Principles of Disease Prevention , Diagnosis , and Control Chapter 1 Introduction

Poultry product prices have not kept pace with rapidly escalating input costs, causing profit margins to diminish throughout the poultry industries. Producers are faced with the challenge of consistently achieving expected performance while satisfying stringent food safety and animal welfare requirements; they can no longer tolerate even the slightest deviation from expected performance. In an effort to cost-effectively meet demand, producers have had to increase the size and throughput of their production systems. These large close confinement rearing systems, designed to improve economies of scale and maximize productivity by optimizing bird comfort, unfortunately also increase the risk of disease challenge. The physiological stress of keeping pace with genetic potential for production makes birds more vulnerable to disease challenge, and the close proximity of susceptible hosts increases the chance and rate of infectious disease spread. Diseases previously recognized as unimportant, because they have been adequately controlled, have now reemerged as significant concerns. Most of today’s disease challenges are not new problems; rather, they have merely expanded their geographic distribution or reemerged primarily because of management techniques and production system design constraints. Methods of disease control have evolved with intensification of the industry. While initially focused on diseases of catastrophic nature, attention has rapidly shifted from defined, clinical disease at the individual house or farm level to less well-defined subclinical disease and bird welfare. Similarly, cost justification in decisions on whether or not to implement prevention or control measures has become more complex, requiring the aid of formal economic appraisal. To maximize flock efficiency, disease challenge management requires a carefully designed, multi-tiered approach, which includes consideration of elements ranging from flock health and productivity to chick or poult viability. In addition, the term “efficiency” implies the all-important economic component. Because the production system is profit driven, decisions regarding disease challenge can rarely be made based solely on biological grounds. Disease management intervention also requires sound economic justification, which begins with clearly defining the financial risk associated with disease. Unless a disease poses a specific risk to human health or animal welfare, its mere presence in a flock may not be significant from a business perspective. It is often difficult for the veterinarian, trained in disease prevention, diagnosis, and control, to appreciate that the presence of a disease in a flock could be considered superfluous. Unless it is economically advantageous to take action against a disease challenge, its presence in a flock is tolerated. Intervention strategies are consequently chosen based on both their economic and biological efficiency. This process requires a dynamic, integrated combination of an epidemiologic and economic analysis to determine and quantify the production effect of the disease challenge as well as a proposed intervention strategy. Such integrated analysis has become far more significant in today’s intensive production systems because the outcome of disease challenge is so markedly influenced by the environmental conditions. The economic impact of disease is difficult to assess. This is particularly so in a production system in which the economic return is governed not only by flock productivity but also by product quality and viability. In addition, the consequential loss from disease challenge will be, at best, only partially recoverable. Using the cost of disease to justify intervention over-emphasizes the consequence of inaction and it is only useful in justifying intervention strategies directed at disease prevention. As the process of economic analysis has evolved, the focus has shifted from the cost of disease to the benefit derived from disease control strategies.