Several deadly new viruses in recent years have emerged in China — Severe Acute Respiratory Syndrome (SARS), bird flu, and now the novel coronavirus (nCOV). The reason could lie in the busy food markets dotting cities across the country — where fruits, vegetables, hairy crabs and butchered meat are often sold next to bamboo rats, snakes, turtles, and palm civets. Closely packed stalls in busy marketplaces, the Chinese taste for exotic meats, and the high population density of cities create the conditions for the spread of zoonotic infections, experts say.
The relationship between zoonotic pathogens — those of animal origin — and global pandemics is not new. The Justinian Plague (541-542 AD), the Black Death (which started in Europe in 1347), yellow fever in South America in the 16th century, the global influenza pandemic in 1918, and modern pandemics such as HIV/AIDS, SARS, and triple-reassortant A H1N1 influenza have one thing in common: the causal organisms came to humans from animals.
The World Health Organisation (WHO) estimates that globally, about a billion cases of illness and millions of deaths occur every year from zoonoses, i.e, diseases and infections naturally transmitted between people and vertebrate animals. Some 60% of emerging infectious diseases globally are zoonoses. Of the over 30 new human pathogens detected over the last three decades, 75% originated in animals.
Animal markets everywhere…
“Wherever there is close mixing of humans and animals, especially the unregulated handling of blood and other body products, as happens for example in China’s animal markets, there are greater chances of transmission of a virus from animals to humans, and its mutation to adapt to the human body,” a senior WHO functionary told The Indian Express from Geneva.
It isn’t just China, the official said. “It has happened wherever in the world there is unregulated mixing of humans and animals, either wild or domesticated.” The official referred to the Ebola outbreak in Africa: “There it was wild chimpanzees who had the disease. It came into humans after these were killed and consumed. Animal markets are breeding grounds because there is free interchange of pathogens between species and mutations.”
…And especially in China
Dr K S Reddy, former professor of AIIMS and president of the Public Health Foundation of India (PHFI) noted that the majority of new outbreaks and pandemic threats over the past five decades had arisen from microbes transmitted from animals to humans, either directly or through another animal reservoir host.
“Proximity to animals grows from wild food markets and captive animal breeding, with deforestation creating a conveyor belt for viruses and vectors to move from wildlife to captive animals, and from them to humans. The wild food markets in China offer both a mix of many animals which harbour deadly viruses, and an opportunity to transmit with ease to crowds of humans whose taste for a diversity of wild as well as close-bred animals provides a conveyor belt for animal-to-human transmission. Once the virus gains entry into humans who travel and transport animals, the infection spreads,” Dr Reddy said.
The more virulent strains emerge from mutation which occurs when a large human host community offers itself for easy transmission, Dr Reddy said. “Human folly opens the ecological window and microbial genetics seize the opportunity. Deadly viruses can then play Chinese Checkers leaping from species to species. This happens in other parts of the world too, but the Chinese taste for exotic animal foods and the population density makes it a prime playground for zoonotic infections,” he said.
Ecology of infections, spread
With a population of nearly 1.4 billion and 50% of the world’s livestock, China’s ecology poses a risk for emerging, re-emerging, and novel diseases that could threaten China and the rest of the world, says the US federal agency Centers for Disease Control and Prevention (CDC).
“Moreover, the world’s growing network of air travel routes dramatically increases the risk for infections to rapidly spread, and for potential pandemics that can cause illness, death, and costly disruption to global trade,” the CDC states.
The SARS epidemic began in November 2002 in the Guangdong province of southern China, and spread across the world. Bird flu of various provenances — the virus keeps mutating — have been repeatedly reported from China after the first H7N9 novel avian influenza outbreak of 2013. In 2018, a 68-year-old patient from Jiangsu province was infected with H7N4. Last year, there was an outbreak of H5N6 bird flu in Horgos in the far western Xinjiang region.
In the wake of the Wuhan coronavirus outbreak, Dr Takeshi Kasai, Regional Director for the Western Pacific, WHO (under which China falls), wrote: “This New Year’s wake-up call reminds us to be vigilant against SARS, bird flu and the causes of more recent outbreaks in the region… In fact, two of the last four influenza pandemics began in the Western Pacific Region — home to 1.9 billion people and a hot spot for outbreaks of emerging infectious diseases and natural disasters. These were threats that put people’s health and safety and economic development at risk… It is fair to ask: are we safer from health security threats than we were a decade ago, following the H1N1 influenza pandemic? Or than we were when SARS emerged 17 years ago?”
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