The invention provides methods and compositions for the treatment and prevention of a transmittable disease in a subject, such as avians and mammals. The methods and compositions of the invention specifically make use of avian antibodies to the disease to be treated or prevented. Administration of such avian antibodies to a subject has been shown effective for reducing mortality in a population of subjects that are infected, or become infected, with the disease. The invention also provides kits useful for detecting the presence of transmittable diseases in subjects.