When we think about melting glaciers, our foremost concerns are the declining animal populations and rising global sea levels. However, virologists have known about the other effects of melting glacial ice for a long time, including the release of micro-organisms and viruses that were frozen in the glaciers thousands of years ago.
Will viruses frozen in melting glaciers cause more pandemics?
It is unlikely that the viruses frozen in melting glaciers will cause new pandemics, said Dr Laura Kalinienė, a virologist at Vilnius University’s Life Sciences Centre. However, we should not forget about bacteria, such as anthrax or bubonic plague, which can also be released into the environment from melting glaciers and are just as dangerous.
As Dr Kalinienė explained, micro-organisms and viruses can enter permafrost zones, mountain tops and rock glaciers in different ways. “Some viruses simply exist in these environments and, as the ecological conditions and balance change, they are frozen in the ice. Other viruses in such ecosystems freeze along with the remains of a once-living host, such as an animal or a human. The question is how many years such viruses can stay frozen in the ice and remain infectious,” she said.
According to Dr Kalinienė, scientists have successfully recovered infectious virions from samples taken from the permafrost areas of Siberia. In this way, the 30,000-year-old viruses Pithovirus sibericum and Mollivirus sibericum, thought to infect amoebae, were revived.
As for the bacteria found in frozen areas, scientists have been able to revive micro-organisms of the genus Arthrobacter, which were around 8 million years old, in samples collected from AntarcticaFormos viršus Formos apačia, as well as to obtain samples of bacterial nucleic acids dating back as far as 34 million years.
“In permafrost zones, the lack of exposure to temperature differentiation and ultraviolet light combined with the lack of oxygen create very favourable conditions for the preservation of viruses. Nonetheless, not all viruses will survive in freezing conditions. The length of time and ability for a virus to survive in a frozen condition without losing its infectivity is an individual characteristic of each virus, which needs to be clarified. Similar research is being conducted with the new coronavirus, with experts looking at how tolerant it is to freezing, to determine how long it can remain infectious on frozen food or in frozen water, etc.,” explained Dr Kalinienė.
According to the scientist, the prevailing view is that large DNA viruses – such as smallpox or amoeba-infecting mega-viruses, which can be seen under a light microscope – are better able to tolerate freezing, as their structures and genomes are better suited to such conditions. However, influenza or coronaviruses containing RNA, which are normally considered to be more vulnerable, can also be frozen for some time and remain infectious once thawed due to the structure of their greasy envelope.
Spreading of defrosted viruses is unlikely
Although various models have been developed in scientific papers to show how defrosted micro-organisms and viruses could spread from glaciers to other geographical areas, Dr Kalinienė remains sceptical about the potential for such viruses to cause a pandemic.
“A virus needs a certain concentration of hosts to become established, but such concentrations are usually not present in extreme areas. Even if an expedition brings together a large group of scientists to conduct research who may potentially encounter new viruses, that does not result in an increased likelihood for the viruses to spread, because viruses have different routes of transmission – one type may spread through the host’s bloodstream, another through airborne droplets and another through faecal contamination.
Therefore, if a scientist has unearthed an ancient blood-borne or insect-borne virus, but there are no insects in the environment that are capable of spreading it and the scientist does not touch the specimen with bare and wounded hands, such a virus will likely die when it is exposed to an oxygen- and UV-rich environment,” Dr Kalinienė explained.
The evolution of molecules also plays a role in preventing new pandemics. “From a molecular point of view, we are now different than we were 30,000 years ago. Therefore, it is likely that a virus which was dangerous to humans back then will no longer find a suitable host today, because the structure necessary for that virus to attach to our cells has greatly altered or has simply disappeared during the course of human evolution,” she said.
According to the virologist, traces of the Spanish flu virus, which created a worldwide epidemic between 1918 and 1920, have also been found in permafrost areas. The virus could not be revived, however, even if viable virions were present, so the Spanish flu could not cause a similarly deadly pandemic again.
“In 1918, at the time when this virus was spreading ruthlessly, we had no antibiotics. Often, it is not so much the flu itself that is dangerous, but the secondary bacterial infections. Nowadays, we have medicines and our population is not war-torn. Therefore, such an outbreak would be more easily contained,” Dr Kalinienė explained.
She also pointed out that bacteria, such as anthrax or bubonic plague, can also be released into environment from melting glaciers and are just as dangerous: “In 2016, an outbreak of anthrax was recorded in Siberia. It is thought to have originated from a deer that died of anthrax almost 100 years ago and had been frozen, later infecting other deer after it thawed. In the end, over 20 people were infected, including a 12-year-old boy who did not survive. Although the disease did not spread in this particular case, we do not know whether something similar has affected other small ethnicities that do not have contact with the rest of the population. Even more worrying is the surprising fact that the old bacteria taken from permafrost areas and revived often have a resistance to many of our antibiotics, which could add to the already significant problem of antibiotic resistance in the future.”
One of the effects of melting glacial ice is the release of micro-organisms and viruses that were frozen in the glaciers thousands of years ago. However, such viruses are unlikely to cause a new pandemic. This is because a virus needs a certain concentration of hosts to become established; and moreover, humans are now different from a molecular point of view than they were 30,000 years ago. If such an outbreak did occur, it would be easier to contain it now since we have certain medicines and better living conditions. Nevertheless, bacteria such as anthrax or bubonic plague can also be released into environment from melting glaciers, and these are just as dangerous.
Author: Gretė Gerulaitytė, Communications Specialist at Vilnius University