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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia 6 Technologies for Improving Animal Health and Production ROLES OF ANIMALS IN SOCIETY The importance of livestock in the economies of developing countries can be measured in terms of human health, as a contribution to gross domestic product, as a pathway out of poverty, and as a buffer against unforeseen disasters often faced by small-holder farmers. In addition to the direct financial benefits they provide, animals play many roles for smallholder farmers: they provide food, manure (as a soil amendment or fuel), traction, a savings mechanism, and social status (Randolph et al., 2007). When household members on crop-livestock farms in western Kenya were asked why their incomes had risen above the rural Kenyan poverty line (US$0.53/day), the top three reasons given were off-farm employment of a family member, production of cash crops, and livestock acquisition (Kristjanson et al., 2004). More than half the farmers who remained poor cited funeral expenses that typically involved the slaughter of livestock. Animals are perceived by farmers to be a useful hedge against drought, pests, and health problems. However, many farmers appear unwilling to sell animals even in stressful times, so economists debate whether they truly serve as a financial buffer (Dercon, 1998; Fafchamps et al., 1998). Animal protein plays an important role in human nutrition in sub-Saharan Africa (SSA) and South Asia (SA). Small amounts of meat or milk added to typical diets of Kenyan primary-school children increased their performance in school, improved results on cognitive-ability tests and activity levels, and reduced the incidence of stunted growth (Neumann et al., 2003).
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia This chapter discusses the farming systems in which animals are produced in SSA and SA and describes technologies for improving the health nutrition of food animals, the genetic foundation of food animal herds, and the protection of animals against disease. ANIMAL PRODUCTION SYSTEMS Animals are raised in several production systems in SSA and SA, each of which is constrained in different ways. Interventions to improve livestock (and the welfare of farmers) in each system must take into account the nature of its relationship to sources of animal feed or forage, the availability of food-processing facilities, and access to the intermediary or direct consumer markets for meat and dairy products. System modeling may be one way to envision the effects of interventions, not only on improving animal productivity but also on increasing income, reducing poverty, and preventing environmental damage associated with livestock production (Box 6-1) (Charles Nicholson, Cornell University, presentation to committee, October 15, 2007). Of the 687 million poor who own livestock, 20 percent produce them in extensive systems (see Box 6-2), 57 percent live on mixed crop-livestock farms, and 23 percent are landless, peri-urban producers (Devendra et al., 2005). In Asia, more than 95 percent of the ruminants and many swine and poultry are raised on small crop-livestock farms. Those operations typically are land-constrained—often less than a hectare—so feed availability is likely to pose a problem. Well-managed crop-livestock farms can take advantage of the value added by livestock by using manure to prevent soil-nutrient depletion. As the demand for meat increases, mixed crop-livestock farms are intensifying and increasing the risks of environmental problems associated with agriculture. The landless livestock systems, mostly in peri-urban areas, typically include swine, poultry, and ruminants. Because very little land is involved, less than 10 percent of the feed resources are produced where the animals are housed (Seré and Steinfeld, 1996). The peri-urban farmers, especially those raising poultry and swine, rely more on concentrates for feeds and are likely to be adversely affected when grain prices increase, for example, in response to international demand for biofuels. The use of byproducts from processing human food could potentially provide valuable feed resources for these farmers. There is a need for improved food processing capabilities (see Box 6-3) that would help small farmers to have better access to markets (Delgado, 2005). The accumulation of nutrients (animal waste) often leads to contamination of water supplies and health issues related to animal density and proximity to people; the use of animal waste for biogas production would
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia BOX 6-1 Environmental Effects of Livestock Production A 400-page review of livestock production in the developing and developed worlds describes its associated environmental effects, including land degradation, contributions to greenhouse gas production (carbon dioxide, CO2; methane, CH4; and nitrogen dioxide, NO2), depletion and contamination of water supplies, spread of zoonotic diseases through poor animal and manure management, and reduction in biodiversity (Steinfeld et al., 2006). The extent to which livestock contribute to environmental problems depends on the production system, but a comprehensive evaluation of livestock production systems is needed, including marketing, land tenure arrangements, and germane policies to minimize adverse effects. Scenario testing of alternative strategies will require robust models to evaluate the effects of changes in management, marketing, and policy. For example, it is estimated that livestock contribute about 9 percent to total anthropogenic CO2 production and 35 to 40 percent of CH4 emission, including those from enteric fermentation, manure management, and livestock-associated fertilizer application, tillage, feed processing, and transportation (Steinfeld et al., 2006). Effective manure management and use of biogas may reduce emissions by as much as 75 percent in warm climates. However, manure gas emissions are affected by temperature, moisture, animal diet, physiological status of the animal, and storage methods, so current predictions of emissions all have huge coefficients of variation. Both data and appropriate models are needed to predict which parts of the system are amenable to useful manipulation to decrease greenhouse gas emissions. be an area worth further exploration. In many cases, the term peri-urban is essentially used to describe agriculture in the slums, where poor sanitation, disease, and non-potable water already pose serious problems. Peri-urban swine and poultry systems are already a major source of food for city dwellers, but because of the hefty initial capital requirements and environmental considerations they are unlikely to become pathways out of poverty. IMPROVING ANIMAL NUTRITION Many of the animals raised by small farmers in SSA and SA suffer from poor nutrition. As a result, they grow slowly, produce small amounts of milk or meat, have low reproductive rates, and are vulnerable to disease, even from birth. This section discusses some current and emerging opportunities to decrease mortality in young livestock and improve the nutrition of farm animals.
