Information

Temperature to kill virus


Why do I see only high temperature advice to kill microorganism, and not low temperature?

Why isn't there any low temperature which kills virus? Are they more resistant to low temperature?


High temperatures means that lots of energy is available in the environment. This energy speeds up chemical reactions, and make possible some reactions that wouldn't happen at all at lower temperatures. In particular, proteins can adopt new shapes as temperatures get higher. It's the misshapen proteins rather than the temperature per se that kills the microorganisms.

Low temperatures mean there is relatively less energy available in the environment. This slows down or stops chemical reactions, including the ones that result in mis-shaped proteins. Extremely low temperatures may slow down a microorganism's metabolism and stop it from reproducing. That's why we keep perishable foods in refrigerators. However, if you warm the microorganisms back to a normal temperature, most of them will pick right where they left off. A few may be killed by the formation of ice crystals inside the cells that mechanically break the cell membrane.

If you walk into a microbiology lab you'll often see a wall of refrigerators, used to preserve microorganisms for later revival and use.


What temperature kills germs? How to use heat properly to get rid of bacteria and viruses

This article was medically reviewed by Tania Elliott, MD, who specializes in infectious diseases related to allergies and immunology for internal medicine at NYU Langone Health.

  • Hot temperatures can kill most germs — usually at least 140 degrees Fahrenheit.
  • Most bacteria thrive at 40 to 140 degrees Fahrenheit, which is why it's important to keep food refrigerated or cook it at high temperatures.
  • Freezing temperatures don't kill germs, but it makes them dormant until they are thawed.
  • This story is part of Insider's guide on How to Kill Germs.

Germs — like viruses, bacteria, and fungus — respond differently to cold and hot temperatures. For example, the flu virus thrives in colder weather, which is why flu season is in the winter.

In general, hot temperatures are better suited to killing germs, but that doesn't mean you should start sterilizing everything with heat. "It's not realistic or necessary," says Manish Trivedi, director of the Division of Infectious Diseases at AtlantiCare. "The most effective intervention to prevent the spread of germs is proper hand-washing."

In fact, for the COVID-19 virus, the World Health Organization (WHO) warns against using temperature methods to 'prevent' or 'kill' infection: spending time in cold weather or snow, taking a hot bath, using hot hand dryers, or ultraviolet lamps has no effect on this new Coronavirus strain.

But there are other cases where high temperatures can kill germs — boiling water to kill off bacteria in food products, using a dishwasher to sterilize plates, or washing and drying clothes to decontaminate them. Here's what you need to know.


This Is the Temperature That Kills Coronavirus

If you were hoping the summer heat would stop the coronavirus in its tracks, think again, experts say.

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Temperature's impact on the coronavirus has been a hotly debated topic these days. Many people take comfort in believing that warm weather will have a significant impact on the COVID-19 contagion, but it may not be as simple as that. Yes, studies have shown that intense heat can kill many viruses—including coronaviruses, the family of viruses that COVID-19 belongs to. But how hot exactly does it need to be for that to happen?

According to the World Health Organization (WHO), "heat at 56°C [132.8°F] kills the SARS coronavirus at around 10000 units per 15 minutes." The SARS coronavirus behaves similarly to COVID-19, which leads experts to believe that the novel coronavirus would have a similar fate at that temperature.

How does it work exactly? Well, heat is thought to affect the coronavirus in part because it is an enveloped virus with a lipid bilayer. According to BBC, "research on other enveloped viruses suggests that this oily coat makes the viruses more susceptible to heat than those that do not have one."

Since outdoor temperatures rarely reach anywhere near 132.8°F, however, experts do not believe warmer weather will have any significant impact on the novel coronavirus. "While we may expect modest declines in the contagiousness of SARS-CoV-2 in warmer, wetter weather … is not reasonable to expect these declines alone to slow transmission enough to make a big dent," writes Marc Lipsitch, DPhil, director of the Center for Communicable Disease Dynamics at Harvard T.H. Chan School of Public Health.

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So, while you shouldn't assume the summer heat will crush the coronavirus on its own, you can use heat to kill COVID-19 in other ways. For example, if you cook your food at 132.8°F or higher, the heat would be able to eliminate traces of the coronavirus on your food, according to research physician Christine Traxler, MD, of Invigor Medical.

