libvirt users - Oct 2013 - how can I use libvirt to connect vbox

Hi.
I want to connect hypervisor vbox using command of "virsh connect
vbox:///session".
But there is an error occurred:

[root@vbox ~]# virsh connect vbox:///session
error: Failed to connect to the hypervisor
error: internal error unable to initialize VirtualBox driver API

And my os is Fedora 19. The VirtualBox is 4.3. Some other info is there:

[root@vbox ~]# virsh version
Compiled against library: libvirt 1.0.5
Using library: libvirt 1.0.5
Using API: QEMU 1.0.5
Running hypervisor: QEMU 1.4.2

Thanks.