Immune-deficiency diseases have serious consequences and often lower the body’s defenses against infection. Some are inherited, and others are caused by viral infections or cancer.
Phagocytosis is an essential mechanism of the immune system. Phagocytes are cells that engulf (phagocytize), digest, and kill foreign invaders. Phagocytes rapidly respond to infections as part of the nonspecific (innate) immune response. They can also serve as part of the adaptive immune system by presenting antigens to other cells in the adaptive system, thereby alerting them to the presence of the foreign invaders. Phagocytes are produced in the bone marrow, spread throughout the body via the bloodstream, and then gather in either tissue or the blood. Within tissues, they are found in the skin and mucous membranes, spleen, lymph nodes, the coverings of the brain and spinal cord, bone marrow, and near blood vessels throughout the body.
A deficiency in phagocytosis can be caused by a low number of phagocytes in the blood or by a defect in their ability to act normally. They can be congenital (a birth defect) or acquired (caused by diseases or drugs). The deficiency causes an increased susceptibility to bacterial infection of the skin, respiratory system, and gastrointestinal tract. These infections respond poorly to antibiotics.
Leukocyte adhesion deficiency results from the absence of an essential receptor on white blood cells. This prevents white blood cells from exiting the bloodstream to defend the body against infections. Affected dogs repeatedly suffer from severe bacterial infections and delayed wound healing. The condition has been diagnosed in Irish Setters and also occurs in people.
Complement is a set of small immune system proteins that helps other parts of the immune system fight off infections. A congenital lack of the complement protein C3 has been described in Brittany Spaniels. These dogs developed recurrent bacterial infections, especially skin diseases and pneumonia. Although complement is necessary for activating some types of white blood cells, bacterial infections do not always develop in individuals with complement deficiencies, because there are other ways to activate the system even if one pathway is blocked. Diagnosis is based on a blood test showing reduced levels of the protein.
A congenital deficiency in the inhibitor of the complement protein C1 has been recognized in people and occurs rarely in dogs. This can lead to uncontrolled complement activation and inflammation. Affected dogs have repeated bouts of facial swelling.
There is no specific treatment for complement deficiencies. Vaccination and antibiotics are used to prevent and treat infections. As with all inherited diseases, animals used in breeding programs must be carefully chosen to prevent passing the disease to future generations.
Immunoglobulin (antibody) deficiency is due to a failure of the body to produce antibodies (immunoglobulins). This deficiency can be acquired (caused by other diseases) or congenital (present at birth). Congenital deficiencies of one type of immunoglobulin (immunoglobulin A, or IgA) have occurred in Beagles, German Shepherds, and Chinese Shar-Peis, leading to respiratory infections, digestive system disorders, skin disease, or allergies.
Acquired deficiencies occur in puppies that do not receive adequate antibodies from their mothers. For older animals, the cause is often a decrease in antibody production.
Immunoglobulin deficiency can occur as part of any disease that disrupts the production of antibodies in the body. For example, certain tumors (such as lymphosarcoma and plasma cell myeloma) cause the production of abnormal antibodies, which decreases production of normal antibodies. Some viral infections, including canine distemper and parvovirus, can damage the tissues that produce antibody-forming cells. Some puppies also have a transient antibody deficiency that can put them at increased risk for respiratory infections from 1-6 months of age, but these dogs improve by the time they are 8 months old.
Combined immunodeficiency disease involves a defect in both cell-mediated immunity and antibody production. These defects make it impossible for the body to fight foreign invaders. Cases have been seen in Bassett Hounds, Toy Poodles, Rottweilers, and mixed-breed puppies. Affected dogs are healthy during the first several months of life but become progressively more susceptible to bacterial infections as the antibodies they received during nursing disappear. No treatment is available and the longterm outlook is poor.
Rottweiler puppies have a predisposition for severe and often fatal canine parvovirus infections. Their resistance to other diseases is essentially normal, and the basis of this selective immunodeficiency is unknown.
Localized and whole-body fungal infections affect certain types of dogs. Long-nosed breeds, in particular German Shepherds and shepherd mixes, are more likely to develop fungal infections in their nasal passages. Whole-body aspergillosis (a type of fungal infection) is seen almost exclusively in German Shepherds. Signs of this disease include infection of the kidneys, bones, and the discs between the vertebrae of the spinal cord.
These types of diseases can be caused by a number of viruses in animals. In dogs, distemper virus kills lymphocytes, a type of white blood cell. The infection is associated with a progressive decline in levels of antibodies and an increased susceptibility to bacterial infections that are normally controlled by the immune system. Parvovirus infection in dogs causes a huge decrease in the number of white blood cells and a weakened immune response to bacterial and fungal infections.
Also see professional content regarding immunodeficiency diseases.