try this:
wash it with a solution of water and bicarbonate of soda (available in the baking section of tescos, etc) this should neutralise the smell fine. I use it on accidents on carpets and also to clean the fridge and sinks with and it works well for me.
Alternatively, you can just dampen the arean and sprinkle the bicarbonate of soda onto the area and brush it well in with a scrubbing brush or something, and leave it to dry. Then when completely dry, vacuum it up. However, I think the method one will work best.
Bicarb is about 80p a box and I use it for all sorts of things as one of my favourite cleaners next to white vinegar. I hope you find it useful too.
In addition, I have always found it to be non-bleaching, however, if you are worried about colour fastness, test in an inconspicuous place on the carpet first, just in case....
good luck
love
mimififi