If every person in the world isolated from each other for a certain period of time, say a month, would all transmissible diseases disappear? Lily Pauls Post your answers (and new questions) below or send them to nq@theguardian.com. A selection will be published next Sunday. A month, on my own? If I can take my oil painting kit and a few good books, I’m up for it. I miss lockdown. DewinDwl Not in a month, or even a year – a century would probably do it! Philip Nye No, people would still have diseases that last longer than a month, and they would still be stored in other reservoirs, especially animals. Flu frequently jumps the species barrier; obviously Covid has. You might also have some cold virus in your freezer waiting to come out. KHeraty Viruses don’t survive outside a living host. Virus attach themselves due to the lipid outer shell on the particles and that is pretty fragile. Virus samples kept in labs have to be stored in a medium in a vial and then stored in stable temperatures. A home freezer would expose the particles to damp and variable temperatures and cause the lipid and protein shell to break down. Bacteria will survive freezing, but bacterial infections tend to be far less transmissible than viruses. Emilyisobel Some viruses can remain dormant for days, years, decades, millennia. When they are revealed or wake up … they start all over again. Spreading through the populations. Cynthia McLeod As a public health doctor, the simple answer is no. This is for several reasons: chronic infections, colonisation and animal/environmental reservoirs. 1) Chronic infection. While many transmissible diseases either resolve by themselves or following appropriate treatment, many people have persistent or “chronic” infections. So even if a person with a chronic infection isolated for a month, they would still continue to be infectious after this, unless they are on medication that reduces levels in their body to a point where they are not contagious. Examples of chronic infections include human papillomavirus (HPV), chronic hepatitis B and HIV. The same also applies for diseases that haven’t been diagnosed and treated yet, such as tuberculosis, where someone could be infectious for months or years before they get antibiotic treatment. 2) Colonisation. Many people carry microbes that cause transmissible diseases asymptomatically, for example on their skin, or in their throat or gut. This is known as colonisation. It’s different to chronic infection, in that the person isn’t being harmed by the microbes living on their body, but they can spread the microbes to others. Examples include the MRSA bacteria on skin, and Neisseria meningitidis, a bacteria that can cause meningitis, which commonly lives harmlessly in the throat. If people colonised with microbes that can cause disease isolated for a whole month, they are likely to still be carrying the microbes after this, and still able to pass the infection on. 3) Animal/environmental reservoirs. Human-to-human transmission is only part of how infectious diseases spread. Many transmissible diseases have reservoirs in animal species and the environment, so even if human interactions were completely ceased, transmissible diseases would continue to exist in animals, and the environment – particularly soil and water. Affected animals often don’t have symptoms, and animal reservoirs range from salmonella in reptiles, to TB in cows and influenza in birds. When infected animals come into contact with humans, animal-to-human spread can occur. For other diseases, the microbes that cause them can live in the environment too, such as the bacteria that causes tetanus, which can live in soil, and many microbes that live in water, such as parasites such as cryptosporidium and bacteria such as E coli. Dr Judith Ewing Probably in the scenario depicted by Ms Pauls, the rate of infectious diseases among people would go down drastically for a while. Then someone would catch a viral or bacterial infection from, say, contact with an infected bird or mammal – the contact could be as simple as eating some inadequately cooked chicken or beef – and that disease would soon spread to other people. Interestingly, epidemics often start in meatpacking centres such as Hong Kong or Chicago. Not that vegetarians cannot be infected by their food: eating inadequately washed fruits or vegetables, perhaps those contaminated by bird faeces, will do it. Then there are biting insects such as mosquitoes, which are well-known vectors of disease … As long as humans have any contact at all with the natural world, some people will catch infectious diseases. Roland Kuhn Let’s just imagine we do this, what then? You will end up creating a large number of vacant niches for some other virus to evolve in to. And this is pretty much what would happen. We would be encouraging the emergence of new diseases, to which we would also have no immunity by definition. We have co-evolved with our viruses for a long while, typically (there are exceptions), and so evolution has adapted ourselves and the viruses to live in something like an equilibrium. Most viruses we will commonly encounter are pretty mild. We do not want to really start from no viruses and have every new one a deadly disease. Better the devil you (and your immune system) knows. SporadicallySmiling We know the results of this experiment. Not a single one of the 200 respiratory viruses were eradicated from the human population by lockdown. We have only eradicated one virus so far, smallpox, and that was achieved using vaccines that significantly reduced transmission and contact tracing. It took 170 years from the development of the first vaccines. As a footnote there was never any prospect of eradicating Sars-Cov2 because the R number was so high, pre-symptomatic transmission made contact tracing extremely difficult, and there are now numerous animal species that also harbour the virus that would pass it back to us even if we were to eradicate it temporarily.IrritableSteve No. Even if we say we’re only considering short-lived, highly transmissible infections like colds and flu, a month isn’t long enough. All other considerations aside, people with compromised immune systems can remain infected for longer periods of time than healthy people. ElizaBee The answer is no. In order for your plan to work, two things would have to be true: 1) The disease cannot survive anywhere except in the human body. 2) All people infected with the disease would have to be able to completely eliminate the pathogen from their bodies within that one month period. Unfortunately, in most cases, neither of those things is true. Many infectious diseases can persist indefinitely in the body if they’re not treated, and sometimes even if they are treated. Many sexually transmitted diseases work like this, for example – HIV, herpes, and HPV are all incurable; syphilis, gonorrhoea and chlamydia are curable, but will persist indefinitely if not treated. And even diseases which are normally eliminated in a short time can persist for much longer in people who have a compromised immune system. (It’s possible that this is where the Omicron variant of Covid originated – a person with HIV was infected for a very long period of time, with mutations accumulating.) Also, many infectious agents can exist outside the human body for long periods. In particular, many can survive in animal bodies. Covid, for example, infects many animals, including mustelids – remember the cull of farmed mink in Denmark. Monkeypox can also infect a number of animal species. Bubonic plague was famously carried by rats; so is Weil’s disease. Malaria infects mosquitoes, and Lyme’s disease is spread by ticks. (And so on.) Diseases can also survive for a surprisingly long time in frozen meat, or on surfaces, in sewage or in other environments. Legionella, for example, is often found in hot water systems. So no, this wouldn’t be effective at all. Shasarak If we all shaved our heads one day, the head louse would become extinct. redleader I don’t want to nitpick, but … Mobilepope