Molecular detection of Paenibacillus larvae, Melissococcus plutonius and Vairimorpha spp., in historical honey samples from South Brazil.

Honey bee colonies are threatened by several pathogens, including Paenibacillus larvae, Melissococcus plutonius, Vairimorpha apis, and Vairimorpha ceranae. Those infections affect bee health, survival, and productivity. The social behavior of the bees facilitates the spread of these pathogens, making disease management a significant challenge in apiculture. This study aimed to assess the historical presence of Paenibacillus larvae, Melissococcus plutonius, Vairimorpha apis, and Vairimorpha ceranae in honey samples from Rio Grande do Sul, Brazil. A total of 125 archival honey samples collected from 2011 to 2022 were retrospectively evaluated. The samples had previously been analyzed for physicochemical and botanical origins. DNA was extracted from honey and spores, followed by PCR assays targeting the four pathogens. Sequencing was performed to confirm the results. M. plutonius was the most frequently detected pathogen, identified in 112 samples (89.6%), followed by V. ceranae, which was present in 67 samples (53.6%). In contrast, P. larvae were identified in only six samples (8.8%), and V. apis was absent. The high detection rate of M. plutonius suggests its widespread distribution in South Brazilian apiaries. The absence of V. apis suggests that V. ceranae has displaced this specie in the region. The presence of P. larvae spores emphasizes its resilience through the ability to persist for extended periods in the environment. Additionally, the simultaneous detection of multiple pathogens raises the concern for synergic effects or interactions, which could further increase colony losses. Finally, these findings highlight the importance of continuous surveillance and enhanced biosecurity and prophylactic strategies, altogether essential for honey bee health and productivity.