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Opinion: Want to eradicate viruses? They made us who we are

ljm67 — Tue, 28 Feb 2017 16:52:22 +0000

It is cold and flu season so many of us are currently under the weather with a virus. But what exactly is a virus? And are they even alive?

Outside a host cell, these weird microscopic particles, or virions, only consist of a tiny piece of genetic information (about 10,000 times less than that contained in the human genome) and a protein or lipid (fatty molecule) shell. Whether these particles are living things is the subject of much debate, as they don’t meet many of the usual criteria for life.

While there isn’t any formal agreement on what defines life, most definitions include the ability to adapt to the environment, to reproduce, to respond to stimuli, and to use energy.

While the virus particle may fall short of the definition of life depending on the criteria used, for some virologists like myself, thinking of the virion as the “virus” is like calling a sperm or unfertilised egg a “person”. Sure, a sperm is an essential step towards creating a person, but few people would argue that a sperm or unfertilised egg should be described as the finished product.

Flu: part virus, part human. Shutterstock

Much like a sperm, virions are produced in the millions. Many will never reach their destination and are lost and degrade in the environment. It is only when the virus binds to and enters a target cell that its cycle of replication can begin.

A virion doesn’t even always contain a majority of the molecules a virus can create. For example, the norovirus virion contains just three different types of protein and one type of RNA (a nucleic acid like DNA which uses a different sugar to form its backbone). Infected cells, however, make at least eight different viral proteins and four different viral RNAs.

Nor does the virus particle itself usually result in the symptoms of disease. Typically, when you catch a virus, your symptoms come from either infected cells dying, or your immune response to those infected cells.

For these reasons, some virologists consider the infected cell, rather than the virion, to be the virus.

I am virus

While this idea sounds outlandish, from conception to grave, your cells are intricately associated with viruses. Even if you don’t have a cold or the flu, you are still part-virus as human DNA plays host to a range of different viruses.

These are retroviruses, the best-known example of which is HIV. While HIV only entered the human population relatively recently, viruses very much like it have been infecting us and the creatures we evolved from since long before humans even existed.

While HIV infects immune cells, when a retrovirus instead infects the cells that produce eggs or sperm, the viral DNA can be inherited by any offspring. Over millions of years, these viruses have lost their ability to produce infectious particles, but have in some cases found other vital roles, and are now indispensable for human life.

One well-studied example is a protein called Syncytin-1, which is vital for the development of the placenta. This was originally a retroviral protein which entered the monkey population which gave rise to humans around 24m years ago. If we deleted this protein from our DNA, humanity would rapidly go extinct as we could no longer produce a functional placenta.

Transplanting pig organs into humans carries a risk of viral infection. Shutterstock

All these viruses which inserted into our DNA long ago are termed endogenous retroviruses (ERVs). In humans, ERVs have long since lost the ability to produce infectious virions, but this is not the case in all animals. Pig ERVs, for example, can produce infectious particles and are a concern when considering the use of pig organs for transplant, as these are known to be able to infect human cells in the lab.

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If a virus is the infected cell, rather than the virion, you could even think of the viruses that can infect us as more than 99.9% human. This is because they need many of the human proteins or other molecules present in your cells and encoded in your DNA to make more virus.

A human cell is vastly more complex than even the largest virus, and viruses can make use of this to compensate for their own simplicity. Viruses and their host cells share many common needs. They need to be able to produce RNA, protein, lipids and have access to the raw materials to generate these. As a host cell already contains all the needed components to achieve this, a virus can simply provide its own instructions, in the form of the viral genome, and let the cell do most of the work.

It takes many more cellular proteins to make a virus, than it does viral proteins. A virus only needs to provide instructions for the few components the host cell cannot produce. An example of this would be viruses which have a virion with a lipid membrane, such as influenza. This membrane is usually recycled from host cell membranes. ̽��ֱ��addition of a couple of viral proteins converts this into the membrane coat of the virion.

This use of host components by viruses also makes it clear why it has been so difficult to develop effective antiviral drugs. Much as with cancer treatment, there is very little to distinguish infected cells from normal human cells, which makes coming up with a drug that will only target infected cells extremely challenging. To be effective, you have to target that tiny part of the infected cell that is purely virus, without harming the remainder.

So are viruses alive? It’s still not settled, and really depends on what you think a virus is. What does seem clear, however, is that the viruses which infect us can be seen as part human, and we are part virus.

Edward Emmott, Research Associate in Virology, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

We are still part-virus, writes Edward Emmott, Research Associate in Virology, for ̽��ֱ��Conversation. Human DNA plays host to a range of different viruses. And this could help explain why it has been so difficult to develop effective antiviral drugs.

