Human to Human Transmission of
Infectious Diseases

Basics of Disease Control
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Control the environment
Control the host
Control the vector
Why does this make diseases with human hosts the most legally problematic?

Factors that Affect Human Susceptibility to Infectious Diseases
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Genetics
Immunologic system function
Environmental factors

Genetics
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Sickle cell trait
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Evolutionary adaption to malaria
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Damaging as sickle cell disease
HIV
Probably leprosy
Others we do not understand

Environmental Factors
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Factors that affect immunologic function
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Nutritional status
Stress
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What does this tell us about developing countries and refugee camps?
Factors that increase exposure/cause stress
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Crowded housing
Poor sanitation
Poor working conditions

Breaker boys in coal mine - Lewis Hine

Immunosuppressive Drugs
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A post 1960s phenomena
Steroids
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Asthma
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Arthritis
Feel good docs
Chemotherapeutic agents
Anti-rejection agents for transplants
Impact on infection dynamics

Transmission Dynamics
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How hard is it to catch the disease? (Contact effectiveness)
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Measles
Leprosy (Hanson's Disease)
How susceptible is the population?
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Immunity?
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Environmental factors?
How many people are infectious carriers?
How well do the carriers mix with the general population?
Are there high risk subgroups?

Tuberculosis
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#1 Killer, probably for all time
Mycobacterium tuberculosis
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Related to leprosy
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Very hard to kill
Can lay dormant for decades
Can affect any organ system
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Dangerous when it is pulmonary - you cough up the bugs and spread them

Transmission
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Person to person
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Takes significant exposure
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Medicated by fomites
Animal hosts
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Milk
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Still a risk for raw milk

Detection
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TB skin testing
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Looking for antibody reaction
Not so good in immunosuppressed people
Conversion
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You are infected
You may not have actively growing bugs
Confirmation
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HIV test
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X-ray
Treatment - 1 year of isoniazid

Treatment of Active TB
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Active - pulmonary infection that can spread infectious material
Treatment
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Takes time to make the patient non-infectious
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Much longer or never for drug resistant
Long course for cure
Incomplete treatment
 drug resistant worst case - pan drug resistance

Legal Issues for TB
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Detection
Treatment
Treatment failure/drug resistance