That is actually a great idea! At the moment I am not aware that such a “rapid test for hantavirus” exists. I do know that in 1997 a prototype test for Sin Nombre hantavirus was developed to test human blood for hantavirus in a similar way, however they still required a lab setting. Nowadays, we do have the tools to test more than just Sin Nombre hantavirus, but also other relevant hantaviruses like Puumala, Hantaan, Andes and Seoul virus. So I believe that your idea could be a very practical solution. However, there are some questions you need to think about: if a rodent is infected with hantavirus, does that mean its feces or urine contains the virus 100% of the time? If not, that would make the test a little bit less reliable. What is your next step if a rodent turns out to carry hantavirus? Why only test rodents, why not extent the test to humans that are believed to be infected by hantavirus?