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Airborne pathogenic bacteria can present a significant public health risk. Pathogenic Listeria monocytogenes can colonize numerous surfaces as well, through direct and indirect cross contamination. The physical environment can also affect the transmission and viability of Listeria (distance from the source, temperature, humidity, air flow). The purpose of this work was to explore the ability of Listeria innocua (a surrogate for L. monocytogenes) to contaminate a surface after it has become aerosolized in a bioaerosol chamber and a walk-in cooler. L. innocua was nebulized into a 154 L biosafety chamber (~5 log CFU in 1 mL) at two relative humidity (RH) levels (83% and 65%). Oxford Listeria agar plates, stainless steel coupons and polyethylene (HDPE) coupons in the chamber were exposed to the aerosolized bacteria for 5, 10, 20 or 40 minutes. Also, at these times, air samples (100 L) were collected on to gelatin filters which were transferred to Oxford agar plates. In the second part of the research, L. innocua was nebulized into an 11 m3 walk-in cooler where RH ranged from ~29-37%. Aerosolized bacteria were collected on to Oxford agar plates for 10 min intervals and with 50 or 100 L air samples. Recovery of L. innocua from steel, plastic and agar was significantly higher at 83% RH (2.7 cells/cm2) compared to 65% RH (0.45 cells/cm2). Mean cell recovery from air samples (gelatin filters) was significantly higher (p<0.05) when collected 5 or 10 minutes after nebulization at 83% humidity (mean 2.2 CFU/L) compared to collection after 20 or 40 minutes or compared to all times under 65% humidity (mean 0.4 CFU/L). Recovery from HDPE coupons (1.21 CFU/cm2) was 2.5 X recovery from Oxford agar (0.49 CFU/cm2). In the walk-in cooler, total estimated mean recovery from Oxford media at 10 min after nebulizing was 0.48%, but only 0.04% for samples collected after 60 minutes. The recovery of L. innocua from air samples after 60 min was one-fourth of the number recovered 5 min after nebulizing. No significant difference in recovery was found between plates at different distances (2 – 2.5 m) from the nebulizer in the walk-in cooler. Understanding the survival of aerosolized Listeria and how it can colonize over time on a food contact surface will enhance our efforts to prevent transmission on a small and large scale. The food industry will be able to implement better safety measures to prevent contamination by Listeria species. / Ph. D. / Airborne pathogenic bacteria, including Listeria monocytogenes, can present a significant public health risk. Pathogenic bacteria can colonize numerous surfaces as well through direct and indirect cross contamination. The physical environment can also affect the transmission and viability of Listeria (distance from the source, temperature, humidity). The purpose of this work was to explore the ability of Listeria innocua to contaminate a surface after it has become aerosolized in a bioaerosol chamber and a walk-in cooler. Environmental factors of distance from the source, temperature, and relative humidity were explored. L. innocua was nebulized into a 154 L biosafety chamber (~5 log CFU in 1 ml) at two relative humidity (RH) levels (83% and 65%). Oxford Listeria agar plates, stainless steel coupons and polyethylene (HDPE) coupons in the chamber were exposed to the aerosolized bacteria for 5, 10, 20 or 40 minutes. Also, at these times, air samples (100 L) were collected on to gelatin filters which were transferred to Oxford agar plates. In the second part of the research, L. innocua was nebulized into an 11 m³ walk-in cooler where RH ranged from ~29-37%. Aerosolized bacteria were collected with 50 or 100 L air samples. And, Oxford media was placed on the cooler floor in layers (attached to poster boards) at various locations for surface analysis. The three surface samples yielded a greater mean recovery of 2.7 cells/cm² at 83% humidity compared to 0.45 cells/cm² at 65% humidity. Mean cell recovery from air samples (gelatin filters) was significantly higher (p<0.05) when collected 5 or 10 minutes after nebulization at 83% humidity (mean 2.2 CFU/L) compared to collection after 20 or 40 minutes or compared to all times under 65% humidity (mean 0.4 CFU/L). Recovery from HDPE coupons (1.21 CFU/cm² ) was 2.5 X recovery from Oxford agar (0.49 CFU/cm² ). In the walk-in cooler, total estimated mean recovery from the Oxford media at 10 min after nebulizing the Listeria innocua was 0.48%, but only 0.04% for samples collected after 60 minutes. The recovery of L. innocua from air samples after 60 min was one-fourth of the number recovered 5 min after nebulizing. Understanding the survival of aerosolized Listeria and how it can colonize over time on a food contact surface will enhance our efforts to prevent transmission on a small and large scale. The food industry will be able to implement better safety measures to prevent contamination by Listeria species.

