Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
I am so sorry to hear about Lenny....I know this is hard! Luckily, most all diseases are species specific so it is unlikely that Frankie was responsible for Lenny's condition. The stress of briging Frankie into the house may have suppressed Lenny's immune system which allows bacteria to invade and Lennys signs sound like he had developed crystals in his urethra due to a bladder infection. In other words, Frankie had nothing to do with this except for the stress and there was no way for you to know that this would be so stressful on Lenny.
Frankie's issue may be a mild digestive disturbance and the treatment for this is as follows:
Fast Frankie for 12-24 hrs to allow the digestive tract to calm down and heal.
Give him Pepcid AC or Famotidine at 0.5 mg per pound every 8 hrs. That can be purchased over the counter at the pharmacy.
Give only small amounts of water during the fast or ice cubes
After the fast, feed rice and boiled chicken (2/1)
If he is feeling better, wean him back to his regular diet. If he is still having problems, have your vet examine him to be sure we did not miss something.
Hang in there!
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, ***** *****