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia BOX 6-2 Animal Production in Extensive Rangeland Systems In many semi-arid and arid areas in Africa where rainfall is insufficient for reliable cereal harvests, animals contribute more than 80 percent of the agricultural GDP (Winrock International, 1992). The extensive livestock systems in the dry lands produce about 10 percent of the global meat supply, but the areas where these systems dominate make up about one-fourth of the world’s land mass, and low rainfall makes crop production impossible or very risky. Livestock production is the primary food- and income-generating activity for the people in those areas. When market values were assigned to home-consumed goods in a study of the Gabra of northern Kenya, 76 percent of the total was from home-consumed milk and meat, and 21 percent was from goods purchased with revenue from livestock sales, so only 3 percent of household consumption was from non-livestock sources (McPeak, 2003). More people in the world depend on sheep and goats for their survival than any other species; these small ruminants therefore play an important role in the sustainability of humans. Many parts of SSA either do not have the grain-based diets for commercial production of monogastrics such as chickens and pigs or may have religious practices that are not conducive to the development of a swine industry. Also, the lack of disease surveillance, particularly in poor rural areas, makes it difficult to raise swine and poultry in the countries most affected by disease. Consequently, increasing the knowledge of the genetics, physiology, breeding, nutrition, and diseases of small ruminants and the social structures of pastoralism is of paramount importance. It can be argued that the populations of pastoralists and herders are small and that development resources would be better spent elsewhere. That choice would be devastating to the herding populations of Niger, Burkina Faso, Mali, Chad, and Ethiopia, the five Reducing Preweaning Mortality A nutritional intervention for decreasing mortality in young livestock would include the use of colostrum for neonates. Colostrum contains high levels of energy and nutritionally important proteins, and neonates depend on the early infusion of nutrients to maintain body temperature because their energy stores are low at birth. More information on neonatal passive immunity is provided later in this chapter. Improving Grass Forage Many forage-fed animals in the tropics grow slowly and produce small amounts of milk because their diets are inadequate in protein, energy, and micronutrients. The types of forage available to the animals are mainly the
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia countries ranked at the bottom of the UN human development report in 2005. Likewise, drier areas of central and southern Asia, where livestock dominate, suffer from extreme poverty. Dryland livestock production is heavily affected by low and variable rainfall and is thus vulnerable to the effects of climate change. In harsh environments, survival of animals and their owners depends on access to somewhat less marginal areas for part of the year. Changes in land tenure and increases in protected areas have decreased the mobility needed to avert overgrazing and to obtain access to feed reserves during dry seasons. Suboptimal distribution of animals results in localized degradation surrounded by range that remains productive. Post-drought restocking programs often provide families that have lost all their animals with one or two replacements despite data from northern Kenya and southern Ethiopia that show that at least five cattle are needed for self-sufficiency (McPeak, 2003). Nutritional inadequacy is a severe seasonal constraint in dry areas, but pasture improvement of extensive land systems is extremely difficult. Farmers lack the equipment and improved forage varieties needed for pasture establishment, and free-ranging animals often consume newly planted pastures. Although there is potential to improve livestock productivity in dry areas, many of the most feasible solutions involve integrated applications of current knowledge rather than new technologies. Biophysical and socio-economic models that include policy considerations that influence rangeland productivity could be used to predict effects of fluctuations in herd sizes, rainfall, and land tenure. Early warning systems and drought predictions could benefit herders in extensive systems provided they were mobile enough to access reserve pastures or were willing to sell stock. Efforts of that sort are under way, but more comprehensive data and better modeling techniques are both needed. C4 grasses (so named for the metabolic pathway used to fix carbon dioxide). The C4 grasses that predominate in the tropics are less digestible than temperate C3 grasses and have low energy and protein content. As the data in Figure 6-1 show, only 45 percent of the 80 tropical feed samples tested met the maintenance requirements for both protein and energy and 30 percent of the samples were inadequate in both (Van Soest, 1994). Until recently, there was little work on characterization of forage traits that need improvement, and temperate forage still receives far more attention than that grown in the tropics (Spangenberg, 2005; Smith et al., 2007). In general, tropical forage plants have received little attention from plant breeders with a few notable exceptions: alfalfa, which is grown in some tropical highlands; Brachiaria spp.; Pennisetum purpureum (elephant or Napier grass); and Panicum maximum (Guinea, colonial, or Tanganyika grass (Jank et al., 2005).