Similarly, "if you do your laundry and dry on high heat for an hour, the virus is probably dead," says Traxler.

Additionally, boiled water can be effective against coronavirus. Water boils at 100°C (212°F) and a dishwasher's final rinse cycle is generally around 71.1°C (160°F), which makes it the ideal place to disinfect everything from children's toys to sponges.

So, while boiled water or the temperature inside your dishwasher or dryer can help combat the coronavirus, high summer temperatures likely don't have the same effect. And if you're concerned about what's to come with COVID-19, check out Here's How the Second Wave of Coronavirus Could Be Even Worse.


Coronavirus Can Survive High Temperatures for Long Periods, Study Finds

Some strains of Sars-CoV-2, the virus that causes COVID-19, can survive temperatures of 60 degrees Celsius (140 degrees Fahrenheit) for an hour, researchers have found. To kill the virus in a laboratory setting, the team had to heat it to 92 degrees Celsius (197 degrees Fahrenheit) for 15 minutes.

The study, which appears on the pre-print website bioRxiv, has not been published in a scientific journal and has not been peer reviewed by experts, so the findings should be considered with caution.

The team, led by Boris Pastorino, from the Emerging Viral Diseases Unit at Aix-Marseille University, in France, were looking at what heating and chemical requirements are needed to inactivate the virus. They were looking at the risk the virus poses to laboratory workers who are regularly in contact with SARS-CoV-2.

They note that different viruses have different procedures for inactivation, which is necessary to perform tests on them. For Viral Hemorrhagic Fever (VHF) the Centers for Disease Control and Prevention recommends using a detergent called Triton X-100 and to heat the sample for an hour at 60 degrees Celsius.

"Since SARS-CoV-2 was detected in blood during infection, samples will have to be inactivated prior to serological tests are performed," they explain. The best method of doing this, they say, has not been established.

In the study, African green monkey kidney cells were infected with the virus. The researchers then created two different sets of conditions, "clean," representing laboratory conditions, and "dirty," which would be more like conditions real-life samples are taken. The team then ran 10 different experiments using different procedures to kill the virus. These included heating and chemical methods.

Findings showed in the heat tests, only when the virus was exposed to 92 degree Celsius temperatures for 15 minutes was it totally inactivated. The other two heat conditions, 60 degrees Celsius for 60 minutes and 56 degrees Celsius for 30 minutes, resulted in a "clear drop in infectivity," but with some samples with higher viral loads remaining active. "These results were consistent with previous studies on SARS-CoV and MERS-CoV," they said.

The team concluded that because low viral loads are observed in most COVID-19 patients, the lower heat temperatures should be sufficient to deactivate it. However, samples with far higher loads need higher temperatures. "The results presented in this study should help to choose the best suited protocol for inactivation in order to prevent exposure of laboratory personnel in charge of direct and indirect detection of SARS-CoV-2 for diagnostic purposes," they wrote.

Jeremy Rossman, Senior Lecturer in Virology at the University of Kent, U.K., who was not involved in the research, said the findings had important implications for laboratory workers, and could help provide guidance for people researching and performing diagnostics on SARS-CoV-2.

"If the results do hold up to peer review, the paper provides helpful guidance on handling of SARS-CoV-2 samples for laboratory worker," he told Newsweek. "With low levels of virus&mdashas is the case for most mild human cases&mdashthe 56 degree Celsius heat inactivation used in many diagnostic labs is shown to be sufficient however, for samples that potentially contain very high levels of virus&mdashsuch as sputum samples from critical cases&mdashtheir results suggest that a higher heat of 92 degree Celsius is necessary for complete virus inactivation."

Other studies have assessed the stability of the virus under different conditions. In one correspondence published in the Lancet Microbe, researchers found SARS-CoV-2 was "highly stable" 4 degrees Celsius. However, at 70 degrees Celsius, they found the virus was inactivated in five minutes.

In another pre-print paper, researchers from Beijing, China, found air temperature and humidity played a role in transmission of the virus. By analyzing infection rates across 100 Chinese cities, they found higher temperatures and humidity levels appeared to "significantly reduce the transmission of COVID-19." They said this was in line with SARS and influenza, which both have reduced transmission under these conditions.


