This interactive graphic gives a general visual idea of the way an infectious disease can spread around the world, reflecting transmission between people locally and extended by extensive international travel. It can be modified to give an idea of the severity, rapidity and extent of infection. For example, very provisional data for the current H1N1 swine flu pandemic suggests it could infect up to a third of the population, and cause deaths in up to 0.4 per cent of cases.

WARNING: This is not a predictive tool. It was created by the FT graphics department and is not based on any epidemiological model of a particular disease. It cannot show the precise pattern of spread or the relative risk of exposure in a particular location, and does not take into account specific factors that may affect disease, such as the effect of other infections in people, nutrition, genetic factors, the mechanisms of transmission, or medical support and quarantining. It does highlight the speed with which infection can spread globally in the 21st century.

How it works:

The green dots represent a sample of 600 ‘individuals’ moving randomly between 50 locations around the world. About 5 per cent of the people are naturally immune (blue dots). Click on any of the green dots to start an outbreak.

As the infected dot travels it spreads the pathogen to others. The infection rate is initially set to 25 per cent, so approximately one in every four dots that come into contact with the disease will be infected. Increasing the infection rate will increase the speed at which the disease spreads.

Incubation time is the period between infection and the first symptoms. Those incubating the disease (yellow dots) may not know they are infected, so they continue normally until they fall ill (red dots) when they tend to stop travelling. Duration time is how long the disease lasts, before the patient either recovers and becomes immune, or dies from the infection. Increasing the mortality rate will change the number of fatalities. Pathogens with a high mortality rate and short duration, such as Ebola, may not spread far, as they kill the host before the disease can be passed on to another host.

For this graphic the incubation time and duration are measured in hours but in reality often take several days.