The epidemiology of avian influenza in the Mekong River Delta of Viet Nam : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University

Between December 2003 and December 2012 a total of 4,349 commune-level outbreaks of highly pathogenic avian influenza (HPAI) H5N1 were recorded in domestic poultry flocks throughout Viet Nam. Throughout the same period there were 123 cases of HPAI H5N1 virus infection in humans, 61 of which were fatal. The studies presented in this thesis are largely based on data collected from a prospective cohort study of domestic poultry in 157 flocks in the Mekong River Delta of Viet Nam between December 2008 and April 2010. The first research chapter (Chapter 3) provides a description of the components and design features of an animal health decision support system for use in Viet Nam. While not explicitly used for the prospective cohort study, the motivation for development of this system was to provide a means for recording and storing animal health data so as to minimise duplication of data collection efforts. A feature of the system is the inclusion of a flexible reporting tool that provides system users with the capability of developing reports to deal with virtually any animal health issue, not just avian influenza. The intent of this system is that it will allow the Vietnamese Department of Animal Health to identify and respond to existing and emerging threats to animal health in a timely and cost-effective manner. Our descriptive analyses (Chapter 4) show that the overall incidence rate of influenza Type A and H5 virus infection in village poultry was relatively high throughout the 17-month follow up period of the prospective cohort study. This implies that interventions such as vaccination, movement controls and biosecurity measures need to be carried out continuously throughout the year rather than focusing only on the established high risk periods. Broiler ducks had an incidence rate of influenza H5 virus infection that was approximately four times greater than that of layer ducks and in-contact species. This indicates that broiler ducks should be the focus of disease surveillance and control strategies. Survival analyses, accounting for the intermittent sampling of birds throughout the follow-up period of the prospective cohort study (by interval censoring) and for the hierarchical structure of the data set were used to determine the duration of immunity to H5N1 following vaccination (Chapter 5). After adjusting for the effect of known confounders and unmeasured variation at the flock level the duration of immunity to H5N1 following vaccination was estimated to be in the order of 56 (95% CI 51 – 61) days, considerably shorter than the duration of immunity previously reported in laboratory-based studies. A multilevel logistic regression analysis carried out to identify risk factors for influenza Type A virus infection in the prospective cohort study poultry population found that the relative contribution of unmeasured flock- and bird-level factors on influenza Type A virus infection risk were approximately equal (Chapter 6). Most of the significant fixed-effects were flock-level exposures indicating that interventions to reduce the maintenance and transmission of influenza Type A virus in domestic poultry in this area of Viet Nam should be applied at the individual bird and individual flock level. Chapter 7 presents the results of a study of poultry movement events that occurred in the south of Viet Nam between September 2009 and June 2010. Poultry were more likely to be moved between communes with provincial roads and between communes with more than 1,000 poultryowning households. Assuming a causal relationship exists between a commune-to-commune poultry movement activity and HPAI H5N1 risk, a conclusion from this study was that communes more likely to be connected to others as a result of movement should be targeted for disease control and surveillance. The findings presented in each of these chapters of this thesis have broadened our knowledge of the epidemiology of not only the HPAI H5N1 subtype, but influenza Type A viruses in poultry in general. It should be stressed that the methodological techniques that have been used in this thesis can be applied to a wide range of animal health issues, not just HPAI H5N1

A preliminary analysis on the socioeconomic situation of coastal fishing communities in Vietnam

Fish production in Vietnam increased rapidly from 420 000 t in 1981 to 1 130 680 t in 1998. Likewise, there was an expansion in the number of motorized fishing boats from 29 584 units with an average horsepower (HP) of 19.8 boat-1 in 1981 to 71 800 units with an average HP of 26.2 in 1998. In 1995, fish production was valued at VN$2 475 billion (US$0.02 billion at 1 US$= 11 041 VN$; source: oanda. com). However 93% of the total fishing boats in Vietnam have engine capacity of less than 84 HP, thus fishing operations are still small scale and fishing grounds are limited to the coastal waters. The infrastructure facilities for fishing operations and post-harvest are still minimal. Fisheries contribute 3% of the gross domestic product (GDP) in Vietnam. In 1990, the GDP of fisheries was VN$1 281 billion and reached VN$6 664 billion (US$0.60 billion) in 1995. Fisheries labor in Vietnam includes labor for aquaculture, processing, fishery services and fishing. Fisheries labor increased from 1 860 000 persons to 3 030 000 giving a relative increase of 63% from 1990 to 1995. The average level of fish consumption in Vietnam is estimated at 13.5 kgâ•–capita-1. In 1980, there were 28 021 motorized fishing boats that steadily increased to 71 800 in 1998. Likewise, the average engine capacity per boat increased from 19.8 HP in 1980 to 26.2 HP in 1998. The types of fishing gear that provide substantive catch in Vietnam are the trawl, purse seine, gillnet, long line, hand line, lift net and stick-held falling net. The fishing grounds in Vietnam can be classified into: (a) North: trawl, gillnet, lift net, purse seine, hook and line fishery; (b) Central: purse seine, lift net, gillnet, trawl fishery; and (c) South: trawl, purse seine, gillnet and line fishery. In terms of fish catch and net profit contribution the most important are the trawl and purse seine fisheries. Fish production in the Southern provinces is more developed compared to the northern and central provinces. Most of the commercial scale fishing vessels bring trash fish or by-catch to the shore for fish sauce or fish powder processing. Only trawlers that fish offshore and thus stay at sea for several days discard the trash fish. An attempt to estimate the maximum sustainable yield (MSY) of the coastal fishery resources in Vietnam was made. Using the Schaefer and Fox Models, it was found that MSY is equal to 976 378 t and 1 006 850 t respectively, as against the annual catch of 1 130 660 t, implying biological over-fishing. Thus, the total fish catch in the traditional fishing areas of Vietnam is beyond the sustainable limit of 582 000 t. The Government of Vietnam has therefore developed policies and plans to reduce the fishing pressure on the coastal waters and pursue development of offshore fisheries.Fishery resources, Fishery surveys, Catch/effort, Trawling, Population characteristics, Biomass, Coastal fisheries, Mathematical models, Marine fisheries, Ecosystems, Socioeconomic aspects, Artisanal fishing, Economic benefits, Fishery industry, Capture fishery economics, Fish consumption, Fishing gear, Fishery policy, Yield, ISEW, Vietnam,