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia BOX 6-3 Food Processing and Production Post-harvest mishandling of animal products results in substantial product losses and health hazards due to foodborne disease, but lack of refrigeration, inadequacy of fly control, and contaminated water supplies make preservation of highly perishable products difficult. Because risk of contracting foodborne disease is higher by as much as 3,000 percent in malnourished populations (Morris and Potter, 1997), appropriate control is particularly important in food-insecure areas. There are opportunities for local improvements in preserving meat, milk, and fish. In developing countries, people rely on drying, salting, and fermentation for food preservation because of capital constraints and lack of electricity, whereas people in developed countries depend more on refrigeration, canning, freezing, dehydration, and fermentation. Traditional fermentation is used widely around the world (Steinkraus, 2002), but there are promising improvements in the use of bacterial inocula that have nutritional benefits or that stimulate production of bacteriocins to reduce microbial contamination. Amino acid profiles and contents of vitamins and protein may be improved through fermentation. Much is known about these technologies, but adaptive research is needed to ensure their effectiveness in low-resource environments. Investment in interdisciplinary adaptive research in African or Asian universities would both provide better methods to preserve animal-source foods and address the pressing need for more people with expertise in food safety. Such research should include the Hazard Analysis and Critical Control Point approach, which focuses on areas where significant improvements can be made. The collections of germplasm of tropical forage are poorly funded, and loss of current accessions is threatened. The collections include diverse accessions that may be important sources of disease resistance, increase in digestibility, or increase in biomass production. For example, the most recent outbreak of a smut (Ustilago kamerunensis) is affecting Napier grass. In much of eastern and southern Africa, farmers rely heavily on Napier grass because it produces copious amounts of reasonably high-quality forage. The smut has the potential to affect the small-holder dairy industry seriously and has already reduced forage yields in much of the Kenyan highlands (Farrell et al., 2002; Mwendia et al., 2007). Research to understand smut biology and to develop resistant strains of Napier grass is important for the rapidly growing dairy industry in the Kenyan highlands. As noted in Chapter 3, a better understanding of plant chemistry and lignin synthesis could help plant breeding programs to improve the nutritional value of forage because the lignin cross-linkages affect whether
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia FIGURE 6-1 Digestibility and crude protein content of tropical grasses (fertilized and unfertilized) and legumes and their adequacy in meeting maintenance requirements of ruminants. NOTE: 52 percent dry matter digestibility and 8 percent crude protein. SOURCE: Reprinted from Peter J. Van Soest: Nutritional Ecology of the Ruminant, Second Edition. Copyright © 1982 by P. J. Van Soest. Copyright © 1994 by Cornell University. Used by permission of the publisher, Cornell University Press. plants are easily digested (Spangenberg, 2005). There may be advantages in attaching work on this problem to the burgeoning international interest in biofuels, such as switchgrass. There is a common interest in understanding how lignin cross-linkages can be broken down, whether in the context of biofuels or with respect to the processes occurring in forage digestion by ruminants (Box 6-4). Improving Legume Forage In temperate areas, legumes, especially alfalfa and clover, are high-protein, highly digestible forage that permit cows to sustain milk production as high as 20 kg/day on forage alone. In the tropics, however, many
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia BOX 6-4 Rumen Function, Fiber Digestion, and Metagenomics Ruminants will probably be important in livestock strategies to assist the poor (Delgado, 2005), therefore their ability to convert locally available feedstuffs to animal products should be improved. Increasing the efficiency of the ruminal microorganisms that play important roles in fiber digestion and nitrogen metabolism will improve animal productivity. When Hungate (1966) published The Rumen and Its Microbes, about 23 bacterial species were thought to play prominent roles in ruminal metabolism; by 1996, the number exceeded 200 (Krause and Russell, 1996). When several discrete ribosomal DNA libraries were analyzed, 341 operational taxonomic units of organisms were identified (Edwards et al., 2004); this indicated that culture-based estimates of ruminal organisms greatly underestimated ruminal diversity. Simple identification of individual species is far less important than understanding the functions of microbial populations and relating them to sequence-based information to draw ecological inferences (Handelsman, 2004). The recent study of gypsy moth gut