Despite formidable advances in virology and medicine in recent decades, we know remarkably little about the dynamics of the influenza virus in the environment during transmission between hosts. There is still controversy over the relative importance of various transmission routes, and the seasonality of influenza remains unexplained. This work focuses on developing new knowledge about influenza transmission via the airborne route and the virus' inter-host dynamics in droplets and aerosols. We measured airborne concentrations of influenza A viruses (IAVs) and size distributions of their carrier aerosols in a health center, a daycare center, and airplanes. Results indicate that the majority of viruses are associated with aerosols smaller than 2.5 µm and that concentrations are sufficient to induce infection. We further modeled the fate and transport of IAV-laden droplets expelled from a cough into a room, as a function of relative humidity (RH) and droplet size. The model shows that airborne concentrations of infectious IAV vary with RH through its influence on virus inactivation and droplet size, which shrinks due to evaporation. IAVs associated with large droplets are removed mostly by settling, while those associated with aerosols smaller than 5 µm are removed mainly by ventilation and inactivation. To investigate the relationship between RH and influenza transmission further, we measured the viability of IAV in droplets at varying RHs. Results suggest that there exist three regimes defined by RH: physiological conditions (~100% RH) with high viability, concentrated conditions (~50% to ~99% RH) with lower viability, and dry conditions (<~50% RH) with high viability. A droplet's extent of evaporation, which is determined by RH, affects solute concentrations in the droplet, and these appear to influence viability. This research considerably advances the current understanding of the dynamics of the influenza virus while it is airborne and provides an explanation for influenza's seasonality. Increased influenza activity in winter in temperate regions could be due to greater potential for IAV carrier aerosols to remain airborne and higher viability of IAV at low RH. In tropical regions, transmission could be enhanced due to better survival of IAV at extremely high RH. / Ph. D.

The global food supply is being stressed by climate change, a growing population, and harmful diseases. One risk to vital cereal crops such as wheat and barley is Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium graminearum. Ascospores of the fungus are released from perithecia on the residues of corn and small grains and can be transported long distances (>500 m) through the atmosphere. The overall objective of this work was to assess the influence of meteorological conditions and perithecial maturity on ascospore release. The research focuses on F. graminearum because of its damaging impact to staple crops and the global ubiquity of FHB. The first specific objective was to apply state-of-the-science techniques to identify causal meteorological variables of ascospore release. We analyzed field measurements of airborne ascospores against meteorological conditions at Virginia Tech's Kentland Farm, Blacksburg, Virginia, USA and used convergent cross mapping and multivariate state space reconstruction to identify significant causal agents within this complicated natural and dynamic system. We identified relative humidity, solar radiation, wind speed, and air temperature as predictors of ascospore release. Our second research objective was to understand the impact of varying meteorological conditions on ascospore release under controlled environmental conditions. We assessed ascospore release in a chamber with controlled temperature (15°C and 25°C) and relative humidity (60%, 75%, and 95%). Ascospores released from ascospore-producing structures (perithecia) were captured on microscope slides placed inside of 3D-printed ascospore discharge devices. Results showed the sensitivity of ascospore release to relative humidity and temperature, with cool temperature and high relative humidity resulting in greater quantities of ascospores released. Our third research objective was to determine the relationship between the maturity, the number of ascospores, and the hardness of perithecia. A mechanical compression testing instrument was used to investigate the hardness of perithecia at various stages of maturity, producing a mean perithecium compression constant quantifying the uniaxial compression force required to rupture a perithecium. Results indicated that old perithecia contain the greatest amount of ascospores and exhibit increased resiliency, requiring greater forces to rupture, compared to young perithecia. This research has illustrated the complexities of F. graminearum ascospore release by describing the impact of several meteorological conditions and perithecial maturity on the timing and quantity of released ascospores. Collectively, our results may inform wheat growers on the nature and timing of ascospore release, which could help inform FHB management decisions in the future. / Ph. D.

