"Rodents" means 鼠类, it refers to the animals themselves. If you're talking about the PROBLEM of having lots of rodents around, you use "infestation." Example: "We've got an infestation of rats in the house, call the exterminator and get rid of them!" 例句：我们家里发生鼠灾了，快给灭鼠者打电话，把这些老鼠消灭掉！ Some similar words for bad animals in general are "vermin" or "pests," which mean "害虫"

Rodents. http://translate.google.com/#zh-CN|en|%E9%BC%A0%E7%81%BE