I think apply ant-ratting for killing rodent first let the arthropod to escape and left the dead rat and search for other rat for feeding and consequently transmit the infection to man.so i prefer to apply insecticide first before anti -ratting.

Dear :

firstly I endorse  Nashwa answer that u must  prefer to apply insecticide first before using  rodenticides .

secondly I refer u to my article attached in below link about an ' A study in campaign for commensal rodents control in Baghdad area '

http://www.iasj.net/iasj?func=search&template=&uiLanguage=en&query=raad+hammodi&x=0&y=0

Rodents indeed serve as reservoirs for many zoonotic diseases.  Many of these diseases are transmitted via parasitic arthropods, but others are transmitted simply by contamination of the environment by rodent feces or urine.  Also, many arthropod parasites of rodents do not survive long away from the host, and many do not prefer humans as hosts.  Thus, rodent-associated zoonotic diseases that involve synanthropic arthropod transmission actually circulate most effectively in the presence of healthy rodent populations close to human habitation or activity.  Thus, I would start with control of the rodents, then move to comprehensive sanitation of human activity areas that would eliminate both arthropods and other infectious contaminants.