[thefz]

I would challenge your challenge mainly because I don't think that rats have superior immune systems because of eating whatever, but rather they eat whatever due to their superior immune system.

"We assume that many wild animals are resource limited, and so expect that immune responses may be submaximal. However, in truth, high levels of immune responsiveness are, in general, seen in wild rodents." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5694458/

It's part of why they are successful scavengers.