Environmental Problems, Their Causes, and Sustainability 1

A typical virus consists of a shell of proteinssurrounding genetic materialVirusCell membraneThe viral geneticmaterial uses thehost cell's DNA toreplicate againand again.New virusesThe virus attaches to thehost cell. The entire virusmay enter or it may injectits genetic material,or genome.Host cellNucleusGenetic materialSurface proteinsEach new copy ofthe virus directs thecell to make it aprotein shellchains now refuse to buy meat from livestock treatedwith antibiotics.The result of these factors acting together is thatevery major disease-causing bacterium now hasstrains that resist at least one of the roughly 160 antibioticswe use to treat bacterial infections. Consequently,the United States and other countries are seeing an increasein the number of patients who contract infectiousbacterial disease while they are in a hospital orother medical facility. According to a 2002 study by theJoint Commission for the Accreditation of HealthcareOrganizations, each year nearly 2 million Americansleave hospitals with mostly preventable infectionsthey acquired there, and at least 90,000 of them diedprematurely because of such infections.Biologist Paul Ewald suggests that we should stoptrying to obliterate lethal microbes and instead focuson how to weaken their effects by forcing them to mutatein certain ways. Maybe we can get the forces ofevolution on our side by causing viruses to becomeless virulent as they spread among the population.Case Study: The Global TuberculosisEpidemic—A Growing ThreatTuberculosis (TB) kills about 1.7 million peoplea year and could kill 28 million people by 2020.Since 1990, one of the world’s most underreportedstories has been the rapid spread of tuberculosis(TB). According to the World Health Organization,this highly infectious bacterial disease infects aboutDisease(type of agent)Deaths per yearThe new viruses emerge fromthe host cell capable of infectingother cells. This process oftendestroys the first cell.Figure 19-10 How a virus reproduces. (American MedicalAssociation)Pneumonia and flu(bacteria and viruses)HIV/AIDS(virus)Diarrheal diseases(bacteria and viruses)Tuberculosis(bacteria)Malaria(protozoa)Hepatitis B(virus)3.2 million3.0 million1.9 million1.7 million1 million1 millionstudies show that resistant strains of infectious diseasesthat develop in livestock animals can spread tohumans through contact with infected animals or waterand through food webs. Good news. Because of publicpressure, efforts are being made to phase out theuse of antibiotics to boost livestock. Some fast foodMeasles(virus)800,000Figure 19-11 Each year the world’s seven deadliest infectiousdiseases kill about 12.6 million people—most of them poorpeople in developing countries. This amounts to about34,500 mostly preventable deaths every day. (World HealthOrganization)http://biology.brookscole.com/miller14421