The majority of the Earths surface is covered with water, and the air-water interface (AWI) acts as the natural boundary between the atmosphere and the water. The AWI is an important ecological zone in natural aquatic habitats that governs transport of material and energy between bodies of water and the atmosphere. Little is known about temperature profiles and biological transport across the boundary layers at the air-water interface, and how wind interactions at the AWI affects them. New technologies such as sensors and unmanned surface vehicles (USV) need to be developed and used to address this knowledge gap. The goal of the research is to study population densities of the bacteria Pseudomonas syringae below, at and above the AWI using USV equipped with specialized sensors. The first specific objective was to map temperature profiles and resolve the boundary layer at the AWI using high resolution distributed temperature sensing (HR-DTS) on board an unmanned surface vehicle (USV). Our second research objective was to sample microbes from the water with a USV at multiple depths and locations. Our third research objective was to sample microbes from the atmosphere with a USV at the AWI. Our fourth research objective was to track and localize hazardous agents (tracer dyes) using a USV in aqueous environments. / Ph. D. / The majority of the Earths surface is covered with water, and the air-water interface (AWI) acts as the natural boundary between the atmosphere and the water. The AWI is an important ecological zone in natural aquatic habitats. Little is known about temperature profiles and biological transport across the boundary layers at the air-water interface, and new technologies need to be developed and used to address this knowledge gap. The specific objectives of the proposed work are to: (1) map temperature profiles and resolve the boundary layer at the AWI using high resolution distributed temperature sensing (HR-DTS) on board an unmanned surface vehicle (USV), (2) sample microbes from the water with a USV at multiple depths and locations, (3) sample microbes from the atmosphere with a USV at the AWI, and (4) track and localize hazardous agents (tracer dyes) using a USV in aqueous environments.

This work is a multi-scale effort to confront the rapidly evolving threat of biological weapons attacks through improved bioaerosol surveillance, detection, and response capabilities. The effects of bioaerosol release characteristics, transport in the atmospheric surface layer, and implications for bioaerosol sampler design and real-time detection were studied to develop risk assessment and modeling tools to enhance our ability to respond to biological weapons attacks. A simple convection-diffusion-sedimentation model was formulated and used to simulate atmospheric bioaerosol dispersion. Model predictions suggest particles smaller than 60 micrometers in aerodynamic diameter (AD) are likely to be transported several kilometers from the source. A five fold increase in effective mass collection rate, a significant bioaerosol detection advantage, is projected for samplers designed to collect particles larger than the traditional limit of 10 micrometers AD when such particles are present in the source distribution. A family of dynamically scaled wetted-wall bioaerosol sampling cyclones (WWC) was studied to provide bioaerosol sampling capability under various threat scenarios. The effects of sampling environment, i.e. air conditions, and air flow rate on liquid recovery rate and response time were systematically studied. The discovery of a critical liquid input rate parameter enabled the description of all data with self-similar relationships. Empirical correlations were then integrated into system control algorithms to maintain microfluidic liquid output rates ideally suited for advanced biological detection technologies. Autonomous ambient air sampling with an output rate of 25 microliters per minute was achieved with open-loop control. This liquid output rate corresponds to a concentration rate on the order of 2,000,000, a substantial increase with respect to other commercially available bioaerosol samplers. Modeling of the WWC was performed to investigate the underlying physics of liquid recovery. The set of conservative equations governing multiphase heat and mass transfer within the WWC were formulated and solved numerically. Approximate solutions were derived for the special cases of adiabatic and isothermal conditions. The heat and mass transfer models were then used to supplement empirical correlations. The resulting semi-empirical models offer enhanced control over liquid concentration factor and further enable the WWC to be deployed as an autonomous bioaerosol sampler. / text

