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Giovanni Sgroi1†
Luigi Jacopo D’Auria1,2†
Maria Gabriella Lucibelli1
Andrea Mancusi1*
Yolande Thérèsa Rose Proroga1
Mauro Esposito1,2
Simona Rea1
Daniel Signorelli3
Federica Gargano1
Nicola D’Alessio1Ranju Ravindran Santhakumari Manoj4Peyman Khademi5
Giuseppe Rofrano1,2- 1Experimental Zooprophylactic Institute of Southern Italy, Portici, Naples, Italy
- 2Centro di Referenza Nazionale per l’analisi e lo studio delle correlazioni tra ambiente, animali e uomini, Portici, Naples, Italy
- 3Department of Cultural Heritage Sciences, University of Salerno, Salerno, Italy
- 4Department of Population Medicine and Diagnostics, Cornell University, Ithaca, NY, United States
- 5Department of Microbiology and Food Hygiene, University of Lorestan, Khorramabad, Iran
Introduction: The decline of the European/western honeybee (Apis mellifera) population is on account of a plethora of microorganisms, such as Nosema apis and Nosema ceranae, two microsporidian fungi responsible of nosemosis that affects welfare and production of the bee industry. Accordingly, this study aimed to investigate the presence of both pathogens in bees, pollen and honey from apiaries in Southwestern Italy.
Methods: From March to July 2022 and 2023, apiaries (n = 10) were selected and classified as High Impact Areas (HIAs, n = 5) and Low Impact Areas (LIAs, n = 5) according to a 5-point environmental risk index based on factors affecting bee health sand related productions. Bee, pollen and honey samples, were collected and tested for Nosema spp. DNA by specific PCR protocols targeting the 16S rRNA gene. Signs/symptoms of nosemosis were monitored and collected by the cooperation of beekeepers.
Results: Out of 10 apiaries, 6 (i.e., 60%, 95% CI: 31.3–83.2) tested positive for at least one sample to Nosema spp. DNA, being 2 positives for N. apis, 2 for N. ceranae and 2 co-infected (i.e., 20%, 5.7–51.0). Based on the biological samples, honey was positive for N. apis in one apiary, pollen for N. ceranae in two apiaries, and bees for N. apis in 3 apiaries, N. ceranae in 1 apiary, and both species in 1 apiary. In all the apiaries positive to N. apis and N. ceranae, high mortality and low honey production were observed. A higher risk of infection was observed in apiaries from HIAs (OR = 6.00). The sequences of N. apis and N. ceranae had 99.5–100% homology with those in the GenBank database. Whereas all sequences of N. apis were identical to each other, four sequences types of N. ceranae characterized by single nucleotide polymorphisms (SNPs) were identified. The computation of polymorphisms revealed high haplotype diversity (i.e., Hd = 1.000) and low nucleotide diversity (i.e., Pi = 0.00913) of N. ceranae sequence types.
Discussion: This study reveals a high circulation of N. apis and N. ceranae in Southwestern Italy, indicating the need for improved monitoring of these microsporidia to protect bee welfare and bee industry.
1 Introduction
In last years, a plethora of infectious and parasitic agents has affected the population decline of pollinating insects worldwide (1). Among these, the European honey bee (or western honey bee) Apis mellifera is commonly exposed to fungi of the genus Nosema spp. (phylum Microsporidia, family Nosematidae), obligate intracellular microsporidia that infect ventricular epithelium cells of adut bees causing nosemosis (2–5), mainly in high density apiaries (6). Nosemosis is one of the main causes of bee colony collapse and prodution loss for beekeepers (7) due to the severe dysentery caused in bees (8, 9). In addition, the oro-fecal transmission pathway of Nosema spp. and the typical food-sharing behaviour of bees (i.e., trophallaxis) (10) favour the circulation of microsporidian spores among bees, but also pollen and honey, causing organoleptic and production alterations in honey (11–15). To date, two different pathogenic species of Nosema spp. have been reported, Nosema apis (synonym Vairimorpha apis) and Nosema ceranae (synonym Vairimorpha ceranae) (16, 17). While N. apis is known from the beginning of the XX century (18), N. ceranae is an emerging species reported for the first time in 2005 (19) and now spread throughout Europe (20–26), as well as in Canada, USA, and south America (27–30).
In perspective, the fact that long cold winters, intense rain, and high relative humidity can favour the spread of N. apis and N. ceranae is of concern considering the running climatic changes and global warming (31–34), especially for N. ceranae that is considered replacing N. apis in several areas (35). As for Italy, N. ceranae has been reported in apiaries from central and Northern Italy, whereas the last report of N. apis dates back to 2010 in the North of the peninsula according to a nationwide 2 year-monitoring plan (36). Moreover, the occurrence of N. apis has been recently reported in apiaries of Southeastern Italy (15), suggesting the potential spread of this microsporidian also in other Southern areas of the country.
