The Atlanta Journal-Constitution
Why the way we live could mean more pandemics
The coronavirus crisis clearly caught most governments unprepared, yet disease specialists have been warning for decades that such an outbreak was bound to happen.
From bubonic plague and smallpox to Spanish flu and HIV, history is rife with pandemics that have shaped the human story.
Though medical advances help combat such scourges, other aspects of modern life — including deforestation, urbanization and intensive agriculture — contribute to the emergence of new contagions at an alarming rate.
Q: Are we likely to see more pandemics?
A: The danger of a new disease spreading globally has been elevated in the modern age by the leap in air travel and international trade. The number of passenger trips by air more than doubled from the turn of the century to an estimated 4.2 billion in 2018 — before the pandemic walloped travel and tourism. Especially worrisome are pathogens that transmit effectively via the respiratory tract, such as coronaviruses like the one causing the current crisis and new strains of flu, the most common cause of pandemics.
Q: Where do new diseases come from?
A: Novel pathogens that sicken humans have been discovered at an average rate of more than three per year over the past four decades. About 75% come from animals and are known as zoonoses. Bats are thought to be the source of the coronaviruses that cause COVID-19, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). They’ve also been linked to the Ebola virus, as well as the Hendra and Nipah viruses responsible for deaths in Australia and Southeast Asia. The threat from bats is partly a reflection of their sheer numbers; they are among the most populous mammals. Bats roost together by the thousands, creating an environment rich for swapping viruses, and they can transmit them to other animals or humans through their blood, saliva, urine and feces.
Q: What drives the emergence of zoonoses?
A: Researchers have identified a number of factors increasing the potential for so-called spillover events, when a pathogen jumps species:
■ Encroachment into natural ecosystems. As the world’s population has expanded, humans have taken over wilderness areas at a rapid pace. Researchers concluded in 2017 that in the prior two decades people had claimed an additional 10% of the Earth’s wild land, reducing to 23% the area free of disturbance. New settlements and operations such as logging and mining put people in closer proximity to wild animals.
■ Consumption of wildlife. There’s been a growing trade in wild animals, especially for food. In some live animal markets, domestic and wild animals are caged in close proximity and slaughtered under unhygienic conditions. Live markets in China were connected to the emergence of SARS. It was initially but is no longer thought that the novel coronavirus jumped into people at such a market.
■ Urbanization. About 55% of the world’s people live in urban areas, compared with 34% in 1960. Expanding metropolitan areas provide new homes for a variety of wildlife, including rats, monkeys, birds and foxes — animals that can live off the plentiful food humans discard.
■ Intensive livestock farming. Pathogens from wild creatures sometimes make their way to humans via farm animals. As with people, packing many cows, pigs or chickens closely together increases the danger that a disease can spread. Antibiotics used to hasten the growth of animals can also promote pathogens that are resistant to treatment.
■ World temperatures: Rising temperatures have contributed to the expansion of the range of disease-spreading mosquitoes, ticks and biting midges. These species can persist for longer periods, increasing the spread of illnesses such as Lyme disease, hepatitis E, dengue and West Nile virus.
Q: What’s being done about live-animal markets?
A: There have been calls, including from U.S. lawmakers, for China to close its so-called wet markets. But such places, offering fresh meat and produce more cheaply than supermarkets, play a huge role in feeding people, supplying about 60% of fresh food in the city of Guangzhou, for example. In February, China did permanently ban the trade in nonaquatic wild animals, although it made an exception for their use in traditional medicine. African countries have also been called upon to halt the trade in slaughtered wild animals, though it’s unlikely to happen because “bushmeat” provides a much-needed source of protein.
Q: What else could be done to prevent pandemics?
A: Experts point to a need to better monitor emerging diseases and maintain public-health systems that can quickly respond to them. In the most ambitious effort to catalog new pathogens, the U.S.-funded Predict project from 2009 to 2019 identified more than 1,000 viruses with spillover potential. Researchers aim next to assess the biggest disease risks lurking in the animal world in order to focus efforts toward developing tests and prototype vaccines. Those could provide early warning systems for outbreaks and rapid responses to stop them from spreading.