The 1919 epidemic is traced back to pigs and the later pandemics from birds. No cure exists for influenza and the most commonly followed course of action is to develop a vaccination for the next anticipated strain. The WHO estimates that there are more than 50m cases of this flu-like fever each year. This mosquito-borne infection is endemic in more than a hundred countries worldwide. Before 1970 only nine countries had experienced an epidemic.
Dengue is the leading cause of childhood mortality in several Asian countries.
In adults it can lead to a temporary incapacitation but rarely death. Besides fever, the disease is characterised by extreme pain and stiffness in the joints. There is no specific treatment and immunisation is difficult since the virus has four principal strains. Protection against only one or two of them could increase the risk of more serious disease. The most successful prevention is to destroy mosquitoes and their breeding grounds.