its own red blood cells are unknown. However, the disease process is believed to occur when antibodies coat the surface of the red blood cells, tagging them for destruction by the white blood cells. When the body is invaded by an infectious microorganism or agent, it produces a number of antibodies that range in specificity for that particular invading antigen. Some of the antibodies are highly specific, while others bind with less specificity. In the normal immune system, suppressor T-cells ensure that these non-specific antibodies do not react with normal host tissues. However, it is believed that some dogs may have poorly regulated T-cell suppression that allows these non-specific antibodies to attack their own cells.
Breeds Commonly Affected by AIHA and Other Factors
Such a genetic predisposition for AIHA has been suspected in several breeds of dogs, including Old English Sheep Dogs, Cocker Spaniels, Poodles, Lhasa Apsos, and Shih Tzus. Alternatively, some clinical studies exploring potential causative mechanisms have identified several non-genetic factors that may play a role in the development of this disease. For example, the observation that dogs afflicted with AIHA also demonstrate increased antibody titers to viral antigens for canine parvovirus and distemper virus suggests that certain viral infections may trigger an autoimmune reaction. Under such circumstances it is believed that there is adsorption of the virus to the red blood cell. When the immune system launches antiviral antibodies to destroy the virus, these antibodies target and destroy not only the virus, but the red blood cell as well. Similarly, some drugs (such as antibiotics, analgesics, and cardiovascular drugs) as well as viral antigens composing modified-live vaccines are also believed to induce AIHA through this type of mechanism.
Additional Risks of AIHA
AIHA makes a dog vulnerable to another disease, immune-mediated hemolytic anemia (IMHA). IMHA refers to all anemias that occur when the immune system mistakenly destroys its own blood cells secondary to an immune attack directed against an underlying condition such as cancer, endocarditis, or heartworm, or by unidentifiable causes, as in AIHA.
A veterinarian can diagnose AIHA. The clinical signs of AIHA are usually gradual and progressive, but occasionally an apparently healthy pet suddenly collapses in an acute hemolytic crisis. The signs are usually related to lack of oxygen supply. The hemoglobin in RBC is the primary carrier of oxygen in the blood.
The Role of Blood
Blood is considered an organ. It has its own complex and diverse development,
structure and functions. Its unique form, cellular tissue suspended in fluid
plasma, allows it to serve as a main distribution system throughout the body.
Cellular tissues composing the blood include: the red blood cells, which provide
oxygen to tissues of the body; the white blood cells, which prevent invasion
of microorganisms or other foreign substances; the lymphocytes, which carry out
immune surveillance; and the platelets, which are involved in keeping the components
of the blood in balance. Remarkably, all of these cellular components originate
from a common source, called stem cells, located in the bone marrow. These stem
cells give rise to a mature colony of cells which as they continue to divide
and mature undergo a series of changes, a process known as differentiation, and
eventually develop into the specialized blood cells indicated above.
Anemia is a condition brought on by abnormalities which lead to a deficiency
in the number of red blood cells. Although the average life span of a circulating
red blood cell is brief in most organisms (approximately 4 months), under normal
circumstances the red blood cell mass is maintained at a constant level because
new red blood cells are made as old red blood cells are destroyed and removed
from circulation by the white blood cells. When this balance is disturbed and
the level of red blood cells decreases to a point at which demand exceeds the
capacity of the bone marrow to produce them, anemia develops. Because integrity
and function of other organs in the body are dependent upon red blood cells to
deliver oxygen to their tissues, if the red blood cell number decreases to a
point at which the body is unable to compensate for the decrease in oxygen transport,
serious and irreparable tissue and organ damage may occur. Conditions which may
cause a decrease in the circulation of red blood cells include excessive blood
loss (hemorrhage), impaired ability of the bone marrow to produce new red blood
cells, or increased rate of red blood cell destruction.
When a large percentage of red blood cells (RBC) are affected, and they are removed faster then they can be replaced, the animal shows external signs of the disease. To the untrained eye, signs include weakness, lethargy, anorexia, and an increase in heart rate and respiration. Heart murmurs, pale mucous membranes (gums, eyelids, etc.), and discoloration in the urine and/or stool may also be present. More severe cases also have a fever and icterus (jaundice), which is a yellow discoloration of the gums, eyes, and skin. This is due to a buildup of bilirubin, one of the breakdown products of hemoglobin.
Causes of AIHA / IMHA
Unfortunately, as of now, the veterinary medical field has not discovered why an individual dog gets AIHA/IMHA. Certain breeds, such as Cocker Spaniels and Poodles, are at a higher risk than other breeds. Middle-aged female dogs are also at a higher risk. However, immune-mediated hemolytic anemia may occur in any breed at anytime.
Evidence suggests that recent vaccinations (DHLPP), along with the administration of certain medications like sulfa-trimethoprim antibiotics, may be associated with a higher incidence of IMHA. Dogs with serious infections or cancers in their body may also develop IMHA. The thought for the underlying cause is that something (e.g., vaccine, cancer cells) triggers the immune system to react and to create antibodies. Accidentally, the antibodies also destroy the red blood cells and sometimes also the platelets (idiopathic thrombocytopenic purpura), and therefore, the first sign of illness may be anemia.
Summary
In summary, AIHA/IMHA is a life-threatening immune disease that can cause damage to vital organs through the lack of oxygen supply associated with the resultant anemia. Owners of pets with AIHA/IMHA face a guarded to poor prognosis for the pet at the time of diagnosis. If an underlying disease such as cancer is discovered, the prognosis becomes complicated by the limitations associated with the underlying cause as well.
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