Foal Immunodeficiency Syndrome (Fell Pony Syndrome)

This disease is fatal, cannot be cured or adequately treated and is expected to result in the death of the horse.

Foal immunodeficiency syndrome (FIS), previously known as Fell Pony syndrome, is an inherited autosomal recessive disease. It causes fatal anemia and a compromised immune system. Affected foals have abnormally low levels of red blood cells and B-lymphocytes (a specific type of white blood cell). They become progressively anemic and lack the ability to produce their own antibodies, which makes them susceptible to infections. A causative genetic mutation has been identified, and a genetic test is available.

Symptoms

Exclusively found in

Treatment

There is no effective treatment for FIS. Supportive care and antibiotics may be used to treat secondary infections and prolong life, but affected foals ultimately have a shortened lifespan and should be euthanized humanely if their quality in life is poor.

Prevention

All Fell and Dales ponies used for breeding should be tested for FIS carrier status so that carrier-carrier matings are avoided. This will eliminate the production of FIS-affected foals and will eventually reduce the prevalence of the gene defect in the population. Implementation of this testing strategy has significantly decreased the number of FIS-affected foals, but it will take time to reduce the mutant gene frequency in the population given the large number of carriers.