The Spread of Viruses

I came across this piece today here…

It was in Dutch, and frankly needs to be in English, so here it is. I mailed the publisher and told them what I planned but haven’t yet heard back. Hope they do but it’s too important that people get to hear a voice of reason for a change.

An interview with Professor Menno Jan Bouma, by Ruby Tilanus

Menno Jan Bouma
Menno Jan Bouma

Physician, epidemiologist and emeritus professor Menno Jan Bouma lived in Amsterdam Oost for many years. As a guest lecturer he gave lectures at the Tropical Institute in Amsterdam Oost, and while he now lives in Ireland, he still likes to make regular visits to Amsterdam. He devoted his life to researching the ecology and spread of viruses and other pathogens. In this time of the coronavirus, I would like to know a little more about viruses. So I talk to him about that.



Interviewer – Ruby Tilanus

You worked at the Tropical Institute in London but came back to teach at our Tropical Institute in Amsterdam Oost. How was that?

Awesome. There are only a few places in the world with an enormous amount of knowledge about infectious diseases. The Royal Tropical Institute in Amstewrdam Oost was one of them. Unfortunately, in the 1960s, many thought that we had mastered infectious diseases, and in and after the 1980s the Tropical Institute was largely cut back. The library has been closed. Specialists, collections and books disappeared. A lot of knowledge has been lost as a result. And where knowledge is lacking, fear lurks.


That knowledge could now have come in handy when tackling the coronavirus.



Fortunately, you are still here, and you want to share your knowledge about viruses with us. First of all, tell me: what is a virus anyway?

A virus is not a “living” being like you and I are. A virus is not alive.

A virus consists of genetic material (DNA or RNA) surrounded by a packaging (a shell). A virus cannot do anything without a ‘host’ or ‘hostess’. It’s as dead as a piece of plastic.

It shows no sign of life, but if a virus has the viral luck of invading cells of a host’s body, it starts behaving like a bear coming out of hibernation.

The virus uses its host’s building blocks to reproduce itself. That is the only thing a virus can do and a piece of plastic cannot. That is also the only thing that a virus can actively do on its own: reproduce itself. Although: self, active… a virus does need a host for that.


What happens to a virus after it reproduces?

After reproducing, the new, young viruses look for a new host.

That is where such a young virus must travel and penetrate. That is quite difficult for the virus, since it cannot do anything by itself, except reproduce itself. He has to travel passively or hitchhike somewhere, and then get in somewhere. If that is successful, the virus feast of reproducing can take place again. So the virus cycle is: travel, invade, reproduce itself, travel, invade, reproduce itself and so on. A virus cannot or does not do anything else. Because a virus is not “alive”.


How do viruses do that: passive travel and passive intrusion? A virus has no wings, no legs and no webbed feet to travel? And a virus can’t just enter through your skin, can it?

Correct! A virus has no wings, no legs, and no webbed feet to travel from one host to another. And indeed, a virus cannot just enter through your skin. Your skin is literally an impenetrable barrier for a virus.

Viruses have developed various strategies over the course of evolution to travel and to invade their hosts. The way a virus travels is directly related to the way in which the virus enters the body of its host after its journey. So you always have a way of traveling and a way of penetrating that are linked to each other. Each virus species specializes in at least one of those strategies. On that basis, you can divide all the viruses out there into roughly three different main groups.


Please tell me a bit more about those different main groups of viruses…!

 You can give the main groups the following names:

– ‘Opportunists’: they enter the body through damage such as a wound or a blood transfusion (think of the AIDS virus);

– ‘Survivors’: they follow the path of food (think of diarrhoea viruses);

– ‘Kites’: they hitch a ride with the air we breathe (think of flu viruses and corona).


You are the first to mention: Opportunists (like the AIDS virus). What is Opportunists’ strategy?

An opportunist waits until he finds an opening somewhere in the skin of the new host, a wound for example. Then he waits until his old host makes direct contact with that wound with his blood or with his semen. And then he enters the body of the new host through that wound. Opportunists can also enter via an insect sting (stinger).


And Survivors (like diarrhoea viruses)? What is their strategy?

