The timing of this is amazing. I was on a UA DEN-DSM flight on Thursday (10/26). After a few minutes I needed to ask the FA for napkins as I started sneezing and my eyes were running (I was in 1A and my bag was in the overhead). I asked the FA if there were any dogs on the flight and she said no but there had been a dog on the previous flight. I was reassuring the passengers around me it was not a cold but allergies.
After two attempts at take-off we went back to the terminal and after two hours they switched us to a new plane, and voila no more sneezing or runny eyes.
Dog dander lingers (apparently).