lesson 4

Medical Geography of Infectious Diseases

• Focuses on emerging and re-emerging infections

• Presented by Robert J. Leggiadro, MD

• Importance of understanding the geographical context of diseases

Ecology Overview

• Need for reviewing foundational concepts in ecological studies

Triangle of Human Ecology

Components of the Triangle

• Population: Human demographics and genetic factors influencing health.

• Habitat: Environmental factors including air quality, pollutants, and living conditions.

• State of Health: Represents health outcomes within populations.

• Behavior: Practices that affect both individual and population health.

Figure 2.3: Triangle of Human Ecology Example - Childhood Asthma

Population Factors

• Family history of hay fever, eczema, or asthma.

Environmental Factors

• Presence of farm animals, indoor pets, heating systems, age of home, cockroach infestation, pollution.

State of Health

• Development of childhood asthma linked to above factors.

Behavior Factors

• Breastfeeding practices, smoking exposure, use of antibacterial products, pesticide use, pet ownership.

Innate Immunity and Asthma Risk

• Amish Dust vs. Hutterite Dust: Influence on allergy development.

• Role of MyD88 and Trif in immune responses.

• Low-level inflammation linked to allergic asthma development.

Disease Ecology Principles

Key Terminology

• Agent: Microorganism causing disease.

• Host: Organism affected by the disease.

• Reservoir: Source of infection with numerous hosts.

• Vector: Organism that transmits the disease.

Spatial Factors

• Housing arrangements and land use significantly influence disease distribution.

Settlement Patterns

• Nuclear: Densely populated areas.

• Dispersed: Scattered populations.

• Linear: Populations aligned along a route.

Definitions and Terminology

• Infectious Diseases: Result from pathogenic organisms invading the body.

• Contagion: Transmission of pathogens, either directly (person-to-person) or indirectly (through vectors).

Characteristics of Infectious Diseases

• Differentiation from other diseases due to specific transmission mechanisms.

Transmissible Disease Systems

Concepts

• Zoonosis: Diseases primarily found in animals that can infect humans.

• Anthropo-zoonosis: Diseases affecting both humans and animals.

• Reservoir: Animals that continuously harbor infectious agents for human transmission.

Chains of Disease Transmission - Figure 4.2

Types of Transmission

1. Direct Human to Human: Examples include influenza and typhoid.

2. Zoonosis: Examples include rabies and brucellosis.

3. Vectored Human Diseases: Malaria and onchocerciasis.

4. Vectored Zoonosis: Includes encephalitis and Rocky Mountain spotted fever.

5. Anthropo-zoonosis: Diseases like yellow fever and plague.

Disease Endemicity

• Enzootic: Diseases stable in animal populations.

• Epizootic: Epidemics among animals.

• Major arthropod vectors include mosquitoes and ticks impacting disease transmission.

Cultural Ecology of Transmissible Disease

• Regions influence the distribution of diseases based on cultural practices and ecological factors.

Landscape Epidemiology

• Four regional types affecting disease: biomes, evolutionary realms, cultural realms, and natural nidus.

Realms of Evolution in Disease Transmission

• Historical connections between empires contributed to the spread of infectious diseases.

• Key examples: diseases exchanged between the Old World and the New World during explorations.

Natural Nidus

• Small-scale regions where disease agents circulate among hosts.

Categories of Infectious Diseases

Broad Categories

• Established Diseases: Stable behavior patterns (e.g., malaria, tuberculosis).

• Newly Emerging Diseases: Diseases newly recognized in humans (e.g., HIV/AIDS).

• Re-emerging Diseases: Diseases returning after control efforts (e.g., cholera).

Outbreaks and Epidemics (2002-2015)

• Overview of outbreaks and their global impact.

Emerging Infections Factors

Criteria for Emergence

• Newly appearing in populations (e.g., COVID-19).

• Rapidly increasing incidence or geographic spread.

Statistics

• 60% of emerging infections are zoonotic.

• 70% of zoonoses originate in wildlife.

Key Drivers of Emergence

• Ecological Changes: Influence of climate and natural environments.

• Human Demographics: Migration, urbanization influences (e.g., Ebola, Lyme disease).

• Travel and Commerce: Facilitates spread of diseases.

• Technological Impact: Food processing errors, hospital-acquired infections.

• Microbial Adaptation: Developments in drug resistance.

• Public Health Breakdowns: Resulting in disease resurgence.

Climate Impact on Infections

• Hantavirus outbreak case study correlating climate and disease occurrence.

Water and Emerging Infections

• Vectors often utilize water bodies for breeding; significant case examples include Schistosomiasis and Japanese Encephalitis.

Hantavirus Overview

Epidemiology

• Outbreak patterns in the U.S. Four Corners region; environmental factors contributing to contact with rodents.

Social Change and Emerging Infections

• Impact of human behaviors and practices on proliferation of diseases.

International Travel and Commerce

• Historical examples highlighting how trade influenced disease spread (e.g., bubonic plague, yellow fever).

Technology and Industry Effects

• Industrial practices causing new health threats (e.g., E. coli from food processing).

Microbial Adaptation and Change

• Analysis on how pathogens evolve (e.g., COVID-19 variants).

Public Health Measures

• Importance of maintaining effective public health systems to avoid resurgences of diseases.