So sorry to hear this, has your dog been abroad (or are you not in the uk?), as Leishmaniasis has been found mainly in dogs imported to the UK. First aid for nose bleeds is to keep your dog calm as increased blood pressure will increase the bleeding. An ice pack applied to the bridge of the nose will constrict small blood vessels which will slow the bleeding. Make sure he can breathe ok. Your vet should be able to prescribe something like ACP to keep him calm, but make sure he is kept warm as they have trouble regulating their temperature when sedated. I do hope he has a long and trouble free time ahead of him.