4.2: Geography of Disease

Pertussis is an example of an infectious disease because it is transmitted from person to person. Some infectious diseases also are transferred from animals to people. Infectious diseases, also known as communicable diseases, figure prominently among the leading causes of death in developing countries. In the United States, Europe, and other developed regions, people are more likely to die from non-communicable diseases, such as heart disease, stroke, and cancer. Most non-communicable illnesses are also considered chronic diseases because they affect people over a longer period, and generally affect older adults. Infectious diseases, on the other hand, may affect anyone but are more likely to kill people who are poor, already unhealthy and/or children.

Covid-19

The Covid-19 pandemic of 2020 killed hundreds of thousands and caused billions of dollars in economic dislocation and suffering. Epidemiologists and health geographers worked feverishly to track the origins, spread, and retreat of the disease. A recognition of the role of micro-geography in the spread of the disease, one of the hallmark behaviors of the 2020 pandemic was “social distancing”, a recommendation occasionally ignored by individuals who imperiled the health of individuals, family members (especially the elderly) and strangers alike because a large percentage of persons with the virus were asymptomatic.

Early hotspots of the disease were cities with large international airports. The hardest-hit area in the United States during the earliest period of the disease was centered on New York City, which serves more international air travelers than any other city in the US. Ski Resorts hosted other important superspreader events in the US. The George Floyd protests, which erupted in the spring of 2020 brought many thousands of protestors out of quarantine and into the streets also were identified as potentially catastrophic gatherings of people who would share the virus. Especially at risk were African-Americans, who participated in the protests, because of the variety of underlying health issues facing people of color and the lack of affordable health care in black neighborhoods.

As of June 2020, the total number of confirmed cases worldwide had surpassed 6.5 million with close to 400,000 deaths. The United States accounted for an outsized proportion of both cases and deaths, raising significant questions about why the country with the most expensive health care system in the world had, by some measures, worse outcomes than other countries with advanced economies. Many would point to poor political leadership at both national and local levels. The Brazilian and Swedish government, for example, refused to take measures to enforce distancing and face mask guidelines adopted by most countries in the world, probably resulting in elevated death rates in both of those countries. In the United States, vastly different infection and death rates across the country created fascinating, albeit ghastly, patterns on maps of the disease, sparking intense interest in the multiple variables contributing to the spatial evolution of the pandemic.

Influenza

Influenza, popularly known simply as “the flu” is an airborne infectious disease that generally spreads when someone sneezes or coughs microscopic pathogens (germs) into the air. The flu kills thousands of people each year. Sometimes, flu outbreaks are regional and last only a few months. These short-lived regional outbreaks of diseases are called epidemics. Occasionally, diseases like the flu get out of control, spreading across vast areas, and lasting for many months. Massive, worldwide disease outbreaks such as these are termed pandemics. The most infamous flu pandemic was the dreaded Spanish Flu that broke out during World War I and killed somewhere from 50 to 100 million people. Nearly the entire globe was affected, and poor countries, like India and China, suffered exceptionally high death tolls. In the United States, over 1/4th of the population was infected. Over one-half million Americans died from it, far exceeding the number of Americans that died in fighting in World War I.

Figure 4-12: Seattle, WA - Policemen wear masks during the great influenza pandemic of 1918-20 Source: Wikimedia

Recently, a version of the Spanish Flu (now called H1N1) returned. It was declared a global pandemic and generated worldwide panic. Nobody is sure where the flu strain began or where patient zero (index case) lived, but the epidemiologists traced the first obvious signs of the pandemic to Veracruz Mexico. There, factory-style hog farming may have created conditions ideal for the first known cases to develop and diffuse around January of 2009.

