Inflated and transparent abdomen can result due to heavy infection by microsporidia, I have come across these quite often while examining microsporidia infected D. melanogaster. There could however be other possible reasons I am unaware of.
If it's a microsporidian infection then it is something to be concerned about. It can be easily verified by Giemsa staining the abdominal smears of suspected individuals and examining it under light microscopy.
Hope this helps!