Correlation between airborne pollen data and the risk of tick-borne encephalitis in northern Italy

Abstract

Tick-borne encephalitis (TBE) is caused by a flavivirus that infects animals including humans. In Europe, the TBE virus circulates enzootically in natural foci among ticks and rodent hosts. The abundance of ticks depends on the abundance of rodent hosts, which in turn depends on the availability of food resources, such as tree seeds. Trees can exhibit large inter-annual fluctuations in seed production (masting), which influences the abundance of rodents the following year, and the abundance of nymphal ticks two years later. Thus, the biology of this system predicts a 2-year time lag between masting and the incidence of tick-borne diseases such as TBE. As airborne pollen abundance is related to masting, we investigated whether inter-annual variation in pollen load could be directly correlated with inter-annual variation in the incidence of TBE in human populations with a 2-year time lag. We focused our study on the province of Trento (northern Italy), where 206 TBE cases were notified between 1992 and 2020. We tested the relationship between TBE incidence and pollen load collected from 1989 to 2020 for 7 different tree species common in our study area. Through univariate analysis we found that the pollen quantities recorded two years prior for two tree species, hop-hornbeam (Ostrya carpinifolia) and downy oak (Quercus pubescens), were positively correlated with TBE emergence (R2 = 0.2) while a multivariate model with both tree species better explained the variation in annual TBE incidence (R2 = 0.34). To the best of our knowledge, this is the first attempt at quantifying the correlation between pollen quantities and the incidence of TBE in human populations. As pollen loads are collected by widespread aerobiological networks using standardized procedures, our study could be easily replicated to test their potential as early warning system for TBE and other tick-borne diseases.

Seroprevalence of Crimean Congo Hemorrhagic Fever Virus in Occupational Settings: Systematic Review and Meta-Analysis

“…As recently stressed by reports from hyperendemic areas [ 10 , 17 , 54 ], including the occupational report by Atim et al [ 54 ], a radical paradigm shift is, therefore, conceivable when pondering the CCHF-associated actual burden of disease. Similar to other vector-borne diseases such as West Nile Fever [ 66 , 67 , 68 , 69 , 70 , 71 , 72 ], Dengue [ 73 , 74 , 75 , 76 ], and Tick-Borne Encephalitis [ 77 , 78 , 79 , 80 , 81 ], CCHF should be understood as a relatively rare occurrence following CCHFV infection, while majority of cases either go unnoticed or misunderstood as “summer flu” [ 82 ]. Far from dismissing the potential significance of this pathogen, a more appropriate appraisal of CCHFV in the evolving landscape of vector-borne diseases underlines the role of occupational physicians and medical surveillance in occupational settings as instrumental in improving our appropriate understanding of the CCHF epidemiology [ 83 , 84 , 85 ].…”