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Vaccination (continued) rotype displays three neutralizing antigenic sites. A type 1/type 3 chimeric virus constructed from clones of Sabin strain deriva- tives would be useful in the primary vaccination of children to reduce vaccine-associated cases of poliomyelitis. Diarrheal disease vaccines Diarrheal diseases are caused by the double-stranded, segmented RNA enteroviruses, by the single-stranded RNA Norwalk-type caliciviruses, and by enterotoxigenic bacteria (for example, Vibrio cholerae and Escherichia coli). These pathogens cause about 2.5 million deaths per year in children under 5 years of age, especially in countries where food and water are frequently contaminated. Inactivated vaccines and purified toxoids have traditionally been used to prevent cholera and other diarrheal diseases. Recently, however, genetic engineer- ing techniques have enabled scientists to develop new oral vaccines. Rotavirus vaccines Rotaviruses are the most common cause of severe diarrhea and dehydration in infants. In less economically developed countries, rotavirus diarrhea causes about 700,000 deaths per year. In the United States, about one-third of pediatric hospital admissions are the result of rotaviruses, with about 20 deaths per year. Rotaviruses elaborate an enterotoxin (nonstructural protein NSP4) that triggers a signal transduction pathway that alters epithelial cell permeability and chloride secretion. Natu- ral protective immunity against severe rotavirus disease is built up during the first 2–3 years of life. Studies with live attenuated oral rotavirus vaccines have also shown that the majority of severe episodes of rotavirus diarrhea are preventable by oral immunization. In addition, several other candidate rotavirus vaccines, including bovine-human reassortants, are being investigated. Oral transgenic plant vaccines Oral transgenic plant vaccines exemplify another innova- tive approach to vaccine development. Ultimately, the vaccine designers hope to use common, uncooked, edible plants, such as bananas and tomatoes, as transgenic plant delivery systems to express the antigens of pathogenic organisms in the gut, so as to induce secretory IgA, the predominant form of immuno- globulin found in mucosal secretions. Presently, however, only model studies have been completed using transgenic potatoes and tobacco plants; in these studies, human and animal diar- rheal conditions were targeted to demonstrate the feasibility of oral transgenic plant vaccines. Transgenic plants have many potential advantages as vac- cines. In particular, they are easy to grow at minimal cost. More- over, unlike bacteria and animal cells, they do not require spe- cialist media and equipment or stringent purification protocols. Transgenic plants can be conveniently self-fertilized to produce stable, true-breeding lines propagated by conventional horti- cultural techniques and stored or distributed as seeds. Neither sterile syringes nor nurses would be needed for vaccination Cancer vaccines Materials commonly termed cancer vaccines are usually immunotherapeutic preparations targeted to increase the im- mune response to mutated cellular proteins. They are intended to inhibit the growth of previously diagnosed cancers rather than to prevent the appearance of new, spontaneous malig- nant tumors. However, in cases in which infectious agents are strongly associated with cancer induction, vaccines capable of preventing cancers have been made available. Viral hepatitis is a common infectious disease of humans. For example, there are 250–400 million carriers of the hepatitis type B virus (HBV) in the world, and it has been estimated that HBV causes about 1 million deaths worldwide per year. Carri- ers of HBV are at risk of developing hepatocellular carcinomas many years after the initial HBV infection. These carcinomas are quite prevalent in Asia, but various universal HBV vaccination programs have decreased their incidence. Marek's disease virus is a cell-associated herpesvirus of poul- try and causes a naturally occurring contagious malignant lym- phoma in chickens. The disease has been effectively controlled using a live vaccine based on a nonpathogenic serologically related herpesvirus of turkeys. Cancers caused by other known infectious agents (including Epstein-Barr virus and hepatitis C virus) may also ultimately be preventable by vaccination. + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com This article was originally published by McGraw Hill's AccessScience. Click here to view and find more articles like this.