Hi, 

This looks like a common disease of pachysandra called volutella. There is a description with management techniques on the link provided. You need to trim and rake out the infected foliage and it should regrow. It may still get infected but if you are consistent with the removal of infected plants you can keep up with it. Alternatively you could consider replacing it with a native ground cover. Native plants come with their own pest and disease problems but they are more likely to withstand our changing climate and heat/drought/ humidity conditions through the summer. 

Emily