microflora that included quorum sensing, the coordination of biological functions among bacteria, and identification of cell signaling mechanisms (Guan et al., 2007) is an example of the type of research needed to improve ruminal fiber digestion and nitrogen metabolism and to reduce methane production. Because the techniques needed for the study of the rumen are similar to those required for the study of other microbial systems—including soils, food fermentation (such as that of yogurt and cheese), and biofuel production—emphasis on various methods for studying microbial ecology would have broad benefits. Not only is ruminal microbial diversity much greater than early estimates suggested, but the enzyme systems involved in lignocellulosic degradation are much more complex (Huang and Forsberg, 1990; White et al., 1990; Bayer et al., 1998). Each bacterium has many types of enzymes (for example, endoglucanases, exoglucanases, cellobiohydrolases, and xylanases) and many enzymes with overlapping activities. Our knowledge of the enzymes remains incomplete, and novel hydrolases are being discovered (Ferrer et al., 2005). In some cellulolytic anaerobic bacteria (such as Clostridium thermocellum, Ruminococcus albus, and Ruminococcus flavefaciens), the diverse enzymes are organized by scaffolding proteins into cellulosomes in which dockerins permit substrate binding and efficient cellulose degradation (Bayer et al., 2004). Much has been learned in the last 20 years about the functions and organization of cellulosomes and their many enzymes, but this remains a fertile field of inquiry. Recent advances in genomics and proteomics should assist in the research, but the inability to transform and genetically manipulate ruminal microorganisms constrains progress.
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia promising legume species contain high concentrations of anti-nutritional factors (such as proanthocyanidins, hydrolyzable tannins, alkaloids, and terpenoids) that confer disease resistance on the plants and deter herbivory. Condensed tannins have both beneficial and deleterious effects on domestic animals (Mueller-Harvey, 2006). The adverse effects of consuming high-tannin forage include lower feed intake, lower protein and dry matter digestibility, inhibition of microbial and mammalian enzymes, reduced live weight gain and milk yield, and systemic effects that are due to absorption of phenolics and are sometimes offset by lower urinary nitrogen loss, greater parasite resistance, and improved efficiency of nutrient use (Mueller-Harvey, 2006). The apparently contradictory research results are due largely to the heterogeneity of tannin structures and to variation in the quantities ingested. Achieving the goal of developing disease-resistant legumes that provide animals with needed nutrients requires research on tannin chemistry linked to legume breeding programs. Progress has been made in understanding some aspects of tannin synthesis, but the polymerization process that affects tannin chemistry and anti-nutritive effects remains poorly understood (Xie and Dixon, 2005). EXISTING AND EVOLVING TECHNOLOGIES FOR IMPROVING ANIMAL GERMPLASM Since the beginning of domestication of animals, substantial progress has been made in improving their characteristics as food and fiber producers by selectively mating individual animals that had advantageous traits (phenotypes). The importance of phenotypic information is sometimes lost in this age of genomics, and it is astonishing to recognize that animal breeders could triple average milk yield of dairy cattle in 50 years without knowing a single gene involved or having any genome sequence information to guide them. They simply needed to know the milk production traits of members of the dairy cattle family and select the right mates to breed. Although it is possible to practice breeding of that type on a farm or village scale, small-herd owners in SSA and SA are likely to have difficulty in systematically improving the genetic potential of their livestock by using only locally available germplasm. Nor can small-holders apply modern quantitative breeding practices on the basis of the knowledge of genotypic associations with specific traits; information systems to collect phenotypic and genotypic data from populations of the desired species or breeds systematically have not been put into place. The use of quantitative phenotypic methods to improve breeding requires collecting data on a large number of animals in a family that exhibit