In order to verify this hypothesis, this study aimed to investigate the presence and distribution of Nosema spp. DNA in A. mellifera specimens and their products (i.e., pollen and honey) in selected apiaries of southwestern Italy.
2 Materials and methods
2.1 Study area and sampling
This study was approved by the Italian Ministry of Health within the project authorization no. IZS ME 08/22 RC aimed to assess the bee welfare and related productions of Southern Italy.
The study was carried out in the Campania region, Southern Italy, characterized by a typical Mediterranean temperate climate and progressively continental features of mainland and mountainous landscapes (37). In order to investigate aspects potentially correlated to presence of Nosema spp. and health status of bees, sampling areas were selected by using a risk index based on 5 environmental variables (i.e., pollution, land use, hydrographic network, air quality, bee density) and classified as high impact areas (HIAs) or low impact areas (LIAs) (38). Then, from March to July 2022–2023, bees, pollen and honey samples were collected in 10 different apiaries (5 LIAs and 5 HIAs) (Figure 1) by the staff of the Experimental Zooprophylactic Institute of Southern Italy (Portici, Italy) in collaboration with apiary owners that monitored any signs/symptoms of the hive potentially related to the infections. For each apiary, bee specimens, pollen and honey were collected using under-basket cages (39), combs inside the hives, and traps installed in front of the hives. For each apiary, a total of 50 bees, 10 g pollen and 1 g honey were collected from different hives, stored at −20°C into specific 500 mL glass jars labelled, and delivered to the Animal Health Department of the Experimental Zooprophylactic Institute of Southern Italy (Portici, Italy).
Figure 1
Figure 1. High impact areas (HIAs, n = 5) and low impact areas (LIAs, n = 5) investigated for Nosema and Nosema DNAs in the study area.
2.2 DNA extraction, PCR protocol, and sequencing
DNA was extracted from bee, pollen and honey samples using the QIAamp DNA mini-KIT tissue protocol (Qiagen, Hilden, Germany) according to the manufacturer’s instructions. The obtained DNA was diluted 1:10 with Tris-glycine TGBE buffer and centrifuged at 5,000 g for 5 min. For each sample, DNA concentration was determined by BioPhotometer plus biophotometer (Eppendorf AG, Hamburg, Germany). All DNAs were screened for N. apis and N. ceranae by using two species-specific endpoint PCR protocols targeting the 16S rRNA gene, according to the National Reference Laboratory for honeybee health (40); primer details are listed in Table 1. PCRs were performed in a total volume of 25 μL containing 12.5 μL HotStarTaq Master Mix, 0.625 μL of each primer at concentration of 0.25 μM, 9.25 μL of Dnase/Rnase free water and 2 μL of DNA template. Amplification conditions included an initial denaturation/activation step at 95°C for 15 min, followed by 35 cycles of denaturation at 94°C for 15 s, primers annealing at 62°C for 30s and extension at 72°C per 30s, and a final extension step at 72°C for 7 min. Amplicons were displayed by automated capillary electrophoresis with the QIAxcel instrument (Qiagen, Hilden, Germany). Amplicons were then purified with the QIAquick PCR Purification kit (Qiagen, Hilden, Germany) and sequenced in both directions using the same primers as for PCR, with the Big Dye Terminator Cycle Sequencing Kit v1.1 in the automated sequencer 3,500 Genetic Analyzer (Thermo Fischer Scientific, United States). Consensus sequences were aligned and edited via ClustalW Multiple Alignment method in the BioEdit software (version 7.7) (41), and compared with those available in the GenBank database with the Basic Local Alignment Search Tool (BLAST).1 Edited sequences were then exported to DnaSP software (version 6) (42) for the computation of polymorphisms using Tajima’s (43) and Fu’s Fs tests (44).
Table 1
Table 1. Primers for the detection of Nosema apis and Nosema ceranae used in this study.
All the sequences were submitted on GenBank database under the accession numbers PP758584 for N. apis and PP758589-PP758592 for N. ceranae, respectively.
