Impact Of Control Strategies Research Articles

Impacts of control strategies, the Great Recession and weekday variations on NO2 columns above North American cities

The Ozone Monitoring Instrument (OMI) has been estimating NO2 columns from space for over 10 years, and these have been used to estimate emissions and emission trends for point and area sources all over the world. In this study we evaluate the trends in NO2 columns over 54 cities in the USA and Canada to identify the long term trends due to air quality policies, the impact of the Great Recession, and the weekday-weekend effect. A multiple linear regression model is used to fit annual, seasonal and weekly factors for individual swath retrievals along with the impact of temperature, wind speed and pixel size. For most cities, the correlation coefficients of the model fit ranges from 0.47 to 0.76. There have been strong reductions in NO2 columns, with annual decreases of up to 7% per year in most cities. During the years of the Great Recession, NO2 columns were as much as 30% lower than they would have been had they followed the linear annual trend. The analysis yielded insights into the timing of the reductions, with some cities in the northwest and in the east experiencing reductions in 2008 already, and most areas back to where they would have been based on the uniform trend by 2011. The analysis also finds that reductions in columns during the weekend vary significantly from city to city, with a range in reductions of 10%–30% on Saturdays, and 20%–50% on Sundays.

Small distances can keep bacteria at bay for days.

Transmission of pathogens between spatially separated hosts, i.e., indirect transmission, is a commonly encountered phenomenon important for epidemic pathogen spread. The routes of indirect transmission often remain untraced, making it difficult to develop control strategies. Here we used a tailor-made design to study indirect transmission experimentally, using two different zoonotic bacteria in broilers. Previous experiments using a single bacterial species yielded a delay in the onset of transmission, which we hypothesized to result from the interplay between diffusive motion of infectious material and decay of infectivity in the environment. Indeed, a mathematical model of diffusive pathogen transfer predicts a delay in transmission that depends both on the distance between hosts and on the magnitude of the pathogen decay rate. Our experiments, carried out with two bacterial species with very different decay rates in the environment, confirm the difference in transmission delay predicted by the model. These results imply that for control of an infectious agent, the time between the distant exposure and the infection event is important. To illustrate how this can work we analyzed data observed on the spread of vancomycin-resistant Enterococcus in an intensive care unit. Indeed, a delayed vancomycin-resistant Enterococcus transmission component was identified in these data, and this component disappeared in a study period in which the environment was thoroughly cleaned. Therefore, we suggest that the impact of control strategies against indirect transmission can be assessed using our model by estimating the control measures' effects on the diffusion coefficient and the pathogen decay rate.

Impact of control strategies for Varroa destructor on colony survival and health in northern and central regions of Italy

SummaryA comparison among four different summer strategies for the control of Varroa destructor was carried out from summer 2010 until spring 2011, in collaboration with national beekeepers associations in Italy. A total of 170 colonies located in Lazio, Piedmont, Tuscany, Veneto were involved. The control strategies included chemical treatments and biotechnical methods (thymol, formic acid, brood removal and brood interruption). In each colony, bee samples were collected before and after treatment to assess the quantity of Varroa destructor and Nosema spp. and the presence of the main honey bee viruses. Colony strength was assessed several times during the trial. The most effective strategies for maintaining low V. destructor infestation levels and higher colony survival in spring in all regions were brood interruption (caging of the queen for the duration of a brood cycle), followed by brood removal. Brood interruption was the only treatment which yielded a decrease in varroa infestation rates (from 4.36 mites/100 bees (5.61 SD) before treatment to 3.24 mites/100 bees (4.0 SD) after treatment, while the highest average overwintering index (ratio of spring vs. autumn bees) and a lower virus prevalence was observed in the brood removal group. Analyses for virus presence showed that in spring 2011 the most prevalent virus was DWV. Quantification of Nosema spp. spores showed that only N. ceranae was present, with regional differences in infection levels.

Impact of control strategies on Thrips tabaci and its predator Aeolothrips intermedius on onion crops

Thrips tabaci (Thysanoptera: Thripidae) is a major pest of onion worldwide. In 2011, research was conducted in a commercial onion field in northwestern Italy to: (i) assess the presence of autochthonous onion thrips predators on the crop; and (ii) evaluate the impact of the commonly used insecticides and alternative pest management strategies on onion thrips and its autochthonous predators. Toxicity of the active ingredients on local populations of onion thrips and its predatory thrips was also evaluated in laboratory bioassays. During field surveys, the highest and lowest thrips infestations were observed in plots treated with lambda-cyhalothrin and spinosad, respectively. The effectiveness of spinosad on T. tabaci was also confirmed in laboratory bioassays. The dominant zoophagous species Aeolothrips intermedius (Thysanoptera: Aeolothripidae) was more adversely affected by treatment with lambda-cyhalothrin, confirmed by a decrease in predator/prey ratios. The use of spinosad and acibenzolar-S-methyl is suggested as an alternative to conventional insecticides for the preservation of A. intermedius, which proved to be a potential biological control agent of T. tabaci.