Consumption and Investment Optimization under Constraints

We analyze a problem of maximization of expected terminal wealth and consumption under constraints in a general framework including financial models with constrained portfolios, labor income and large investor models. By using general optional decomposition under constraints in a multiplicative form, we first develop a dual formulation under minimal assumption modeled as in Pham and Mnif (2002). We then are able to prove an existence and uniqueness of an optimal solution to primal and to the corresponding dual problem. An optimal investment and consumption plan to the original problem then can be found by convex duality, similarly to the case considered by Kramkov and Schachermayer (1999).Stochastic Optimization, Consumption and Investment Optimization, Duality Theory, Convex and State Constraints, Utility Maximization, Optional Decomposition, Minimax Theorem}

Utility Maximization in Imperfected Markets

We analyze a problem of maximization of expected terminal wealth and consumption in markets with some ``imperfection'', such as constraints on the permitted portfolios, labor income, or/and nonlinearity of portfolio dynamics. By using general optional decomposition under constraints in multiplicative form, we develop a dual formulation. Then, under some conditions imposed on the model setting and the utility functions, we are able to prove an existence and uniqueness of an optimal solution to primal and to the corresponding dual problem by convex duality.Stochastic Optimization, Utility Optimization, Duality Theory, Convex and State Constraints, Optional Decomposition, Optimal Stopping

Investment Optimization under Constraints

We analyze general stochastic optimization financial problems under constraints in a general framework, which includes financial models with some ``imperfection'', such as constrained portfolios, labor income, random endowment and large investor models. By using general optional decomposition under constraints in a multiplicative form, we first develop a dual formulation under minimal assumption modeled as in Pham and Mnif (2002), Long (2002). We then are able to prove an existence and uniqueness of an optimal solution to primal and to the corresponding dual problem. An optimal investment to the original problem then can be found by convex duality, similarly to the case considered by Kramkov and Schachermayer (1999).Stochastic Optimization, Investment Optimization, Duality Theory, Convex and State Constraints, Optional Decomposition

Joint Data compression and Computation offloading in Hierarchical Fog-Cloud Systems

Data compression has the potential to significantly improve the computation offloading performance in hierarchical fog-cloud systems. However, it remains unknown how to optimally determine the compression ratio jointly with the computation offloading decisions and the resource allocation. This joint optimization problem is studied in the current paper where we aim to minimize the maximum weighted energy and service delay cost (WEDC) of all users. First, we consider a scenario where data compression is performed only at the mobile users. We prove that the optimal offloading decisions have a threshold structure. Moreover, a novel three-step approach employing convexification techniques is developed to optimize the compression ratios and the resource allocation. Then, we address the more general design where data compression is performed at both the mobile users and the fog server. We propose three efficient algorithms to overcome the strong coupling between the offloading decisions and resource allocation. We show that the proposed optimal algorithm for data compression at only the mobile users can reduce the WEDC by a few hundred percent compared to computation offloading strategies that do not leverage data compression or use sub-optimal optimization approaches. Besides, the proposed algorithms for additional data compression at the fog server can further reduce the WEDC

Real-time Optimal Resource Allocation for Embedded UAV Communication Systems

We consider device-to-device (D2D) wireless information and power transfer systems using an unmanned aerial vehicle (UAV) as a relay-assisted node. As the energy capacity and flight time of UAVs is limited, a significant issue in deploying UAV is to manage energy consumption in real-time application, which is proportional to the UAV transmit power. To tackle this important issue, we develop a real-time resource allocation algorithm for maximizing the energy efficiency by jointly optimizing the energy-harvesting time and power control for the considered (D2D) communication embedded with UAV. We demonstrate the effectiveness of the proposed algorithms as running time for solving them can be conducted in milliseconds.Comment: 11 pages, 5 figures, 1 table. This paper is accepted for publication on IEEE Wireless Communications Letter