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Lesson17

Aman-madedisease

人为的疾病

Firstlistenandthenanswerthefollowingquestion.

听录音，然后回答以下问题。

Whatfactorhelpedtospreadthediseaseofmyxomatosis?

IntheearlydaysofthesettlementofAustralia,enterprisingsettlersunwiselyintroducedtheEuropeanrabbit.ThisrabbithadnonaturalenemiesintheAntipodes,sothatitmultipliedwiththatpromiscuousabandoncharacteristicofrabbits.Itoverranawholecontinent.Itcauseddevastationbyburrowingandbydevouringtheherbagewhichmighthavemaintainedmillionsofsheepandcattle.Scientistsdiscoveredthatthisparticularvarietyofrabbit(andapparentlynootheranimal)wassusceptibletoafatalvirusdisease,myxomatosis.Byinfectinganimalsandlettingthemlooseintheburrows,localepidemicsofthisdiseasecouldbecreated.Lateritwasfoundthattherewasatypeofmosquitowhichactedasthecarrierofthisdiseaseandpasseditontotherabbits.Sowhiletherestoftheworldwastryingtogetridofmosquitoes,Australiawasencouragingthisone.Iteffectivelyspreadthediseasealloverthecontinentanddrasticallyreducedtherabbitpopulation.Itlaterbecameapparentthatrabbitsweredevelopingadegreeofresistancetothisdisease,sothattherabbitpopulationwasunlikelytobe