Tracing ancient origins of killer diseases leads us back to agriculture

The domestication of plants and animals contained drawbacks that lie behind this virus, writes Alun Evans

‘Epidemics tend to originate in the Far East and this is ascribed to people living in proximity to animals’

THE development of agriculture, which began around 10,000 years ago, brought undoubted benefits — but it also came at a price.

We swapped our nomadic hunter-gatherer lifestyle, with its varied yet unreliable food sources, for a sedentary one. We also settled down, usually employing as a water supply rivers which were liable to pollution with our own effluent, leading to water-borne disease.

The production of weak alcoholic drinks helped provide a source of safe drinking water.

Agriculture also brought ownership and marriage, because it became important to know who should inherit the land and any possessions, and so, in a way, spawned capitalism.

This also entailed the domestication of plants and animals. The plants we domesticated were limited, so our diets became less varied and our consumption of domesticated animals reduced variety, as not all were suitable for domestication.

This also had implications for our health as our consumption of dairy products and meat increased, and the enforced proximity to the domesticated animals came with its own drawbacks.

The great Scottish anatomist, John Hunter, did not limit his interests to anatomy, but ventured into many other fields, including zoology, notoriously establishing a large private zoo, housing exotic animals, near London.

Here he pursued his interest in inter-breeding. His experiments led him to conclude that the wolf, the jackal, the fox and the dog belonged to a common species.

This conclusion was not only based on their physical similarities, but also on the fact that they could mate and produce offspring, albeit that it was not without reluctance that the female animals were induced to mate.

He published his findings in the Philosophical Transactions of the Royal Society in 1787. There is no doubt that Hunter was correct, and in fact ‘man’s best friend’ the dog was his first domestication; until recently this domestication was put at 12,000 years ago, but some have put it back as far as 100,000 years ago.

Today we have over 400 breeds of dogs

The Gloucestershire general practitioner Edward Jenner was another polymath, who described the arcane breeding strategy of cuckoos and bird migration. He had been a student at Hunter’s anatomy school in London during the early 1770s and became his protege, measuring the core temperature of a hibernating hedgehog, after Hunter cajoled him with, “Why think? Why not do the experiment?”

Jenner, however, is best remembered for his ground-breaking work on vaccination for smallpox, a major scourge in the 18th century and beyond.

It was common knowledge where Jenner lived that cowpox, a disease sometimes contracted by milkmaids, gave protection against smallpox. And so, in 1796 Jenner inoculated the eight-year-old James Phipps with some material derived from a cowpox pustule afflicting the milkmaid Sarah Nelmes.

Six weeks later he exposed James to some smallpox material — but the disease did not ensue.

In 1798, Edward Jenner, in the introduction to his Enquiry into … The Cow-Pox, observed: “The deviation of man from the state in which he was originally placed by nature seems to have proved to him a prolific source of disease. From the love of splendour, from the indulgence of luxury, and from his fondness for amusement he has familiarised himself with a great number of animals, which may not originally have been intended for his associates.”

A shining example of the fruits of such association is that we share an estimated 65 diseases with our oldest and best friend, the dog.

The word epidemic, denoting an increasing incidence (number of new cases) of a disease, is derived from ‘Epi’ Greek for ‘upon’ and ‘Demos’ ‘the people’, and an epidemiologist is someone who studies these, and wider, phenomena. Pandemic (‘pan’ means ‘all’) implies a disease increasing on a far greater scale, and the addition of ‘global’ implies ‘worldwide’ and is typically applied to infectious disease. There have been many pandemics throughout history, including, the Black Death, cholera, typhus and influenza.

During the 20th century there were three influenza pandemics. The 1918 Spanish Flu was by far the worst with estimates of mortality varying between 25m and 100m, and which was believed to have originated in pigs. The 1957 Asian Flu, which arose in birds, was much less serious and, interestingly, people who had survived the 1889 Russian

Flu were spared, pointing to a lasting immunity; and Hong Kong Flu in 1968, again from birds. There was also an outbreak of swine flu in 1977, and another in 1997, but these did not become established. A pandemic of louse-borne typhus killed three million people after World War I.

Throughout history there has been a tendency for influenza epidemics to originate in the Far East and this is usually ascribed to large numbers of people living in close proximity to animals. In modern China, the number of animal species being farmed is staggering: nearly 20,000 wildlife farms raising species including peacocks, civet cats (an inefficient way to produce protein as they are carnivores), porcupines, ostriches, wild geese and boar have been shut down in the wake of the coronavirus outbreak.

Covid-19 is believed to have originated in bats or ducks. The name derives from the Greek for ‘crown’: the coronary arteries are supposed to encircle the heart like a crown; in the case of this virus it has projections like the spikes (or jewels) on a crown.

This is not the first coronavirus outbreak: previously we have encountered Severe Acute Respiratory Syndrome SARS which emerged in southern China in 2002, probably from bats (since then it has re-emerged four times, three times from laboratories).

It was an influenza-like disease and resulted in 8,000 cases with a mortality around 10pc; and, Middle Eastern Respiratory Syndrome (MERS) or ‘Camel Flu’ arose in 2012. It kills around a third of diagnosed cases, but, thankfully, it is not particularly infective: the advice is not to touch sick camels.

The present coronavirus outbreak is not nearly as lethal but is extremely contagious, witness its colonisation of the globe in less than six months.

The peak of this pandemic here is yet to arrive.

Alun Evans is professor emeritus at the Centre for Public Health in Queen’s University, Belfast