Is it possible to detect host usb device connected to arduino? and how?
You can't, using stock firmware. And with custom firmware it's still very difficult.

The USB communication chip on the Uno has no out-of-band means of telling the main MCU that it is connected to a host. You might be able to rewrite the communication firmware on the R3 to tell the main MCU over serial that it is connected, but the firmware on the main MCU will need to be written in such a manner that it will anticipate this.

If you want this to work then you should consider using one that has a native USB connection, such as the Leonardo. You will then be able to query the USB facility directly to know whether or not you are connected to a host.