For almost a decade, scientists chased the source of a deadly new virus through China’s tallest mountains and most isolated caverns.
Gotovo su cijelo desetljeće znanstvenici lovili izvor novog smrtonosnog virusa po visokim planinama i osamljenim špiljama Kine.
They finally found it here: in the bats of Shitou Cave. The virus in question was a coronavirus that caused an epidemic of severe acute respiratory syndrome, or SARS, in 2003.
Konačno su ga pronašli ovdje: u šišmišima špilje Shitou. Taj je virus bio koronavirus koji je uzrokovao epidemiju teškog akutnog respiratornog sindroma, poznatijeg kao SARS, 2003. godine.
Coronaviruses are a group of viruses covered in little protein spikes that look like a crown— or "corona" in Latin. There are hundreds of known coronaviruses. Seven of them infect humans, and can cause disease. The coronavirus SARS-CoV causes SARS, MERS-CoV causes MERS, and SARS-CoV-2 causes the disease COVID-19.
Koronavirusi su skupina virusa prekriveni proteinskim izbočenjima koji podsjećaju na krunu, tj. "corona" na latinskom. Postoje stotine poznatih koronavirusa. Sedmero vrsta može zaraziti čovjeka. Koronavirus SARS-CoV uzrokuje SARS, MERS-CoV uzrokuje MERS, a SARS-CoV-2 uzrokuje COVID-19.
Of the seven human coronaviruses, four cause colds, mild, highly contagious infections of the nose and throat. Two infect the lungs, and cause much more severe illnesses. The seventh, which causes COVID-19, has features of each: it spreads easily, but can severely impact the lungs.
Od sedmero ljudskih koronavirusa, četiri ih uzrokuje prehlade: iznimno zarazne, no blage, infekcije nosa i grla. Dva zahvaćaju pluća i uzrokuju mnogo teže bolesti. Sedmi, koji uzrokuje COVID-19, ima značajke oba: lako se širi, no može imati značajan utjecaj na pluća.
When an infected person coughs, droplets containing the virus spray out. The virus can infect a new person when the droplets enter their nose or mouth. Coronaviruses transmit best in enclosed spaces, where people are close together. Cold weather keeps their delicate casing from drying out, enabling the virus to survive for longer between hosts, while UV exposure from sunlight may damage it. These seasonal variations matter more for established viruses. But because no one is yet immune to a new virus, it has so many potential hosts that it doesn’t need ideal conditions to spread.
Kada zaražena osoba zakašlje, kapljice s virusom rasprše se. Virus može zaraziti osobu kada kapljice uđu u nos ili usta. Koronavirusi se najbrže šire u zatvorenim prostorima gdje je razmak među ljudima malen. Hladnije temperature sprječavaju sušenje osjetljive ovojnice i omogućavaju dulji životni vijek virusa u okolini. Izloženost UV-zrakama danjeg svjetla može ga oštetiti. Te su razlike u uvjetima važnije za poznate viruse. Nitko još nije razvio imunitet na ovaj novi virus pa ima brojne moguće domaćine i ne treba idealne uvjete za širenje.
In the body, the protein spikes embed in the host’s cells and fuse with them— enabling the virus to hijack the host cell’s machinery to replicate its own genes.
U tijelu se proteinska izbočenja hvataju za stanice te se s njima se sjedine, što virusu omogućava upravljanje stanicom domaćina u svrhu replikacije vlastitih gena.
Coronaviruses store their genes on RNA. All viruses are either RNA viruses or DNA viruses. RNA viruses tend to be smaller, with fewer genes, meaning they infect many hosts and replicate quickly in those hosts. In general, RNA viruses don’t have a proofreading mechanism, whereas DNA viruses do. So when an RNA virus replicates, it’s much more likely to have mistakes called mutations.
Koronavirusi gene čuvaju u RNK. Virusi mogu biti DNK ili RNK virusi. RNK virusi su manji i imaju manji broj gena, a to znači da mogu zaraziti veći broj domaćina i brže se razmnožiti. Općenito, RNK virusi nemaju mehanizam provjere kao DNK virusi. Prilikom replikacije RNK virusa greške su česte, a te su greške mutacije.
