Health Resource

Immune-mediated (also called autoimmune) diseases are caused by a hyperactive immune system where the body attacks its own cells.  Some Hungarian Vizslas have been diagnosed with immune-mediated blood diseases - such as thrombocytopenia and haemolytic anaemia.  Below is a little bit about these conditions, and some information on a research project that is investigating immune response genes in dogs that have been affected by immune-mediated disease.

Immune-mediated thrombocytopenia (IMT) is a fairly common blood disorder in dogs, so it is seen in most breeds, Hungarian Vizslas included.  Immune-mediated haemolytic anaemia (IMHA) has also been seen in Australian Vizslas, as has Evans syndrome - where both IMT and IMHA occurred concurrently.  

Immune-mediated thrombocytopenia (also called autoimmune thrombocytopenia)

"Thrombocyte" is another name for platelet.  Platelets help with clotting of blood - usually when there are small damages to the blood vessels, they stick to each other to form a mass and plug the leak.  The term for low numbers of thrombocytes is ‘thrombocytopenia’.  In dogs with immune-mediated thrombocytopenia the immune system attacks the dog’s platelets.  If this occurs at a rate faster than the body can replace them, bleeding and bruising caused by bleeding, occur.  

Immune-mediated haemolytic anaemia, (or autoimmune haemolytic anaemia (AIHA))

“Anaemia” means reduction in the number of red blood cells.  In immune-mediated haemolytic anaemia the red cells are destroyed (haemolysed) by the body’s own immune system, faster than the body can produce new cells.  The red blood cells transport oxygen around the body, and signs of anaemia usually relate to the lack of oxygen – weakness, lethargy and exercise intolerance for example.

Pure red cell aplasia

In this uncommon disease, antibodies attack the red blood cells that are being formed in the bone marrow.  This results in a lack of red cells being produced.  This has been diagnosed in Australian Hungarian Vizslas.

Other immune-mediated diseases also occasionally occur.  

Causes of immune-mediated disease

The majority of cases of immune-mediated thrombocytopenia and haemolytic anaemia are idiopathic (we don't know why they happened), but the diseases can also occur secondary to cancers, infections, or as a drug-induced reaction.  In primary immune-mediated haemolytic anaemia or thrombocytopenia, there is a failure of the normal control mechanisms of the immune system.  Normally the immune system attacks foreign antigens like bacteria, but in autoimmune disease, self-antibodies (autoantibodies) recognise an antigen on the red blood cells or platelets, respectively, resulting in their destruction by the immune system.  When these diseases are secondary (triggered by other factors), antibodies are specific for a foreign antigen, but this antigen is associated with the surface of the red blood cell or platelet, and the cells are destroyed as bystanders.  

Because immune-mediated diseases are more common in some breeds than in others, it is thought some dogs, or families within a breed may be genetically predisposed to develop autoimmune disease, just as autoimmune disease runs in human families.  It's not something we are currently able to test for, nor predict.  The major histocompatibility complex (MHC) is a group of several gene families that are responsible for the regulation of immune response.  Many human autoimmune diseases are associated with particular MHC gene combinations, and recent research has found that some autoimmune diseases in dogs are also associated with certain MHC haplotypes.  Differing MHC types have been found to be associated with immune-mediated haemolytic anaemia in different dog breeds, and particular MHC gene combinations have been found to be associated with hypothyroidism in Dobermanns and Labradors, but not other breeds tested so far.  A number of years ago in the USA, it was reported that immune-mediated thrombocytopenia and haemolytic anaemia may be present in some Vizsla families.  Given how inter-related our Aussie Vizslas are (98.5% of pups registered between 2001-2005 were descended from our first two imports), common heritage/families can describe our breed population.