Six Modern Plagues and How We Are Causing Them

1. Environmental disruption fuels the emergence of new diseases

Show me almost any new infectious disease, and I'll show you an environmental change brought about by humans that either caused or exacerbated it.

Human-driven ecological changes are at the root of many emerging infectious diseases. Deforestation, urbanization, and agricultural expansion disrupt natural habitats and bring humans into closer contact with wildlife, creating opportunities for pathogens to jump species. This phenomenon, known as zoonosis, is responsible for diseases like Ebola, SARS, and COVID-19.

Climate change exacerbates the problem by altering ecosystems and expanding the range of disease vectors like mosquitoes and ticks. As temperatures rise, these vectors can survive in new areas, introducing diseases to previously unaffected populations. For example, warming temperatures have contributed to the spread of West Nile virus in North America and the expansion of malaria-carrying mosquitoes to higher altitudes in Africa.

2. Intensive agriculture practices create antibiotic-resistant superbugs

It's cheaper to keep animals drugged than to keep them clean.

Overuse of antibiotics in livestock farming has led to the emergence of antibiotic-resistant bacteria. Farmers routinely administer antibiotics to prevent disease in crowded, unsanitary conditions and to promote growth. This practice creates an ideal environment for bacteria to develop resistance.

The consequences of antibiotic resistance are severe:

• Infections that were once easily treatable become life-threatening
• Medical procedures become riskier due to the potential for untreatable infections
• New antibiotics are developed at a slower rate than bacteria evolve resistance

The spread of resistant bacteria from farms to humans occurs through:

• Contaminated meat products
• Environmental pollution (e.g., water runoff from farms)
• Direct contact between farm workers and animals

3. Mad cow disease: A cautionary tale of industrial farming gone wrong

We've forced these hoofed grazers into cannibalism.

The BSE crisis emerged from the practice of feeding cattle with meat and bone meal derived from other cattle, effectively turning herbivores into cannibals. This unnatural diet, aimed at increasing profits, created a pathway for the transmission of prions – misfolded proteins that cause fatal brain diseases.

The consequences of this industrial farming practice were severe:

• Thousands of cattle infected and culled
• Human deaths from variant Creutzfeldt-Jakob disease (vCJD)
• Massive economic losses in the beef industry
• Erosion of public trust in food safety

This case illustrates how prioritizing efficiency and profit over natural animal behavior can have catastrophic consequences for both animal and human health.

4. HIV/AIDS: The consequence of increased human-wildlife interaction

The bushmeat trade is draining the remaining forests of their wildlife, including gorillas, chimpanzees, and nearly every other kind of remotely palatable animal living there.

The origin of HIV is traced to simian immunodeficiency viruses (SIVs) in African primates. The virus likely jumped to humans through contact with infected animals, possibly during hunting or butchering of bushmeat. This zoonotic transmission was facilitated by:

• Increased human encroachment into primate habitats
• Expansion of the bushmeat trade due to poverty and lack of alternative protein sources
• Rapid urbanization and improved transportation networks that allowed the virus to spread

The global impact of HIV/AIDS has been staggering:

• Millions of deaths worldwide
• Devastating economic and social consequences, particularly in sub-Saharan Africa
• Ongoing public health challenges despite advances in treatment

The HIV/AIDS pandemic serves as a stark reminder of the potential consequences of disrupting natural ecosystems and the delicate balance between humans and wildlife.

5. Lyme disease thrives in fragmented ecosystems with reduced biodiversity

High biological diversity did tend to minimize the rate of Lyme disease infection in the human population.

Ecosystem fragmentation has led to an increase in Lyme disease cases. As forests are broken up by human development, edge habitats favorable to ticks and their hosts (mice and deer) expand. Simultaneously, the loss of predators and competing species allows tick populations to flourish.

The ecological dynamics of Lyme disease:

• Fragmented forests favor "generalist" species like mice and deer
• Reduced biodiversity means fewer alternative hosts for ticks
• Lack of predators leads to overpopulation of tick hosts
• Human proximity to these edge habitats increases exposure risk

Research suggests that maintaining biodiversity can act as a natural buffer against Lyme disease transmission, highlighting the importance of preserving intact ecosystems for human health.

