L7 - Causes, Determinants, Transmission

Pathogenicity

Ability of disease to produce disease in a range of hosts → not based on severity of disease

Virulence

Measure of severity of disease caused by an agent → how sick it makes you

What are some examples of host factors?

• Species (ex. panda vs. dog distemper)

• Breed (ex. Rotties and parvo,

• Sex, Age, Conformation, Genotype

• Physiologic and

• Pathological Status → comorbidities

What is the most common inherited bleeding disorder in dogs? What host factor determines pathogenicity?

Hemophilia A (Factor VII deficiency)

Sex Factor → females carry gene for dz without showing signs, males show signs

What host factor increases susceptiblity for arthritis in cats?

Age → common in cats, just severe in older cats

Examples of environmental factors

• Weather

• Housing

• Geography

• Mangement practices

• Noise

• Water/Air Quality

• Food, Chemicals

Koch’s Postulates for Infectious Diseases

1. Agent present in all cases

2. Agent can be isolated and grown in pure culture

3. Agent capable of causing disease when introduced to healthy animals

4. Same organism can be recovered from diseased animal

What are the limitations of Koch’s postulates?

1. Don’t apply for inapparent infections or carrier states (Cholera, Typhoid Fever)

2. Some organisms are hard/don’t grow in pure culture (M. leprae)

3. Rarely apply to viral infections/diseases

4. Do not apply to multi-factorial etiologies

What is direct transmission?

• Physical contact between an infected individual and susceptible individual that causes the transfer of microorganisms

• Touching, licking, sexual contact, transplacental, body secretions/lesions

• Airborne

• Droplet

What are airborne diseases? Examples?

• Caused by pathogens transmitted through air

• FMD

Examples of droplet transmission

Coughing

Sneezing

Examples of indirect transmission

• Foodborne

• Vectorborne

Is horizontal transmission direct or indirect? What about vertical?

Horizontal: Both

Vertical: Direct

Zoonosis

Any disease that is naturally transmissible between animals and humans