Causes of Disease

4-H Veterinary ScienceExtension Veterinary Medicine 

Texas AgriLife Extension ServiceCollege of Veterinary Medicine and Biomedical Science

Texas A&M Systemhttp://aevm.tamu.edu

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

G F

D

E

CB

H

C

D

E

F

A

B

Diseased Non-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