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Covid-19: Årsaker

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Årsaken til covid-19 er en ny type koronavirus kalt SARS-CoV-2, fordi virusets arvestoff ligner SARS-viruset sitt. Viruset smittet sannsynligvis opprinnelig fra dyr til mennesker. Dyret som overførte smitte til mennesker, enten direkte eller via et annet dyr, er trolig flaggermus. Koronaviruset som er funnet å ha mest likhet med SARS-CoV-2, ble oppdaget hos flaggermus i Wuhan, Kina. I begynnelsen av smittespredningen var mange smittetilfeller, men ikke alle, knyttet til et matmarked i byen Wuhan.

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Viruset smitter mellom mennesker på samme måte som forkjølelse eller influensa. Smitte kan overføres når viruset kommer i kontakt med mottakerens slimhinner i øyne, nese eller munn, eller hvis viruspartikler trekkes ned i lungene.  

Smittemåten som har hatt mest betydning, er såkalt dråpesmitte. Små dråper som inneholder viruset, slenges ut fra luftveiene av personer med covid-19 når de puster, nyser eller hoster. Faren er størst ved nær kontakt med den smittsomme personen. Når bittesmå dråper (aerosoler) som inneholder virus, smitter over avstander lengre enn to meter, kalles det luftsmitte. Risikoen for luftsmitte ser ut til å være høyest i små rom med dårlig ventilasjon. 

Når viruset overføres via direkte kontakt med en smittsom person eller via kontakt med overflater som er blitt forurenset med virus, kalles det kontaktsmitte. Viruset kan overleve på overflater utenfor kroppen i opptil noen få dager. Kontaktsmitte kan også ha en rolle i smittespredningen. 

Mesteparten av smitten har skjedd fra pasienter med symptomer, spesielt i starten av sykdommen. Men smitte har også forekommet i inkubasjonstiden (se under) eller fra personer som var smittet, men som ikke utviklet symptomer (asymptomatiske smittetilfeller).

Varianter

Arvestoffet til SARS-CoV-2 består av ribonukleinsyre (RNA). I motsetning til DNA, som er dobbel-trådet, er RNA enkelt-trådet. RNA-virus har en høy mutasjonsrate. Det finnes flere tusen varianter av SARS-CoV-2. De fleste mutasjonene endrer ikke virusets egenskaper i vesentlig grad. Men hos noen av variantene er det observert forskjeller med tanke på smittsomhet, alvorlighetsgrad av sykdommen eller måten kroppens immunforsvar reagerer på infeksjonen. Det finnes en oversikt over aktuelle og tidligere varianter på ECDC sine nettsider .    

Dette dokumentet er basert på det profesjonelle dokumentet COVID-19 . Referanselisten for dette dokumentet vises nedenfor

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