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in species that are microscopic。
indeed； according to woese； if you totaled up all the biomass of the planet鈥攅very living thing； plants included鈥攎icrobes would account for at least 80 percent of all there is； perhapsmore。 the world belongs to the very small鈥攁nd it has for a very long time。
so why； you are bound to ask at some point in your life； do microbes so often want to hurtus？ what possible satisfaction could there be to a microbe in having us grow feverish orchilled； or disfigured with sores； or above all expire？ a dead host； after all； is hardly going toprovide long…term hospitality。
to begin with； it is worth remembering that most microorganisms are neutral or evenbeneficial to human well…being。 the most rampantly infectious organism on earth； abacterium called wolbachia； doesn鈥檛 hurt humans at all鈥攐r； e to that； any othervertebrates鈥攂ut if you are a shrimp or worm or fruit fly； it can make you wish you had neverbeen born。 altogether； only about one microbe in a thousand is a pathogen for humans；according to national geographic 鈥攖hough； knowing what some of them can do； we couldbe forgiven for thinking that that is quite enough。 even if mostly benign； microbes are still thenumber…three killer in the western world； and even many less lethal ones of course make usdeeply rue their existence。
making a host unwell has certain benefits for the microbe。 the symptoms of an illnessoften help to spread the disease。 vomiting； sneezing； and diarrhea are excellent methods ofgetting out of one host and into position for another。 the most effective strategy of all is toenlist the help of a mobile third party。 infectious organisms love mosquitoes because themosquito鈥檚 sting delivers them directly to a bloodstream where they can get straight to workbefore the victim鈥檚 defense mechanisms can figure out what鈥檚 hit them。 this is why so manygrade…a diseases鈥攎alaria； yellow fever； dengue fever； encephalitis； and a hundred or soother less celebrated but often rapacious maladies鈥攂egin with a mosquito bite。 it is afortunate fluke for us that hiv； the aids agent； isn鈥檛 among them鈥攁t least not yet。 any hivthe mosquito sucks up on its travels is dissolved by the mosquito鈥檚 own metabolism。 whenthe day es that the virus mutates its way around this； we may be in real trouble。
it is a mistake； however； to consider the matter too carefully from the position of logicbecause microorganisms clearly are not calculating entities。 they don鈥檛 care what they do toyou any more than you care what distress you cause when you slaughter them by the millionswith a soapy shower or a swipe of deodorant。 the only time your continuing well…being is ofconsequence to a pathogen is when it kills you too well。 if they eliminate you before they canmove on； then they may well die out themselves。 this in fact sometimes happens。 history；jared diamond notes； is full of diseases that 鈥渙nce caused terrifying epidemics and thendisappeared as mysteriously as they had e。鈥潯e cites the robust but mercifully transientenglish sweating sickness； which raged from 1485 to 1552； killing tens of thousands as itwent； before burning itself out。 too much efficiency is not a good thing for any infectiousorganism。
a great deal of sickness arises not because of what the organism has done to you but whatyour body is trying to do to the organism。 in its quest to rid the body of pathogens； theimmune system sometimes destroys cells or damages critical tissues； so often when you areunwell what you are feeling is not the pathogens but your own immune responses。 anyway；getting sick is a sensible response to infection。 sick people retire to their beds and thus areless of a threat to the wider munity。 resting also frees more of the body鈥檚 resources toattend to the infection。
because there are so many things out there with the potential to hurt you； your body holdslots of different varieties of defensive white cells鈥攕ome ten million types in all； eachdesigned to identify and destroy a particular sort of invader。 it would be impossibly inefficientto maintain ten million separate standing armies； so each variety of white cell keeps only afew scouts on active duty。 when an infectious agent鈥攚hat鈥檚 known as an antigen鈥攊nvades；relevant scouts identify the attacker and put out a call for reinforcements of the right type。
while your body is manufacturing these forces； you are likely to feel wretched。 the onset ofrecovery begins when the troops finally swing into action。
