Boxwood turning brown

I have a row of large boxwoods down the side of my house. One of them is starting to turn brown, just a small spot for now, but I know it will grow and eventually kill it. A few years ago one them did this and I lost it. I wasn't so worried about losing that one because that particular bush made getting to the water spout difficult, but I'd sure hate to lose the one turning brown now. I've noticed the ones at my work turn brown and die periodically.

Does anyone know what causes this and how to stop it before the bush dies?

 

Check out box blight:
http://www.rhs.org.uk/advicesearch/profile.aspx?PID=96

 

Thank you. That's what it looks like. Hopefully we'll be able to heal it and save the plant.

 

Box are also prone to root rot etc.