Since the central theme of this book is the transmission of disease agents through the food chain, we will examine influenza viruses from this perspective. Influenza A viruses are found in humans, pigs, horses, sea mammals, and also in wild aquatic and domestic birds 23]. How are they spread? Between mammals, influenza is an airborne infection, but between birds, influenza can be either an airborne or waterborne infection. Influenza viruses of aquatic birds periodically transmit to domestic birds sometimes with catastrophic effects; this transmis sion can be either airborne or waterborne....