Survivors can withstand the extreme acidic gastric juices and the extreme conditions of the gut, and can survive there. They reproduce in the gut. If an old host doesn’t wash their hands after pooping, a tiny bit of faeces can get on the old host’s hands, which can then end up on a table, elevator button, or other surface, for example. If the new host touches that surface, or shakes the old host’s hand, the Survivor can land on the new host’s hands. If the new host then licks its fingers and does not wash its hands before eating, the Survivor may enter the new host’s stomach and intestines through the mouth.


 What interests me especially in this corona time: what is the strategy of Kites (such as flu viruses and corona)?

The strategy of kites is to hitch a ride with small droplets that the old host releases through the mouth. When the old host exhales, talks, sings or coughs, small droplets come out of his mouth. Kites try to hitch a ride with those tiny droplets. A kite that is lucky leaves the body of the old host in a small drop. It then travels through the air to a new host, and enters the body along with the inhaled air. There he tries – still wrapped in a droplet – to hitch a ride to the alveoli, deep in the lungs. Deep in the lungs, the lung wall is very thin: only one cell layer thick. Our immune system is weak there: much fewer virus particles are needed to make you sick.


How small are those droplets?

The droplets are all small. But some droplets are many times smaller than other droplets. We call the smallest droplets ‘aerosols’ and they can fly.

The larger droplets do not float in the air for long. They fall to the ground within a few seconds due to gravity. They cover a distance of about half a meter with normal breathing to several meters with a strong cough. To reach the new host, the Kites must get to nose or mouth level of the new host. However, the larger droplets quickly bend towards Earth due to gravity. The aerosols stay in the air for a very long time. If not properly ventilated, they can circulate in the air for hours. They can travel enormous distances.


Okay, this is the story from the virus side. But what about our side of the story? What is our defense against viruses?

Humans have been living with viruses since their inception. We and our distant ancestors in the animal kingdom have, as it were, evolved together with the viruses. There are many forms of innate and attainable defenses that have developed over time. Antibodies are just one of them. We have developed corresponding defense strategies for each of the different strategies of viruses for survival (Opportunists, Survivors and Kites).


Tell: what is our defense strategy against opportunists (such as the AIDS virus)?

Our oldest defences may have been developed against Opportunists. We have a skin. Our skin blocks almost everything harmful that wants to enter our body. If we have a wound, our body is very capable of healing that wound very quickly.


And what is our defense strategy against Survivors (such as diarrhoea viruses)?

We have developed an extremely sour stomach for them, among other things. Our gastric juice damages almost all viruses, so that they can no longer reproduce. Most Survivors also do not survive our gastric juice – only the few who do get the chance to reproduce.


And now the most important thing: what about our defences against Kites (such as flu viruses and corona)?

To get deep into the lungs, a Kite must first go through the mouth or nose. We all have multiple defense mechanisms in our nose and in our mouth and pharynx, including immune cells. An entire army with a vanguard, a rear-guard and many layers of commanders is ready to stop the Kites.

Most invaders get stuck in the labyrinth of mucous membranes and small hairs in your nose and are neutralized here. The mouth and pharynx also participate in the defense against the Kites. If they end up in the stomach, they don’t stand a chance there.


Does it matter whether a Kite enters via a large or a small drop (aerosol)?

Yes. If a Kite rides along with a small drop (aerosol), the chance of breaking through the defense line is much higher than with a large drop. Just as small fish have a much greater chance of slipping through the mesh of a net than large fish. In addition, together with the inhaled air, the Kite can – if he is lucky – fly deep into the lungs. After all, the drop is so small that – with a bit of luck – it can go straight into the lungs. The Kite virus then rides along with the aerosol.

If a Kite piggybacks on a large drop, it will have a much harder time upon the arrival of the new host. The chance that he will be stopped at the gate (in the nose, mouth or pharynx) is then maximum.


What exactly happens in the nose?

Everything in the nose is aimed at preventing viruses, bacteria and other germs from entering our body. In addition to the nose, the mouth and pharynx are also extremely adept at this. Our defenses are ready to deal with intruders. In most cases, we manage to effectively stop intruders (such as viruses and bacteria) in the nose and make them harmless. In the meantime, we did get ‘acquainted’ with the intruder. This means that the next time the same intruder shows up at our front door, we can intervene more quickly and effectively. You can compare that with a kind of standing up and getting acquainted at the front door: our body is introduced to the hitherto unknown virus, and can start to build up an immune system and make antibodies against the virus.


You have researched the role of seasons and weather on the spread of infectious diseases. Does that also play a role in the spread of corona?