Cette étude s’inscrit dans le cadre de l’amélioration des connaissances sur la dégradation photocatalytique des bioaérosols bactériens. La photocatalyse est une technique d’épuration basée sur l’excitation d’un semi-conducteur par un rayonnement le plus généralement ultraviolet. Cette technologie permet, en théorie, de minéraliser pas à pas les polluants. Or, si les conditions optimales ne sont pas réunies, la minéralisation incomplète peut conduire à des sous-produits de dégradation de toxicité potentiellement préoccupante.L’objectif de ces travaux a donc été d’apporter des éléments de compréhension quant aux mécanismes de dégradation photocatalytique d’un bioaérosol bactérien modèle d’E.coli, où de nombreux phénomènes sont couplés. Ainsi, pour distinguer les différents processus mis en jeu, deux approches expérimentales ont été menées. La première, nommée approche « batch », a permis d’isoler la réaction photocatalytique, à proprement parler, en étudiant les étapes d’inactivation, de libération de sous-produits et de minéralisation progressive. La seconde, appelée approche « dynamique » a permis quant à elle la mise en place d’un dispositif expérimental adapté à la dégradation photocatalytique d’un bioaérosol d’E.coli. Les capacités de la photocatalyse à inactiver et minéraliser des espèces bactériennes ont pu être démontrées. Les paramètres clés d’une dégradation efficace ont été mis en évidence et ont permis de décrire les verrous indispensables à une industrialisation sûre du procédé / This study comes within the scope of improving knowledge concerning the photocatalytic degradation of bacterial bioaerosol. Photocatalysis is a purification technology generally based on the excitation of a semiconductor by an ultraviolet radiation. This technology can, in theoretical ways, mineralize pollutants step by step. However, if optimal conditions are not gathered, this mineralization is incomplete and can lead to the formation of potentially toxic by-products. The aim of this work was therefore a better understanding of the mechanisms of photocatalytic degradation of a bacterial bioaerosol of E.coli, where numerous phenomenon are linked. Thus, to distinguish the different processes, two experimental approaches were used. The first one, called “batch approach”, allowed to consider the photocatalytic reaction itself, by studying the steps of inactivation, by-products formation and progressive mineralization. The second one, named “dynamic approach”, consisted to design an experimental setup suited to the photocatalytic degradation of a bioaerosol of E.coli. The abilities of photocatalysis to inactivate and mineralize bacteria could be demonstrated. The key parameters of an efficient degradation were highlighted and allowed to underline the problems to solve before having a safe industrialization of the photocatalysis

The first part of this study is focused on numerical studies of light scattering from a single microscopic particle using the Discrete Dipole Approximation (DDA) method. The conventional DDA formalism is generalized to two cases: (a) inelastic light scattering from a dielectric particle and (b) light scattering from a particle with magnetic permeability u /= 1. The first generalization is applied to simulations of Raman scattering from bioaerosol particles, and the second generalization is applied to confi rmation of irregular invisibility cloaks made from metamaterials. In the second part, radiative transfer in a coupled atmosphere-ocean system is solved to study the asymptotic nature of the polarized light in deep oceans. The rate at which the radiance and the polarization approach their asymptotic forms in an ideal homogeneous water body are studied. Effects of the single scattering albedo and the volume scattering function are studied. A more realistic water body with vertical pro files for oceanic optical properties determined by a Case 1 water model is then assumed to study the e ffects of wavelength, Raman scattering, and surface waves. Simulated Raman scattering patterns computed from the generalized DDA formalism are found to be sensitive to the distribution of Raman active molecules in the host particle. Therefore one can infer how the Raman active molecules are distributed from a measured Raman scattering pattern. Material properties of invisibility cloaks with a few irregular geometries are given, and field distributions in the vicinity of the cloaked particles computed from the generalized DDA formalism con rm that the designated material properties lead to invisibility. The radiative transfer model calculation in deep oceans suggest that the underwater radiance approaches its asymptotic form more quickly than the polarization does. Therefore, a vector radiative transfer solution is necessary for asymptotic light field studies. For a typical homogeneous water body whose scattering property is characterized by the Petzold phase function, a single scattering albedo of w0 > 0:8 is required in order that the asymptotic regime can be reached before there are too few photons to be detected.