By April 2009, it was clear the flu was rapidly spreading in Mexico. In response, officials drastically curtailed public activity in Mexico City. The European Union Health Commission issued travel advisories, urging people not to travel to Mexico, or the United States, where flu cases were beginning to appear. A variety of quarantine orders swept the globe, keeping people in motels, on cruise ships, and in airports. After about six months, the incidence of new flu cases began to fall, and by February 2010, the pandemic was over. The 2009-2010 flu pandemic officially killed 18,000 worldwide, but other estimates suggest as many as 500,000 died because so many deaths were in parts of Africa and Asia where few laboratories exist capable of confirming the exact causes of death. In the United States, where the public health system responded quickly and efficiently, Americans appear to have suffered only about 10,000 deaths from H1N1, which was nearly normal for a flu season.

Figure 4-13: Canoga Park, CA. This billboard appeared in LA’s San Fernando Valley in early 2010 as part of a large public health campaign to dampen the effects of the H1N1 influenza outbreak. The campaign was generally successful.

While the 2009 version of H1N1 appeared to have been less deadly than its 1918 ancestor, the activity of health departments around the world was essential in averting disaster. Geographers working at the CDC in Atlanta, Georgia knew that a flu outbreak diffusing outward from Mexico was likely to appear first in California or Texas. Indeed, the first American cases appeared in San Diego and Imperial Counties, California, on the Mexican border. Other early cases were in Texas. Armed with data from previous flu outbreaks, computer models and GIS technologies, health geographers working at the CDC were able to accurately predict where and when the flu would flare up in various parts of the United States. Being able to predict the spatial patterns of disease helps health officials direct vaccines and other resources necessary to combat diseases to locations where populations are most at-risk. The outsized effort by the CDC and other public health agencies probably saved thousands of lives in 2009-10. Similar efforts characterized government efforts to treat or otherwise combat the spread of Covid-19, with mixed results.

Figure 4-14: US Map by State. The severity of the flu by state in October, 2009. Note the contagion pattern from Southwest to Northeast. The color ramp violates standard cartographic principle – how? Source: CDC – Interactive Map

Malaria

Malaria is another infectious disease that kills at least a million people worldwide every year. It sickens millions more, and by doing so, creates huge burdens on the developmental potential of many regions in Africa and Asia. Malaria is a parasitic infestation of the blood. Malaria is transmitted when female mosquitoes inject parasites into the blood through their saliva as they take a blood meal. Mosquitoes carry around the parasite, so mosquitos are called the disease vector because they transport the infectious parasites between hosts. Flies, ticks, fleas, and lice are other common disease vectors. Malaria is a very complex disease because the parasite that harms people goes through many life stages. The parasite can also lay dormant for long periods, living part of its life in a human host, and some of its life in the mosquito. The parasite can invade multiple parts of the body. Sometimes the parasite is hosted by an animal (monkeys, e.g.) Mosquitos, hosts, and parasites all have different spatial behaviors and environmental needs, which contributes to the difficulty of controlling malaria. Solutions require spatial methods and geographic tools.

Malaria has been around for thousands of years, and likely contributed to the fall of the Roman Empire, but it was nearly eradicated in the 1950s. Or so it was believed. After World War II, effective drugs and massive insecticide spraying campaigns appeared to be working miracles against this age-old scourge. However, both the mosquitoes that carry malaria and the disease-causing pathogen evolved over the last few decades, rendering many drugs and pesticides largely useless in the fight against today’s version of malaria.

Malaria in the United States

English colonists who came to the region thought North America to be free of malaria. They didn’t yet understand the source of the disease. They mistakenly thought that it, like cholera, was a product of miasma. Because both European and African settlers brought with them reservoirs of malarial blood within their bodies across the Atlantic Ocean, the disease had only to find a suitable mosquito vector (i.e., Anopheles quadrimaculatus) to begin spreading. Within a generation, malaria had become a serious problem in the American colonies, especially where rice plantations created ideal breeding grounds for mosquitoes. Africans had some measure of resistance to malaria, contributing to their desirability as slaves in the plantation system that grew in during the 1800s.

