why cannot connect to libvirtd using virsh ???

[root@test2 ~]# virsh -c quem+ssh://root@192.168.10.175/system root(a)192.168.10.175&#39;s <mailto:root@192.168.10.175's> password: error: failed to connect to the hypervisor error: no connection driver available for quem:///system But, on the same terminal using virt-manager to connect to 192.168.10.175 is successful. Why ?