Die aerogene Übertragung von Infektionskrankheiten stellt ein sehr wichtiges Thema in der Medizin dar. Für genaue Untersuchungen dazu, sind geeignete Sammel- und Nachweismetho-den essentiell. Die Untersuchung verschiedener Sammelgeräte sowie unterschiedlicher Nach-weismethoden zur Virusquantifizierung aus der Luft war daher die zentrale Aufgabenstellung in dieser Arbeit. Als Sammelgeräte wurden der Impinger AGI 30 und der Gelatinefilter ausge-wählt. Alle grundlegenden Untersuchungen zur Ermittlung der Eignung und Effizienzen der Geräte bezüglich der Virusisolierung aus Luftproben wurden an experimentell erzeugten Virus-aerosolen durchgeführt. Dabei wurden zwei Geflügelviren verwendet, das Newcastle-Disease-Virus Stamm LaSota (NDV) und das Infektiöse-Bursitis-Virus Stamm Cu-1M (IBDV). Die quan-titative Bestimmung der Viren aus den Luftproben erfolgte durch Titration im Zellkultursystem bzw. in embryonierten Hühnereiern. Parallel dazu wurde eine Titerbestimmung mittels einer in dieser Arbeit etablierten quantitativen Real-Time-PCR durchgeführt. Zusätzlich wurden die Sammelgeräte unter praktischen Bedingungen getestet und verglichen. Dazu erfolgten lufthy-gienische Messungen nach Vakzinierung von Geflügel mit Lebendimpfstoffen (NDV LaSota und IBDV Cu-1M). Es wurden umfangreiche Untersuchungen unter experimentellen Beding¬ungen und später exemplarische Untersuchungen in konventionellen Geflügelhaltungen durch-geführt. Die Evaluierung der Sammelgeräte mit Hilfe der experimentell erzeugten Virusaerosole er-gab, dass mit beiden Geräten sowohl infektionsfähiges Virus als auch Virusgenom nachgewie-sen und quantifiziert werden kann. Die Effizienzen unterschieden sich jedoch z.T. deutlich. So stellte sich der Gelatinefilter zur Sammlung in Kombination mit dem quantitativen Virusnach-weis mittels Real-Time-PCR als die Methode mit der höchsten Virusnachweisrate (angegeben als geometrischer Mittelwert mit geometrischer Standardabweichung) von 22,3 % ×/ 3,1 für NDV und 36,1 % ×/ 3,4 für IBDV heraus. Der Nachweis von infektionsfähigen Viren jedoch, war für beide Testkeime aus den Proben des Impingers erfolgreicher (NDV 4,0 % ×/ 1,7 und IBDV 31,8 % ×/ 1,8). Die signifikant niedrigere Nachweisrate des Newcastle-Disease-Virus ist auf die höhere Empfindlichkeit dieses behüllten Virus beim Sammelprozess und daraus folgen-der Inaktivierung zurückzuführen. Die Quantifizierung mit Hilfe der Real-Time-PCR erfolgte mit Normalisierung aller Proben. Diese bisher zur Analyse von Luftproben noch nicht ange-wandte Methode erwies sich als sehr gut. Durch die Normalisierung werden nicht nur die ab-weichenden Effizienzen der Nukleinsäureisolierung sowie der reversen Transkription ausgegli-chen, sondern auch die unterschiedliche Inhibition der PCR der Proben verschiedener Luftkeimsammler. Damit sind die Proben untereinander besser vergleichbar und die Quantifi-zierung exakter. Erstmals wurden auch systematische Untersuchungen zu Geräteeffizienzen in Kombination mit verschiedenen Virusnachweismethoden durchgeführt. Bei den lufthygienischen Untersuchungen nach Vakzinierung von ca. 50 Hühnern gegen Newcastle Disease (ND) bzw. Infektiöse Bursitis (IBD) unter experimentellen Bedingungen, waren drei Luftproben nach der Impfung gegen ND viruspositiv, jedoch keine nach der gegen IBD. Diese positiven Nachweise gelangen mit dem Gelatinefilter und nachfolgender Analyse mittels quantitativer Real-Time-PCR. Schlussfolgernd ist zumindest bei dem NDV eine aeroge-ne Ausscheidung des Impfvirus anzunehmen. Wahrscheinlich liegt die Viruskonzentration in der Luft jedoch meist unter der Nachweisgrenze der eingesetzten Geräte. Auch die Auswertung von Luftproben nach Vakzinierung gegen oben genannte Krankheiten in konventionellen Tierhal-tungen mit mehreren Tausend Tieren Besatz pro Stall führte zu keinen viruspositiven Ergebnis-sen. Anscheinend wurden die Viren auch trotz der großen Tierzahl in der Luft so stark verdünnt oder in so geringem Maße ausgeschieden, dass sie mit den in dieser Arbeit entnommenen Luft-probenvolumina von 1000 l nicht detektiert werden konnten. Für weiterführende Untersuchun-gen müsste daher ein Sammelgerät verwandt werden, mit welchem schnell große Probenvolu-mina entnommen werden können und das Endvolumen der Probenflüssigkeit dennoch gering ist, um die luftgetragenen Viren optimal zu konzentrieren. Schlussfolgernd erwies sich die Filtration in Kombination mit der normalisierten quantitati-ven Real-Time-PCR dennoch insgesamt als eine sehr valide und praktikable Methode zum Nachweis luftgetragener Viren aus Tierhaltungen.

