News articles published in October 2010 quoted researchers who had discovered that Nosema fungus had joined with a previously unsuspected virus, Invertebrate Iridescent Virus, or IIV6, dealing test bee colonies a lethal blow. Neither the fungus nor the virus alone kill all the test group, but the two combined do. Both the fungus and the virus are found together with high frequency in hives that have suffered CCD. Final testing is in progress with field tests on colonies.
N. ceranae and N. apis have similar life cycles, but they differ in spore morphology. Spores of N. ceranae seem to be slightly smaller under the light microscope and the number of polar filament coils is between 20 and 23, rather than the more than 30 often seen in N. apis.
The disease afflicts adult bees and depopulation occurs with consequent losses in honey production. One does not detect symptoms of diarrhea like in Nosema apis.
The most significant difference between the two types is how quickly N. ceranae can cause a colony to die. Bees can die within 8 days after exposure to N. ceranae (Higes et al. 2006), a finding not yet confirmed by other researchers. The forager caste seems the most affected, leaving the colony presumably to forage, but never returning. This results in a reduced colony consisting mostly of nurse bees with their queen; a state very similar to that seen in CCD. There is little advice on treatment but it has been suggested that the most effective control of Nosema ceranae is the antibiotic fumagillin as recommended for Nosema apis. The genome of Nosema ceranae was sequenced by scientists in 2009. This should help scientists trace its migration patterns, establish how it became dominant, and help measure the spread of infection by enabling diagnostic tests and treatments to be developed.