There are a number of pathogens impacting the honey bee. The American Foulbrood (Paenibacillus larvae) and the European Foulbrood (Melissococcus pluton) are bacterial diseases which infect the gut of bee larvae. Both of these are widespread diseases and the American Foulbrood, especially, has negative effects on the brood of the colony.
There are about 20 bee viruses including Deformed Wing Virus, Acute Bee Paralysis Virus and Chronic Bee Paralysis Virus.
Fungal diseases, such as Chalkbrood which infests the gut of honey bee larva, also present health risks for colonies.