Prevalence of Paenibacillus larvae, the Causative Agent of American Foulbrood Disease, in Apiaries of Iran

Abstract

Honey bees are among the most crucial pollinators, significantly contributing to the growth of flowers and wild plants within ecosystems. Extensive epidemiological studies have been undertaken to identify and mitigate bacterial, fungal, and viral diseases affecting these insects. One particularly severe and highly contagious bacterial disease is American foulbrood (AFB), which impacts honey bee (Apis mellifera) larvae caused by a gram-positive bacterium known as Paenibacillus larvae. This bacterium can produce resilient spores capable of surviving for years under suitable environmental conditions. If not promptly diagnosed and addressed, AFB can infect the entire hive and potentially spread to neighboring hives. The objective of this research was to assess the prevalence of AFB disease in apiaries nationwide. From Autumn to Winter 2022, the study involved sampling adult bees and honey from 266 apiaries across various regions of the country (31 Provinces). All 532 samples were prepared using standard protocols and DNA extraction was performed. Two sets of specific primers were employed to identify the P. larvae using PCR and nested-PCR methods. The selected PCR positive samples were subsequently sequenced and phylogenetic tree constructed. Based on the findings, among 266 honeybee samples only 14 (5.26%) samples, and among 266 honey samples 42 (15.78%) samples were positive. Among 31 Provinces investigated, P. larvae infection was detected in 18 provinces (61%). The highest incidence of AFB disease was noted in the Northern Provinces (28.78%) and the central regions of the country (25.35%). Conversely, the Eastern Provinces exhibited the lowest rate of infection (5.71%), which was statistically significant. The majority of positive, honeybee samples originated from the Central Provinces, while honey samples were predominantly from the Northern Provinces. The results of this study indicate that AFB is prevalent bacterium in apiaries throughout Iran.