Impact of control strategies on bellyache bush (Jatropha gossypiifolia L.) mortality, seedling recruitment, population dynamics, pasture yield and cost analysis

Bellyache bush (Jatropha gossypiifolia L.) is an invasive weed that has the potential to greatly reduce biodiversity and pasture productivity in northern Australia’s rangelands. This paper reports an approach to develop best practice options for controlling medium to dense infestations of bellyache bush using combinations of control methods. The efficacy of five single treatments including foliar spraying, slashing, stick raking, burning and do nothing (control) were compared against 15 combinations of these treatments over 4 successive years. Treatments were evaluated using several attributes, including plant mortality, changes in population demographics, seedling recruitment, pasture yield and cost of treatment. Foliar spraying once each year for 4 years proved the most cost-effective control strategy, with no bellyache bush plants recorded at the end of the study. Single applications of slashing, stick raking and to a lesser extent burning, when followed up with foliar spraying also led to significantly reduced densities of bellyache bush and changed the population from a growing one to a declining one. Total experimental cost estimates over 4 successive years for treatments where burning, stick raking, foliar spraying, and slashing were followed with foliar spraying were AU$408, AU$584, AU$802 and AU$789 ha–1, respectively. Maximum pasture yield of 5.4 t ha–1 occurred with repeated foliar spraying. This study recommends that treatment combinations using either foliar spraying alone or as a follow up with slashing, stick raking or burning are best practice options following consideration of the level of control, changes in pasture yield and cost effectiveness.

The impact of control strategies on the management of returnable transport items

This research examines the impact of different control strategies on the management of returnable transport items (RTIs) in closed-loop supply chains. A simulation model is developed based on an empirical case and is used to explore different scenarios. The results suggest that the choice of control strategy has a significant impact on investments and operating costs, and that RTI shrinkage can be controlled either through the use of tracking systems, or choice of control strategy. Moreover, a simulation-based method for estimating the fleet size required to operate the system for the different strategies is presented.

Effects of host social hierarchy on disease persistence

The effects of social hierarchy on population dynamics and epidemiology are examined through a model which contains a number of fundamental features of hierarchical systems, but is simple enough to allow analytical insight. In order to allow for differences in birth rates, contact rates and movement rates among different sets of individuals the population is first divided into subgroups representing levels in the hierarchy. Movement, representing dominance challenges, is allowed between any two levels, giving a completely connected network. The model includes hierarchical effects by introducing a set of dominance parameters which affect birth rates in each social level and movement rates between social levels, dependent upon their rank. Although natural hierarchies vary greatly in form, the skewing of contact patterns, introduced here through non-uniform dominance parameters, has marked effects on the spread of disease. A simple homogeneous mixing differential equation model of a disease with SI dynamics in a population subject to simple birth and death process is presented and it is shown that the hierarchical model tends to this as certain parameter regions are approached. Outside of these parameter regions correlations within the system give rise to deviations from the simple theory. A Gaussian moment closure scheme is developed which extends the homogeneous model in order to take account of correlations arising from the hierarchical structure, and it is shown that the results are in reasonable agreement with simulations across a range of parameters. This approach helps to elucidate the origin of hierarchical effects and shows that it may be straightforward to relate the correlations in the model to measurable quantities which could be used to determine the importance of hierarchical corrections. Overall, hierarchical effects decrease the levels of disease present in a given population compared to a homogeneous unstructured model, but show higher levels of disease than structured models with no hierarchy. The separation between these three models is greatest when the rate of dominance challenges is low, reducing mixing, and when the disease prevalence is low. This suggests that these effects will often need to be considered in models being used to examine the impact of control strategies where the low disease prevalence behaviour of a model is critical.

Quantifying the risk from ovine BSE and the impact of control strategies

Although no naturally infected sheep with bovine spongiform encephalopathy (BSE) has ever been discovered, it remains possible that BSE once infected the UK sheep population, has been transmitted between sheep, and is still present today. We constructed a mathematical model to assess the current maximum theoretical exposure to consumers from BSE-infected ovine material and to estimate the risk reduction that could be achieved by abattoir-based control options if BSE-infected sheep were ever found in the national flock. We predict that, if present, the exposure to consumers from a single BSE-infected sheep would be high: one sheep, close to the end of its incubation period, is likely to contribute 10-1000 times more infectious material than a fully infectious cow. Furthermore, 30% of this exposure comes from infectivity residing in lymphatic and peripheral tissue that cannot be completely removed from a carcass. We are 95% confident that throughout Great Britain, no more than four sheep flocks currently harbour an ongoing BSE epidemic. However, since the exposure from a single infected sheep is high, the annual human exposure from four 'typical' BSE-infected flocks could be considerable. Small reductions in exposure could be achieved by strategies based on tissue testing, a 12-month age restriction or expanded definitions of high-risk tissues. A six-month age restriction is likely to be more effective and genotype-based strategies the most effective.

Measurement needs for developing and assessing ozone-control strategies

The monitoring programs needed to design control strategies differ from those required to assess the impact of the strategies on air quality. The former are short-term and intensive. They are designed to obtain the data required to apply an urban-scale grid model, like the Urban Airshed Model, or a combination of an urban-scale and regional-scale model, like the Regional Oxidant Model, to an area without having to assume important input data. Such measurements include three-dimensional pollutant and meteorological measurements throughout the modeling domain. Detailed and accurate emissions inventories are also required. Model validation should compare not only the O3 predictions with actual data, but also include comparisons for NO x , individual volatile organic compounds (VOC), and if possible, additional species such as PAN, H2O2, formaldehyde, and HNO3. To assess the impact of control strategies, long-term monitoring networks that measure O3, NO x and speciated VOC are needed. O3 trends should be examined using robust, meteorologically-adjusted O3 statistics. Such statistics need to be related to a robust National Ambient Air Quality Standard.