Many of these mutations are useless or even harmful. But some make the virus better suited for certain environments— like a new host species. Epidemics often occur when a virus jumps from animals to humans. This is true of the RNA viruses that caused the Ebola, Zika, and SARS epidemics, and the COVID-19 pandemic. Once in humans, the virus still mutates— usually not enough to create a new virus, but enough to create variations, or strains, of the original one.
Većina je mutacija beskorisna ili čak štetna za virus. Zbog nekih pak virus bolje opstaje u određenim okruženjima, kao kod nove vrste domaćina. Epidemije se često javljaju kada virus prijeđe s životinje na čovjeka. To se dogodilo s RNK virusima koji su uzrokovali epidemije ebole, Zike i SARS-a te pandemiju COVID-19. Kada zarazi ljude, virus i dalje mutira, no ne dovoljno kako bi stvorio novi virus, ali dovoljno kako bi nastale varijacije, ili sojevi prvotnog virusa.
Coronaviruses have a few key differences from most RNA viruses. They’re some of the largest, meaning they have the most genes. That creates more opportunity for harmful mutations. To counteract this risk, coronaviruses have a unique feature: an enzyme that checks for replication errors and corrects mistakes. This makes coronaviruses much more stable, with a slower mutation rate, than other RNA viruses.
Koronavirusi se razlikuju od drugih RNA virusa. Iznimno su veliki, što znači da imaju velik broj gena. To stvara veći broj mogućnosti za nastanak štetnih mutacija. Za smanjenje rizika, koronavirusi imaju jedinstvenu moć: imaju enzim koji traži greške replikacije i ispravlja ih. Zato su koronavirusi stabilniji i sporije mutiraju od drugih RNK virusa.
While this may sound formidable, the slow mutation rate is actually a promising sign when it comes to disarming them. After an infection, our immune systems can recognize germs and destroy them more quickly if they infect us again so they don’t make us sick. But mutations can make a virus less recognizable to our immune systems— and therefore more difficult to fight off. They can also make antiviral drugs and vaccines less effective, because they’re tailored very specifically to a virus. That’s why we need a new flu vaccine every year— the influenza virus mutates so quickly that new strains pop up constantly. The slower mutation rate of coronaviruses means our immune systems, drugs, and vaccines might be able to recognize them for longer after infection, and therefore protect us better.
Možda ne zvuči obećavajuće, no sporije mutacije su dobre jer ih je lakše zaustaviti. Nakon infekcije, imunosni sustavi mogu prepoznati patogene i brže ih uništiti ako se opet zarazimo pa mi ne obolimo. Zbog mutacija virusi također mogu biti teže prepoznatljivi imunosnom sustavu te se tako teže s njima boriti. Zato lijekovi i cjepiva mogu izgubiti na efikasnosti - oni su osmišljeni za specifičan virus. Zato svake godine trebamo novo cjepivo protiv gripe. Influenza mutira toliko brzo da novi sojevi nastaju stalno. Sporija mutacija koronavirusa znači da ih imunosustavi, lijekovi i cjepiva mogu prepoznati duže nakon što se zarazimo i tako nas bolje zaštititi.
Still, we don’t know how long our bodies remain immune to different coronaviruses. There’s never been an approved treatment or vaccine for a coronavirus. We haven’t focused on treating the ones that cause colds, and though scientists began developing treatments for SARS and MERS, the epidemics ended before those treatments completed clinical trials.
Ipak, ne znamo koliko dugo zadržavamo imunitet na koronaviruse. Nikada nije postojao odobreni lijek ili cjepivo za koronavirus. Nismo se usredotočili na one koji uzrokuju prehlade. Znanstvenici su počeli terapiju protiv SARS-a i MERS-a, no te su epidemije završile prije kliničkih testiranja lijekova.
As we continue to encroach on other animals’ habitats, some scientists say a new coronavirus jumping to humans is inevitable— but if we investigate these unknowns, it doesn’t have to be devastating.
I dalje zadiremo u staništa životinja te znanstvenici kažu da je prijelaz novog koronavirusa na ljude neizbježan. Ako istražimo nepoznanice, taj prijelaz ne mora biti koban.