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia BOX 6-5 Genetic Improvement of Fish for Aquaculture Fish provide substantial amounts of protein and other frequently deficient nutrients in Asia and parts of Africa. In SSA and SA and globally, aquaculture is growing in economic and nutritional importance. The World Fish Center (2005) recently identified strategies for aquaculture development with representatives of Bangladesh, China, India, Indonesia, Malaysia, Philippines, Sri Lanka, Thailand, and Viet Nam. The use of molecular markers associated with genetic improvement of fish, including disease resistance, has long been recognized as feasible (Austin, 1998), and one can identify a wide array of disease susceptibility in fish populations (Kettunan et al., 2007; Quillet et al., 2007). The development of inbred lines and the use of markers for selection are meeting with success (Gilbey et al., 2006; Zhang et al., 2006). wide variation in the traits of interest. That kind of effort typically takes place in breeding centers, where resource populations of animals can be developed over a decade or two and individual phenotypes can be collected and recorded to make it possible to identify genetically superior animals (Meuwissen and Goddard, 2000, 2001). Infrastructure is needed to distribute the germplasm to farmers through artificial insemination and embryo transfer techniques. In industrialized countries, that approach has been used over the last 50 years to develop animals with superior genetics, and it is the model used in developing countries, often successfully (Box 6-5). However, the scientific community is now in a position to bypass many of the heavily resource-dependent approaches used in the industrialized world. Emerging technologies offer potentially practical approaches for more rapidly discovering superior livestock genetics and delivering them to subsistence farmers in SSA and SA. LEAPFROGGING SELECTIVE BREEDING WITH MOLECULAR SAMPLING: DNA-DERIVED PEDIGREES There are about 170 million buffalo (Bovidae) in the world, 96 percent of which are in Asia, including 95 million in India alone (Borghese, 2005). The American bison is also included in that estimate. The current status of buffalo production and research has recently been described in detail (Borghese, 2005). The buffalo is a primary source of milk protein and is
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia used for draught and as a supplementary source of meat in parts of Asia. Ten major breeds exist in India, some having been selected and maintained for each of the three functions, which are essential to the farm economy. National programs to improve milk and meat production have been initiated and are being termed the “white” and “red” revolutions, respectively, in keeping with the name of the Green Revolution. Genetic improvement for production traits and disease resistance in buffalo does not benefit from the availability of the powerful genomic tools recently generated for domestic cattle in the United States, for two main reasons: the areas of the world where buffalo are economically important lack the financial resources for genomic research, and the application of genomic research to identify genetically meritorious individual animals can be applied only within families of animals. There is no such information on Bubalus bubalis, the Asian water buffalo, or on any farm animals (such as goats and hair sheep) raised by subsistence farmers in SSA and SA, so the use of well-established quantitative genetic tools is precluded. However, it may be possible to construct an equivalent dataset from the bottom up with the aid of molecular genetic tools. To implement that approach, a reference genome of the breed of interest would need to be generated with DNA sequencing, and DNA samples and phenotypic data would have to be collected from several thousand animals in geographic regions that have common environmental stresses. Single nucleotide polymorphisms (SNPs) would be generated from the DNA samples by sequencing regions of the genome that have proved to be informative in related species. The database of tag SNPs generated from the sequencing data would be aligned with the reference sequence to build family pedigrees. With pedigrees in hand, traditional quantitative tools could be applied to identify animals of superior genetic merit. The approach requires several lines of research. An inexpensive field kit for preserving DNA in tissue samples (ear snips, buccal swabs, or the equivalent) that does not require refrigeration would have to be developed, as would an effective questionnaire for gathering trait phenotypes. Whole genome sequencing (6X coverage) of Bubalis Bubalis, the African buffalo (Syncerus caffer), Bos indicus cattle, sheep, and at least a few representative milk- and meat-producing breeds of goats and sheep should be included in the sequencing project. Finally, substantial investment in developing informatics algorithms for what is essentially reverse engineering of pedigrees from SNP data would be needed. With today’s sequencing capability, it might take 2 years to generate a reference genome sequence for a species. It might take a year each to develop a DNA tissue-sample preservation kit and a phenotype questionnaire, 3 to 5 years to collect DNA samples and phenotypic data, and a year to build pedigrees and test the hypothesis that animals of high genetic merit can be identified with this approach. All the steps except the last can be