This Temperature Can Kill COVID in Minutes, New Study Says

But research shows that some household appliances might not get hot enough to help.

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New research has shown that going overboard to keep surfaces in your home free from coronavirus may not be as worthwhile an effort as being diligent about wearing a mask or avoiding crowds. But when it comes to sanitizing clothing or masks, which are worn out into public, keeping them coronavirus-free takes on a new level of importance. Fortunately, a new study has found that keeping items at a high temperature can kill COVID in minutes. Read on to see how hot you need to go to sanitize, and for more on how you can keep yourself safe, check out These 3 Things Could Prevent Almost All COVID Cases, Study Finds.

According to a recent study out of the University of St. Thomas published in the journal Wiley Public Health Emergency Collection, the importance of textile hygiene has taken on new meaning during the pandemic as mask-wearing has become a factor of daily life. And while researchers point out that SARS-CoV-2 viruses that infect will die off naturally with time alone, a variety of factors including the type of material and overall humidity can drastically change the time needed. Additionally, sanitizing solutions could have different effects on different types of materials, which could decrease their effectiveness over time.

"Some clothing types, for instance, are very capable of retaining moisture and consequently, this affects the survival of virus contained therein," the study authors write. "The general consensus is that viruses can survive up to a few days in clothing. It is reasonable to expect a similar survival duration for viruses on/in protective face masks."

By testing cultures exposed to a wide range of temperature levels for varying lengths of time, researchers were able to find out exactly which temperature ranges were capable of inactivating COVID effectively. But the results also pointed to the fact that using heat as a sanitizing tool at home may not be as easy as one might think.

The researchers were also careful to point out that shooting higher than the suggesting range was ideal. "Because of the seriousness of the current coronavirus infection, we suggest a reasonable safety factor can be obtained by increasing the … listed temperatures by [18 degrees Fahrenheit]," the study authors write.

So how hot is hot enough to kill coronavirus? Read on to see, and for the latest warning, check out The Moderna CEO Just Made This Scary Prediction About COVID.

Read the original article on Best Life.

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Length of time required to kill COVID: 20 minutes

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Length of time required to kill COVID: 5 minutes

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Length of time required to kill COVID: 3 minutes

Andrey_Popov / Shutterstock

Despite being able to pinpoint which temperatures were effective at killing COVID from clothing and masks, the researchers also pointed out that the household items you would likely use to get them warm enough aren't up to the task. "These recommendations are hotter than encountered in residential clothes dryers, clothes washing machines, and dishwashers," the study authors write. "For these appliances, temperatures are typically at or below [135 degrees Fahrenheit]. These temperatures are also much hotter than residential hot water (in the United States), for example, because plumbing codes limit hot water to [120 degrees Fahrenheit]." Still, the researchers point out that their findings uphold World Health Organization (WHO) guidelines that 133 degrees Fahrenheit can kill coronavirus within 15 minutes.

And fortunately, there's another old-fashioned way of cleaning that will make up for the lack of heat in your appliances, pointing out that "of course, since soap has some virucide characteristics, washing with soap is expected to inactivate viruses by nonthermal means." And for more on how the pandemic is affecting where you live, check out This Is How Bad the COVID Outbreak Is in Your State.


1. INTRODUCTION

As societies put themselves into voluntary or enforced isolation, large populations of people are experiencing reduced contact with others in public. When people venture into public, they are often donning masks (homemade or industrially produced) or other protective clothing. Upon returning to isolation, masks and other clothing should be treated as contaminated with virus.

How should masks, clothing, and other items be treated? In many instances, simply setting items aside for a long enough period of time will kill the virus. However, the required durations are not known absolutely, and certainly depend on the type of surface. 1 , 2 , 3 , 4 , 5 Some clothing types, for instance, are very capable of retaining moisture and consequently, this affects the survival of virus contained therein. The general consensus is that viruses can survive up to a few days in clothing. It is reasonable to expect a similar survival duration for viruses on/in protective face masks. That is, contaminated masks can be treated by merely setting them aside for some required duration until the viruses die. But to our best knowledge, there is no scientific study on the required duration, and any required duration would depend on the materials that form the mask. For instance, woven fibers differ from non‐woven polymeric filter media. Mask users can apply sanitizing chemicals (such as alcohol) but it is not clear whether this type of sanitizing would adversely affect the porous structure of masks and thereby make them less effective over time. Similarly, there is no current advice available for the use of heat to destroy SARS𠄌oV𠄂.

