Causes of Disease 4-H Veterinary Science Extension Veterinary Medicine Texas AgriLife Extension Service College of Veterinary Medicine and Biomedical Science Texas A&M System

Objectives Distinguish between infectious and non- infectious causes of disease Discuss risk factors Discuss primary cause factors Discuss secondary cause factors

Infectious Diseases Infectious disease An illness due to a specific infectious agent or its toxic products that arises through transmission of that agent or its products from an infected person, animal or reservoir to a susceptible host, either directly or indirectly

Agents involved Germs Bacteria Viruses Fungi Rickettsiae Helminths Protozoa Arthropods

Damage caused Feed off of body tissue Reproduce in tissue Release toxins Pressure

Reproduction Lag phase Usually incubation period where organism is settling in to new surrounding Growth phase Exponential growth is rapid Plateau phase Growth = Death Time Number of Organisms Lag Phase Growth Phase Plateau Phase

Lag phase maybe long Non-disease dormancy or latency multiple when conditions are optimal or when organism is ready May break if bacteria is in stressful environment Bacteria and virus are precipitated by stress  Ex. Anthrax go into dormancy (spore form) when exposed to oxygen, once in anaerobic environment, bacteria multiply and cause fatal disease Causes disease

Non-Infectious Disease Disease cause Dysfunction or disorder of reproductive disease Example - hypo/hyper-thyroidism Nutritional deficiencies or imbalances Example - copper toxicity - damage liver Chemical and plant poisoning Example - acorns and green tomatoes Physical injuries and stress

Causal pathway Variables present A GF D E CB H C D E F A B DiseasedNon-Diseased

Primary Cause ALWAYS present when occurs and Risk factors increase or decrease probability of disease in individual Disease Example - not washing hands after using restroom Dysfunction Example - cryptorchidism Disorder Example - type 1 diabetes - body does not produce enough insulin

Secondary Causes Primary cause not as evident Secondary is noticeable when individual is sick Need tissue damage from primary cause Invade and multiply Dividing Bacteria Video

Risk Factors Causative factors Increase chances of getting sick Examples Overcrowding Pollution Weather Inbreeding

Protective factors Decrease chances of getting sick Examples Vaccination Husbandry Crossbreeding Good management practices