Nosema ceranae

Nosema ceranae is a microsporidian, a small, unicellular parasite that mainly affects Apis cerana, the Asiatic honey bee. It may cause nosemosis, also called nosema (see Nosema apis, the most widespread of the adult honey bee diseases). The dormant stage of nosema is a long-lived spore which is resistant to temperature extremes and dehydration.

Nosema ceranae was first described in 1996 and was identified as a disease of Apis mellifera in 2004 in Spain.

Researchers in Spain have analysed samples of Apis mellifera, the European honey bee, mostly sent from colonies suffering unexpected decreases in bee population per hive or lower honey production, as reported by the beekeepers during the last two/three years. In 2004, 90% of some 3,000 samples had positive results for N. ceranae. In 2005, of 800 samples, 97% had positive results. During 2006, both France and Germany have detected the disease and recognized the genetic sequence of Nosema ceranae in their respective territories.

This pathogen has been tentatively linked to Colony Collapse Disorder, a phenomenon reported primarily from the United States, since fall of 2006. Highly preliminary evidence of N. ceranae was reported in a few hives in the Merced Valley area of California (USA). "Tests of genetic material taken from a "collapsed colony" in Merced County point to a once-rare microbe that previously affected only Asian bees but might have evolved into a strain lethal to those in Europe and the United States. "  The researcher did not, however, believe this was conclusive evidence of a link to CCD; "We don't want to give anybody the impression that this thing has been solved. " A USDA bee scientist has similarly stated, "while the parasite nosema ceranae may be a factor, it cannot be the sole cause. The fungus has been seen before, sometimes in colonies that were healthy." Likewise, a Washington State beekeeper familiar with N. ceranae in his own hives discounts it as being the cause of CCD.

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 inflicts adult bees and depopulation occurs with consequent losses in honey production. One does not detect symptoms of diarrhea like in Nosema apis.

Without doubt, the most significant difference between the two types is just how quickly N. ceranae can cause a colony to die. Bees can die within 8 days after exposure to N. ceranae, which is faster than bees exposed to N. apis. The foraging force seems to be affected the most. They leave the colony and are too weak to return, thus dying in the field. This leaves behind a small cluster and a weak colony, very similar to the symptoms of 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.