Hi, I have a wild mouse from my live hurt-free trap in my kitchen. I have been riding my bike a few blocks and release them in some bushes/ trees in our small neighborhood. I live in Hawaii. I am concerned why this mouse has black growth looking stuff on ears (look swollen, shiny black), tail has black lumps along entire length, and there are a few lumps on underside of its bottom. All are black. I have seen the same type mouse in my traps on three occasions prior over last few months, but w/out these abnormalities. I am concerned if this is an indication of some toxin in the environment, like roundup (lots of people use here), or any other old chemicals from previous pineapple growers/ sugar cane, etc. What do you think? BTW how far do I need to drop them off to make sure they dont return? Rodents here can carry leptospirosis. we love little creatures and have two guinea pigs, a cat, and dog. I hope the mice in our house could not infect our guinea pigs with lepto/ other disease. Happy for any info you have, mahalo!
The mouse in the pictures looks to be experiencing edema (a build-up of fluid) and restricted circulation, but what is causing it could be any number of environmental toxins (very low humidity can also cause this, but since you mentioned you were in Hawaii, I thought this would be an unlikely culprit). Many pesticides and other chemicals cause varied reactions in animals, including reduced circulation, which can cause necrosis in extremities. It doesn't look like the tissues on the tail and ears are sloughing like normal necrotic tissue would in an advanced situation, but I am assuming they did not start out black, since the toes look a happy, healthy pink.
While it sounds ugly and unpleasant, it likely does not hurt, and the risk of complications or spreading tissue death is very low. Imagine your foot going to sleep - without circulation, it just goes numb and doesn't hurt until it gets bloodflow again. It just looks kind of gross!
There is also a chance this could be a result of a genetic disorder, but I have not witnessed anything like it before. To be any more specific about the cause or possible chemicals, you'd need to bring the mouse into a veterinarian or other specialist who could take a better look. If the other mice have been healthy and normal, I wouldn't be too concerned - each animal reacts to chemicals in the environment differently.
As far as dropping them off goes - the further the better. If you can get about a mile away that'll be more than enough, but a few blocks is probably doing the trick just fine. Since they seem to be different mice each time, I think your humane traps and careful releasing sounds to be working wonderfully.
Leptospirosis is a complex issue that affects a lot more than mice and people, so I think the best person to ask for that one would actually be your veterinarian. While it's true that mice can carry and pass on lepto, there are many different strains that affect different species. I know certain strains affect people, a different strain affects dogs, but I can not tell you if cats or guinea pigs are at risk to be carriers or affected by the disease. What I can tell you is to ask your veterinarian if your dog's distemper combination vaccination comes with protection against leptospirosis - this is a noncore (not required) addition to your dog's normal annual vaccine that protects him or her against the disease, but since you mention it is present in your area, Hawaii vets may provide it more commonly to help reduce the spread of infection. It's available either way, and you can ask your vet to provide it if they don't normally.
Another thing to know about leptospirosis is that it is spread by the urine of mice that are carrying it (or other animals carrying the bacteria), but as far as I can find, is only active as long as it is still moist. This means your pets won't contract it by simply being in the same room, but you should be cautious about, for example, letting your dog drink from puddles. I know it's tough to keep kitties away from wild rodents sometimes, so if your cat likes to chase them around, I would consult with your veterinarian to see if there is a way to protect your cat like there is your dog.
I hope I helped, but I know I just gave you a ton of info, so if you have any questions or need clarification just let me know by writing me a followup question. Best of luck, and thank you for being so kind to these little guys! :)