As far as the flu that's been going around, the main symptoms are similar to kennel cough, just a bit more extreme. Coughing, high temp, runny nose, lethargic, loss of appetite. I've also heard they could include rapid breathing/heartbeat.
We believe Gunther had this flu, so I memorized all the symptoms, to which he showed signs of all of them.
And I should say that reverse sneezing alone does not necessarily signify allergies..... .......Keiko has several other allergy problems, the sneezing was just the one that showed up last.