Estudio de "Alternaria" y del alérgeno Alt A 1 en el bioaerosol urbano

Résumé

The atmospheric aerosol, defined as the ensemble of particles suspended in the air, excluding hydrometeors, plays a pivotal role in several climatic and environmental processes essential for the planet´s functionality. These particles exhibit a wide range of characteristics and are typically classified based on various criteria, including their origin (natural or anthropogenic), formation (primary and secondary), and size distribution. The primary biological aerosol, or bioaerosol, consists of organisms, their fragments or their reproductive units, which are directly released from the biosphere into the atmosphere. This aerosol is primarily comprised by viruses, bacteria, and fungal spores, which collectively exhibit the highest concentration levels. Additionally, pollen grains, pteridophyte spores, algae, and lichen propagules are common components. However, the composition and concentration of these particles fluctuate significantly over time due to various environmental factors such as seasonal cycles, meteorological conditions, anthropogenic activities and ecosystem dynamics. For that, assessing their contribution to total atmospheric particulate matter is a challenge. The significance of bioaerosol primarily lies in its role in organism dispersal, facilitating the colonization of new ecosystems and influencing ecological dynamics. Despite living organisms constituting a share of the primary biological aerosol, atmospheric conditions such as temperature, radiation, and nutrient scarcity favor the presence of resilient structures and reproductive units, which are adapted for aerial transport. These particles also contribute significantly to the hydrological cycle, as many of them serve as cloud or ice condensation nuclei, thereby impacting precipitation patterns. However, bioaerosol also poses health risks to both humans and animals, as many airborne organisms, just as their fragments or dispersal units, have toxic or allergenic properties. Pollen grains and fungal spores found in bioaerosols are the main responsible for inducing symptoms of pollinosis in sensitive individuals, particularly outdoors. Allergic Rhinitis is nowadays recognized as a significant global public health concern, not only due to its high prevalence but also because of the important economic burdens associated with it. Therefore, aerobiological monitoring networks have been established worldwide with the aim of providing information on particle concentrations and atmospheric dynamics to diverse end-users. These data aids in managing various preventive measures and enhancing etiological diagnoses. Most operational aerobiological networks, particularly in Europe, utilize Hirst-type volumetric impact samplers. This methodology is considered, to date, the gold standard to carry out the sampling of airborne pollen and spores, enabling precise, continuous, and comparable measurements. Aerobiological pollen and spore counts have traditionally served as the primary method for assessing environmental exposure to these allergens. However, certain environmental conditions can lead to modifications in these particles, facilitating the release of allergenic sub-particles into the atmosphere. This can produce a discrepancy between the recorded spore-pollen counts and the actual allergen load present. Moreover, the allergenic sub-particles release represents a greater risk for patients, as their small size enables an easier inhalation, reaching the lower respiratory tract and triggering more severe allergic reactions, or even asthmatic episodes. For this reason, the development of methodologies to detect these sub-particles has been encouraged. The integration of these methodologies with pollen and spore counts not only enhances the assessment of the real allergenic load but also improves our understanding of bioaerosols. The close relationship between aerobiology and allergology has led to most traps being located in large urban areas, often overlooking other criteria for their placement. In consecuence, aerobiological networks may not adequately capture the environmental diversity of the region and, hence, fail to accurately depict atmospheric spore and pollen dynamics. While numerous scientific studies detail pollen spectra across various locations, few have assessed the effectiveness of operational aerobiological networks. Presently, such investigations are crucial in aerobiology, particularly for networks that covers large territories with significant geographic and vegetation variations. The scientific literature also highlights a significant gap in understanding the presence and behavior of fungal spores in the atmosphere. Despite being one of the most abundant components of the bioaerosol, and some being implicated in acute asthma episodes, fungal spores have often been neglected in aerobiological studies due to the challenges associated with taxonomic identification. The genus Alternaria is one of the most important fungal taxa in aerobiology due to its allergenic potential, its wide geographical distribution and the fact that many of its species are phytopathogenic. While the influence of certain meteorological factors like temperature, humidity, and precipitation on Alternaria spore concentrations is already known, substantial variations have been observed even in locations with similar climates. This underscores the complexity of spore dynamics, which cannot be fully elucidated by these climatic variables alone. The risk days for exposure to Alternaria conidia have traditionally been established when the concentration exceeds 100 spores per cubic meter of air. Nonetheless, recent research indicates that individuals sensitive to this fungus may present clinical symptoms at lower concentrations, possibly attributed to the presence of free allergenic sub-particles. Currently, there is a lack of aerobiological studies investigating fungal allergens, since most research focus on pollen's major allergens. However, the Alt a 1 glycoprotein, the major allergen of Alternaria, exhibits the highest sensitization rate among individuals with respiratory allergies to fungi. The aim of this thesis has been to