What sort of owner would leave a cat to suffer from an easily visible tick for any length of time? Sort the cat out, it needs help and is not being cared for enough.
I have had a variety of pets over the years. More recently cats as I have posted on here before. I have come to realise that cats are only ‘borrowed’ and not owned and now realise that if my cats become unhappy they will find a way to move out and live somewhere else, just as one of them choose to come and live here. I don’t want them to leave, but they are not creatures you can forcibly keep for any length of time.
If the cat wants to move in with someone new, it will succeed in the end. If its you or someone else. Its not happy where it lives, if it lives anywhere or it would not be trying to re-locate.
Our vet told us it is difficult to legally claim any ownership of a cat even if it is chipped as the law for cats is different to dogs. You can be sued if your dog bites someone as you own that dog. You cannot be sued if ‘your’ cat attacks someone as technically a cat cannot be owned in law.
Some cats just like to visit. They will hang around with a ‘friend’ cat for a few hours and then go home and this will never become ‘moving in with you’ even if it happens every day.
People who have to try to force their cats to stay with them are getting something wrong and need to change the house environment to something the cat is content with, or accept it will leave in the end.
As they say “If you love something let it go free, if it comes back its yours. If it doesn’t, it never was.”