Why Your Health Depends on Your Address
Exploring Jacques M. May's revolutionary ecological approach to understanding disease patterns
What if we told you that your risk of catching a disease could be mapped not just in your body, but across the entire globe? That the very soil beneath your feet, the rhythm of the seasons, and the layout of your village could be as important as the germ itself? This is the revolutionary idea at the heart of Dr. Jacques M. May's groundbreaking 1958 work, The Ecology of Human Disease .
"Long before 'geographic medicine' was a common term, May proposed a radical concept: to understand why we get sick, we must stop looking just at the pathogen and start looking at the world it lives in."
This isn't just about pandemics; it's about the mysterious patterns of everyday illness. Why is one valley riddled with a particular parasite while the next is free of it? The answer, May argued, lies in ecology—the intricate and invisible web connecting us to our environment .
Disease patterns follow geographic and ecological boundaries, not just biological ones.
May's 1958 work predated modern GIS technology but anticipated its importance in public health.
Dr. May introduced a powerful framework to understand disease, known as the "Ecological Triad." Imagine disease as a three-legged stool. For the stool to stand—for a disease to occur—all three legs must be present .
This is what we typically think of as the cause of disease: a virus, bacterium, parasite, or even a genetic flaw or nutritional deficiency.
This is the human being. Our age, genetics, immunity, and overall health determine how we react to the agent.
This is May's crucial, expanded definition. It includes physical, biological, and socio-cultural factors that influence disease transmission.
The brilliance of this model: It shows disease is never inevitable. If you remove just one leg of the stool, it collapses. A deadly virus (Agent) may be present, but if it can't survive the dry climate (Environment) or if the local population has strong immunity (Host), the disease won't take hold.
Pathogens, toxins, genetic factors
Human susceptibility, immunity
Climate, geography, social factors
To see May's theory in action, let's perform a thought experiment based on his work, investigating a classic ecological disease: Malaria .
Two villages sit 50 miles apart in a tropical region. Village A, nestled by a river, has a high rate of malaria. Village B, on a windy plateau, has almost none. Why? An ecologist would not just test people for the parasite; they would map the entire ecosystem of both villages.
Confirm the presence of the Plasmodium parasite in blood samples from sick patients in Village A.
Record the age, health status, and genetic backgrounds (like sickle-cell trait prevalence) of the populations in both villages.
Physical: Chart seasonal rainfall, temperature, and humidity in both locations.
Biological: Survey both areas for the presence of the Anopheles mosquito. Map breeding grounds.
Cultural: Document housing construction, sleeping habits, and water storage practices.
The investigation would reveal a perfect—and fragile—ecological balance in Village A. The parasite (Agent) depends entirely on the Anopheles mosquito to travel between humans (Hosts). The mosquito, in turn, can only thrive in the specific warm, humid climate with standing water found in Village A (Environment). Village B's windy, dry plateau breaks this chain.
| Characteristic | Village A (High Malaria) | Village B (Low Malaria) |
|---|---|---|
| Malaria Cases (per year) | 150 | 5 |
| Dominant Age Group Affected | Children under 10 | All ages (rare) |
| Primary Agent | Plasmodium falciparum | Not Endemic |
| Factor | Village A (High Malaria) | Village B (Low Malaria) |
|---|---|---|
| Avg. Temperature & Humidity | High year-round | Moderate, with low humidity |
| Mosquito Breeding Sites | Abundant (riverbanks, pools) | Very few |
| Primary Vector Present | Yes (Anopheles gambiae) | No |
| Common Housing Type | Thatched roofs, open windows | Concrete, screened windows |
The scientific importance is profound. This ecological view shows that fighting malaria isn't just about killing the parasite with drugs. You can also break the chain by: Altering the Environment (draining stagnant water), Protecting the Host (distributing bed nets), or Interrupting the Vector (using insecticides). This is the power of May's ecological thinking: it multiplies our options for prevention.
What does a scientist need to map the landscape of disease? It's not just a microscope and a petri dish.
Computer-based mapping to overlay disease cases with environmental data to find hidden patterns.
Tools for collecting and identifying insect vectors to understand their distribution and behavior.
Testing blood samples from a population to see who has been exposed to a pathogen.
Analyzing genetic and immune responses to understand why some resist infection.
Long-term environmental records to predict disease outbreaks.
Advanced analytics to identify patterns and predict disease spread.
Climate Change
Deforestation
Urbanization
Global Travel
Agriculture
Housing
Jacques May's The Ecology of Human Disease was a work of remarkable foresight . He gave us a new lens through which to see sickness—not as an isolated event, but as a disturbance in a complex, global ecosystem. His "Ecological Triad" remains a cornerstone of modern public health, guiding our responses to everything from local Lyme disease outbreaks to global pandemics like COVID-19.
"In an era of climate change and rapid globalization, May's ideas are more relevant than ever. As we alter our planet, we are also redrawing the map of human disease."
By understanding the delicate balance between Agent, Host, and Environment, we are better equipped to predict, prevent, and ultimately, build a healthier world for everyone, no matter their address.
May's ecological framework has influenced generations of epidemiologists and public health professionals. His work established the foundation for: