Weak Immune System Due to Hereditary Disorder in Dogs

Recurrent or persistent infections can indicate an immunodeficiency disorder, especially in young animals. Most cases of immunodeficiency are related to a secondary disorder, such as a tumor on the thyroid or an allergic reaction to something in the environment. Primary immunodeficiencies are disorders that are genetic in nature and often related to the breed of the animal. This deficiency in the immune system leaves the affected animal more open to contracting communicable diseases and less able to rid their body of them once they are acquired. There is no consistently effective treatment for these disorders in canines and they often prove fatal very early in life.

Primary immunodeficiency disorders are genetically transmitted dysfunctions in the immune system that weaken the dog’s natural ability to fight infections. This disorder is often fatal before the canine reaches maturity.

The most significant symptom of a weakened immune system is the development of secondary infections. There are many different ways that an immune system can be undermined by hereditary factors. Immunodeficient animals may acquire multiple diseases at the same time. Symptoms that are common across most immune deficient canines can include: 

• Fever
• Loss of appetite
• Lymphadenopathy
• Recurrent infection
• Severe reactions to infection
• Skin lesions
• Weight loss

Types        

Canine leukocyte adhesion deficiency

• This is an autosomal recessive mutation that can affect Irish Setters and Irish Red and White Setters
• The white blood cells in affected dogs are unable to adhere to invading cells, and therefore become unable fight off infections
• This form of immunodeficiency is usually fatal before the canine reaches 6 months of age

Immunoglobulin Deficiency

• This disease is characterized by the failure of the body to produce immunoglobulins
• This particular disorder is often hereditary, but can also be a secondary form of immunodeficiency when triggered by disease or inadequate maternal antibodies in the first several days of life

Selective Immunodeficiencies

• Some breeds have a predisposition to acquiring specific bacterial, viral and fungal infections
• Severe combined immunodeficiency (SCID) - This form of immunodeficiency involves a defect in antibody production and cell-mediated immunity characterized by a lack of either T or B cells
• This can be either an X-chromosome linked disorder similar to the human form of the condition or an autosomal recessive form that more closely resembles the equine version of the disease
• Both are often fatal within the first 4 months of age for canines

The causes of these inherited diseases are passed down from parents to offspring. There is a strong breed related component to most of these disorders.

• Canine Leukocyte Adhesion Deficiency (Irish Red and White Setter, Irish Setter)
• Immunoglobulin Deficiency (Beagle, Chinese Shar-Pei, German Shepherd
• Selective Immunodeficiencies - some breeds have a genetic predisposition for susceptibility to a specific disease 
• For example Rottweilers are prone to canine Parvovirus
• Long-nosed breeds (German Shepherd and Collies)  are prone to aspergillosis in the nasal passages and systemic aspergillosis
• Severe Combined Immunodeficiency (SCID) is predisposed in the Basset Hound, Cardigan Welsh Corgi, Jack Russell, Rottweiler, and Toy Poodle

Primary hereditary immunodeficiency disorders are uncommon in dogs. Dogs that present with recurrent and persistent infections usually have immune systems that have been suppressed due to a secondary cause such as tumors, severe viral infections such as distemper, or as a side effect from radiation or chemotherapy. The first thing your veterinarian is going to want is a medical history for your dog to determine how often the patient is getting ill, and how long each illness lasts. If a hereditary immunodeficiency is suspected blood tests will be run to determine the amount and efficiency of the immune cells in the body. Tests will also be run to determine if the levels of thyroid hormone are adequate as the thyroid is often involved with immune disorders. Due to the speedy lethality of some of these disorders, the diagnosis is sometimes delayed until the necropsy is completed. There are genetic tests available for some of these disorders which can give a definitive diagnosis. If your pet is diagnosed with a genetically induced immunodeficiency tests should also be run on siblings. It is particularly important to test the close female relatives in disorders that are X-linked recessive traits. Female dogs who have these genetic anomalies may never develop the disorder, but they are likely to pass it to their offspring and should not be bred.

In most primary disorders relating to the immune system, there is no real treatment at this time. Supportive therapy may be attempted with antibiotics or antifungals to treat the acquired infection but it often proves to be resistant to treatment. In humans with these disorders bone marrow transplant is the treatment of choice. This is a complicated process and is often not technically feasible for canines at this time. In most cases, genetically related immune deficiencies are fatal before the dog reaches maturity. Treatment, therefore, focuses on reducing the effect of symptoms from secondary infections and attempting to prevent any further infections. Due to the immunocompromised animal’s susceptibility to contagions, this can prove a daunting task and success is rare. A colony of dogs affected by the X chromosome linked SCID has been established to further research in both the disease itself and in more effective treatments for the disorder, particularly better methods of bone marrow transplant and gene therapies. These findings may help treat cases of X-SCID more effectively for canines and for humans in the future.

These disorders are most often fatal quite early in life, generally before the pups reach 6 months of age. A common cause of death in puppies with impaired immune systems are the vaccinations designed to protect them, particularly the canine distemper vaccination. Their immune systems are often inadequate to fight off the modified live version of the vaccination. As there are fewer reports of transient adverse responses in canines treated with the modified live vaccination it is often recommended over the killed virus. Those dogs that survive the modified live vaccinations or are given the killed version of their vaccines are still predisposed to infection, particularly bacterial, and have difficulty recovering from any contagion that they do acquire. Testing and genetic counseling are the most practical approaches to reducing the number of animals affected by these disorders.