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HIV-infected T cell

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Opinion: Why is the norovirus such a huge problem for the NHS?

ljm67 — Fri, 13 Jan 2017 12:54:18 +0000

Norovirus, also known as winter vomiting disease, is on the rise again according to a report in the BMJ. A familiar set of warnings about ward closures and avoiding visits to patients in hospital was also issued, but why does this one virus cause the NHS such difficulty?

While norovirus does occur year-round, there is a winter peak in cases that clashes with the winter rush on the NHS. ̽��ֱ��symptoms of norovirus – diarrhoea and vomiting – typically last a day or two. While you may spend those days wishing you were dead, the chances of long-term harm from the infection are extremely low if you are otherwise healthy. ̽��ֱ��people most at risk from norovirus are the very young, the elderly and people with impaired immune systems (those said to be immunocompromised). Unfortunately, these are exactly the groups most likely to find themselves in hospital.

As a result of advances in transplant medicine and cancer treatment that suppress or affect the immune system, these immunocompromised patients make up an increasingly large portion of the population. While norovirus only lasts a few days at most in healthy people, those who are immunocompromised can struggle to clear the infection; it can linger for weeks, months or even years. Fortunately, it is rare that full-blown norovirus symptoms are experienced for this long. It does make it hard to absorb food and gain weight, which is a worry after major surgery and can make recovery much more difficult. As such these patients are a particular concern.

It is very easy to pass on the norovirus. One tablespoon of diarrhoea from a single patient can contain enough infectious virus to infect everyone in the world many times over. To make things worse, like many other viruses, people may remain infectious for several days after symptoms have resolved and not every infected person may even be symptomatic. Many cases are traced back to food handlers who may appear well and have no idea they are infectious. ̽��ֱ��virus can be spread through touching infected surfaces or material and a lack of suitable handwashing or hygiene before.

Outbreaks tend to occur in closed environments such as hospitals, cruise ships, schools and retirement homes, as these all share common dining and social areas and have many people eating food prepared by others. In the case of hospitals, many of these have a food court or canteen which is shared by staff, patients and visitors. In summer, many escape outdoors on lunch breaks to enjoy the weather. But in winter when norovirus peaks, everyone crowds together inside, away from the cold.

An expensive virus

Hospital staff are at an increased risk of catching norovirus themselves as they deal with large numbers of patients. This is not only unpleasant for the individuals concerned, but also means it’s possible for asymptomatic staff to spread the virus to patients and so exacerbate the problem. For this reason hospitals are very careful about decontamination, staff training, and discouraging ill staff from working for up to 48 hours after symptoms have resolved.

For an organisation which runs 24/7, and relies on a great deal of shift work, this can be very disruptive. All these disruptions come at a cost – lost hospital beds and closed wards, at a time when beds are already at a premium. In the two weeks before Christmas 2016, there were 15 hospital outbreaks of norovirus in the UK, 14 of which resulted in closed wards or restrictions on patient admissions. Past estimates of the costs of norovirus to the NHS put the total at over £100m (in 2002-03 prices). This is the same as employing over 3,000 extra specialist nurses, or around a third of the total cancer drugs budget.

̽��ֱ��cost to the global economy of norovirus has been estimated at a whopping US$44 billion, with US$4.2 billion of that to healthcare systems. At a time when NHS budgets are stretched, and hospitals are in debt, these additional costs are ones that hospitals can ill afford. With other seasonal and highly contagious diseases such as influenza, the NHS is able to offer and encourage its staff to take up free vaccinations in order to try and reduce the impact on staff, patient and visitor health. However, the absence of a vaccine means this is not yet an option for norovirus.

Vaccine trials are underway

While no drugs or vaccines are available, several vaccine candidates are in clinical trials. Sadly, immunity to norovirus does not last for long so, much like the flu vaccine, it is expected that regular vaccinations would be needed to make sure you remain immune. This would still be a huge benefit, and allow vaccination of workers at particular risk, or most likely to transmit the virus, such as NHS staff or those in the catering industry. ̽��ֱ��recent discovery of a means of growing different human norovirus strains in the lab, rather than having to rely on related animal viruses for research, will also boost efforts to find antivirals to help treat infection.

If you have norovirus, there is little your GP or hospital can do for you. ̽��ֱ��most a visit in person is likely to achieve is to spread the virus to other people. ̽��ֱ��NHS recommends that you stay at home, drink lots of water and, if you are concerned, phone your GP or NHS 111 for further advice.