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[mynah]

Extract from an article I wrote for the South African Encyclopedia (available online, but unfortunately not without subscription) a few years ago:

Apart from the Black Death - the bubonic plague pandemic that ravaged Europe and Asia in the 1340s – no epidemic yet recorded spread so fast and affected such a number of people.

Although the pandemic reached Spain early and was given much publicity in that country, the devastating strain had its origins elsewhere. The movements of large numbers of soldiers who participated in World War One would no doubt have contributed greatly to the spread of the disease in an era before civil aviation.

In the spring of 1918 an army cook was the first person to get influenza at Fort Riley, a military base in the US state of Kansas. Within two days, 522 soldiers were affected. The base bred and slaughtered its own pigs and poultry, and it is possible that the cook was infected while working with meat of afflicted animals.

The initial cases were not unusually severe – but in August 1918 the virulent strain emerged almost simultaneously in France, the United States and Liberia. From the beginning it was clear that this no ordinary flu: Sufferers would often be too weak to walk within hours of becoming ill. Shortly afterwards the faces of many would take on a bluish tinge and, as they struggled for breath, bloody froth would bubble from their mouths. Millions of people died within a day of two after the first symptoms appeared. In the US the pandemic reached its peak in October 1918, and elsewhere the disease spread like wildfire. Almost 140 000 deaths were recorded in South Africa before the last cases occurred in 1919.

The Spanish flu pandemic was remarkable in a number of ways.

Mortality rates in influenza and most other infectious diseases typically form a U-shaped curve when plotted against age on a graph, indicating that elderly and very young patients are at greatest risk of dying from the disease. The Spanish flu, however, yielded a W-shaped curve, as young adults were more likely to die than those just younger or older. At the time the deaths were often noted to be due to “unusually severe pneumonia” – but it is now believed that sufferers mostly died as a result of cytokine storm. Healthy young adults were most at risk because of the efficiency of their immune systems.

Another characteristic of the pandemic was the rate at which it spread and the high percentage of people affected: The largest inhabited area unaffected by disease was an island in the estuary of the Amazon River. Mortality varied greatly from area to area: Although the average figure of around 2,5 percent in the industrialised countries was considerably higher than that usually reported for flu, the pandemic was not nearly as devastating there as in remote areas where the disease had never been recorded before: Among some Eskimo communities in Alaska a third or more of those who were infected died, and it is believed that entire villages in the Third World disappeared off the face of the earth.

The viral strain, which would later be named H1N1, showed the characteristics of a virus that had undergone species jumping. The high rate of contagion, prevalence of the disease and extraordinary virulence had the hallmark of a foreign virus that had found its way around the human immune system, and against which humans had little resistance. Variants of H1N1 are still circulating among humans – but because most people have developed a degree of resistance, as well as the fact that vaccines and antiviral drugs are now available, the virus is not in the least as threatening as in 1918.

It was long assumed that H1N1 originated in pigs, which are susceptible to a similar strain. In 2005, however, tests on the frozen body of a woman who died of the Spanish flu in Alaska proved that this disease was a form of avian influenza. It is, however, possible that the virus was first assembled in a pig that was infected by both avian and human flu viruses. On the other hand, the original mixing vessel may have been a human, and it could be that pigs were infected later by contact with humans.