white cells are merciless and will hunt down and kill every last pathogen they can find。 toavoid extinction； attackers have evolved two elemental strategies。 either they strike quicklyand move on to a new host； as with mon infectious illnesses like flu； or they disguisethemselves so that the white cells fail to spot them； as with hiv； the virus responsible foraids； which can sit harmlessly and unnoticed in the nuclei of cells for years before springinginto action。
one of the odder aspects of infection is that microbes that normally do no harm at allsometimes get into the wrong parts of the body and 鈥済o kind of crazy；鈥潯n the words of dr。
bryan marsh； an infectious diseases specialist at dartmouth鈥揾itchcock medical center inlebanon； new hamphire。 鈥渋t happens all the time with car accidents when people sufferinternal injuries。 microbes that are normally benign in the gut get into other parts of thebody鈥攖he bloodstream； for instance鈥攁nd cause terrible havoc。鈥�
the scariest； most out…of…control bacterial disorder of the moment is a disease callednecrotizing fasciitis in which bacteria essentially eat the victim from the inside out； devouringinternal tissue and leaving behind a pulpy； noxious residue。 patients often e in withparatively mild plaints鈥攁 skin rash and fever typically鈥攂ut then dramaticallydeteriorate。 when they are opened up it is often found that they are simply being consumed。
the only treatment is what is known as 鈥渞adical excisional surgery鈥濃�攃utting out every bit ofinfected area。 seventy percent of victims die； many of the rest are left terribly disfigured。 thesource of the infection is a mundane family of bacteria called group a streptococcus； whichnormally do no more than cause strep throat。 very occasionally； for reasons unknown； someof these bacteria get through the lining of the throat and into the body proper； where theywreak the most devastating havoc。 they are pletely resistant to antibiotics。 about athousand cases a year occur in the united states； and no one can say that it won鈥檛 get worse。
precisely the same thing happens with meningitis。 at least 10 percent of young adults； andperhaps 30 percent of teenagers； carry the deadly meningococcal bacterium； but it lives quiteharmlessly in the throat。 just occasionally鈥攊n about one young person in a hundredthousand鈥攊t gets into the bloodstream and makes them very ill indeed。 in the worst cases；death can e in twelve hours。 that鈥檚 shockingly quick。 鈥測ou can have a person who鈥檚 inperfect health at breakfast and dead by evening；鈥潯ays marsh。
we would have much more success with bacteria if we weren鈥檛 so profligate with our bestweapon against them： antibiotics。 remarkably； by one estimate some 70 percent of theantibiotics used in the developed world are given to farm animals； often routinely in stockfeed； simply to promote growth or as a precaution against infection。 such applications givebacteria every opportunity to evolve a resistance to them。 it is an opportunity that they haveenthusiastically seized。
in 1952； penicillin was fully effective against all strains of staphylococcus bacteria； to suchan extent that by the early 1960s the u。s。 surgeon general； william stewart； felt confidentenough to declare： 鈥渢he time has e to close the book on infectious diseases。 we havebasically wiped out infection in the united states。鈥潯ven as he spoke； however； some 90percent of those strains were in the process of developing immunity to penicillin。 soon one ofthese new strains； called methicillin…resistant staphylococcus aureus； began to show up inhospitals。 only one type of antibiotic； vanycin； remained effective against it； but in 1997a hospital in tokyo reported the appearance of a strain that could resist even that。 withinmonths it had spread to six other japanese hospitals。 all over； the microbes are beginning towin the war again： in u。s。 hospitals alone； some fourteen thousand people a year die frominfections they pick up there。 as james surowiecki has noted； given a choice betweendeveloping antibiotics that people will take every day for two weeks or antidepressants thatpeople will take every day forever； drug panies not surprisingly opt for the latter。
although a few antibiotics have been toughened up a bit； the pharmaceutical industry hasn鈥檛given us an entirely new antibiotic since the 1970s。
our carelessness is all the more alarming since the discovery that many other ailments maybe bacterial in origin。 the process of discovery began in 1983 when barry marshall； a doctorin perth； western australia； found that many stomach cancers and most stomach ulcers arecaused by a bacterium called helicobacter pylori。 even though his findings were easily tested；the notion