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia specific response by the host’s immune system. In theory, DNA vaccines can be manufactured far more easily and less expensively than vaccines composed of inactivated pathogens, protein subunits, or recombinant proteins. Other potential advantages include stability, resistance to extreme temperatures, efficacy as an oral vaccine, and the ability to introduce multiple antigens (Mwangi et al., 2007). However, substantial development is needed before DNA vaccines become an alternative to conventional methods. Most of the experimental DNA vaccines have not shown as great protective immunity as conventional vaccines, but new technologies, such as the coating of colloidal gold with DNA, that are in development could improve effectiveness. If future research can deliver a DNA vaccine that offers protective immunization, this approach would add flexibility to the custom designing of vaccines for regional needs. For instance, it is easier to change the sequence of an antigenic protein or to add heterologous epitopes. The protective immunity of the expressed protein can be easily evaluated after the DNA is injected into a model animal, such as the mouse. This simple, elegant method could quickly allow researchers to learn about the effectiveness of candidate antigens. The final goal of effective DNA vaccines is considered to be far in the future because of the many unresolved problems, but the potential high payoff will continue to draw investment. Animal Disease Surveillance It is pointless to develop and deliver drugs and vaccines without knowing which syndromes are present in a region, because protecting an animal against one pathogen only to have it succumb to another will not reduce the burden of disease on a small-holder farmer. Developing a database of such information will require field research, trained technicians, and diagnostics. The relatively new World Animal Health Information Database managed by the World Organization for Animal Health (OIE) is a significant database that tracks disease prevalence in all regions of the world. In cooperation with the Food and Agriculture Organization of the United Nations (FAO), the OIE is investigating disease rumors that surface on ProMED or other non-scientific sources of information; these early warning systems serve as good alert systems for emerging disease outbreaks. The use of satellite-based remote sensing technologies could be useful as early warning systems for the emergence of serious infectious diseases, particularly those that are transmitted by arthropods. The FAO’s Emergency Prevention System (EMPRES) for Transboundary Animal and Plant Pests and Diseases program currently uses remote sensing technologies to determine the Normalized Difference Vegetation Index (NDVI), and the use of such data has led to the successful advanced prediction of Rift Valley fever outbreaks (FAO, 2008). Similar technologies have been used for
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia the advanced notification of blooms of desert locus and of outbreaks of Venezuelan Equine Encephalomyelitis (FAO, 2008). Inexpensive diagnostic tests, like that developed for rinderpest (Yilma, 1989; Ismall et al., 1994), are needed for disease detection and vaccination campaigns. Other similar rapid pen-side tests for the recognition of infectious diseases have been developed and are in use, such as the field diagnosis of human and avian influenza outbreaks. Increasing in greater numbers are the development, validation, and deployment of rapid RT-PCR technologies for accurate diagnosis of a variety of diseases affecting SSA and SA. These tests require only a nasal swab as a sample and are not sensitive to the effect of higher temperatures in the transportation to diagnostic laboratories. Furthermore, emerging technologies, such as biosensors (Box 6-8), are promising because of their sensitivity, speed, portability, and ease of use and could be developed for a variety of surveillance efforts and especially useful in resource-constrained countries in SSA and SA. Moreover, if farmers have BOX 6-8 Biosensors for Rapid Diagnosis A biosensor is an electronic device that contains a biological receptor close to a transducer that converts the interaction between the receptor and the target of analysis (such as a pathogen) into a measurable electric signal whose strength is related to the concentration of the target. There are a number of experimental configurations and platforms. In one type of biosensor, very thin nanowires are bound to a biomolecule, such as a short piece of DNA (an oligonucleotide), whose conformation changes when a target binds to it; the change in conformation produces a change in charge that is detected by and transmitted by the nanowire. Biosensor technology has progressed quickly in recent years because of the homeland security interest in rapid detection of small amounts of biological agents that could be used for terrorism. Several technologies feed into the development of biosensors, including genomics, nano- and micro-fabrication and instrumentation, chemical and polymer science, and signal processing and data transmission. New generations of biosensors have automated signal transmission to record and send information from remote locations. The key advantages of biosensors are sensitivity, speed (4 to 6 minutes vs. 2 hours for the polymerase chain reaction), portability, and ease of use. Specificity, cost, and manufacture will need additional research. SOURCE: Evangelyn Alocilja, Michigan State University, presentation to committee, August 17, 2007.
