Causes of Disease

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Causes of Disease

• 4-H Veterinary Science
• Extension Veterinary Medicine 
• Texas AgriLife Extension Service
• College of Veterinary Medicine and Biomedical
  Science
• Texas AM System
• http//aevm.tamu.edu

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Objectives

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

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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

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• Agents involved
• Germs
• Bacteria
• Viruses
• Fungi
• Rickettsiae
• Helminths
• Protozoa
• Arthropods

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

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• Reproduction
• Lag phase
• Usually incubation period where organism is
  settling in to new surrounding
• Growth phase
• Exponential growth is rapid
• Plateau phase
• Growth Death

Plateau Phase
Number of Organisms
Growth Phase
Lag Phase
Time
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• 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

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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

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• Causal pathway
• Variables present

C
B
C
B
D
A
D
A
E
H
E
G
F
F
Diseased
Non-Diseased
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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

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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
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Risk Factors

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

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