## 4 Discussion
Interestingly, the prevalence of DWV-A decreased in 2021 in all the apiaries found positive the previous year, except in apiary A, which still remained negative, and apiaries D and H. DWV-B, instead, behaved in a heterogeneous way among all the apiaries (except in apiaries A and C, with no positive samples found in both years) with an overall slight decrease from 2020 to 2021. Although a strong connection between DWV-B and _Varroa_ was previously demonstrated [44; 105; 106], no significant association was found in this survey even if the overall prevalence of _Varroa_ in the sampled apiaries declined in 2021 similarly to DWV-B. Regarding the other viruses investigated in this study, IAPV and KBV were not detected, in accordance with their distribution, which is predominant in Israel, Australia, Asia and USA and less prevalent in Europe [2; 28; 33; 65; 78; 94], while ABPV and CBPV were observed in almost all the nine apiaries. As reported by [PERSON] et al. [74], since ABPV, IAPV and KBV share a high level of genetic similarity (the high virulent \"AKI complex\"), it is supposed that these viruses derive from a common ancestor and then evolved and distributed independently in different geographical areas around the world. This hypothesis is also reinforced by the fact that in Veneto region and in Italy in general, as well as in the near Austria, Slovenia and Croatia [74; 107; 108], most of the reported cases identified ABPV as the predominant viral species instead of KBV or IAPV. The overall prevalence of ABPV found in Veneto region was between 32.1% (2020) and 34.4% (2021), but not in all the apiaries analysed the value increased from one year to the next: if indeed in apiaries C, E, F and G the ABPV positive hives increased with different percentages, in the apiaries B and I there was a decrease of more than half of infected colonies, and in the apiaries A and F the virus has never been detected. It is known that this virus is quite commonly found in apparently healthy families and it plays a decisive role in the sudden and asymptomatic collapse of the colonies, especially in winter. Moreover, it was supposed that ABPV infection, like DWV, might be spread to honey bees by _V. destructor_, but the presence of very low infested colonies in the apiaries analysed suggested that these viruses could replicate and transmit through other ways. CBPV occurred in eight out of nine apiaries (the mountain apiary A always tested negative in both years) with an overall prevalence of 98.8% in 2020 and 82.2% in 2021. Although CBPV is widespread in honey bees worldwide and probably due to intensive commercial exchange of insects and hive materials [81], these values were very high compared to what was reported in other European countries, such as France (28%), Slovenia (18.3%), Austria (9%), Czech Republic (8%) and Denmark (4%) [74; 78; 90; 108; 109], even if the colonies considered in these studies, unlike ours, showed clinical symptoms of viral infection. The appearance of the clinical form of the disease is linked to episodes of overcrowding in the hive, especially in spring or summer, in the event of persistent adverse weather conditions, and/or the consumption of honeydew. No data about this kind of event resulted from the questionnaires provided by the beekeepers, and the honey bees did not show any symptom of paralysis or malaise. Finally, different pathogens prevalence and distribution were observed when comparing the different landscapes (plain, hill, and mountain) where the apiaries were located. From the data obtained in 2020, a median decrease in the number of coinfections from the plain (5.3) and hills (5.7) to the mountains (3.0) could be observed. However, the number of co-infections in the honey bees reared in the mountain area derived from the analysis of only one hive of the apiary A. For this reason, the three locations could not be evaluated from a statistical point of view.