By the mid-1800s, malaria was out of control in the United States. A series of changes in American society nearly eradicated malaria within 100 years. The remarkable turnaround was created by several changes in the American economy. The demise of wet-rice culture in the Deep South was the first change. During the 1800s, thousands of mosquito-infested, wet rice paddies were drained all over the southern US as cotton and corn crops became more profitable. The profitability of these new crops also encouraged farmers to drain thousands of acres of swamps and wetlands for use farmland, thus destroying ideal mosquito habitats. By the mid-1800s railroads also began to replace river and canal transportation across the US, thereby redirecting many thousands of travelers away from the places where they were most likely to be bitten by mosquitos. At the same time, steam power began replacing waterpower, eliminating the need for thousands of mill ponds all over the country. People also became more prosperous, moved to cities, built houses with windows and screens, and generally got healthier. Eventually, the anti-malarial drug quinine became widely available in the United States, helping deplete the blood reservoir of the disease. Another important moment in the battle against malaria came in the early 1900s when scientists discovered that mosquitos transmitted malaria. Slowly, health officials in the US took steps toward mosquito eradication. Government workers drained swamps and manipulated water levels in lakes by constantly raising and lowering dams. They removed vegetation from lakes at the shoreline and provided houses within a mile or so of lakes or ponds window and door screens.

Figure 4-15: US Map - Malaria killed and sickened many thousands in the United States prior to the 20th century. The US Census produced this map from 1880 data. Source: Wikimedia.

After World War II thousands of soldiers returned from Asia carrying the malaria pathogen in their blood. The government took steps to prevent malaria from spreading once again. The biggest effort was in the US South where the military already had practice preventing malaria on southern military bases. The secret weapon in this post-war campaign was a new, highly effective insecticide called DDT. The government launched a massive effort spraying DDT on millions of acres across the US. By 1949, the government declared the US free of malaria. The headquarters of the anti-malaria effort was chosen to house the CDC.

Figure 4-16: Atlanta, Georgia - The Center for Disease Control headquarters includes several emergency management command and control centers featuring GIS displays of data on outbreaks, resources and threats. Source: CDC, press release.

Other countries copied America’s strategy for fighting malaria. Unfortunately, the widespread and indiscriminate application of DDT across the globe created a different crisis of interest to biogeographers. After about 10 years of widespread use of DDT in the US, it became apparent to wildlife biologists and birdwatchers that DDT and related insect poisons were harming animals other than just insects. Anything that ate insects regularly, like birds and fish were at risk. Alarmed by the unusual number of bird deaths in areas sprayed with DDT, environmentalist Rachel Carson wrote the book, Silent Spring, detailing the numerous ecological dangers posed by the overuse of chemical pesticides. In addition to pointing out how chemicals could be responsible for human cancers, and the near inevitability of pesticide resistance, the book also detailed how the toxic effects of pesticides grew slowly over time in the bodies of predators (like birds) through a process called bioaccumulation. Carson’s book also condemned chemical companies for misleading the public about pesticides, which of course drew scathing rebuttals from chemical companies and their allies in Congress. Nevertheless, the book became a best seller and is widely regarded today as a significant milestone in the American environmental movement. The US government banned DDT for agricultural use in the US in 1972, though it is still used in Mexico. Scientists credit the ban on DDT for helping Bald Eagles and other birds-of-prey return from the brink of extinction.

Cancer

One of the leading causes of death in the United States is cancer. Cancer is a group of diseases that are characterized by an out-of-control growth of specific body cells that erode life functions. Of the many varieties of the disease, skin cancer is the most common among Americans. It is associated with overexposure to the ultraviolet light from the sun and/or tanning beds. Lung cancer kills more Americans than any other type of cancer, and about 90% of lung cancer fatalities are associated with smoking tobacco. Smoking also causes a host of other deadly cancers. Other behavioral factors linked to cancer involve alcohol, weight control, and dietary practices. Cancer is not contagious, but many cancers display spatial patterns like infectious diseases. Geographers study cancer and their techniques offer insights into both behavioral and environmental causes of cancer, and as a result – insights into strategies to combat cancer.

Cultural practices can both cause and help prevent cancers. There are clear regional differences in the rates at which people smoke, exercise, drink booze, and eat healthy, making it easy to measure the correlation between lifestyle and cancer rates.

