Adenovirus in Foals

Severe combined immunodeficiency (SCID) is an autosomal (not linked to the chromosomes for sex) recessive genetic disease affecting Arabian foals. These foals cannot produce B and T lymphocyte cells and thus cannot mount an antigen-specific immune response. These foals seem normal at birth, but in the first few months of life, as the passive transfer (immune protection from the mare’s milk) wears off, they suffer from a variety of infections.

One of the most common causes of infection in SCID foals is adenovirus, which causes a severe bronchopneumonia. These foals all die before five months of age. Testing for the SCID gene is now available.

Symptoms and Types

• Nasal discharge
• Coughing
• Trouble breathing
• Diarrhea
• Fever
• Weight loss

Causes

• Lack of B and T lymphocyte cells (white blood cells) needed to fight off infections; due to being an Arabian foal homozygous for severe combined immunodeficiency

Diagnosis

In the past testing was done by observing for clinical signs and checking complete blood count results for a consistent dearth of white blood cells (lymphocytes). To support a diagnosis a radial immunodiffusion test commonly known as a Coggins test was performed. If it showed no serum IgM in presuckling blood serum from the foal, then the foal has SCID.

Currently, a genetic test for SCID is available. It only requires whole blood or cheek swabs and is dependent on polymerase chain reaction techniques to amplify DNA present. This test can also reveal carriers of the gene so as to allow horse owners to prevent two carriers from breeding (producing an SCID foal).

Treatment

If you can cure the foal of adenovirus, any number of other bacteria, viruses and parasites can still infect the foal since it has no antigen-specific immune system to protect it. There is no cure for this condition, and since all foals die around or before five months of age, euthanasia is recommended.

Living and Management

Before breeding your Arabian mare or allowing your Arabian stallion to service a mare, be sure to test your horse for severe combined immunodeficiency syndrome in case it is a carrier. This is of the utmost importance, as this disease is fatal in foals.