Studies of vampire bats in Peru may point to better ways of controlling diseases.
As a newly identified coronavirus sweeps the world, Latin American countries have had a slight advantage. The virus, SARS-CoV-2, emerged in China, country-hopped in Asia and took hold in Europe before cases of the illness it causes, Covid-19, cropped up in Latin America.
That bought some time for countries to chart their response, with measures ranging from the lockdowns begun in Ecuador and Peru on March 16 to slower, far less urgent action by regional giants Brazil and Mexico.
But it also raised some questions. Why have relatively few epidemic pathogens emerged in Latin America? Could a virus in Latin American animals nevertheless infect humans and set off a global pandemic?
“In the broadest sense, definitely yes,” says Marcela Uhart, who heads the Latin America program at the One Health Institute at the University of California, Davis. “Such a zoonotic virus could potentially emerge anywhere where we have wildlife reservoirs and the opportunity for those viruses to come in contact with people.”
Those opportunities are increasing as people clear forests for farming, ranching or urban development, and as human activity generates greenhouse gases that warm the climate, Uhart says. Eating wild meat and selling wild animals in markets are also potential hazards. SARS-CoV-2 is one of several viruses that are believed to have jumped from wild animals to humans in crowded markets in China.
With all of those potential hazards present in Latin America, why hasn’t a pandemic emerged from, say, the Amazon? “I don’t think there’s a concrete answer,” says Daniel Streicker, a senior research fellow at the University of Glasgow’s Institute of Biodiversity, Animal Health and Comparative Medicine.
For one thing, pandemics are still fairly rare, he says, so scientists still lack data that could lead to forecasts. They also depend on a series of events. An animal with a virus that can be transmitted to humans must come into contact with people. Then the virus must not only jump; it must also be capable of being transmitted from person to person. And it cannot be so aggressive that it quickly kills new hosts, as Ebola does, reducing its chances of survival.
So when a pandemic virus does appear, “it’s like an aligning of a whole lot of stars at the same time,” Streicker says. “There are probably millions or billions of viruses out there circulating in animals,” he adds. Some will be able to make the jump to humans, become contagious and survive over the long term. “We have no good way at present of working out which viruses can do that.”
But scientists are looking. A 10-year program launched in 2009 to study emerging pandemic threats, funded by the U.S. Agency for International Development, included an effort called Predict, which identifies animal-borne diseases, or zoonoses, that could pose a potential threat to humans. The program ended, ironically, just before the SARS-CoV-2 outbreak.
Latin nations studied
Predict focused on places or activities likely to bring wildlife—especially primates, rodents and bats—into contact with humans or domestic animals, mainly in Africa and Asia, but also, for several years, in potential “hot spots” in Mexico, Brazil, Peru and Bolivia.
Scientists took samples of saliva, blood, urine and feces from wild and domestic animals, as well as samples of wild meat. They also interviewed people who could be at higher risk, including farmers living along forest edges, hunters, and wildcat miners who might eat game or come into contact with wildlife, says Uhart, one of the project leaders.
Worldwide, they identified 984 viruses, of which 169 were known and 815 were new.
Latin America was home to just 73 of the total, but that does not mean serious illnesses cannot arise in the region. Hemorrhagic fevers traced to previously unknown viruses have broken out in Venezuela, Argentina and Bolivia. The most recent, an outbreak of Chapare virus in Bolivia, caused several deaths in 2019.
Relentless deforestation for farming and ranching in Latin America brings humans and domestic livestock close to wild animals that could harbor pathogens. But the relationship is complicated. Changes in forest cover and in food supply—less from the forest, for instance, and more from crops—shift animal populations, as some adapt and some move away. “You are changing the composition of animal communities,” Streicker says. “That could be a good thing or a bad thing,” depending on whether species that thrive in the new conditions carry pathogens that can infect humans.
And climate change alters the range of insects like mosquitoes, which transmit diseases such as dengue (a virus) and malaria (caused by parasites) from animals to humans. Wild meat and wild-animal markets also put humans in contact with pathogens. Latin American forest dwellers who rely on wild meat for protein should take precautions, such as not eating animals they find dead in the forest, Uhart says.
Markets where live wild animals are sold are more hazardous, as they allow viruses to jump from species to species and to domestic animals and humans. Transnational criminal groups contribute to the demand for such animals through black market distribution and sales within the region and abroad. “In Latin America it’s a serious issue,” says Erika Alandia Robles, a Bolivian veterinarian who headed the Predict project in her country. Governments of countries such as Bolivia lack the resources to combat wildlife trafficking effectively, she says, and controlling it is not a priority.
Many experts hope the current coronavirus pandemic could convince governments of the need to ban the wildlife trade and curb illegal wildlife trafficking. Streicker says the pandemic also highlights other lessons.
“I think the biggest is going to be about the unpredictability of some of these disease-emergence events, and how important early detection and early response are,” he says. He hopes his vampire-bat research in Peru will shed light on disease transmission, surveillance and control that help planners prepare for future disease outbreaks.
For Uhart, the linkages of human health to the health of wildlife, domestic animals and the environment—a concept she calls “one health”—are key to forecasting and managing pandemics. She says wild animals “are essential to sustain healthy, functional ecosystems that provide us with vital ecosystem services. We must learn to live safely with wildlife.”
- Barbara Fraser