Hi, I am Dr. Peter and would like to help.
1- Can you describe the appearance of the lesion?
In response to your question, pick up in your local pet store an antibacterial shampoo with the ingredient "chlorhexidine." Clean the lesion with this shampoo twice a day and apply topical Miconazole.
If you have additional questions I will be glad to answer them.
How long will it take to see improvement? How contagious is it to humans or my other dog?
It is contagious, some humans are more susceptible then others (don't know why). Bath him with the same shampoo recommended above and once the hair follicle are flushed, dogs are not asymptomatic carrier. You will notice improvement in about 2 weeks. Hair will take longer to grow back.