Here, we summarize all the existing temperature/duration information for both SARS𠄌oV𠄂 and its sensitivity to heat. The summary is used to provide a reasonable recommendation for users to thermally destroy viruses on masks, clothing, or other objects.

1.1. Summary of the existing literature

An example of the state of knowledge on temperatures and coronavirus survival is provided by the CDC, which states:

“Generally coronaviruses survive for shorter periods at higher temperatures and higher humidity than in cooler or dryer environments. However, we don't have direct data for this virus, nor do we have direct data for a temperature�sed cutoff for inactivation at this point. The necessary temperature would also be based on the materials of the surface, the environment, etc.”. 6

But despite official statements such as the above, there is, in fact, some literature on the temperature and exposure durations that are required to inactivate SARS𠄌oV𠄂. In the following, a list of temperature/duration/inactivation rates is provided for coronavirus pathogens. In the listing, we report log reductions in viral load obtained from the references. In some studies, the heating protocol was such that no viral presence was detected afterwards. We have substituted an equivalent log reduction of 7 for these cases. Of course, the actual log reduction would be based on the sensitivity of the measurement instruments however, for practical purposes, we consider a viral reduction of 7 or greater to be at or near total sterilization.

In Table ​ Table1, 1 , we present this literature information. We note that there are differences in the strains and media in which the virus was cultivated. We also acknowledge that there are different thermal sensitivities for differing strains. It is further known that the media can affect the viral survival. For instance, media with protein content make the virus more resistant to heating. With this acknowledged, we opt to not provide separate analysis for different strains or media. Rather, our intent is to provide a single thermal recommendation that can be used to sterilize a broad range of materials.

TABLE 1

List of exposure temperatures and durations for inactivating coronavirus strains

Temperature ( ° C, ° F)Duration (minutes)Log reductionVirusReferences
56, 133105SARS𠄌oV (Urbani strain) 9
56, 133206SARS𠄌oV (Urbani strain) 9
65, 14936SARS𠄌oV (Urbani strain) 9
75, 167157SARS𠄌oV (Urbani strain) 9
55, 1311205Gastroenteritis coronavirus 10
56, 133607Canine coronavirus 11
65, 149407Canine coronavirus 11
75, 167157Canine coronavirus 11
56, 133505Canine coronavirus 11
65, 14955Canine coronavirus 11
75, 16745Canine coronavirus 11
56, 13330ϥSARS CoV, FFM1 no protein 12
50, 122301.9SARS, CoV, FFM1 With 20% protein 12
60, 14030ϥSARS CoV, FFM1 no protein 12
60, 14030ϥSARS, CoV, FFM1 With 20% protein 12
56, 13355.8SARS CoV (Hanoi strain) 13
56, 133106.5SARS CoV (Hanoi strain) 13
56, 13330Ϧ.4SARS CoV (Hanoi strain) 13
56, 133302𠄵SARS CoV (FFM1 strain) 13
56, 13320Ϥ.3SARS CoV (Urbani strain) 13
60, 14030ϥSARS CoV (FFM1 strain) 13
60, 14030ϤSARS CoV (FFM1 strain) 13
60, 14060ϤSARS CoV (FFM1 strain) 13
65, 14910Ϥ.3SARS CoV (Urbani strain) 13

What is seen from these tabulations is that the independent studies are mutually reinforcing. The results from Table ​ Table1 1 can be used to formulate general guidelines for the public.

1.2. Recommendations for thermally destroying coronavirus

We provide a reasonable estimate for near complete thermal destruction of coronavirus. For temperatures above 65ଌ (149ଏ) is expected to cause near complete inactivation with exposures greater than 3 minutes. For temperatures between 55 and 60ଌ (131�ଏ) heating should last 5 minutes or more. However, for temperatures in the range 50�ଌ (122�ଏ) we recommend 20 minutes or longer of exposure. At these levels, we expect the viral concentration to be lowered by log 5𠄇, near or below the detectable limit.

