Hello @alexiasc and welcome to Mayo Clinic Connect. What an unfortunate circumstance your friend has found himself in after, what I would imagine, was a likely a wonderful trip otherwise.

I found this article and video that may be helpful as you walk this journey alongside your friend. Dr. Tosh does a nice job of talking about Leptospirosis and may be helpful until others join this discussion.

- Infectious Diseases A-Z: Leptospirosis in Puerto Rico:
https://newsnetwork.mayoclinic.org/discussion/infectious-diseases-a-z-leptospirosis-in-puerto-rico/
Do you know if you friend was administered antibiotics like that of Dr. Tosh's recommendation early on? Is there competing symptoms between this exposure and his previous health conditions declining as well?