Culture | Infectious diseases

Passing through

Mankind knows a lot about diseases and how they spread. It still has a lot to learn

Pandemic: Tracking Contagions, from Cholera to Ebola and Beyond. By Sonia Shah. Sarah Crichton Books; 288 pages; $26.

ZIKA, the world’s newest pandemic, arrived down a well-trodden path. Between 1940 and 2013, more than 300 contagious diseases, including HIV/AIDS, SARS and antibiotic-resistant tuberculosis, were identified for the first time, appeared in populations that had never seen them or reappeared after having been eliminated (see map). Sonia Shah explains how human missteps can mesh with biological happenstance to turn harmless microbes into global disease monsters.

Ms Shah is an American science journalist and broadcaster who gave a TED talk in 2013, offering three reasons why malaria still had not been eradicated. It has since been viewed more than 1m times. In her new book, “Pandemic”, she combines history with reporting from disease hotspots around the world. She frames the narrative around the journey of cholera, “an old hand at pandemics”, which terrorised London, New York and Paris in the 19th century, to draw out worrying parallels between the mistakes of the past and today’s treatment of pandemic threats.

New pathogens often arise as a result of making the jump from animals to humans, as Ebola is likely to have done from bats in the jungle. The scariest among them learn to spread easily from one human to another, which is luckily still tricky for bugs like H5N1, the avian influenza virus that kills more than half the people it infects. But newcomers may be getting craftier and opportunities are plentiful, as Ms Shah finds out in poultry markets and pig farms in China and state fairs in America. Climate change and felled forests bring together species that have never crossed paths, which lets microbes mutate among them and make their way into humans.

INTERACTIVE: Click/tap to explore an interactive version of this map

Epidemics stand little chance without crowds and filth. “Pandemic” contains vivid descriptions of the tenements of New York in the 1850s, when nearly six times as many people were packed into one square mile (2.6 sq km) as there are in Manhattan today, and sewage covered the streets, seeping into the drinking water. Slums in developing countries are more crowded now, and with appalling sanitation.

Corrupt politics is often to blame when disease spreads. In the past, quarantines were sometimes shunned for the sake of trade. A convention negotiated in 1903 obliged countries to report disease outbreaks to each other, only to be flouted shortly after by the Italian authorities, who bullied and bribed doctors and journalists to deny a cholera outbreak. Ms Shah lists recent similar cover-ups, including SARS in China in 2002, an antibiotic-resistant bacterium in India in 2010 and MERS, a respiratory virus, in Saudi Arabia in 2012—all of which spread around the world.

Pandemics have shaped human evolution and society, argues Ms Shah. People pick, through smell, mating partners who have the pathogen-recognition genes that others lack, for example. The book brims with anecdotes. In 1892, for one, 28 doctors disputed Robert Koch’s discovery of the cholera bacterium by drinking, publicly, the watery stool of a cholera patient. (Despite the telltale diarrhoea, they still disagreed—because none died.)

Whether the world can forestall the next, unknown pandemic threat is uncertain, although serious efforts are being made. (The book was written before Zika erupted.) Hotspots where new pathogens are most likely to hatch, such as factory farms, urban slums and wild habitats that are rapidly invaded, are being watched. New ways of spotting outbreaks include vigilance about what is trending on social media or selling in pharmacies (thermometers in flu’s off-season can be one alert). But fewer than half the world’s countries have proper surveillance systems—which is why Ebola, and probably Zika too, had a long head-start on epidemic fighters.

The world’s ability to put the lid on pandemics has come a long way since the days when the plague, cholera and smallpox ravaged unchecked. Ms Shah’s book is a superbly written account of how we got here and what might await us.

This article appeared in the Culture section of the print edition under the headline "Passing through"

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