<prompt> What is the best indicator for a potential explosiveness of plague outbreak ?Total flea indexCheopis indexSpecific percentage of fleasBurrow index  <response>: Ans. is b i.e., Cheopis index Flea indices o Flea indices are useful measurments of the density of fleas. o They are also useful in evaluating the efectiveness of a spraying programme. o The following indices are widely used in rat flea surveys : - i Total flea index It is the average number of fleas of all species per rat. ii Cheopis index -- It is the average number of X. cheopis per rat. It is a specific flea index, so it is a more significant index than total flea index. If this index is more than one, it is regarded as indicative of potential explosiveness of the situation, should a plague outbreak occur. iii Specific percentage of fleas --- It is the percentage of different species of fleas that are found on rats. iv Burrow index --- It is the average number of free - living fleas per species per rodent burrow. 