Figure 4-17: US Map – The overall cancer rate is highest in
Southern and Appalachian States where cultural behaviors
elevate the risk of getting cancer. Source: CDC Cancer Atlas.

Some cancers are associated with ethnicity or national heritage. Partly this is because some cancers are inherited. Some forms of breast cancer, for example, are inherited, prompting numerous women with a family history of breast cancer to undo preventative mastectomy surgery. Because genetic traits are often shared among groups of people living in a region, ethnic or national groups often have genetic anomalies predisposing them to specific types of cancer. For example, studies have found that the rate of stomach cancer is above average for Finns and Koreans and that liver cancer for Vietnamese men is higher than in other groups. However, because ethnicity and national origins also predict many cultural and economic practices, it is difficult to statistically determine causality. Children who are adopted by people from a different ethnic group, or people who move beyond their ethnic homelands are often studied by medical geographers because such people help separate genetic causes from cultural ones.

Exposure to environmental pollutants is also linked to certain cancers, making geographic methods indispensable in the search for causes and preventative measures. Unlike the national or state maps of cancer showing general trends occurring within arbitrary boundaries, maps plotting cancer clusters at regional or neighborhood levels can be compelling. In Los Angeles’, for example, one study found elevated levels of some types of cancer among residents living near the Santa Susanna Field Lab in the hills between Simi Valley and the San Fernando Valley.

Consider, for example, mesothelioma, a rare type of lung cancer that showed signs of geographic clustering in the 1960s. By mapping mesothelioma clusters and various types of industry, researchers saw that locations where asbestos was mined and processed had much higher rates of the mesothelioma than regions where mining and processing asbestos was absent. This finding later allowed biomedical researchers to establish a causal relationship between various lung diseases and prolonged exposure to asbestos fibers.

Figure 4-18: Baton Rouge, LA - One of the largest oil refineries in the United States is located on banks of the Mississippi River
where transportation advantages accrue. Related industries cluster nearby. What are the health effects of this cluster of
petrochemical industries on the health of Louisianans? Source: Wikimedia.

Cancer Cluster – Cancer Alley

The most famous cancer cluster in America, an area known as Cancer Alley, may not be a cluster at all. The gap between perception and reality here highlights the difficulty of identifying the environmental causes of cancer. Cancer Alley lies along the Mississippi River in Louisiana between Baton Rouge and New Orleans and shares territory with a significant number of petrochemical factories.

This corridor does have one of the highest cancer rates in the United States, but because “Cancer Alley” does not have a statistically significant greater cancer rate versus other parts of Louisiana health geographers doubt that the region is actually a cancer cluster, and doubt that the factories are the cause. Unhealthy lifestyles, poverty, and poor access to affordable, high-quality health care both within and beyond this industrial corridor make it difficult to separate the effect of the petrochemical industry on cancer rates from the effects of poverty and unhealthy lifestyles that characterize the entire region.

Some health problems, such as birth defects, asthma, and miscarriages, are easier to connect to exposure to toxic chemicals. The most well-known toxic pollution site in America is Love Canal, a neighborhood once home to some 900 families near Niagara Falls. It was abandoned in the mid-1970s after hundreds of residents were sickened by toxic chemicals that had been buried nearby 20 years earlier by a chemical company. Poor construction practices and lax environmental laws resulted in chemicals seeping upwards through the soil and into basements. The health of hundreds of residents suffered. Elevated rates of illness were common in Love Canal indicating that the chemicals were the cause.

Figure 4-19: Niagara Falls, NY – The Love Canal neighborhood stands abandoned after toxic waste from a landfill was found in the local soil and water in the 1970s. Source: Wikimedia.

In recent years, the Flint Michigan Water Crisis has brought some renewed attention to the danger of lead poisoning, a health issue that had declined greatly in the US since the government banned lead additives in paint and gasoline in the 1970s. Flint’s problem grew out of a reliance on very old city water pipes, a search for a cheap source of drinking water and mistakes by Flint’s water management team. As a result, people living in older parts of town (poor, African-American) were exposed for many months to poisoned water.