I regret that this word actually is part of the English language. When I saw the question, I thought this looks so ugly that it must be either not English at all, or US English only (apologies to US readers, no offence intended). However, I found this quote from Hansard that shows it was in official use way back in 1930.

"BRITISH SHIPS (DERATISATION CERTIFICATES).
HC Deb 04 March 1930 vol 236 cc268-9W 269W

Mr. WEST RUSSELL

asked the Minister of Health whether his attention has been called to the fact that certain Continental ports are refusing to recognise the deratisation certificates granted to British ships in this country on the grounds that the necessary fumigation has not been carried out by hydrocyanic acid; and whether he will take steps to mitigate the inconvenience that is being caused by drawing up a list of the ports in question and by representing to the countries concerned that other methods of fumigation used in this country are equally effective for the purpose?"

Would getting rid of dogs be 'dedogisation' and getting rid of cats 'decatisation'? Oh for the days of the good old fashioned rat catcher who simply killed the rats!