pandemics

pandemics infectious diseases and their causal organisms survive alongside mankind in the relationship of parasite and host, and in stable, populous societies achieve an equilibrium in which acquired immunities in the settled population mitigate the worst ravages of the infections. Pandemics, by contrast, occur when an infection escapes from its endemic habitat to reach populations without a specific acquired immunity. By definition, pandemics are distinct from epidemics: they sweep out to affect a whole country, or one or more continents, or the whole world. Epidemics may involve a much smaller community — one family; a school; or a village, town, or county. Pandemics may thus be characterized as epidemic disasters, involving disease and usually death on a massive scale.

Early pandemics

While new infectious diseases emerge from time to time as a result of human contact with normally elusive animal reservoirs of disease (Lassa fever, for example, was discovered in 1973 to have originated among rodents in Nigeria), they require special circumstances of human activity to achieve pandemic status. Human mobility — notably migration and warfare, but also exploration, travel, and trade — has played a key role in past pandemics. It is likely that pandemics have occurred periodically since the establishment of the earliest civilized, urban societies between 3000 and 500 bc, but the surviving historical records do not permit conclusive distinctions between pandemics and epidemics until late in human history. It is clear, however, that epidemic disaster struck the Roman Empire in ad 165–80, and again in ad 251–66, with an unidentifiable infection breaking out in different cities year by year, and sometimes returning. It is possible that one or both of these pandemics were due to smallpox, or even measles.

Smallpox was (the WHO declared it eradicated in 1977) a very ancient scourge related to, and possibly deriving from, one of the various animal poxes. It may have originated in India, where ancient temples still survive to Sitala, the Hindu goddess of smallpox, and where smallpox in recent times retained very much the character of an endemic disease. One attack of smallpox conferred a lifelong immunity, which permitted it eventually to establish itself as an endemic disease in the urban societies of Europe and elsewhere. It was one of the disease which, imported into the Americas by Spaniards in the fifteenth century, caused terrible devastation among the native populations, and facilitated the European conquest.

The best attested pandemics belong to relatively recent history, and to three diseases in particular: bubonic plague, cholera, and influenza. Bubonic plague, which devastated medieval and early modern Europe with successive pandemics between 1346 and the early eighteenth century, caused alarm worldwide with another pandemic between 1894 and 1900. The Black Death of 1346–50 remains the classic pandemic of popular memory.

Cholera

Since bubonic plague, cholera in the nineteenth century, and influenza in 1918, have both achieved classic pandemic status, even though their full horror has not remained in popular memory. Cholera, like smallpox, has its natural home in India, in the delta of the Ganges river. The cholera bacillus is extremely sensitive to heat and humidity, but can survive almost indefinitely where the conditions are right. In the early nineteenth century, the activities of British traders and troops in India led to its breaking out of its historic heartland in the Ganges delta, and moving beyond its established epidemic hinterland in India and neighbouring areas. Between 1817 and 1823, travelling both by land and by sea, the disease reached out through south-east Asia, China, and Japan, and through Arabia to Africa, the Persian Gulf, and southern Russia, before being cut short, perhaps by the very severe winter of 1823–4. The rapid development of trade and travel at this period ensured further pandemics of increasing geographical range.

Cholera infection is spread by food and water via the faecal–oral route, and is especially explosive when it enters a widely-distributed water supply. In the great, insanitary cities of newly industrializing Europe and America, opportunities for infection were legion. Six pandemics of cholera swept out of India between 1817 and 1923: 1817–23, 1826–37, 1846–62, 1864–75, 1883–94, and 1899–1923. The second pandemic was perhaps the most severe, with succeeding pandemics having a more variable global impact. Britain, for example, as a result of improved surveillance systems and public health reform, experienced no epidemic after 1866, while the 1866 epidemic was largely centred on London, and in particular in the water field of the East London Water Company, which had distributed contaminated supplies.

Cholera's ability to travel the nineteenth-century world was the result both of military activity and of the human and commercial interests which impelled ever-increasing numbers of people to travel or to migrate long distances. The disease regularly travelled the long-established trade-route across Russia, for example, and the 1893 epidemic at Hamburg was introduced by Russian Jews fleeing from persecution at home to a new life in the US, and who sought to travel on the regular migrant ships that sailed out of Hamburg port.

Both cholera and bubonic plague are example of diseases whose pandemic potential was eventually broken by patient observation and public health responses. Although it is likely that the cessation of plague pandemics was multicausal, the transmission routes of both diseases made them relatively susceptible to public health interventions. Infections which spread by direct contact, or the respiratory route, present a more serious challenge to human societies. The great influenza pandemic of 1918–9 illustrates the potential which such infections still have to devastate human populations.

Influenza

Influenza assumes many degrees of severity. It is caused by a notoriously unstable virus, which spreads with great speed and facility, and leaves only a brief immunity. Although it is another old disease, and although the evidence suggests some sixteen pandemics between c.1100 and 1900, on the scale of global epidemic problems it was not highly rated by public health authorities before 1918. The pandemic of 1918–9 was a very different matter: with a death toll of more than 21 million persons worldwide, it was quite simply the worst disease pandemic ever experienced by human populations — a human catastrophe equalled only by the carnage of World War II. The disease strain was a particularly virulent one, and was especially lethal to young adults in the age group 20–40, although no age group was immune. Originating in America in the spring of 1918, the disease was rapidly disseminated through Europe by American troops arriving in support of the Allied armies for the final offensive against Germany, only assuming its extreme lethal character in the autumn of that year. In the climax of local outbreaks, public services broke down entirely, medical services were unable to cope with the numbers of sick and dying, and burial services were overwhelmed by the number of bodies needing interment. Those who survived often acknowledged it as one of the most profound experiences of their lives. The American writer Katharine Anne Porter spoke for many when she said of it that ‘It just simply divided my life, cut across it like that.’

Sexually transmitted diseases

The airborne nature of influenza gave the 1918 pandemic its peculiarly immediate, universal, and devastating quality. The global pandemic of HIV infection which has spread out of the US since 1980 has less of this character and more in common with the pandemic of syphilis, which spread across Europe in the late fifteenth and sixteenth centuries, and whose initial characteristics were far more florid and alarming than those which it has subsequently manifested as an endemic disease. Both HIV and syphilis are essentially sexually-transmitted diseases, slower in manifestation and spread than airborne influenza. Nevertheless, the relatively rapid global spread of HIV as the result not only of late twentieth-century sexual mores but also of the ease and speed with which humans travel across the globe, taken together with the experience of 1918, affords some indication of the likely devastation should another lethal airborne — or easily transmitted — infectious disease acquire pandemic impetus.

Anne Hardy

Bibliography

Garrett, L. (1996). The coming plague. Newly emerging diseases in a world out of balance. Penguin Books, London.
McNeill, W. H. (1979). Plagues and peoples. Penguin Books, Harmondsworth.

See also epidemics; infectious diseases.