I'm sorry that your question wasn't answered in a timely manner. I'm not familiar with the term "rat flu". "Rat fever" is caused by the bite of a rodent which is carrying one of two bacteria in its mouth - either Strep or Spirillum. Please clarify. It's unlikely that the dog and cat are sharing the same infection. Both are immunocompromised, however, and are more susceptible to infection. In general, prescribing a broad spectrum antibiotic such as Clavaseptin is appropriate for both of your pets and both can be prescribed another broad spectrum antibiotic - this time in the fluoroquinolone class such as enrofloxacin if the Clavaseptin isn't helpful. If necessary, advanced testing can be performed by culturing the nose or nasopharynx of your pets in order to determine just which bacteria are present and then which antibiotic would be best to prescribe. This is likely to be more helpful in your dog than cat because your cat is likely to be sneezing due to the feline herpesvirus which doesn't respond to antibiotics but, instead, an antiviral drug such as famcyclovir.