Why take animals to Mars and increase the risk of a pandemic there?

I would take animals to eat if I had to be honest. Although a human can get by without animal protein it definitely makes my stomach feel better to eat animal protein and gets rid of hunger pains plant based protein can't. Also just plants gets very boring. A chicken can provide not only meat but also eggs and those are good in so many dishes. Chicken soup, chicken wings, chicken thighs, breasts, and so on. Also pet chickens are very therapeutic as pets. If we are talking about animals like cats well they too are very therapeutic as companionship. Humans suck a lot of the time also. It is nice to have a pet. There is probably lots of reasons why others would want to bring pets. To study them on another planet. Rats for studies on mars. Just tossing some ideas off the top of my head.

A sterile environment isn't practically possible, and probably isn't healthy if it was. Why not spread life where we can? The microbes are going to be coming with us regardless.

It’s not happening so don’t worry about it. You may as well ask why take animals to heaven.

If people ever get to Mars, with or without other animals, pandemic disease will be the least of their problems.