Because of the seriousness of the current coronavirus infection, we suggest a reasonable safety factor can be obtained by increasing the above‐listed temperatures by 10ଌ (about 18 ଏ). Extensive research has confirmed that at least for living cells, the sensitivity of thermal destruction is very strongly linked to temperature. That is, small increases in temperature cause large increases in the death rate. As an example, for mammalian cells and other pathogens (bacteria, viruses, and protozoa) the death rate rises rapidly as temperature increases. 7 , 8 Another reason for using a safety factor is that the temperatures experienced by the virus during heating will not necessarily equal the temperature of the applied heat. Thermal inertia causes a heating lag that depends, in part, on the media being heated.

With this conservative approach, the following become the recommendations:

In order to kill COVID�, heat virus𠄌ontaining objects for:

3 minutes at temperature above 75ଌ (160ଏ).

5 minutes for temperatures above 65ଌ (149ଏ).

20 minutes for temperatures above 60ଌ (140ଏ).

It should be noted that these findings agree with WHO guidelines which report a 4 log reduction of coronavirus for 56ଌ (133ଏ) with 15‐minute exposures 14 and is consistent with information for killing other infectious agents. 15

These recommendations are hotter than encountered in residential clothes dryers, clothes washing machines, and dish washers. For these appliances, temperatures are typically at or below 57ଌ (135ଏ). These temperatures are also much hotter than residential hot water (in the United States), for example, plumbing codes limit hot water to 49ଌ (120ଏ).

Of course, since soap has some virucide characteristics, washing with soap is expected to inactivate viruses by nonthermal means.


This Temperature Can Kill COVID in Minutes, New Study Says

New research has shown that going overboard to keep surfaces in your home free from coronavirus may not be as worthwhile an effort as being diligent about wearing a mask or avoiding crowds. But when it comes to sanitizing clothing or masks, which are worn out into public, keeping them coronavirus-free takes on a new level of importance. Fortunately, a new study has found that keeping items at a high temperature can kill COVID in minutes. Read on to see how hot you need to go to sanitize, and for more on how you can keep yourself safe, check out These 3 Things Could Prevent Almost All COVID Cases, Study Finds.

According to a recent study out of the University of St. Thomas published in the journal Wiley Public Health Emergency Collection, the importance of textile hygiene has taken on new meaning during the pandemic as mask-wearing has become a factor of daily life. And while researchers point out that SARS-CoV-2 viruses that infect will die off naturally with time alone, a variety of factors including the type of material and overall humidity can drastically change the time needed. Additionally, sanitizing solutions could have different effects on different types of materials, which could decrease their effectiveness over time.

"Some clothing types, for instance, are very capable of retaining moisture and consequently, this affects the survival of virus contained therein," the study authors write. "The general consensus is that viruses can survive up to a few days in clothing. It is reasonable to expect a similar survival duration for viruses on/in protective face masks."

By testing cultures exposed to a wide range of temperature levels for varying lengths of time, researchers were able to find out exactly which temperature ranges were capable of inactivating COVID effectively. But the results also pointed to the fact that using heat as a sanitizing tool at home may not be as easy as one might think.

The researchers were also careful to point out that shooting higher than the suggesting range was ideal. "Because of the seriousness of the current coronavirus infection, we suggest a reasonable safety factor can be obtained by increasing the … listed temperatures by [18 degrees Fahrenheit]," the study authors write.

So how hot is hot enough to kill coronavirus? Read on to see, and for the latest warning, check out The Moderna CEO Just Made This Scary Prediction About COVID.


The limits of tardigrades

Tardigrades are well-loved among science enthusiasts for their oddly adorable appearance. They have plump bodies and four sets of stubby legs. This cuteness has earned tardigrades the nicknames "water bears" and "moss piglets." Most species measure less than 0.02 inches (0.5 millimeters) in length.

