Occurrence and distribution of nosema ceranae in honey bee colonies in the Comoros Islands

Abstract

Nosemosis is a parasitic disease caused by microsporidian pathogens of the genusNosemainfecting both the Western honey bee,Apis mellifera, and the Asian honey beeApis cerana.The disease may adversely affect bee colonies and eventually result in high losses in apicul-ture and agriculture. We determined theNosemaspecies infecting honey bees and theirprevalence in two islands of the Comoros Archipelago (Grande Comore (GCO) and Moh eli(MOH)) in the Southwest Indian Ocean. In Comoros, beekeeping is largely traditional andpracticed at subsistence-level, including honey hunting. Five honey bee foragers from 69 col-onies in different localities within the two islands were selected and screened forNosemainfection using microscopy and Polymerase Chain Reaction-restriction fragment length poly-morphism (PCR-RFLP). Selected positive samples were sequenced to confirm the speciesidentified using PCR-RFLP. We also examined spore loads to determine the intensity ofNosemainfections.Nosema ceranaeis the only species detected in the two Comoros islands.High prevalence occurred in the large island, GCO (73.9%), while MOH (25.0%) had a lowprevalence. Spore counts indicated higher infection intensities in GCO compared to MOH.Generally, PCR-RFLP underestimated the prevalence, although microscopic and moleculardiagnostics were well in agreement at the colony level. MOH had lower prevalence andinfection intensity compared to GCO, which is the larger island with a higher density ofhuman population. We postulate that the lower levels of pathogen prevalence in MOH incomparison to GCO could arise from minimal human interference.