Yes, most infectious diseases are seasonal diseases. For Kites, this mainly has to do with temperature and humidity. Kites such as flu viruses and corona thrive in cool, dry air, while Survivors dehydrate faster and die in dry air. It is not yet entirely clear whether the humidity is bad for the virus itself, or for the life of the aerosol. In moist air, aerosols may deflect quickly towards the earth.

Aerosols can circulate much longer in dry air. In the summer we saw many corona cases worldwide in the meat processing industry: there the air is kept cool and dry and in order to save costs insufficiently refreshed with outside air: a ‘Valhalla’ for kites (aerosols). In winter we heat our houses and are more indoors. The air dries out and we live together in a smaller space. You can then ingest a larger dose of viruses into the lungs, your most vulnerable place. That makes flu and corona real winter viruses. Savings on heating (from draft excluders to intelligent systems that supply fresh air only when it is really needed) is usually at the expense of fresh and more humid outside air. So we have to be careful with that!

With the winter season approaching, I advise everyone to ensure good humidity in the house. By placing a bowl of water on several radiators, for example.


Do you think it’s wise to meet outside with people?

It is indeed wise to meet outside. The behaviour of aerosols can be compared to the behaviour of cigarette smoke. When you smoke a cigarette outside, your smoke dissipates quickly and it doesn’t bother others unless you blow them in the face. It is the same with aerosols. If you carry the coronavirus with you and you meet people outside, they will not be bothered by your aerosols. Except when you blow them in the face.


And what about ventilation? Does that make sense?

Yes, that certainly makes sense. Compare it to cigarette smoke again. If you smoke a cigarette in my living room and I don’t ventilate properly, well, I can still smell your cigarette days later. But if I open the windows opposite each other for a while, the smell is gone.

It is the same with aerosols. If you ventilate well and open the windows against each other, they are gone in no time. Especially in winter, the peak season for the virus, fresh air is very important.


What else can we do to contain Kites like the coronavirus?

It is very important in the fight against all infectious diseases: make sure that your natural immune system can function properly. Think of a healthy diet, sufficient exercise and sufficient sleep. Take an extra dose of vitamin C and D every day to strengthen: these vitamins help your immune system.

Also take care of psychological well-being. We call this ‘vitamin P’ where the P stands for pleasure. Do things that make you happy. Dance, make music, meet up with friends, go out.

And always avoid super spreader events.


What about super spread events? Tell me more about it…

The coronavirus can spread very quickly during so-called ‘super spread events’. These are events in which many people spend hours together in a poorly ventilated room. For example, think of Après-ski bars or carnival cafes. Only one person needs to carry the coronavirus. That one person blows many aerosols into the air unnoticed. Probably some coronavirus carriers do that more intensely than others. All those present then breathe in these aerosols for hours. The virus has a very good chance of penetrating many people, in numbers that our defences cannot handle.


I don’t hear you about washing hands, disinfecting, keeping your distance, not shaking hands, and not cuddling…!

Those measures are perfect to tackle Survivors such as diarrhoea viruses. Survivors travel from host to host through hands, surfaces, and touch. If you want to tackle these viruses, it is indeed very good to disinfect everything and to keep your distance and not to touch each other.

But now we know that corona is a Kite. Kites have a different strategy for traveling from host to host, and for invading hosts.

As mentioned: Kites mainly spread through the air. Compare it again with cigarette smoke: it hardly spreads through hands or surfaces. Just go and blow cigarette smoke against your hands, and then give someone else a hand or a hug. The chance that your cigarette smoke will end up deep in the lungs of the other person in this way is minimal. Pilots need a lift of aerosols, in order to reach deep into the lungs where our body has less resistance. The measures for washing hands, disinfecting, keeping your distance, not shaking hands and not cuddling are therefore not or hardly effective when you want to tackle Kites such as flu viruses or corona.


But Menno, isn’t that the opposite of what Mark Rutte is asking of us?!

Partly yes. But Rutte has also asked us several times to use our common sense…


I’ve heard you say, “Viruses are like burglars. You have to stop them at the front door.” What exactly do you mean by that?

There is a big difference between a burglar who is stopped at the front door, and a burglar who enters your house for a while and then rushes out again, and a burglar who settles in your house and lives there. It is the same with viruses. If you ‘stop a virus at the front door’, in other words if you stop a virus in your nose, mouth and pharynx and make it harmless there, then you are doing well. You literally get to know the virus up close, so that you can react even faster next time. If you inhale a virus for a while and then exhale again, there is not much to worry about. But if a virus settles deep in your lungs and starts reproducing there, yes, you can get really sick.


