From what I understand, the catering company was traced as the source of the rat menace. Their trucks were not properly fumigated as per regulations. The airline has levied a large fine in addition to costs incurred in cleanup. The same caterer, ironically one of the better names in the business, had goofed up similarly with a European carrier in BOM. That airlines PR however works better so the story barely got out!
Air India pulled the A321 out of service and sent it to a remote bay for fumigation. An all-economy A320 fresh out of D-check was sent as a substitute. Caused some problems due to full loads in both J and Y.