抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

世界経済・社会統計 = World development indicators

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world's future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture's environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing 'yield gaps' on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

https://escholarship.org/content/qt6xw5g085/qt6xw5g085.pdf?t=ovfwpc

Solutions for a cultivated planet

Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.

/pdf/use-of-u-s-croplands-for-biofuels-increases-greenhouse-gases-48xnl16nx3.pdf

Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change

Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

/pdf/biofuels-from-microalgae-a-review-of-technologies-for-1t1wwr5e69.pdf

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

A team of U.S. analysts visited China to assess the potential for use of distillers dried grain plus solubles (DDGS) in China's livestock sector. They examined the economics of the use of DDGS in feeds, the policy issues surrounding the use of the product, and transportation-logistic constraints in the expansion of DDGS imports. The team collected actual and secondary data to conduct a micro-economic analysis of the impact of DDGS on feed cost, solicited official and expert opinions through interviews, and conducted site visits. They found the development of the DDGS import market in China to be very promising. The microeconomic analysis showed a clear economic incentive for feed millers and livestock producers to use DDGS in their feed ration, with a potential savings of $1 per hundredweight of mixed feed, representing a 6% feed cost savings. Moreover, China has the livestock numbers to support a DDGS market. Concerns about myctoxin contamination and nutrient profile variability must be addressed, however. Clearly differentiating imported DDGS from domestic DDGS is key in positioning U.S. DDGS in the Chinese market. Also, a science-based, and pro-active approach is needed to address policy-induced barriers.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1005&context=card_staffreports

Assessing China's Potential Import Demand for Distillers Dried Grain: Implications for Grain Trade

We summarize a large set of recent simulations and policy analyses based on FAPRI’s world multimarket, partial-equilibrium models. We first quantify and project the emergence of biofuel markets in US and world agriculture for the coming decade. Then, we perturb the models with incremental shocks in US and world ethanol consumption in deviation from this projected emergence to assess their effects on world agricultural and food markets. Various food−biofuel trade-offs are quantified and examined. Increases in food prices are moderate for the US ethanol expansion and even smaller for the ethanol expansion outside the United States, which is based on sugarcane feedstock, and which has little feedback on other markets. With the US expansion, the high protection in the US ethanol market limits potential adjustments in the world ethanol markets and increases the demand for feedstock within the United States. Changes in US grain and oilseed market prices propagate to world markets, as the United States is a large exporter in these markets. With changes in world prices, land allocation in the rest of the world responds to the new relative prices as in the United States but with smaller magnitudes because price transmission to local markets is less than full.

The Global Bioenergy Expansion: How Large Are the Food−Fuel Trade-Offs?

The study finds that the emergence and expansion of the ethanol sector was associated with a fundamental transformation of the integration of the energy and agricultural sectors. In particular, the correlation structure between crude oil and grain prices increased dramatically, becoming more statistically significant, and with all anomalous signs corrected. Before the ethanol boom, the correlation of the crude oil price and corn was -0.117. It increased to 0.876 in the ethanol boom period. Soymeal correlation increased from 0.182 to 0.909, and distillers dried grains with solubles increased from -0.252 to 0.834. As a result, the energy market is also now impacting the livestock sector through feed costs, which account for more than half of total costs. From a weak correlation of the crude oil price and feed cost of 0.02, correlation increased to 0.89 during the ethanol boom period. Hence, any variability originating from the energy sector will also now have stronger ripple effects in the livestock sector.

The Impact of the Crude Oil Price on the Livestock Sector under a Regime of Integrated Energy and Grain Markets

The US pork industry routinely adds antibiotics to rations of weaned pigs both to prevent illness before symptoms emerge and to increase growth rates. The EU is in the process of restricting feed use of antibiotics, and the U.S. is currently reviewing the practice. The strategic issue facing US pork producers is whether another food safety dispute with the EU is worthwhile. This paper evaluates the economic impact of such a ban in the U.S. The analysis uses a set of technical assumptions derived from the experience of a similar ban in Sweden and finds such a ban would increase production costs per head between $5.24 and $6.05; net profit would decline $0.79 per head. On the consumer side, the effects of a ban would raise the retail price of pork by 5 cents per pound.

Jacinto F. Fabiosa

Papers

Assessing China's Potential Import Demand for Distillers Dried Grain: Implications for Grain Trade

The Global Bioenergy Expansion: How Large Are the Food−Fuel Trade-Offs?

The Impact of the Crude Oil Price on the Livestock Sector under a Regime of Integrated Energy and Grain Markets

Economic Impact of a Ban on the Use of Over the Counter Antibiotics in U.S. Swine Rations

The FAPRI global modeling system and outlook process.