I have a duckling and it got the red skin around its neck only at one side (right side near and below its neck) . Following are some pictures of that area of duckling... Age of my duckling is about 2 weeks.
It is more red than looking in the picture.
Is it a disease ?
I don't think it's a disease, but it might be that his crop is irritated from something he ate. I suggest that you contact someone in your country that breeds chickens, ducks, peafowl, quail or other poultry and figure out a way to get some poultry food.