They're also survivors. Tardigrades can handle being frozen, dried out, deprived of oxygen and blasted with radiation &mdash they've even survived trips into the vacuum of space. The critters do this by going into what's called a "tun" state. They draw in their limbs and contract their bodies, suspending their metabolism and essentially entering a state of suspended animation. There may even be tardigrades in this tun state on the moon right now, after a crash landing by an Israeli lunar probe likely sent some specimens scattering.

Previous research found that tardigrades could even survive being boiled at up to 303.8 F (151 C) for an hour, Neves told Live Science. But no one had studied how tardigrades handle heat for longer periods. That's what Neves and his colleagues set out to do.

Their methods were simple. The research team exposed tardigrades of the freshwater species Ramazzottius varieornatus to temperatures of up to 104 F (40 C) in increments of 2, 24 or 48 hours. The tardigrades were in either an active or a tun state. Researchers also tested the the creatures' survival when the temperature increase was gradual rather than immediate, exposing some of the tardigrades to acclimation periods of 2 hours at 86 F (30 C) and then 2 hours at 95 F (35 C).

The result? Too long in the heat wasn't great for tardigrade health and happiness. After 48 hours at 104 F, all tardigrades in the active state died. At 98.6 F (37 C), about 46% of the active tardigrades died within 48 hours. Acclimation helped, though. Active tardigrades that went through the acclimation steps had a 72% survival rate at 48 hours, meaning just 28% died.


Why The Flu Virus Is More Infectious In Cold Winter Temperatures

A finding by a team of scientists at the National Institutes of Health may account for why the flu virus is more infectious in cold winter temperatures than during the warmer months.

At winter temperatures, the virus&rsquos outer covering, or envelope, hardens to a rubbery gel that could shield the virus as it passes from person to person, the researchers have found. At warmer temperatures, however, the protective gel melts to a liquid phase. But this liquid phase apparently isn&rsquot tough enough to protect the virus against the elements, and so the virus loses its ability to spread from person to person.

&ldquoThe study results open new avenues of research for thwarting winter flu outbreaks,&rdquo said National Institute of Child Health and Human Development (NICHD) Director Duane Alexander. &ldquoNow that we understand how the flu virus protects itself so that it can spread from person to person, we can work on ways to interfere with that protective mechanism.&rdquo

Influenza viruses are usually spread from person to person through coughs and sneezes. Infection with flu virus can cause mild to severe illness, and at times can lead to death.

In October of 2007, researchers working with guinea pigs showed that animals sick with the flu were more likely to get other guinea pigs sick at colder temperatures than at warmer temperatures.

In the current study, the NIH researchers used a sophisticated magnetic resonance technique, developed and previously tested in NIAAA's Laboratory of Membrane Biochemistry and Biophysics, to create a detailed fingerprint of how the virus&rsquos outer membrane responded to variations in temperature. The virus&rsquos outer membrane is composed chiefly of molecules known as lipids, explained the study&rsquos senior author, Joshua Zimmerberg, Ph.D., chief of NICHD&rsquos Laboratory of Cellular And Molecular Biophysics. This family of molecules does not mix with water, and includes oils, fats, waxes, and cholesterol.

Dr. Zimmerberg and his colleagues found that at temperatures slightly above freezing, the virus&rsquos lipid covering solidified into a gel. As temperatures approach 60 degrees Fahrenheit, the covering gradually thaws, eventually melting to a soupy mix.

Cooler temperatures, apparently, cause the virus to form the rubbery outer covering that can withstand travel from person to person, Dr. Zimmerberg said. Once in the respiratory tract, the warm temperature in the body causes the covering to melt to its liquid form, so that the virus can infect the cells of its new host, he added.

&ldquoLike an M&M in your mouth, the protective covering melts when it enters the respiratory tract,&rdquo Dr. Zimmerberg said. &ldquoIt&rsquos only in this liquid phase that the virus is capable of entering a cell to infect it.&rdquo

In spring and summer, however, the temperatures are too high to allow the viral membrane to enter its gel state. Dr. Zimmerberg said that at these temperatures, the individual flu viruses would dry out and weaken, and this would help to account for the ending of flu season.

The finding opens up new possibilities for research, Dr. Zimmerberg said. Strategies to disrupt the virus and prevent it from spreading could involve seeking ways to disrupt the virus&rsquos lipid membrane.