6. Climate change amplifies the spread of vector-borne diseases

Global warming is intensifying many of the natural cycles such as El Niño. There's no doubt about it, in my opinion.

Changing climate patterns are altering the distribution and behavior of disease vectors. Warmer temperatures, altered precipitation patterns, and extreme weather events create new opportunities for pathogens and their carriers to thrive and expand their range.

Examples of climate change impacts on disease:

• West Nile virus: Warmer winters and drought conditions favor mosquito breeding
• Hantavirus: El Niño-driven rainfall increases rodent populations
• Malaria: Rising temperatures allow mosquitoes to survive at higher altitudes

These shifts in disease ecology pose significant challenges for public health systems, particularly in areas where these diseases were previously rare or absent.

7. Global trade and travel accelerate the transmission of pathogens

In today's world, bacteria travel the microbiological equivalent of the interstate highways—or, rather, international air routes or shipping lanes.

Rapid globalization has dramatically increased the speed and scale at which diseases can spread. International travel and trade create numerous pathways for pathogens to move between countries and continents.

Factors contributing to global disease spread:

• Air travel allowing infected individuals to cross continents in hours
• Shipping of goods (including live animals) potentially harboring pathogens
• Urbanization creating dense populations where diseases can quickly take hold
• Global supply chains potentially spreading contaminated products worldwide

The COVID-19 pandemic vividly illustrates how quickly a new pathogen can become a global threat in our interconnected world. This reality underscores the need for robust international cooperation in disease surveillance and response.

8. Overuse of antibiotics in livestock threatens human health

If anything, we are in the process of writing entirely new volumes.

Antibiotic resistance is one of the most pressing public health threats of our time. The widespread use of antibiotics in livestock farming, often for non-therapeutic purposes, has accelerated the evolution of resistant bacterial strains.

The pathway from farm to human infection:

1. Antibiotic use in animals selects for resistant bacteria
2. Resistant bacteria spread through food products, environmental contamination, or direct contact
3. Humans acquire resistant infections that are difficult or impossible to treat

The consequences of antibiotic resistance are severe:

• Increased morbidity and mortality from previously treatable infections
• Higher healthcare costs due to prolonged illnesses and need for more expensive treatments
• Potential loss of ability to perform routine medical procedures safely

Addressing this crisis requires a "One Health" approach, recognizing the interconnectedness of human, animal, and environmental health.

9. Ecological imbalances contribute to the resurgence of old diseases

People's health was linked to acorn production.

Disrupted ecosystems can lead to the resurgence or amplification of diseases that were previously under control. Changes in land use, loss of biodiversity, and altered species interactions can create conditions favorable for pathogens to spread.

Examples of ecological imbalances affecting disease dynamics:

• Lyme disease: Fragmented forests and loss of predators increase tick populations
• Hantavirus: El Niño-driven vegetation growth leads to rodent population booms
• Malaria: Deforestation creates new breeding habitats for mosquitoes

Understanding these complex ecological relationships is crucial for predicting and preventing disease outbreaks. Conservation efforts that maintain ecosystem integrity can serve as a form of public health intervention.

10. Understanding disease ecology is crucial for effective prevention

We will probably never know if Lyme disease afflicted forest dwellers there five hundred years ago, but the diverse ecology at that time would have weighed against it.

Holistic approach to disease prevention requires considering the broader ecological context in which pathogens emerge and spread. This involves:

• Studying the natural reservoirs and transmission cycles of pathogens
• Identifying environmental factors that influence disease risk
• Recognizing the role of biodiversity in buffering against disease emergence

Benefits of an ecological perspective on disease:

• More accurate prediction of outbreak risks
• Development of targeted prevention strategies
• Identification of environmental interventions to reduce disease transmission

By integrating ecological knowledge into public health practices, we can create more effective and sustainable approaches to disease control and prevention.

Last updated: November 20, 2024