Réutiliser les eaux usées en irrigation agricole aide à répondre aux besoins croissants en eau, réduit leur décharge dans les eaux conventionnelles et participe à la fertilisation des sols. Les eaux usées d'origine domestique contiennent des virus entériques de l'homme responsables d'épidémies transmises par voies hydrique et alimentaire. Leur transmission aérienne avec maladie à la clé a été mise en évidence dans d'autres contextes, mais il existe peu d’études sur le devenir de virus déposés à la surface du sol ou de végétaux. Aussi cette thèse de Doctorat avait-elle pour objectifs d'évaluer et décrire (i) l'aérosolisation des virus préalablement apportés au sol par irrigation avec des eaux usées et (ii) leur inactivation dans l'atmosphère.Pour répondre à ces objectifs, des suivis expérimentaux ont été réalisés en conditions semi-contrôlées pour l'aérosolisation (virus déposés in situ sur des placettes de sol couvertes par des tunnels) et en conditions contrôlées pour l'inactivation (virus en réacteur atmosphérique de laboratoire). La souche MC0 du mengovirus murin a été utilisée pour l'ensemble des expérimentations. Elle a été multipliée sur des cellules BGM. La teneur en ARN viral a été suivie par RT-qPCR et, pour l'étude de l'inactivation, les virus infectieux ont été simultanément dénombrés par comptage de plages de lyse sur cellules BGM. Ces suivis ont été couplés au suivi des conditions environnementales (rayonnement global, température, humidité relative de l'air, teneur en O3, auxquels s'ajoutent l'humidité et la température de surface du sol pour l'étude de l'aérosolisation). Ces travaux ont nécessité de concevoir un nouveau réacteur atmosphérique, d'évaluer les performances de biocollecteurs (Impingers et filtres), et d’améliorer le dénombrement des virus infectieux.Un modèle a été proposé pour décrire l'aérosolisation d'un ou plusieurs pools de virus aérosolisables, chacun étant caractérisé par sa taille et un coefficient cinétique d'aérosolisation. Nous l'avons utilisé pour générer des expériences numériques reproduisant la variabilité des mesures réelles, et pour ajuster à ces expériences numériques des simulations portant soit sur l'aérosolisation cumulée soit sur l'aérosolisation « instantanée ». Les ajustements sur l'aérosolisation instantanée donnent des estimations plus précises du coefficient cinétique d'aérosolisation ; il n'en va pas forcément de même pour l'estimation de la quantité de virus aérosolisables. Un modèle de dépendance du coefficient d'inactivation à l'humidité relative de l'air a été proposé.Eu égard à l'aérosolisation des virus à partir du sol, les Impingers donnent des aérosolisations estimées plus élevées que les membranes en raison de différences de piégeage et/ou d'extraction. Toutefois, ils ne piègeraient qu'environ 77 % des virus et relargueraient des virus piégés avec un coefficient de réaérosolisation de 0.11. Ces imperfections aboutissent à des estimations des quantités de virus aérosolisés environ 2 fois moins élevées qu'en réalité ; à l'inverse, elles n'affectent pas les estimations des coefficients cinétiques d'aérosolisation. Sans tenir compte de ce biais, entre 1 et 10% des virus apportés ont été aérosolisés. À notre connaissance, c'est la première mise en évidence d'un tel phénomène. On distingue un pool de virus aérosolisés quasi-instantanément (environ 1/3 des virus aérosolisés) d'un pool de virus aérosolisés de manière cinétique. Pour ce dernier pool, la constante cinétique