Residual speed of kill: Understanding its importance in eliminating fleas from a household
When it comes to controlling flea infestations, one thing more important than the initial speed of kill of a flea adulticide is the residual speed of kill of the adulticide. That is, the adulticide's speed of kill throughout the entire treatment interval — on every day between
the initial application of and retreatment with the product. The speed of kill and resulting efficacy of the product at the
end of the treatment interval is likely more important than the product's efficacy at the start of treatment. If a flea adulticide
loses significant speed of kill throughout the month after its application, it allows fleas to feed long enough that they
could elicit an allergic reaction in pets and, if the fleas live for 24 hours, they could lay eggs that repopulate the environment.
Michael W. Dryden, DVM, MS, PhD, DAVCM (Parasitology)
To appreciate the differences in residual adulticide flea control treatments for dogs and cats, it's helpful to understand
the experimental methods used in flea treatment studies. Two important, distinct evaluations of flea adulticides are initial
speed of kill studies and residual speed of kill studies.
Initial speed of kill studies measure how quickly a flea adulticide kills fleas when it is first administered; these studies do not indicate the speed of
flea kill of the product at other times during the treatment period. In contrast, residual speed of kill studies are more clinically relevant and provide flea kill information for the entire post-treatment interval.
In addition, a third type of study, which can be combined with a residual speed of kill study, is a reproductive breakpoint study.
6-9 This type of study measures whether a residual flea control treatment can prevent a flea population from maintaining itself.
In this Spotlight on Research, I will explain the different studies and discuss which results are most important in evaluating
the efficacy of flea-control products.