Pandemic: Causes and Prevention Factors

By Joyce West | 6/16/17 10:26 AM

*PANDEMIC: an epidemic occurring over a widespread area (multiple countries or continents) and usually affecting a substantial proportion of the population.

A survey of epidemiologists found that most believe a pandemic that kills 165 million people is possible within the next two generations.

Award-winning science journalist Sonia Shah cited that survey and explored the history and future of pathogens in her talk as part of the 2016 IdeaFestival™ in Louisville. Shah is the author of “Pandemic: Tracking Contagions, from Cholera to Ebola and Beyond.” Her talk at the Kentucky Center for the Arts was recorded for KET’s “STEAM—Ideas that Shape Our World.”

 

Loading video player...

 

“The health of individuals is really connected to the health of our animals, our wildlife, our societies, and our ecosystems,” Shah said. “And as we sort of re-imagine our relationship to the microbial world … it will just open up a lot more opportunities to prevent pandemics by undermining the conditions that allow them occur.”

Shah advocates a multi-pronged strategy, involving protecting wildlife habitats, protecting the health of people living in slums as well as animals living in factory farms, and increased surveillance in disease hot spots.

Though we can’t get rid of infectious disease, she said, we can get rid of pandemics. ”All it really is going to require is political will,” she said.

The History of Cholera
The pathogens that historically cause pandemics are bubonic plague, influenza, smallpox, HIV, and cholera, Shah said. Cholera has caused seven pandemics, including the current one that reached Haiti in 2010.

Disease can begin when humans make contact with a novel microbe in new habitats. The first cholera pandemic began in India in the early 1800s, when humans began living in wetlands that were converted to rice fields. The cholera bacterium, a marine microbe, then adapted to living in the human intestine.

The disease was spread across oceans by a new, efficient means of transportation, the steamship, and river canals helped spread it inland.

Rapid urbanization amplified the threat. “Nineteenth century New York, in the crowded parts of it, there were about 77,000 people per square kilometer. That’s six times more crowded than modern day Tokyo,” Shah said. “And it’s a thousand times more crowded than anyone had ever lived before.”
A sanitation crisis also amplified the spread. Sewage from cesspools, privies and outhouses, spilled into the streets and wells.

Shah said the rise of powerful private interests also spread disease. Doctors knew that cholera was spreading down rivers, but could not convince business to restrict traffic on the river. Wells for drinking water were sunk in areas known to be contaminated by sewage.

Could this happen today?

Shah believes the same factors exist today for new pandemics. Among those factors are habitat destruction, rapid urbanization, a sanitation crisis, a global transportation network, and the power of private business interests.

The role of wildlife habitat destruction can be seen in numerous outbreaks, Shah said.

Ebola — War in Liberia, Guinea, and Sierra Leone caused deforestation and led to human contact with fruit bats. “If you have a fruit tree where fruit bats are around, the ground is littered with saliva covered, half eaten fruits,” Shah said. In late 2013, a boy playing near a tree with a fruit bat roost became infected with Ebola. Ebola reached 3 million people within weeks.

West Nile virus — Shah said one reason the West Nile virus spread in the United States in 1999 was a decline in bird biodiversity. Woodpeckers and rails, which repel the West Nile virus, have become less common. Robins and crows, however, are good carriers of West Nile. “These are birds that can live anywhere in any kind of disrupted habitat,” she said. Mosquitoes bite infected birds, then become infected with West Nile and bite humans, infecting them.

Lyme disease — As the forest of the northeastern United States has become more of a patchwork, fewer opossums and chipmunks make their home there, Shad said. “These types of creatures actually control the tick population. The typical opossum actually destroys 6,000 ticks a week, through grooming,” Shah said. White-footed mice and deer are abundant in disrupted habitat, but a mouse destroys only 50 ticks a week. “So the fewer opossums you have around, and the more mice you have around, the more ticks you have around,” she said, adding that now about 300,000 American are diagnosed with Lyme disease annually.

What amplifies the threat of pandemic?

By 2030, most people will live in cities. “And they’re not going to be cities like Washington, D.C., and Los Angeles. They’re going to be cities more like Monrovia and Freetown in West Africa, where there’s a lot of ad hoc development and a lot of slums,” she explains.

Pathogens spread when humans are in close contact. “But it’s not just people that are crowding together these days. It’s also our animals,” Shah said. More animals are under domestication today than under the last 10,000 years until 1960 combined, she said. “A greater proportion of them are living in what you could only call the animal equivalent of a slum,” she said.

Factory farms crowd animals together and they are exposed to each other’s waste, creating a new sanitation crisis. For example, Shah said avian influenza spread quickly through captive chickens.
Livestock produce 7 billion tons of excreta each year. In old days people spread manure on cropland, she said. “Well, 7 billion tons is far more than our croplands can possibly absorb.”

Manure lagoons that are used to store waste have become a new disease transmission opportunity. About half of American cattle on American feedlots are infected with Shiga toxin-producing E. coli (STEC), Shah said. About 70,000 Americans are infected with STEC each year.

The vast flight networks of the 21st century, including regional airports, also amplify transmission of pathogens, Shah said.

The Challenges Ahead
Among the challenges Shah identifies in the fight against pathogens are scapegoating and xenophobia:
In Western Europe and America, xenophobia is rising, “in part being justified by the idea that migrants are diseased. People are threatening to build walls and close the borders. Not only does this violate people’s human rights, but it also allows these pathogens to spread, because, of course, this isn’t the essential problem.”

She also said that private interests today block needed public health measures, adding that it has been known for decades that overuse of antibiotics leads to resistant “superbugs.” “To this day, 80 percent of antibiotics that are consumed in this country are used for commercial reasons. They’re not medically necessary. These antibiotics are used by farmers to help fatten their livestock for market faster.”

Shah said it’s a mistake to address pandemics as solely a biomedical problem. She argued that a better approach would be to marshal the efforts of wildlife biologists, veterinarians, ecologists, political scientists, engineers, and economists to address both ecological and social issues.

For example, Shah said the 2008 housing crisis left Florida with many foreclosed homes and empty swimming pools, which filled with rainwater and mosquitoes. The next year, dengue returned to the state and remains there today. Shah also noted that more recently, the Zika virus took hold in a Miami neighborhood that had a vacancy rate five times the national average.

“Would addressing the housing crisis have helped contain or even prevent outbreaks of dengue and ZIka virus? We don’t know. Because nobody tried that,” she said.

Shah said earlier detection and response are needed. The earliest public health officials learn about an outbreak, she said, is after it’s already growing exponentially. In West Africa, 9 of 11 Ebola clinics set up by the U.S. military never saw a patient, she said. “We got there too late.”

What Can Be Done Locally?
What can a city like Louisville do to reduce the threat of disease?
Inequality is a risk factor in many U.S. cities, Shah explains. “When you have a lot of people who are living in impoverished conditions…they’re going to be more vulnerable and they’re going to amplify any new epidemic that occurs,” she said.

She recommended looking at a number of items to improve people’s lives, including better garbage collection, fixing broken windows, better housing and drainage, and offering better access to basic health care. She also recommended better surveillance for disease, by checking mosquitoes before there’s an outbreak and identifying the diseases they carry.

*Pandemic definition from the Centers for Disease Control and Prevention

STEAM explores the world of ideas with leading innovators who spoke at the 2016 IdeaFestival™ in Louisville. Topics range from infectious disease and evolutionary biology to virtual reality, the future of higher education, and art at the cutting edge.