Question regarding health of pets

I have noticed that two of my mice are experiencing major hair loss from the top of their head down to their neck! Could this possibly be mites or some other disease?

Note: One of them is heavily pregnant.

A reason for hair loss is an allergy. Some mice can't have peanuts, sunflower seeds, wheat, and a number of other things. Most mice should be given a low protein diet (13% or less) but some mice can't even handle that much. If your mouse has a protein problem or a food allergy then your mouse will develop what's known as "hot spots". Hot spots are spots on your mouse that are very itchy. The mouse ends up scratching these places bald and they often bleed. Most, yet not all, of the time mice get hot spots on the back of their ears and neck between their head and back, sometimes continuing down their back. Many people have mistaken hot spots for mites or lice. Some even treat for parasites when that's not the cause at all. Treating for parasites can be harmful to your mouse, especially when doesn't have them. In my experience, many people who think their mice have mites actually give their mice to much protein or food the mouse is allergic to, causing hot spots. If your mouse has this problem, take out all peanuts form the diet. Peanuts seem to be the most common allergy among mice. next take out some, if not all, sunflower seeds. Then try cutting back on the protein. If you have a mouse that is brindle or red (genetically Avy or Ay) then you might have more problems with this. In my years of experience, these mice are at a higher risk for developing hot spots. Theses mice my need an even lower protein diet than other mice. If you suspect that your mouse has an allergy try removing all of the common things that a mouse is allergic to such as peanuts, sunflower seeds, and any wheat. If your mouse within a week, then you know it was an allergy. Once you have established that it is a food allergy you can start bringing back types of food one at a time. Start, for instance, bringing back sunflower seeds to your mouse's diet. If he/she isn't showing any signs of getting worse in a week or 2 than your mouse can continue having it (always in moderation though). Now try to bring back another food type just as you did before. Keep doing this until you find the cause. While doing this remember that it could be protein in general. In this case all you need to do is cut back protein in general. Pre mixed food says on it how much protein is in it. If it has a lot you might want to consider getting a different brand. If you can't find any that is fewer than 13% then try taking out things from the mix that you know are high in protein. Be careful though. A mouse does need some protein in its diet to stay healthy!