Sentence:  Bats host many high-profile viruses that can infect humans, including severe acute respiratory syndrome and Ebola. A recent study explored the ecological variables that may contribute to bats' propensity to harbor such zoonotic diseases by comparing them with another order of common <WSD>reservoir</WSD> hosts: rodents. 
Meaning of the word marked with <WSD> tags:  A supply or source of something.