Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisors: Yan Jin, Dept. of Plant & Soil Sciences; and Pei C. Chiu, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Nucleic acid hybridization (gene probe) and polymerase chain reaction (PCR) techniques have been used to detect viral nucleic acid in water. However, gene probe and PCR may not distinguish between infectious and noninfectious viruses. This study evaluated the ability of gene probe to detect viable poliovirus 1 (polio 1), from sterile and nonsterile groundwater, and the ability of PCR to detect infectious human immunodeficiency virus (HIV-1) from tap and wastewater. The plaque forming (BGM cells), and the tissue culture infectious dose fifty (TCID₅₀) (PLC/PRF/5 cells) procedures were used to detect infectious polio 1 and HIV-1, respectively. Detection of polio 1 by gene probe and cell culture was similar in nonsterile water and in filter sterilized water, but not in autoclaved water. These results suggest that in some natural waters, detection of polio 1 by gene probe may correlate to detection by cell culture procedures. Although detection of infectious HIV-1 by cell culture decreased gradually, until no virus could be found, detection by PCR remained positive throughout the study. Therefore, it was concluded that the use of PCR to assess the risk associated to the presence of HIV-1 in polluted waters, may not be adequate. The enteric adenovirus types 40 (Ead 40) and 41 (Ead 41) are considered the second most important cause of viral gastroenteritis in children, but their role as waterborne pathogens is uncertain. This study compared the survival of Ead 40 and Ead 41 with polio 1, and hepatitis A virus (HAV) in different types of water. The Enteric adenoviruses survived longer in tap and sea water than either polio 1 or HAV, but only slightly better in wastewater. These results suggest that the enteric adenoviruses may survive for prolonged periods in water, representing a potential route of transmission. This study evaluated also the concentration of Ead 40 by the filter adsorption-elution method. With negatively-charged filters, recovery efficiencies of 22, 36, and 38% were obtained from secondary sewage, tap and sea water, respectively. Using electropositive filters, Ead 40 was recovered from tap water with an efficiency of 26.5%. These results show that Ead 40 can be concentrated, from water, with an efficiency comparable to that of other enteric viruses.

The isolation of viruses from treated drinking water has raised concerns that water treatment methods may not always adequately insure the removal of viruses from water designated for human consumption. The isolation of enteroviruses and rotavIruses from treated drinking water in a distribution system and at a water treatment plant has been previously reported. Isolation of viruses from drinking water that met recommended levels of coliform bacteria, chlorine and turbidity. The question is raised as to whether or not current drinking water standards ensure safe drinking water. The isolation of enteroviruses and rotaviruses from treated drinking water In a distribution system and at a water treatment plant. This study reports the results of a more extensive investigation on the removal of naturally occurring viruses by water treatment processes including prechlorination/clarification, filtration, and chlorination at a fullscale water treatment plant. The removal of enteroviruses and rotaviruses was studied at a full scale 205 mgd water treatment plant involving chemical clarification, sand filtration and chlorination. Enteric viruses, as well as coliphages, indicator bacteria, physical and chemical variables were measured in water samples taken at each stage of the drinking water treatment facility. Linear intercorrel ations were analyzed for all the variables. The numbers of standard plate count bacteria and coliphage were positively correlated to the presence of enteroviruses in the raw water while coliphage counts were positively correlated to the presence of rotaviruses in the finished water. Samples were taken during the dry and rainy seasons. During the dry season, it was found that reduction of enteroviruses and rotaviruses averaged 81% and 93%, respectively, for the complete treatment process and were the least efficiently removed as compared to the other microorganisms. The greatest reduction of enterovIruses occurred during pre-chlorination/flocculation and filtration, while a significant reduction of rotav I ru ses occurred during prechlorination/ flocculation and final chlorination. Enteroviruses or rotaviruses occurred in 24% of the finished water samples containing chlorine levels of >0.2 mg/L, and meeting coliform bacteria (1/100 ml) and turbidity (1 NTU) standards. During the rainy season removals were found to be far less efficient for all the variables and rotaviruses were isolated from all finished water samples. The results of this study indicate that finished water having measurable levels of free residual chlorine and meeting standards for col iform bacteria, and turbidity cannot be assumed to be virus free.

Phytophthora pini Leonian, recently re-established from P. citricola I, is a pathogen with a wide range of forest and nursery hosts. It causes foliar infections in horticultural nurseries in Oregon, where recirculating irrigation systems are common. Increased use of recirculating irrigation systems may contribute to disease caused by waterborne plant pathogens. Simulated nursery chamber experiments were utilized to investigate the relationship between Phytophthora pini zoospore inoculum dose and disease on Rhododendron. Disease incidence in this system was unexpectedly low despite high inoculum levels tested, so further experiments under lab conditions were conducted to explore possible causes. Detached leaf assays were conducted to determine how inoculum dose, leaf wounding, and agitation of zoospore inoculum affected foliar infection of Rhododendron. Wounded and nonwounded leaves were dipped into suspensions of zoospores that were either untreated, mechanically agitated by vortexing to cause encystment, or pumped through an irrigation sprayer system. Disease severity (lesion area) and incidence (number of lesions per leaf area) were measured over seven days. At inoculum levels of ���10,000 propagules/mL, motile zoospores infected both wounded and nonwounded leaves. Vortexing or pumping resulted in zoospore encystment, and inoculation with these treatments caused disease almost exclusively on wounded leaves. No disease symptoms were observed following inoculation with any inocula at ��� 2,000 propagules/mL. Scanning electron microscopy of leaves inoculated with encysted propagules showed germinated cysts with hyphae growing over and around stomata without entering leaf tissue until reaching a wound site. Nonwounded leaves inoculated with motile spores showed stomata penetrated by hyphae. These findings indicate the importance of zoospore motility in reaching suitable infection sites, and demonstrate the impact of zoospore encystment on disease development. This has implications for disease management in nurseries where pruning wounds are common and the pumping of infested irrigation water may influence zoospore motility and infectivity. / Graduation date: 2013