carry out a study of Alternaria spores and its major allergen Alt a 1, in the atmosphere of two localities of Castilla y León, and to analyze the influence of different environmental variables on the atmospheric dynamics of these particles. This has been performed to improve the prediction models of risk days due to exposure to this type of spores. To fulfill this objective, the doctoral thesis has been structured into seven chapters. Chapter I offers a concise theoretical overview of bioaerosols and their implications for both the environment and human health, with particular emphasis on the significance of aerobiological researches concerning pollen and spores. Chapter II presents a detailed justification for the realization of this thesis, as well as the objectives to be achieved during its development. Chapter III details the diverse materials and methodologies employed in data collection and processing. Chapters IV to VI present the findings in a similar format to that of published scientific articles. Finally, Chapter VII recaps the conclusions derived from this doctoral research. Prior to the aerobiological study of Alternaria conidia, the two most suitable localities were meticulously chosen from among the 13 monitoring stations in Castilla y León. Chapter IV includes a study in which the atmospheric dynamics of the ten most abundant airborne pollen types were analyzed, over an eight-year period, at the 13 monitoring stations. This study employed clustering analysis, utilizing six distinct mathematical distances, to delineate homogeneous station groups based on their pollen season behavior. These station groups, in combination with altitude and various bioclimatic variables derived from temperature and precipitation data, were subsequently analyzed. The findings indicate that the monitoring stations that comprise the Aerobiological Network of Castilla y León effectively represent the majority of environmental variability within the region. Moreover, this aerobiological network can be geographically divided into two main areas, and five sub-areas, based on the onset and duration of the mean pollen season, coinciding with the division of the territory according to its climatology. The bioclimatic variables that showed significant differences between the groups of stations, and that influence the atmospheric pollen dynamics, were the seasonality of precipitation and the maximum temperature of the warmest month. However, it is important to consider the impact of orography as well. Chapter V presents the study of Alternaria conidia in the atmosphere of the cities of León and Valladolid, previously selected according to the results obtained in Chapter IV. Both cities are located at a relatively close distance, in two different aerobiological areas and with differences in land use. The objective of this chapter was to determine the main sources of Alternaria spore emissions and the impact on their atmospheric concentration, as well as to establish the potential transport routes that increase the concentration of these conidia. For that, daily spore concentrations were analyzed over a five-year period in both locations. In addition, to establish potential emission sources, an analysis of land use was performed within a 30 km radius around each trap, in combination with wind direction and speed data. The findings revealed significant spatial variability between the two proximate areas, with spore concentrations notably higher in Valladolid than in León. This discrepancy is mainly attributed to prevailing winds in Valladolid, which come from the north, where large areas destined to cereal crop are located, particularly during harvest season. This highlights the potential of these regions as major emission sources. On the other hand, the low spore concentration recorded in León is due to the origin of the prevailing winds from areas where forest masses and scrubland predominate, which indicates the low contribution of this type of vegetation to the atmospheric spore load. In addition, the few risk days recorded in the city of León are linked to the unusual southerly winds, where the main cereal areas are located. The annual variation of Alternaria spore concentration and the localization of emission sources in León make this city an appropriate place to investigate the complex relationships between spore concentration, the presence of the Alt a 1 allergen and environmental variables. Hence, Chapter VI presents a five-year aerobiological study of the Alt a 1 allergen. This study employed a non-hierarchical clustering analysis to classify days based on their meteorological and aerosol characteristics, subsequently examining the number of days with allergen presence in each established group. Furthermore, to assess whether selected variables could predict the presence of Alt a 1 in the atmosphere, a quadratic discriminant analysis was conducted. The results revealed that warm temperatures and absolute humidity favor the presence of this allergen in the air, while precipitation duration is associated with allergen-free days. Additionally, using the selected parameters, the quadratic discriminant analysis predicted days with allergen presence with an accuracy range of 67% to 85%. The mismatch between spore concentration and the Alt a 1 allergen can be attributed to a greater contribution of medium-long distance transport of the allergen compared to spores from the major emission sources. This thesis has highlighted the importance of evaluating aerobiological networks to know whether they faithfully represent a territory and understand the different atmospheric dynamics that may occur according to different environmental variables. Moreover, in order to improve the reliability of predictive models, it is necessary to incorporate new variables beyond those traditionally used. These include the location of the emission sources, the main routes of particle transport or the environmental characteristics that favor the allergens presence in the air. In addition, the results obtained suggest that the clinical threshold of exposure to Alternaria spores should be redefined, since the Alt a 1 allergen is present in the air even on days with low spore concentrations.