The spread of the killer virus

Written by Thomas Hesselberg

Wednesday, 06 February 2008

Transmission electron microscopy image of the influenza virus. Magnified around 100,000 times. Courtesy of the Public Health Image Library.

The risk of a deadly pandemic virus has become frightening real in recent years with the SARS and the avian flu scares. Imagine a virus that develops at some continent, from there spreads to the globe and within half a year kills more than 25 million people worldwide…Unfortunately this is not pure imagination. It can happen and it has happened. The 1918 flu pandemic (or the Spanish flu as it commonly known as) first appeared on March the 4th, 1918 in Kansas, USA. In August a more virulent strain simultaneous appeared in Boston, Sierra Leone, France and Spain. When the pandemic was finally over in June 1920, most regions including remote Pacific Islands had been affected and world wide between 50 and 100 million people, including healthy young adults had died from the flu. The main reason for this was an extremely high infection rate of 50%.

In order to avoid something like this happening in the future, we need to know more about the beginning of the pandemic. The biostatistician Laura White and Marcello Pagano from Boston University studied the recorded spread of the disease in Maryland communities and aboard two ships in order to develop reliable models.

An important and easily measured aspect of the rate of spreading of the disease is the serial interval, which is the time between the first infected person develops symptoms and the person infected by the first develops symptoms. The researchers found a serial interval of 3-4 days on average for the Spanish flu, which is very fast for instance compared to the 8-10 days of the 2003 SARS outbreak. They, furthermore, found a very consistent serial interval in the confined communities aboard the ships while the Maryland communities showed a high variance in serial interval. Thus the population dynamics is an important factor to consider when developing models to predict the spread of the pandemic.

More research into the Spanish flu and other pandemics are needed as information like the one described here may help to save many lives if (or more likely when) a pandemic killer virus appears again.

Source: White LF, Pagano M (2008) Transmissibility of the Influenza Virus in the 1918 Pandemic. PLoS ONE 3(1): e1498. doi:10.1371/journal.pone.0001498

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