Three experiments were conducted to characterize the concentration of microorganisms in biosolids, the plume of aerosols created during land application of biosolids and the occupational risk of infection due to pathogens aerosolized during land application of biosolids in the United States. In all, more than three-hundred air samples were collected immediately downwind of biosolids applications throughout the United States using liquid impingers, and more than one-hundred air samples were collected downwind of microbially seeded, land applied water, which served as a conservative model system of aerosol generation. The novel model system made it possible to calculate the flux of microorganisms through a virtual plane defined by air samplers in vertical and horizontal arrays, located immediately downwind of a passing spray applicator. The rate of aerosolization during land application of biosolids near Tucson, Arizona, was calculated to be less than 33 plaque forming units (PFU) of coliphage and 10 colony forming units (CFU) of coliform bacteria per meter traveled by the spray applicator. Rates of aerosolization from the model system were shown to be much greater. To assess the risk to occupational health from bioaerosols generated during land application of biosolids, coliform bacteria, coliphages, and heterotrophic plate count (HPC) bacteria were enumerated from air and biosolids at 10 land application sites throughout the nation. The method of land application strongly influenced aerosolization, while relative humidity, temperature and wind speed showed limited correlation to concentrations of fecal indicator microorganisms in air. Occupational risks of infection and illness from aerosolized Salmonella and enteroviruses were calculated for a variety of land application scenarios. Realistic exposure scenarios carried occupational risks of Salmonella infection ranging from of 0.0001% to 0.013% per year. The corresponding occupational risk of infection from enteroviruses, using coxsackievirus A-21 as a model, ranged from 0.78% to 2.1% per year, depending on the type of activity performed by the worker. In addition, samples of biosolids from the Southwestern United States were characterized to provide up-to-date information about pathogens in biosolids for environmental regulators, biosolids producers, researchers, and public health agencies.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 120-131). / Microfiche. / xiii, 131 leaves, bound ill. 29 cm

Thesis (Ph. D.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2005. / Includes summary. Title from opening screen (viewed March 20, 2006). Includes bibliographical references.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Water-borne infections have been a menace in many countries around the globe, claiming millions of lives. Cholera in particular has spread to all continents and now on its seventh epidemic. Although control measures have been continually developed through sanitation, vaccination and rehydration, the infection still devastates populations whenever there is an outbreak. In this research work, mathematical models for cholera transmission dynamics with focus on the impact of sanitation and hygiene, metapopulation spread, optimal control and biological control using a bacteriophage specific for pathogenic Vibrio cholerae are constructed and analysed. Vital analyses for the models are precisely given as well as numerical results depicting long term behaviour and the evolution of populations over time. The results of our analysis indicate that; improved sanitation and hand-hygiene are vital in reducing cholera infections; the spread of disease across metapopulations characterised by exchange of individuals and no cross community infection is associated with synchronous fluctuation of populations in both adjacent communities; during control of cholera, the control measures/efforts ought to be optimal especially at the beginning of the epidemic where the outbreak is often explosive in nature; and biological control if well implemented would avert many potential infections by lowering the concentration of pathogenic vibrios in the aquatic environment to values lower than the infectious dose. / AFRIKAANSE OPSOMMING: Water-infeksies is ’n bedreiging in baie lande regoor die wêreld en eis miljoene lewens. Cholera in die besonder, het op sy sewende epidemie na alle kontinente versprei. Hoewel beheermaatreëls voortdurend ontwikkel word deur middel van higiëne, inentings en rehidrasie, vernietig die infeksie steeds bevolkings wanneer daar ’n uitbraak voorkom. In hierdie navorsingswerk, word wiskundige modelle vir cholera-oordrag dinamika met die fokus op die impak van higiëne, metabevolking verspreiding, optimale beheer en biologiese beheer met behulp van ’n bakteriofaag spesifiek vir patogene Vibrio cholerae gebou en ontleed. Noodsaaklike ontledings vir die modelle is gegee sowel as numeriese resultate wat die langtermyn gedrag uitbeeld en die ontwikkeling van die bevolking oor tyd. Die resultate van ons ontleding dui daarop dat; verbeterde higiëne is noodsaaklik in die vermindering van cholera infeksies; die verspreiding van die siekte oor metapopulaties gekenmerk deur die uitruil van individue en geen kruis gemeenskap infeksie wat verband houmet sinchrone skommeling van bevolkings in beide aangrensende gemeenskappe; tydens die beheer van cholera,behoort die beheermaatreëls/pogings optimaal te wees veral aan die begin van die epidemie waar die uitbreking dikwels plofbaar in die natuur is; en biologiese beheer, indien dit goed geïmplementeer word, kan baie potensiële infeksies voorkom deur ’n vermindering in die konsentrasie van patogene vibrio in die water tot waardes laer as die aansteeklike dosis.

No description available.