In cold temperatures, the hard lipid shell can be resistant to certain detergents, so one strategy could involve testing for more effective detergents and hand-washing protocols to hinder the spread of the virus.

Similarly, Dr. Zimmerberg added that flu researchers might wish to study whether, in areas affected by a severe form of the flu, people might better protect themselves against getting sick by remaining indoors at warmer temperatures than usual.


Why fever can be your friend in times of illness

Fevers are more than just a symptom of illness or infection, claim researchers elevated body temperature sets in motion a series of mechanisms that regulate our immune system, they found.

Share on Pinterest Does elevated body temperature actually help to boost our immune response?

When we are healthy, our body temperature tends to gravitate around a constant 37°C (98.6°F).

But when our bodies are faced with an infection or virus, body temperature often goes up and we experience fever.

A slight fever is characterized by a minor rise in body temperature to about 38°C (100.4°F), with larger increases to around 39.5°C (103.1°F) counting as “high fever.”

When we have the flu, for instance, we may come down with a mild and somewhat uncomfortable fever, driving many of us to seek natural or over-the-counter remedies against it.

Fevers aren’t always a bad sign you may even have heard that mild fevers are a good indication that your immune system is doing its job. But fevers aren’t just a byproduct of our immune response.

In fact, it’s the other way around: an elevated body temperature triggers cellular mechanisms that ensure the immune system takes appropriate action against the offending virus or bacteria.

So say researchers hailing from two academic institutions in the United Kingdom: the University of Warwick in Coventry and the University of Manchester.

Senior researchers Profs. David Rand and Mike White led teams of mathematicians and biologists to understand what happens at cellular level when fever takes hold.

Their findings, which have recently been published in PNAS, reveal that higher body temperatures drive the activity of certain proteins that, in turn, switch genes responsible for the body’s immune response on and off, as required.

A signaling pathway called Nuclear Factor kappa B (NF-κB) plays an important role in the body’s inflammation response in the context of infection or disease.

NF-κB are proteins that help to regulate gene expression and the production of certain immune cells.

These proteins respond to the presence of viral or bacterial molecules in the system, and that is when they start switching relevant genes related to the immune response on and off at cellular level.

Dysregulated NF-κB activity has been linked with the presence of autoimmune diseases such as psoriasis, Crohn’s disease, and arthritis.

The researchers note that NF-κB activity tends to slow down the lower the body temperature. But when the body temperature is elevated over the usual 37°C (98.6°F), it tends to become more intense.

Why does this happen? The answer, they hypothesized, might be found by looking at a protein known as A20, encoded by the gene with the same name.

A20 is sometimes hailed as the “ gatekeeper ” of inflammatory responses, and the protein has a complex relationship with the NF-κB signaling pathway.

NF-κB switches on the gene that produces A20 protein, but the protein, in turn, regulates NF-κB activity, so that it is appropriately slow or intensive.

The researchers involved in the new study wondered whether blocking the expression of the A20 gene would affect the way in which NF-κB functioned.

And, sure enough, they found that in the absence of the A20 protein, NF-κB activity no longer reacted to changes in body temperature, and its activity therefore no longer increased in case of a fever.

These findings might also be relevant to the normal fluctuations in temperature that our bodies undergo every day, and how these may affect our response to pathogens.

As Prof. Rand explains, our body clock regulates our internal temperature and determines mild fluctuations — of about 1.5°C (34.7°F) at a time — during wakefulness and sleep.

So, he says, “[T]he lower body temperature during sleep might provide a fascinating explanation into how shift work, jet lag, or sleep disorders cause increased inflammatory disease.”

Although many genes whose expression is regulated by NF-κB were not temperature-sensitive, the researchers found that certain genes — which played a key role in the regulation of inflammation and which impacted cell communication — did, in fact, respond differently to different temperatures.

Together, the findings suggest that developing drugs to target temperature-sensitive mechanisms at cellular level could help us to alter the body’s inflammatory response when needed.

“ We have known for some time that influenza and cold epidemics tend to be worse in the winter when temperatures are cooler. Also, mice living at higher temperatures suffer less from inflammation and cancer. These changes may now be explained by altered immune responses at different temperatures.”

Prof. Mike White


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