Governments must have early warning when a disease spreads, to prevent it becoming an epidemic.

A website called HealthMap provides real-time alerts on emerging outbreaks across the world.

The map shows alerts for 12 types of diseases, colour-coded for the “noteworthiness” of each event. Larger circles indicate a national alert, and smaller circles are for local alerts. It lets you filter alerts by disease, location, source, animal species and time.

The website aggregates data from sources that might not be traditionally used by officials. It scours tens of thousands of freely available sources on the internet, including social media, news reports, eyewitness reports, online discussions and government websites. An algorithm then filters the data and plots the relevant bits on an online map.

Last year, the map spotted early social media reports of a “haemorrhagic fever” in West Africa, nine days before the World Health Organisation issued its first statement on the Ebola outbreak.

Developed in 2006 at the Boston Children’s Hospital, the tool is now available in 15 languages and has over one million users a year, including government agencies, public health officials and international travellers.

There are challenges, however. Since the algorithm has to filter through free text, it can pick up unrelated alerts which don’t give a true sense of what is happening, a World Bank blog post says. For instance, it could turn up disease-related terms, like scientific findings or vaccination campaigns, which don’t necessarily indicate a risk.

While the HealthMap cannot replace lab tests to confirm disease outbreaks, it is a useful tool for public health officials to find out where to look for possible threats.

You can view the real-time alerts on this website: healthmap.org