2.3 Statistical analysis
Exact binomial 95% confidence intervals (95% CIs) by Wilson’s method were calculated for the proportions of infection herein found. The Fisher’s exact test was used for assessing any statistical differences in the frequency of infection according to the geographical origin of samples; a value of p < 0.05 was considered statistically significant. The Odds Ratio (OR) was used to verify the difference of infection risk according to the geographical origin of samples. Statistical analyses were performed by using the online software Epitools-Epidemiological Calculators (45). The distribution of Nosema spp.—positive samples in the study area was obtained with QGIS software (version 3.34.10-Prizren LTR).
3 Results
Out of 10 apiaries investigated, 6 (i.e., 60%, 95% CI: 31.3–83.2) tested positive for at least one sample to Nosema spp. DNA, being 2 positives only for N. apis, 2 only for N. ceranae and 2 co-infected (i.e., 20%, 5.7–51.0). Details of positivity to N. apis and N. ceranae, according to the different samples examined (i.e., bee specimen, pollen and honey) and apiary typology (i.e., HIAs or LIAs), are reported in Table 2. In all the apiaries tested positive for N. apis and N. ceranae, high mortality and low honey production were observed.
Table 2
Table 2. Bee farms tested negative (Neg) and positive to Nosema spp. DNA, according to different samples (i.e., bee specimens, honey, pollen).
Although the difference of infection according to the origin of apiaries from HIAs and LIAs was not statistically significant (χ2 = 1.667, p = 0.200), a high risk of infection was observed for apiaries located in HIAs (OR = 6.00).
All the 16S rRNA partial sequences of N. apis and N. ceranae herein found had 100% query coverage and 99.5–100% nucleotide identity with those available in the GenBank database. Whereas all sequences of N. apis were identical to each other, four different sequences types of N. ceranae (i.e., ST1 in pollen, ST2 in pollen, ST3 in bee, ST4 in pollen) were identified showing single nucleotide polymorphisms (SNPs) in the positions 34, 122, 192 (Figure 2). The computation of polymorphisms revealed high haplotype diversity (i.e., Hd = 1.000) and low nucleotide diversity (i.e., Pi = 0.00913) of N. ceranae 16S rRNA sequences from this study, with not statistically significant negative values of both Tajima’s D and Fu’s Fs tests (Table 3).
Figure 2
Figure 2. ClustalW multiple alignment of Nosema ceranae 16S rRNA sequence types showing single nucleotide polymorphisms in BioEdit software (version 7.7) (35).
Table 3
Table 3. Diversity and neutrality indices of Nosema ceranae 16S rRNA sequences (n = 4) from Southern Italy.
4 Discussion
This study reports for the first time N. apis and N. ceranae infections in A. mellifera populations, pollen and honey, from apiaries of Southwestern Italy.
The high prevalence of Nosema spp. in the apiaries herein investigated (i.e., 60%) indicates a wide spread of infection in the study area, in agreement with the national average (30–69%) (36), and with the last data available from Central (63.2%) (46), Northern (42.9–54.5%) (47, 48) and Southeastern Italy (100%) (15). The finding of N. apis is of concern due to its high pathogenic potential (49, 50) and the fact that this species has been previously reported only in 2010 in Northern Italy (36, 51), and recently in the Southeast (15). This study also confirms the occurrence of N. ceranae in the south (15, 36), as already outlined in areas of Northern (47, 48) and Central Italy (46, 52).
As well as in bees, the finding of N. apis and N. ceranae in honey and pollen samples, respectively, is not surprising given that the small size of their spores (2–6 μm) (53, 54), allow them to be transferred as wind-dispersed bioaerosols from the air to different surfaces, including pollen and honey (14, 55). Another potential route of transmission may occur via bee feces contaminated with spores, which are usually left by bees near the apiary, carried by the wind to the flowers, and then collected again by bees during pollination (56). In addition, feeding bee colonies with infected honey and pollen may represent a further risk for the transmission of Nosema spp. infections (57, 58).
The signs of infection herein observed, such as high mortality and low honey production, are in accordance with the clinical picture of nosemosis (13, 15, 52, 59).
Although no statistically significant difference between apiaries in HIAs and LIAs is observed (p = 0.200), a higher risk of infection is emerged in HIAs than LIAs (OR = 6.00), suggesting that environmental aspects of HIAs (i.e., pollution, intense land use, low air quality, high bee density) (38) are implicated in the epidemiology of Nosema spp., as well as in the overall welfare of the bee industry. This hypothesis finds support in studies indicating that environmental stressors may increase the virulence of N. ceranae (60) and influence the bee microbiota, thus altering the immune system (61) and susceptibility to pathogens (62–65). Accordingly, further studies for assessing the correlation between apiary typology and susceptibility to Nosema spp. infections are required.
