Diseases in other countries

I know that there are a lot of diseases in other countries. If I bring my cat with me on vacation, then it's not like he's going to roam around freely. If he is to leave the house, then it's in  a leash. Would there then still be a risk? If so, what?

What we have here is: feline viral rhinotracheitis, feline calicivirus infection and feline panleukopenia. 

Yeah there is still risk flea and mosquitoes can carry disease. I all depends on which country you live in and which other country your going to.

Some countries require passport, vaccination proof and flea and tick proof before entry into that country and the same when returning back to your country if it requires it.