Tag Archives: climatechange

Destroying Nature Unleashes Infectious Diseases

Elephants move through southern Sudan’s Boma National Park

This article is from 2012, but illustrates how we currently find ourselves in lock down in our homes. Our carelessness with the environment has repercussions. If the extreme storms and wildfires aren’t going to get our attention and force us to change, then the Earth will shake society to its core by spreading dangerous, highly infectious diseases.

“If we fail to understand and take care of the natural world, it can cause a breakdown of these systems and come back to haunt us in ways we know little about. A critical example is a developing model of infectious disease that shows that most epidemics — AIDS, Ebola, West Nile, SARS, Lyme disease and hundreds more that have occurred over the last several decades — don’t just happen. They are a result of things people do to nature.

Disease, it turns out, is largely an environmental issue. Sixty percent of emerging infectious diseases that affect humans are zoonotic — they originate in animals. And more than two-thirds of those originate in wildlife.

Teams of veterinarians and conservation biologists are in the midst of a global effort with medical doctors and epidemiologists to understand the “ecology of disease.” It is part of a project called Predict, which is financed by the United States Agency for International Development. Experts are trying to figure out, based on how people alter the landscape — with a new farm or road, for example — where the next diseases are likely to spill over into humans and how to spot them when they do emerge, before they can spread. They are gathering blood, saliva and other samples from high-risk wildlife species to create a library of viruses so that if one does infect humans, it can be more quickly identified. And they are studying ways of managing forests, wildlife and livestock to prevent diseases from leaving the woods and becoming the next pandemic.

It isn’t only a public health issue, but an economic one. The World Bank has estimated that a severe influenza pandemic, for example, could cost the world economy $3 trillion.

The problem is exacerbated by how livestock are kept in poor countries, which can magnify diseases borne by wild animals. A study released earlier this month by the International Livestock Research Institute found that more than two million people a year are killed by diseases that spread to humans from wild and domestic animals.

That’s why experts say it’s critical to understand underlying causes. “Any emerging disease in the last 30 or 40 years has come about as a result of encroachment into wild lands and changes in demography,” says Peter Daszak, a disease ecologist and the president of EcoHealth.

Emerging infectious diseases are either new types of pathogens or old ones that have mutated to become novel, as the flu does every year. AIDS, for example, crossed into humans from chimpanzees in the 1920s when bush-meat hunters in Africa killed and butchered them.

IT’S not just the invasion of intact tropical landscapes that can cause disease. The West Nile virus came to the United States from Africa but spread here because one of its favored hosts is the American robin, which thrives in a world of lawns and agricultural fields. And mosquitoes, which spread the disease, find robins especially appealing. “The virus has had an important impact on human health in the United States because it took advantage of species that do well around people,” says Marm Kilpatrick, a biologist at the University of California, Santa Cruz. The pivotal role of the robin in West Nile has earned it the title “super spreader.”

And Lyme disease, the East Coast scourge, is very much a product of human changes to the environment: the reduction and fragmentation of large contiguous forests. Development chased off predators — wolves, foxes, owls and hawks. That has resulted in a fivefold increase in white-footed mice, which are great “reservoirs” for the Lyme bacteria, probably because they have poor immune systems. And they are terrible groomers. When possums or gray squirrels groom, they remove 90 percent of the larval ticks that spread the disease, while mice kill just half. “So mice are producing huge numbers of infected nymphs,” says the Lyme disease researcher Richard Ostfeld.

“When we do things in an ecosystem that erode biodiversity — we chop forests into bits or replace habitat with agricultural fields — we tend to get rid of species that serve a protective role,” Dr. Ostfeld told me. “There are a few species that are reservoirs and a lot of species that are not. The ones we encourage are the ones that play reservoir roles.”

Dr. Ostfeld has seen two emerging diseases — babesiosis and anaplasmosis — that affect humans in the ticks he studies, and he has raised the alarm about the possibility of their spread.

The best way to prevent the next outbreak in humans, specialists say, is with what they call the One Health Initiative — a worldwide program, involving more than 600 scientists and other professionals, that advances the idea that human, animal and ecological health are inextricably linked and need to be studied and managed holistically.

“It’s not about keeping pristine forest pristine and free of people,” says Simon Anthony, a molecular virologist at the Center for Infection and Immunity at Columbia University’s Mailman School of Public Health. “It’s learning how to do things sustainably. If you can get a handle on what it is that drives the emergence of a disease, then you can learn to modify environments sustainably.”

The scope of the problem is huge and complex. Just an estimated 1 percent of wildlife viruses are known. Another major factor is the immunology of wildlife, a science in its infancy. Raina K. Plowright, a biologist at Pennsylvania State University who studies the ecology of disease, found that outbreaks of the Hendra virus in flying foxes in rural areas were rare but were much higher in urban and suburban animals. She hypothesizes that urbanized bats are sedentary and miss the frequent exposure to the virus they used to get in the wild, which kept the infection at low levels. That means more bats — whether from poor nutrition, loss of habitat or other factors — become infected and shed more of the virus into backyards.

It might mean talking to people about how they butcher and eat bush meat or to those who are building a feed lot in bat habitat. In Bangladesh, where Nipah broke out several times, the disease was traced to bats that were raiding containers that collected date palm sap, which people drank. The disease source was eliminated by placing bamboo screens (which cost 8 cents each) over the collectors.

EcoHealth also scans luggage and packages at airports, looking for imported wildlife likely to be carrying deadly viruses. And they have a program called PetWatch to warn consumers about exotic pets that are pulled out of the forest in disease hot spots and shipped to market.

All in all, the knowledge gained in the last couple of years about emerging diseases should allow us to sleep a little easier, says Dr. Epstein, the EcoHealth veterinarian. “For the first time,” he said, “there is a coordinated effort in 20 countries to develop an early warning system for emerging zoonotic outbreaks.”