Introduction
In veterinary pathology, the study of the causes of disease constitutes the foundation for understanding the origin, development, and manifestation of pathological processes affecting animals. The identification of etiological factors and of those elements that predispose or trigger disease is essential for diagnosis, prevention, and control of pathologies in veterinary medicine (Zachary; McGavin).
Diseases are rarely the result of a single isolated factor, but rather of the interaction between the causal agent, the host, and the environment. In this context, etiological, predisposing, and triggering factors help explain why the same agent may cause disease in some animals but not in others, or why the severity of damage varies among individuals and species (Kumar et al.).
Definition of etiological factors
Etiological factors are all direct causes responsible for the onset of a disease. In veterinary pathology, etiological factors include physical, chemical, biological, nutritional, genetic, or metabolic agents that, when interacting with the organism, produce structural and functional alterations in tissues and organs (Zachary).
Among the most common etiological factors are infectious agents such as bacteria, viruses, fungi, and parasites; physical agents such as trauma, radiation, or extreme temperatures; chemical agents such as toxins, drugs, or contaminants; as well as nutritional deficiencies or excesses. Identification of the etiological factor is essential for establishing an accurate etiological diagnosis and guiding appropriate treatment (McGavin & Zachary).
Extrinsic and intrinsic predisposing factors
Intrinsic predisposing factors are characteristics inherent to the animal that increase its susceptibility to developing disease. These include species, breed, age, sex, physiological status, and genetic background. For example, certain canine breeds show a genetic predisposition to cardiac or dermatological diseases, while young or geriatric animals are often more vulnerable to infections due to immaturity or deterioration of the immune system (Zachary; Kumar et al.).
Likewise, conditions such as pregnancy, lactation, or physiological stress may modify the organism’s response to an etiological agent, favoring disease development without being the direct cause.
Extrinsic predisposing factors correspond to environmental or management-related elements that increase the likelihood of disease. These include adverse climatic conditions, overcrowding, poor ventilation, inadequate hygiene, nutritional errors, and inappropriate sanitary management practices (McGavin).
For example, in intensive production systems, high animal density and associated stress may predispose animals to respiratory or digestive diseases, even when the causal agent is present at low levels.
Extrinsic and intrinsic triggering factors
Intrinsic triggering factors are internal changes within the organism that precipitate the clinical onset of disease. Metabolic, endocrine, or immunological alterations may act as triggers in previously predisposed animals. A classic example is immunosuppression, which allows reactivation of latent infections or proliferation of opportunistic agents (Zachary).
Similarly, hormonal imbalances or internal nutritional deficiencies may trigger clinical signs in the absence of an immediate external agent.
Extrinsic triggering factors are external stimuli that provoke the onset of clinical disease in a predisposed animal. These include sudden temperature changes, transportation, surgical procedures, vaccinations, trauma, exposure to toxins, or acute infections (McGavin & Zachary).
For example, prolonged transportation and associated stress may trigger pneumonia in predisposed cattle, or episodes of metabolic disease in animals with limited reserves, highlighting the interaction between predisposition and triggering events.
Conclusion
Analysis of the causes of disease in veterinary pathology requires understanding not only the etiological factor, but also the predisposing and triggering factors that influence the onset and evolution of pathological processes. This comprehensive approach allows better interpretation of disease, facilitates prevention, and optimizes management, diagnostic, and treatment strategies in veterinary medicine (Zachary; McGavin).
References
Zachary, J. F. Pathologic Basis of Veterinary Disease. Elsevier.
McGavin, M. D., & Zachary, J. F. Pathologic Basis of Veterinary Disease. Elsevier.
Kumar, V., Abbas, A. K., & Aster, J. C. Robbins and Cotran Pathologic Basis of Disease. Elsevier.