archives@tulane.edu / We extend the conventional models in mathematical epidemiology to account for more practical (yet complicated) situations in infectious disease transmissions, such as behavior change, risk level differentiation and infectiousness as a function of time since infection. We allow the transmission rate and recovery rate to vary as functions of time since infection. We present the derivation of the integral differential equation model and analyze the associated analytical and long-time solutions. We prove the well-posedness of an initial boundary value problem for the model. We also derive the threshold quantities for the epidemic to grow. We then extend the approach for the vector-borne infectious disease models. We compare several risk distribution functions due to geographic reasons. We construct the behavior change factor for the host population to account for different levels of infectiousness due to behavior distinction and behavior change. We establish the well-posedness of an initial boundary value problem of the new model. Sensitivity analysis shows that different risk distribution functions that are designed to adjust for spatial and geographic reasons have a large impact on the solution. / 1 / Li Guan

Production of hot peppers, Capsicum spp., in Jamaica is constrained by the aphid-transmitted potyviruses, tobacco etch virus (TEV) and potato virus Y (PVY). The virus epidemiology was not understood and no effective virus management system existed for these viruses. This study sought to identify possible management strategies for aphid-transmitted viruses of hot peppers in Jamaica, using TEV and Capsicum chinense, var. 'Scotch Bonnet' and 'West Indian Red', as models. Field spread of TEV to pepper was mainly by secondary spread from primary infections. Secondary infections were spatially correlated to primary infections for up to 25 meters. Natural infections of TEV were associated with aphid flight activity. Over 30 species of aphids were collected on pepper farms in St. Catherine parish. These aphids included five known vectors of TEV, Aphis gossypii Glover, A. craccivora Koch, A. spiraecola Patch, Lipaphis erysimi Hille Ris Lambers and M. persicae (Sulzer), and 12 new records for Jamaica, Aphis amaranthi Holman, Brachycaudus helichrysi (Kaltenbach),Capitophorus hippophaes (Walker), Geopemphigus floccosus (Moreira), Hysteroneura setariae (Thomas), Lipaphis erysimi Hille Ris Lambers, Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), Schizaphis rotundiventris (Signoret), Trichosiphonaphis poligoni (van der Goot), Uroleucon ambrosiae complex (Thomas) and Uroleucon pseudoambrosiae (Olive). A. amaranthi and U. ambrosiae were associated with TEV spread. Weeds on and near farms influenced the abundance and species of aphids captured. West Indian Red pepper showed tolerance to TEV. Scotch Bonnet pepper yield reduction was greater if plants were infected with TEV during the vegetative stage through flower initiation rather than after the start of fruit set. Stylet oil and reflective mulch used together delayed the incidence of TEV in pepper plots for over two months. TEV management programs should aim to delay the virus from infecting peppers during the first two months after transplanting. A risk analysis is proposed for management of TEV and other aphid-borne viruses. / Ph. D.

This dissertation presents a collection of manuscripts that describe development of models and model implementation to analyze impact of potential A(H7N9) pandemic influenza outbreak in the U.S. Though this virus is still only animal-to-human transmittable, it has potential to become human-to-human transmittable and trigger a pandemic. This work is motivated by the negative impact on human lives that this virus has already caused in China, and is intended to support public health officials in preparing to protect U.S. population from a potential outbreak of pandemic scale. An agent-based (AB) simulation model is used to replicate the social dynamics of the contacts between the infected and the susceptible individuals. The model updates at the end of each day the status of all individuals by estimating the infection probabilities. This considers the contact process and the contagiousness of the infected individuals given by the disease natural history of the virus. The model is implemented on sample outbreak scenarios in selected regions in the U.S. The sampling results are used to estimate disease burden for the whole U.S. The results are also used to examine the impact of various virus strengths as well as the efficacy of different intervention strategies in mitigating a pandemic burden. This dissertation, also characterizes the infection time during a A(H7N9) influenza pandemic. Continuous distributions including exponential, Weibull, and lognormal are considered as possible candidates to model the infection time. Based on the negative likelihood, lognormal distribution provides the best fit. Such characterization is important, as many critical questions about the pandemic impact can be answered from using the distribution. Finally, the dissertation focuses on assessing community preparedness to deal with pandemic outbreaks using resilience as a measure. Resilience considers the ability to recover quickly from a pandemic outbreak and is defined as a function of the percentage of healthy population at any time. The analysis, estimations, and metrics presented in this dissertation are new contributions to the literature and they offer helpful perspectives for the public health decision makers in preparing for a potential threat of A(H7N9) pandemic.

<I>Bean pod mottle virus </I>(BPMV, Genus <I>Comovirus</I>, Family: <I>Comoviridae</I>)is an important virus in soybean (<I>Glycine max</I> (L.) Merrill), causing quality and yield loss due to seed coat mottling and seed weight reduction. Although BPMV has been known in Virginia since 1958 and has always been regarded as causing negligible losses, its impact is changing as BPMV incidence has increased in many soybean growing areas of Virginia and the USA in general. From 1997 to 2001, a total of five BPMV isolates (V-W1, V-W2, V-S98-1, V-S98-15 and V-S01-10) were collected in Virginia and characterized. In this study, the effects of these isolates were studied, alone or with Soybean mosaic virus (SMV, Genus Potyvirus, Family Potyviridae) strain SMV G1, and isolates S98-51 and S98-52, on selected soybean cultivars. Individual isolates of BPMV showed variable symptom severity, and resulted in yield loss of between 40.4 to 58.1%, while SMV caused 23.7% in the most severe interactions. Up to 100% yield loss was realized from double inoculations of selected BPMV and SMV isolates, BPMV V-S98-1 + SMV S98-52 and BPMV S98-15 + SMV S98-52 on Hutcheson and Hutcheson Roundup Ready&#174; (BC5) soybeans, respectively. Time of inoculation, a critical factor in the impact of many virus diseases, affected seed coat mottling in four cultivars and seed weight in two cultivars, in tests with four BPMV isolates and three stages of soybean development. All BPMV isolates inoculated to plants at vegetative stage V1-V3 severely increased seed coat mottling and reduced seed weight than those inoculated at V4-V6 and reproductive stage R1-R3. Seedlings grown from non-mottled seeds germinated more uniformly had fewer thin-stemmed seedlings and grew faster than those grown from mottled seeds. Inoculation of various cultivars and breeding lines showed that there was no correlation between the severity of virus-induced foliar symptoms, relative accumulation of SMV, and extent of seed coat mottling. Thus, by avoiding the presence of BPMV at an early growth stage through proper timing of planting to avoid vectors, proper cultural practices like weed control, use of SMV free seeds, and chemical control, it is possible to greatly improve seed quality and reduce yield losses in soybean. / Ph. D.

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