We are currently seeing a huge increase in the number of corona infections. Also here in East. How do you view that?

The infections are now measured with the so-called ‘PCR test’. That test examines whether you have the coronavirus in your nose, mouth or pharynx or leftovers of the dead virus if the infection has already passed. Many people who have the virus in their nose, mouth or pharynx are engaged in ‘meeting and standing at the front door’. As I just said: in normally healthy people with a normal immune system, there is a whole army of immune cells ready in your nose, mouth and pharynx. That army gets acquainted with the virus, makes the virus harmless, and at the same time has got to know the virus, so it can respond even better next time. I personally think that the word ‘contamination’ is therefore not so well chosen. I would rather speak of ‘acquaintance’. Yes, it is true that the number of ‘acquaintances’ with the virus is increasing (hugely).


But isn’t it very bad that the virus is in the nose of more and more people?

Yes and no. People who have learned about the virus and managed to stop at the front door function as a kind of ‘living shield’ for all the vulnerable in our society. I’m talking about the famous ‘group immunity’ here. As a community, you need some time to build up group immunity. As a rule, young, vital people are not or hardly affected by corona. They almost always end up with a little sniffling. In the Netherlands there is a great sense of community, and the care for the elderly is wonderful. A nice appropriate slogan could be: ‘Take good care of your grandmother: make sure you have had corona.’ For corona, the more favourable that is for our fellow humans with a very weak defense.


That brings me to the question: how deadly is corona really? Do virologists and epidemiologists have a standard yardstick for this?

In the Netherlands we live with 17 million people. Every day people are born, and every day people die. That is a natural process. If more people die than average, we speak of ‘excess mortality’. If fewer people die than average, we speak of ‘under-mortality’. In the Netherlands we had excess mortality in the months of March and April 2020. After that, there was a months-long period of under-mortality in our country.

We express the lethality of a virus with the IFR, the Infection Fatality Rate. That is the percentage of people who have been in contact with the virus who die from the virus. Corona has an estimated IFR of 0.5 percent or lower. This can be compared with the IFR of a moderate to severe flu.

Yes, corona is a new virus. But I want to advocate moving from fear to trust. We count the brothers and sisters of the coronavirus under our ‘medium winter flu’. Global panic is not necessary. People are generally much more rational with the much more serious infections that you see in the tropics.


But in the US, a lot of people die from corona, right?

Correct. In areas with a high mortality, it is striking that the socially deprived part of the population in particular dies. This part of the population is at increased risk for a serious course of the disease, such as obesity and diabetes. Bad food, bad air, bad housing, bad (clean) water supplies all contribute directly or indirectly to a weakened immune system.


At the moment there is a lot of fuss about face masks in schools. What’s your take on that?

Masks may be of some help in not passing on the virus to others if you have the COVID-19 disease.

In schools, however, the advantages seem smaller than the disadvantages: risk of shortness of breath, concentration problems, headaches and possibly brain damage.


How do you think it will continue with corona in the coming months and years?

It is to be expected that we will have an increased risk of aerosols in the months of November to April. If we protect the vulnerable in society well, and if we ventilate well, the second wave will not be as severe as the first wave. After all, many people have already become acquainted with the virus. In the future, corona will continue to come back in the winter months. But it never has to get as intense as last spring when the virus was completely new to everyone.


You’ve devoted your life to studying how to tackle infectious diseases. What strikes you worldwide about the approach to the coronavirus?

Cutting back on care and downsizing the bed base in hospitals has contributed significantly to the fear and panic measures to prevent us from being overwhelmed by the volume of patients. Unfortunately, this does not only apply to Amsterdam East and the Netherlands.

Unfortunately, because the benefits of austerity are often not evenly distributed, much of the world’s population has become even more vulnerable because for them a healthy lifestyle is very difficult to maintain.

With regard to the approach, I think that a study of the older literature and targeted research based on this can contribute to an effective policy. A policy devoid of fear, panic and the need to sacrifice personal freedoms.





Original Interview NL


Robijn Tilanus  writes as a freelance journalist for oost-online about subjects that touch her: nature, music, health and striking people with a mission.

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