Immunodeficiency diseases manifest clinically as a predisposition to infections. They are usually recognized when an animal makes multiple visits to a veterinarian for infections that would normally be relatively easy to control. Two major groups of immunodeficiency disease occur. One group is inherited as a result of mutations or other genetic disease. These primary or congenital immunodeficiency diseases Primary Immunodeficiencies in Animals Phagocytosis is a central feature of innate immunity and inflammation. Phagocytic cells are found either in the tissues (histiocytes, synovial macrophages, Kupffer cells, etc) or in the bloodstream... read more usually develop in very young animals (<6 months of age). The second group of immunodeficiency diseases Secondary Immunodeficiencies in Animals In adult animals, immunodeficiencies often result from virus infections, malnutrition, stress, old age, or toxins. These are called secondary immunodeficiencies. Virus-induced secondary immunodeficiencies... read more are secondary to some other stimulus such as a viral infection or tumor. These secondary or acquired diseases tend to occur in adult animals. One other general rule in diagnosing immunodeficiencies is that defects in the innate and antibody-mediated immune systems tend to result in uncontrollable bacterial infections, whereas defects in the cell-mediated immune system tend to result in overwhelming viral and fungal infections.