Module 2.1

Lecture 7: Emerging Infectious Diseases and Conservation Medicine

Definition of Emerging Infectious Diseases (EIDs)

• EIDs encompass new and reemerging diseases.

• Defined by:

  • Recent increase in incidence (new cases over a period).

  • Geographic expansion of host range (impacts of climate change and habitat expansion).

  • Newly recognized pathogens (never documented before).

  • Newly evolved pathogens (existing pathogens that mutate to exploit new hosts).

Historical Context of EIDs

• The term "emerging infectious disease" was coined in the 1970s and gained traction in the 1980s with notable diseases:

  • AIDS

  • Hantavirus pulmonary syndrome

  • Legionnaires' disease

  • Toxic shock syndrome

  • Lyme disease

• EIDs became a focused area of research, notably published by the CDC.

Reemerging Infectious Diseases

• Discusses diseases that reappear after being under control:

  • Examples include:

    • Drug-resistant tuberculosis and malaria

    • Rabies (circulating in wildlife reservoirs).

Significance of EIDs

• EIDs have substantial consequences for human health:

  • High morbidity and mortality rates.

  • Lack of vaccines and therapeutics (e.g., Ebola, Hendra, Nipah viruses).

  • Potential for societal disruption (e.g., Ebola outbreak in West Africa).

Resource Limitations

• Limited funding for surveillance, education, disease prevention, and therapeutics.

• Public reacting to outbreaks ("catch-up" response) rather than proactive measures.

EIDs in Animals and Plants

• Impact on domestic animals:

  • Examples: Foot and mouth disease, Newcastle disease, Blue tongue virus (vector-dependent).

• Impact on plants:

  • Citrus canker (historically troublesome in the U.S.).

  • Chestnut blight (led to extinction of native chestnut trees).

Ecological and Economic Consequences

• Examples of ecological impacts due to EIDs:

  • Importation of harmful species that disrupt local biodiversity (e.g., kudzu).

  • Disease outbreaks affecting wildlife populations (e.g., distemper in black-footed ferrets).

Anthropogenic Factors and Disease Emergence

• EIDs often arise due to:

  • Increased human populations and urbanization leading to reduced natural barriers.

  • Technological advances in agriculture leading to habitat encroachment.

  • Breakdown of public health measures, particularly in developing countries.

  • Pathogen adaptation and climate change facilitating new disease vectors.

Interface Between Humans, Animals, and Environment

• EIDs often emerge at the interface of humans, domestic animals, and wildlife.

• Vulnerability in developing countries due to closer contact with animals, poor healthcare, and malnutrition.

Pathogen Pollution

• The introduction of pathogens into new habitats can result in catastrophic outcomes:

  • Historical examples: Smallpox and measles decimating indigenous populations.

  • Recent examples: West Nile virus outbreaks after introduction.

Impact of Disease on Biodiversity

• EIDs can cause significant biodiversity loss:

  • Direct mortality in susceptible wildlife populations.

  • Cascade effects in ecosystems influenced by disease.

Extinction Due to Infectious Diseases

• Various forms of extinction related to infectious diseases:

  • Deterministic extinction: Disease kills hosts faster than recovery.

  • Hyperdisease extinction: Extremely virulent pathogens introduced to naïve populations.

  • Stochastic extinction: Random factors post-outbreak that affect surviving populations.

  • Micro-extinctions: Localized extinction events affecting genetic exchange.

Prevention and Management Strategies

• Importance of integrating conservation practices with public health efforts.

• Maintaining reservoir species as part of ecosystem health can mitigate risks (e.g., vaccinating domestic animals).

Conclusion

• Anthropogenic stressors are major contributors to the emergence of infectious diseases.

• Future focus on addressing these challenges through conservation medicine.