Continued from page 1The Diagnosis
Diagnoses represent the 'what' in medicine. They answer the questions 'What is wrong?', and 'What disease process does this patient have?'. These diagnoses may be clinical, morphological, or etiological. Suppose an individual bird has diarrhea. Diarrhea is the clinical sign, as might be anorexia (loss of appetite) or dehydration. The clinical signs are occurring for a specific functional reason. This reason is the lesion, which may be functional or morphological. The lesion is the 'abnormality' in this bird's tissues that is causing the development of the clinical sign, diarrhea. The lesion may involve morphological changes such as the selective cellular destruction of a particular component of the bird's intestinal tract, or it may simply be a non-infectious factor causing alterations in transit time of the gastrointestinal system. The cause of this bird's diarrhea-producing lesion is the etiology, and might represent the pathogen involved in the clinical and morphological diagnosis of E coli infection, but this agent still only represents the 'what' - not the important question 'why'.
To put this all together; Clinical signs are explained by the diagnosed condition of the patient. That patient has specific lesions that are responsible for the generation of those clinical signs. One or more specific etiologies may be be identified as the cause of the lesions that are producing the clinical signs of the patient.
The Pathogenesis
Pathogenesis is the 'how' or 'why' of medicine - the step by step progression from the normal state through the abnormal structural or functional state. The sequence of events from the point at which disease began through its entire development is called the pathogenesis. It is absolutely necessary to know the pathogenesis of disease in order to make a rational judgment regarding proper treatment, control and prevention of flock disease.
Pathology Theory vs. Clinical Flock Medicine
'The study of things caused must precede the study of the causes of things'.The theory of pathology involves the description of lesions and their known or assumed pathogenesis and etiology. Based on the description of 'what', treatment can easily be applied on an individual as well as a group basis; however, this poses risk of medical incompleteness.
Clinical flock medicine involves being able to describe lesions, to recognize the disease process, an explain how it might have occurred. perhaps most importantly, clinical flock medicine combines theory with action directly or preventatively aimed at the multiple steps required for a flock to progress from a normal state to an abnormal one. This multifaceted action requires action requires practical experience, exposure to clinical cases, and problem-solving ability of the veterinarian as well as the aviculturist. If we understand the causes of things (pathogenesis), we can have a better grasp on how to prevent them than if we only understand what kinds of things (diseases) were caused alone.
A sage colleague of mine of whom I have immense respect once told me that a good doctor will ask what disease the patient has; an excellent doctor will ask what kind of patient has the disease. It is time for more aviculturists as well as veterinarians to strive for this level of excellence.
The main roles of the avicultural veterinarian are to diagnose, treat, prevent and control bird disease to reduce losses or increase productivity in the aviary. The of these functions is to diagnose. The key to flock prognosis is the ability to recognize lesions in the live or dead animal and to understand the pathogenesis. Through this understanding, rational conclusions and recommendations for treatment, control, and most importantly, prevention.
Infectious disease results from the interaction of an infectious agent with the host in a particular environment. The actual cause may exist in the external environment or in a defect in host response, rather than only in the infectious agent alone. The significance of host and environment in the pathogenesis of disease becomes much greater when flock health issues are considered rather than the individual bird.
The Environment
The factors that are perhaps of greatest importance in initiating or influencing disease are environmental, particularly among animals in which intensive husbandry practices are followed. This circumstances, in most cases, directly applies to aviculture. These factors may change subclinical, or latent infections into acute or chronic disease, or generate circumstances that allow for the actual development of subclinical or clinical disease itself. For example, high dust and ammonia levels in poultry houses increase the incidence of respiratory disease.
In contrast to Koch's postulates, the agents that cause disease in some of these situations are members of the normal flora or were truly inapparent infections until environmental influences precipitate a state of disease.
Many of these adverse environmental influences are well recognized, but in other circumstances, we still have significantly more to learn about environmental roles in the pathogenesis of disease. The significant problem in flock management is how to prevent disease from occurring. This problem is not one that is new to animal production industries. Antibiotics and vaccines, alone, cannot replace the significant preventative value of good management.
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