d'aérosolisation varie entre 0.007 et 0.21 h-1 : 90 % des virus du pool cinétique sont aérosolisés au bout de respectivement 13 j et 11 h dans nos conditions. La taille du pool cinétique est bien prédite à partir de la vitesse du vent, de la température de surface du sol et de la nature de l'eau d'irrigation. / Wastewater reuse for agricultural irrigation allows coping increasing water requirements, reduces wastewater discharge in conventional water bodies, and contributes to soil fertilization. Wastewaters of domestic origin are contaminated with human enteric viruses responsible for waterborne and foodborne outbreaks. Air transmission of viruses that leads to diseases has been noted in other contexts, but nothing is known about the fate of viruses brought at the surface of the soil. The aims of this PhD thesis were to assess and describe the aerosolization of viruses previously brought to the soil surface by wastewater irrigation, and their inactivation in the atmosphere.To fulfil these objectives, experiences were performed in semi-controlled conditions for aerosolization (viruses brought in situ on soil small plots covered by wind tunnels) and in controlled conditions for inactivation (viruses in laboratory atmospheric reactor). The MC0 murine mengovirus strain was used for all these experiences. It was propagated on BGM cells. The viral RNA content was monitored by RT-qPCR; for inactivation studies, infectious viruses were simultaneously enumerated by plaque assay on BGM cells. Variations in the total or infectious virus numbers were analyzed with regard to variations in global radiation, air temperature and relative humidity, O3 concentration, as well as soil surface moisture and temperature. This work required to design a new laboratory atmospheric reactor, to assess the performance of air biocollectors (impingers and membranes), and to optimize method for infectious virus enumeration.A model has been proposed to describe the aerosolization of one or some pools of viruses, each of these pools being characterized by its size and a kinetic coefficient of aerosolization. We used it to generate numerical experiences having the same variability as actual measurements, and to fit simulations of either cumulative or "instantaneous" aerosolized virus quantities to these numerical experiences. Fitting simulations to "instantaneous" aerosolized virus quantities leads to more precise estimates of the kinetic coefficient of aerosolization; it didn't lead to better estimates of the total amount of viruses that could be aerosolized. A relationship between the kinetic coefficient of virus inactivation and air relative moisture has also been proposed.Dealing with virus aerosolization from the soil, the amount of aerosolized viruses estimated from impinger data were higher than those estimated from membrane data, because of differences in trapping and/or latter extraction. Impingers would have trapped about 77% of air virus and virus re-aerosolization from Impingers would have concerned about 11% of the trapped viruses every hour. These limits would have resulted in estimates of the total amount of viruses that could be aerosolized about 2 times lower than in reality; conversely, they do not affect the estimates of the kinetic coefficient of aerosolization. Regardless of this bias, between 1 and 10% of viruses supplied to the soil were aerosolized. To our knowledge, this is the first evidence of such a phenomenon. We distinguish a pool of viruses that could be aerosolized nearly instantaneously (about 1/3 of aerosolized viruses) from a pool of viruses that would be aerosolized kinetically. For this last pool, the kinetic aerosolization coefficient varied between 0.007 and 0.21 h-1: 90% of the viruses belonging to the kinetic pool would be aerosolized after 13 days or 11 hours, respectively. The total amount of viruses belonging to the kinetic pool is correctly predicted by a model accounting simultaneously for the wind, the soil surface temperature and the type of irrigation water.