A fundamental measure of the overall transmission potential of a pathogen in a given setting is the basic reproduction number, R 0 . This is defined as the mean number of secondary cases generated by a typical case in a fully susceptible population [16, 17] . If the transmissibility of each infected host remains constant throughout its infectious period, and if each infected host has an equal chance of infecting each susceptible host, then R 0 is simply the product of the mean rate at which an infected host generates secondary infections and the mean infectious period (provided the two are not correlated).