Flea infestation is treated with medicated powders/dusts or sprays that are designed kill the fleas. To prevent reinfestation, disinfect and clean your rat's cage and surrounding environment thoroughly.
Follow your veterinarian’s instructions regarding the application of medicated dusts and sprays to your pet rat and its living environment. Although it is important to eradicate the fleas, there are also precautions that you need to take to make sure that your rat is not harmed by the chemicals you are using against the fleas.
In addition, whenever you have handled a rat that is not your own, even an apparently clean and uninfested rat, you must take care to wash your hands and clothes after you have handled it, before handling your own rat.
To attack something or take it over, as in the way ticks can infest a dog