Completing the Deadout checklist will help you determine why your hive died.
Check out The NH Honey Bee Diagnostic Network website for more information:
USDA Bee Laboratory-Beltsville, MD
The "Beltsville Bee Lab" is recognized for its research on bee diseases and pests and for providing a bee disease diagnostic service for 100+ years.
Nosema is a disease found in the gut of honey bees. Nosema apis and N. ceranea are fungal pathogens that infect the gut of honey bees and can cause dysentery and death. Because the spores are so small, Nosema can only be detected using a microscope.