A brief history of pandemics
Source: By Alok Sheel: The Financial Express
The Covid-19 crisis is a grim reminder of the negative externalities associated with globalisation. Influenzas are amongst the most ‘virulent’ diseases known to man, spread by little-understood entities that inhabit the twilight world between life and matter. They can lie dormant for long periods mutate quickly and spread quickly from person to person, and through the air. In a highly mobile world, they spread rapidly across the globe, challenging the best public health systems as vaccines and antidotes take time to develop. Covid-19 is also the first pandemic played out in the full glare of social media, evoking panicked policy responses even where epidemiological patterns are very different and normal influenza mortality much lower.
The world before the great age of European discovery was a very local one. The means of communication were slow, based on animal traction on land, wind traction on water, and limited in range. Most people were born and died at their place of birth. Epidemics right up to the end of the medieval period were localised affairs. Mortality rates could be high, generating panic that revived longstanding social prejudices like anti-Semitism, just as they do today. Pestilence, along with famine and war, were the three equilibrating devices that kept the pre-modern population in check despite high basal birth rates.
Bubonic Plague was in a class of its own. The first plague pandemic was the Plague of Justinian between 6th-8th centuries AD during the high tide of the Roman Empire. The second pandemic, the Black Death of the 14th century, was also in the pre-modern era. It was only the third pandemic of the mid-19th to the early 20th century that took place in the post-industrial age.
Plague, however, is a disease primarily of rodents. Ordinarily, humans cannot infect each other, except in the rare pneumonic form, or when the rat flea is looking for a new host following the death of its current host. Rat colonies thrived on coastal ships, and infected rats were transported from port to port. Once established inland, bubonic plague became a creeping epizootic, spreading only as fast as the underlying rat population travelled. Modern technology transformed plague epidemics. In the early 20th century, the epidemic spread fast in the Indian hinterland after landing by ship, being carried rapidly up the country through grain movements by railway with their complement of infected rats. It, however, reverted to the medieval creeping epizootic away from railway links.
As the means of communications improved, large numbers could now be transported over long distances. Maritime technology transited from coastal shipping to trans-continental oceanic voyages even before the engine age following new scientific inventions that heralded the European Age of discovery and imperialism from around the 16th century. As Europeans discovered and conquered new lands, they brought with them unfamiliar diseases against which the local populations had no herd immunity. In the Americas, the arrival of Europeans decimated 90-95% of the indigenous population through small-pox, measles, typhus, cholera, diphtheria, influenza and the like.
It is intriguing why a similar phenomenon did not occur in the East Indies and India. Europe and Asia was a single landmass with low-level long-distance links over centuries through the Indian Ocean trade extending from the southern coast of China, through the straits of Malacca and India, right up to the horn of Africa and terminating in Venice. Eurasia, therefore, shared a common pool of disease.
The first modern pandemic was cholera, imported into Europe from Asia in the early 19th century following the colonial link. Why cholera had not reached Europe earlier through the Indian Ocean trade route remains a mystery. Was this because the cholera pathogen could not survive long outside its warm moist tropical environment on long coastal shipping journeys and was transported to Europe only in the age of faster steamships invented towards the end of the 18th century?
The break between the epidemics of the past and today is provided by the public health revolution that followed, but did not coincide with, the Industrial Revolution that sharply reduced mortality from infectious diseases. One of the more interesting debates in English population history is centred on the spike in mortality in the immediate aftermath of the Industrial Revolution. This is attributed to the squalor in urbanised industrial counties and greater population movements. The decline in mortality followed the public health revolution. Likewise, mortality increased in India in the 19th century despite improved food security following modern developmental works like all-weather roads, railways and canals that also led to the rapid spread of malarial fevers, keeping population stagnant right up to 1921.
Viruses present a grave threat to globalisation. Most viruses are either highly virulent but relatively benign, causing low mortality like seasonal flu, or have been less virulent but deadly, like Ebola, SARS, MERS. But, now and then the perfect storm will occur, a strain both virulent and deadly with the potential of causing death on a mind boggling scale. The value attached to human life has changed over time, but a quarter-million deaths from Covid-19 to date is far from being a perfect storm. The Spanish flu a century ago claimed an estimated 40-50 million people globally. The first two plague pandemics claimed 30-50 and 200 million lives respectively, and the third 10-12 million in China and India alone. Over 40 million perished from cholera in the 19th century. It is only a matter of time when a perfect storm arrives again. Hopefully, with the experience gained with handling Covid-19, the world would be better prepared.
