Surveillance is critical to:

• assess pre-specified diseases or infections known to be continuously present (endemic) in the population,
• determine the potential emergence of a previously unknown or re-emergence of a known disease as early as possible (particularly in ‘rabies-free’ situations),
• determine the spatio-temporal distribution and spread of a disease once it has been detected,
• gather insights about which factors contribute to disease emergence and distribution,
• estimate the burden of a specific disease both in humans and other organisms,
• monitor the effectiveness of control or elimination programmes aimed at reducing the disease burden,
• demonstrate freedom once the disease has been eliminated.