Severe Combined Immunodeficiency (SCID) in Dogs

Severe combined immunodeficiency (SCID) is a genetic disorder associated exclusively with humans, mice, horses, and dogs. In dogs, only three breeds have ever been diagnosed with this extremely rare and devastating autoimmune disease: the Jack Russell Terrier, the Basset Hound and Cardigan Welsh Corgi. SCID is a rare immune disorder characterized by the puppy’s inability to fight recurrent systemic or localized infections of the eye, ear or respiratory system, as well as conditions such as distemper. When symptoms of the disorder arise in puppies under six months of age, SCID is attributable to inherited chromosomal mutation. These affected puppies will die anytime within six months of birth. Cause of death is ascribed to a failure to thrive or fallen puppy syndrome.

When invaded by bacterial, fungal or parasitic infections, puppies born with SCID are unable to provide an immune response on par with uninfected littermates. The embattled puppies become immunocompromised and weak once the mother’s protective antibodies are withdrawn. While only male puppies are susceptible to SCID (since it is an X-linked recessive trait), female dogs are carriers, and thus able to transfer the trait to their young.

Unfortunately, SCID is an incurable disease; however, relatively new forms of testing are not only able to identify dogs with this type of immune deficiency, but also successfully pinpoint the female carriers of the trait. Treatment options have largely been unsuccessful, particularly antibiotic therapy. In most cases, the puppy’s veterinarian will suggest humane euthanasia in order to prevent pain and suffering.

Severe Combined Immunodeficiency (SCID) is a rare genetic disorder that leads to early mortality in male Jack Russell Terriers, Basset Hounds, and Cardigan Welsh Corgi puppies.

A puppy born with severe combined immunodeficiency will present with symptoms typical of failure to thrive or fallen puppy syndrome. These puppies are unable to develop their own antibodies once maternal immune support is withdrawn according to appropriate developmental staging. Immediately vulnerable, these puppies are unable to sustain growth in the face of recurrent, devastating infections. Death typically occurs within three to four months of birth, even after consistent antibiotic treatment. Symptoms include:

• Retarded growth
• Inability to gain weight or weight loss
• Diarrhea
• Vomiting
• Lethargy
• Lack of palpable lymph nodes
• Respiratory infections
• Skin/eye/ear infections
• Death within four months

Types

Two types of SCID are associated with dogs. One is linked to the X chromosome and the other is an autosomal (not sex-linked) type that mirrors the disease in equines. Both types render an affected puppy unable to resolve the impact of viral, bacterial or fungal infections.

Canine severe combined immunodeficiency is an X-linked recessive trait, meaning that only male puppies are directly impacted by the disease. However, female dogs are carriers and capable of passing the genetic mutations to their offspring. Fifty percent of male puppies will inherit the mutation while in utero. A common cause of early mortality is canine distemper.

Affected puppies die from SCID, so diagnosis often occurs during necropsy. If the vet suspects an immune system disorder in a live puppy, an exam, blood testing, and an assessment of serum proteins is likely in order. If living, affected puppies will likely have been seen for a variety of infections. Testing the efficacy of antibiotics is helpful in establishing a diagnosis.

Unfortunately, severe combined immunodeficiency disease is incurable. Treatment options such as antibiotics are rarely successful in sustaining or improving the dog’s life. However, an experimental type of genetic therapy is currently being tested in puppies affected by inherited immunodeficiency disorders. Bone marrow transplants have also indicated some success, but due to high expense and the lack of specialists and treatment facilities, the surgery is mostly experimental.

Associated symptoms of systemic or localized infections will be treated with antibiotics, though success is very limited. The veterinarian will aim to keep the puppy comfortable during this period. The veterinarian will likely discuss the option of humane euthanasia for the dog, especially to avoid potential pain and suffering.

Since SCID is a fatal disease, recovery will not be possible. The veterinarian may discuss your options, such as keeping the puppy comfortable during its few months of life or else practicing humane euthanasia. Be sure to ask the vet any questions you have about the manifestations of this disease due to the likelihood of frequent, untreatable infections.

Since SCID is genetic, breeding puts other dogs at risk. While only males are affected by the disease, females are carriers of the genetic mutation. Since the disease leads to early mortality, discuss options for the puppy’s care with the vet.