The presence of SNPs in all the 16S rRNA sequences of N. ceranae from pollen (i.e., ST1, ST2, ST4) and bees (i.e., ST3) of this study, could be due to a wide genetic variability of this pathogen, in accordance with previous studies showing the presence of several sequence types of this species (51, 66–70). The high haplotype diversity and low nucleotide diversity of N. ceranae sequences herein found are indicative for a rapid demographic expansion of this microsporidian. In accordance, although not statistically significant, the negative values of Tajima’s D and Fu’S Fs suggest an excess of rare polymorphic sites which are typical features of both recent population expansion and presence of rare haplotypes compared to what is expected under neutrality, pointing to past bottleneck and/or purifying selection events (43, 44).
Finally, the fact that nosemosis is no longer a notifiable disease (71) underlines the importance of epidemiological investigations as the only way to highlight the presence of Nosema spp. in apiaries (15). Accordingly, future large-scale surveys are needed to investigate the circulation of Nosema spp. in other areas of Italy and the potential implications to the honey bee industry. At the same time, epidemiological and pathogenetic insights are required on little-investigated trypanosomatids (e.g., Lotmaria passim) circulating in bee colonies (72) and honey with a high percentage (80%) of co-occurrence with N. ceranae microsporidia (55).
Data availability statement
The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: https://www.ncbi.nlm.nih.gov/genbank/, PP758584; https://www.ncbi.nlm.nih.gov/genbank/, PP758589; https://www.ncbi.nlm.nih.gov/genbank/, PP758590; https://www.ncbi.nlm.nih.gov/genbank/, PP758591; https://www.ncbi.nlm.nih.gov/genbank/, PP758592.
Ethics statement
Ethical approval was not required for the studies involving animals in accordance with the local legislation and institutional requirements because this study was approved by the Italian Ministry of Health within the project titled “Studio degli alcaloidi pirrolizidinici e dei metaboliti secondari nei prodotti dell’alveare: verso la definizione di mappe apistiche in ottica di sicurezza alimentare” (grant number: IZS ME 08/22 RC). Written informed consent was not obtained from the owners for the participation of their animals in this study because in accordance with national legislation and institutional requirements.
Author contributions
GS: Conceptualization, Writing – original draft. LD’A: Conceptualization, Writing – review & editing. ML: Methodology, Writing – review & editing. AM: Methodology, Writing – review & editing. YP: Data curation, Formal analysis, Writing – review & editing. ME: Data curation, Formal analysis, Writing – review & editing. SR: Data curation, Formal analysis, Writing – review & editing. DS: Data curation, Formal analysis, Writing – review & editing. FG: Data curation, Writing – review & editing. ND’A: Writing – review & editing, Data curation, Formal analysis. RM: Writing – review & editing. PK: Writing – review & editing. GR: Funding acquisition, Project administration, Resources, Writing – review & editing.
Funding
The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work was supported by the project entitled “Studio degli alcaloidi pirrolizidinici e dei metaboliti secondari nei prodotti dell’alveare: verso la definizione di mappe apistiche in ottica di sicurezza alimentare” (grant no. IZS ME 08/22 RC) funded by the Italian Ministry of Health.
Acknowledgments
The authors are grateful to Anna Granato (Istituto Zooprofilattico Sperimentale delle Venezie, Padua, Italy) for support in molecular analysis and to the apiary owners involved in this study for their kind cooperation in sampling and monitoring activities.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declare that no Gen AI was used in the creation of this manuscript.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
Supplementary material
The Supplementary material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fvets.2024.1530169/full#supplementary-material
Footnotes
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Keywords: bee decline, honeybee, honey, pollen, Nosema, nosemosis, Vairimorpha, Italy
Citation: Sgroi G, D’Auria LJ, Lucibelli MG, Mancusi A, Proroga YTR, Esposito M, Rea S, Signorelli D, Gargano F, D’Alessio N, Manoj RRS, Khademi P and Rofrano G (2025) Bees on the run: Nosema spp. (Microsporidia) in Apis mellifera and related products, Italy. Front. Vet. Sci. 11:1530169. doi: 10.3389/fvets.2024.1530169
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Jevrosima Stevanovic, University of Belgrade, SerbiaPetar Hristov, Bulgarian Academy of Sciences, Bulgaria
Copyright © 2025 Sgroi, D’Auria, Lucibelli, Mancusi, Proroga, Esposito, Rea, Signorelli, Gargano, D’Alessio, Manoj, Khademi and Rofrano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Andrea Mancusi, YW5kcmVhLm1hbmN1c2lAaXpzbXBvcnRpY2kuaXQ=
†These authors have contributed equally to this work and share first authorship