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia tools to detect the presence of disease, they are more likely to seek out a drug or vaccine. Farmers’ confidence in medical treatment and vaccination depends on their seeing a benefit, which they will not if a problem is not solved by a drug or vaccine that targets a single pathogen (Guy Palmer, Washington State University, presentation to committee, September 24, 2007). Transgenic Arthropods The genetic engineering of arthropods to alter vector competency and disease transmission could conceivably reduce vector-borne diseases in animals, plants, and humans. By genetically manipulating vectors, such as mosquitoes, and eventually changing their life-cycle dynamics in the field, the ability of local populations of arthropod vectors to transmit diseases could be significantly altered (Scott et al., 2008). NEEDS FOR DRUG AND VACCINE DEVELOPMENT FOR SUB-SAHARAN AFRICA AND SOUTH ASIA Knowledge of Pathogen and Host Variability In addition to the very presence of a pathogen, pathogen serotype is important in drug and vaccine development. For example, although it is not difficult to find conventional vaccines for many major animal diseases, it is not clear that vaccines based on pathogen serotypes in the industrialized world would necessarily provide protection to animals in SSA and SA, because a given causative agent might have different immunogenic characteristics in different regions. Moreover, most vaccines have not been tested on the indigenous animals to be protected, and knowledge of the diversity of the major histocompatibilty complex in a region must be accounted for. Genomic tools can be used to identify differences in geographic strains of a pathogen by comparing highly useful epitopes (that offer immune protection for the host) according to the homology of a pathogen in two distinct regions of the world. Sequencing can help to identify potential antigens of the pathogen of interest that could be evaluated as vaccines. If a pathogen has a standard reference sequence, partial sequencing can help to identify differences in epitopes of a similar strain in a developing country. Faults in a vaccine could be identified and result in the design of a better vaccine for a region. Genomics research on important animal pathogens should be supported because it will lead to better vaccine designs (Dertzbaugh, 1998).
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Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia Adjuvants A vaccine stimulates a host’s production of antibodies specific to antigens of the pathogen. For various reasons, however, vaccines do not always produce an immune reaction strong enough to protect the host. That is especially true of parasitic diseases that require a vaccine to elicit strong T-cell-mediated immunity in addition to stimulating protective antibodies. Adjuvants are compounds added to vaccines that cause the immune system to respond more vigorously, and they include organic and inorganic salts, virosomes, and experimental compounds. Most adjuvants have been developed by pharmaceutical companies and held as proprietary property (Guy Palmer, Washington State University, presentation to committee, September 24, 2007). There is a need to develop and make available adjuvants to improve current vaccines. Distinguishing Vaccination from Infection Livestock and meat from regions where infectious diseases persist are prohibited from exportation to other countries regardless of whether the animals have been vaccinated. Until recently, it was not possible to distinguish between vaccinated and diseased animals in that both will have produced antibodies to a pathogen. That has served as a major barrier to entry markets for farmers in SSA and SA where several diseases persist. The ability to distinguish between animals exposed to a whole virus and vaccinated animals consistently and reliably would be important in the development of vaccines. Such a diagnostic system for differentiating infected from vaccinated individuals (DIVA) already exists and has been applied successfully for pseudorabies and avian influenza (Pasick, 2004). In addition, several DIVA vaccines and their companion diagnostic tests are on the market and can be applied for foot-in-mouth disease and classical swine fever (Pasick, 2004). Attenuated vaccines have been widely used in SSA and SA for the control of diseases such as peste des petits ruminants, sheep and goat pox, and hemorrhagic septicemia. The use of preimmunization, or the deliberate infection of animals with viable pathogenic organisms followed by a treatment with chemotherapeutic agents, for several homoparastic diseases such as Anaplasma marginale, Babesia bovis, Ehrlichia ruminantium, and Theileria annulata in SSA and SA are not safe technologies because they do not propagate the infectious organisms to naïve populations. In this respect, live attenuated vaccines provide better immunity than subunit or killed vaccines. The development of stable strains and insertion of marker genes into these strains to differentiate them from wild-type strains would facilitate vaccine deployment for diseases most relevant to SSA and SA.
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