ABSTRACT
Immunodeficiency may be simply defined as the presence of impairment in function of part or parts of the immune system that renders the immunodeficient patient more susceptible to infectious disease. Two broad types of immunodeficient state are recognized. A primary immunodeficiency occurs when there is a mutation in a gene encoding a molecule of the immune system. Such diseases are inherited and congenital, with clinical signs often becoming apparent in early life. There is a spectrum of such disorders, with some mutations consistently leading to increased mortality and others related to only mild and chronic clinical presentation. In contrast, a secondary immunodeficiency occurs in an adult animal that has previously had normal immune function and may be related to age, infection, medical therapy or the presence of chronic disease.
