Veterinary Epidemiology and Zoonosis

PRIMARY AND SECONDARY DETERMINANTS

Primary determinants

• Factors whose variations exert a major effect in inducing diseases.
• Frequently, primary determinants are necessary causes.
  • Eamples: Exposure of dogs to distemper virus is a primary determinant of canine distemper.

Primary determinants
Intrinsic determinants	Extrinsic determinants
Genetic constitution Metabolism Behaviour	Animate		Inanimate
	Endoparasitic	Ectoparasitic	Physical	Chemical	Allergic
	Viruses Bacteria Fungi Protozoa Metazoa	Arthropods	Trauma Climate Radiation Stressors	Excesses Deficiency Imbalance Poisons Photosensitizers	Allergens

Secondary determinants

• Determinants correspond to predisposing, enabling and reinforcing factors.
  • Examples: Sex is the secondary determinant of canine heart valve incompetence; Male dogs are more likely to develop incompetence than females.
• Season is the secondary determinant in clostridial infections. Monsoon season favours clostridial infections.

Secondary determinants
Intrinsic determinants	Extrinsic determinants
Genetic constitution (breed, sex, species.) Age Size and conformation Hormonal status Nutritional status Immunological status Functional status (e.g. pregnancy, lactation) Behaviour	Location Climate Husbandry (Housing, diet, general management, animal use) Trauma Concurrent disease Vaccination status Stressors