- Today, I'm going to give the last lecture in a series on the different routes of transmission, and this is transmission via touch. And the reason why I wanted to concentrate on the routes of transmission, is once you know the route of transmission, you have a much better idea how you can intervene to prevent a disease, and you have a better understanding of what it's going to do. And there are broadly five different routes of transmission. The vector-borne with insects and arachnids, oral, mainly by food and water, sexual and bloodborne, respiratory, and the last one I'm doing tonight, which is touch. Usually, one route is dominant, meaning that a particular infection, does almost all of its transmission, primarily by one of these routes. But sometimes they have a secondary route as well. And we'll come onto that with touch. Now, getting an infection via touch, seems an obvious way to pass on infections, but actually it's a lot harder than you might think. And many infections are not passed on by touch or only to a small degree. The principle reason for this is that the skin is both tough, and very well defended. If bacteria, viruses, or others get onto the skin, unless they are highly specialized, they're fairly unlikely to get through the skin, and when they do they meet a very effective immune response. But there are also cultural and social reasons, why we are defended against touch diseases. There are actually very strong cultural norms not to touch strangers. And then clothes add a further layer of defense. If you bump into someone, both of you are wearing clothes, that again reduces the risk of transmission. And in the modern era, frequent bathing and washing and ironing of clothes, add additional ways in which the risk of transmission is reduced. So there are social reasons which help protect us as well as the biological ones. But, to go back to the skin itself, it has very good immunological defenses, with a relatively small number of things that sort of poke through those such as hair and sweat follicles. Different sorts of skin have different levels of protection. So the very tough skin you have on the soles of your feet and the palms of your hands, have a slightly different set of risks to the skin you have in other parts of the body. This social aspect though to touch is important when thinking about both how diseases are transmitted, and when there are epidemics, for example, how you can go about reducing the risk of transmission. When is it normal for any of us to touch a non-family member? Well, it's an important part of affection and closeness and trust. So that means people tend to touch people within their close social group, certainly within their families. But this is very strongly bounded. And actually most people do not touch strangers, if they can possibly avoid it. And you'll see this if you go into a lift for example, people moving apart from one another. And in fact, at the extremes, it is actually illegal to touch someone intentionally, who does not want it. But there are situations where touch is normal. Children touch one another the whole time. And that's important. You'll see in many of the touch diseases, are particularly common among children. There are social interactions which are just completely normal to touch someone, shaking hands for example, many physical sports, it's completely normal to touch someone. And then, and importantly, healthcare and social care, are settings where touching people is absolutely essential, both physically, to help people move for example, and to provide reassurance. So there are situations where touch is normal, but in most situations, in fact touching strangers is not. Now, there are several ways that an infection can be passed on principally by touch. They include, skin-to-skin infections, and I'll go through each of these groups, like viral warts or scabies, several bacterial skin infections, hospital acquired infections. And this goes back to the fact that hospital is a place where touching people is an essential part of treating them. Then you have many diseases where someone might touch a person or excretions from a person, and then touch their mucus membranes, particularly their mouth or eyes. And these, in some cases, can be quite severe diseases, like Ebola or Lassa fever. Then there are some diseases which you catch things by touching soil, sand, or water. And several parasites, fungi, and bacteria, do this either as a part of their life cycle, they've designed in this way of being transmitted, or in a sense incidentally. And finally, there are some diseases which are passed on by puncturing the skin by some mechanism and I'll come onto these in the end. And these include very severe diseases, such as rabies or tetanus. But all of these require you physically to touch someone, or to touch an object which is infected in some way. So this is quite different for example, from the respiratory infections I was talking about in the last lecture. Where you actually can infect someone at a moderate distance, or the vector-borne infections where you can actually infect people at really quite some distance away. Now the fact that some things are transmitted by touch does not necessarily mean that the skin is where the disease will be most important although in some cases it will be. Infections transmitted by touch can affect every organ of the body. Some of the infections are skin diseases, but many actually affect other organs such as the gut or the nerves. And these include some of the most feared multisystem diseases of humans at all. And on the other hand, there are many infections which manifest in the skin, but in fact are transmitted by different routes. So, for example, syphilis, transmitted by the sexual route, or leprosy, transmitted by the respiratory route, manifest through the skin. So you can actually see that there isn't a straight correlation between which organ transmits and which organ is primarily affected. Now I'm going to start off, with the more straightforward in a sense, skin-to-skin infections, many of which are relatively mild, but they are common and they can be distressing. Several viruses specialize in transmission by touch. And these include, warts of the hands and feet, in feet often called verrucas. And these tend to be passed on by direct contact between two people or via an object, particularly wet objects like walking in a swimming pool which hasn't got proper protections when they're wet. These are not usually dangerous, but they're sometimes unsightly and particularly on the feet can be uncomfortable. And there are treatments given for them, but they are very common. And then there are a variety of other viruses. I've just chosen one called molluscum contagiosum on the bottom of these slides, which are rarer but also are viral passed on by touch often in childhood because remembering this is a time of people's lives and they do tend to touch a lot more people who are their own age, and do that as part of their normal play and behavior. Then there are parasites which are passed on person-to-person by touch and these are highly, again, highly specialized parasites to be transmitted by this route. Probably the one that most people, the two that most people have come across most are scabies. Now scabies is a mite. It's very small. You can't see it on the top right. There's a photomicrograph of it. It's significantly magnified. And it burrows into the skin and then moves around in the skin. It can be very itchy, particularly with a heavy infestation. Now you don't get this just by brushing against someone in the tube or a quick handshake. You usually get this by prolonged contact. So it tends to be in very enclosed environments and within families. Usually not serious in the UK, but it does need to be treated. And people who have very severe infections as well as being distressing can in some cases get, bacterial infection on top and this can cause significant problems. And then a different sort of a parasite which is passed on by touch are nits, head lice. Anybody who's been at school will have had friends who've had nits. Many people in fact will have had them themselves, extremely common, and they are passed on when people bring their heads close together. They can be passed on by other things but that's the majority of the situations. Again, relatively easy to treat. Once they're in a family, because families tend to huddle together, they tend to get passed around extremely straightforwardly. So that's viruses and parasites. There are then some fungi, which are again, passed on person-to-person. The one that is probably the most striking of these is ringworm, shown rather typically on the top left and a different form in the hair of someone on the right. And this comes from contact again between two people touching one another, or through things like infected towels, sharing towels with strangers, will come onto several other infections, is generally not a sensible idea if they haven't been washed in betweenwhiles. And then another very common thing, athletes foot. This is very commonly caught, particularly walking barefoot in showers, or in changing rooms. And athletes foot is, for most people relatively trivial, again, unsightly, but potentially a route by which other infections can get into the body because it breaks the skin down. So they are, again, they do need treating. These kinds of fungal infections, can usually be treated relatively straightforwardly, using creams or other treatments which you can buy straight from a pharmacist, although in severe cases, some people may need antifungal drugs from a GP, but treatments are available. Bacteria also have infections which are typically passed on and a bit specialized, to be passed on person-to-person by touch. And a good example of this, is something again which is really relatively common in childhood. Most people will know someone who's had it, they may well have had it themselves, impetigo. This causes a crusting kind of infection, and it's passed on by people touching one another. There are two bacteria which typically cause it: Streptococcus pyogenes and something I'll come back to because it comes up repeatedly in the touch diseases, an infection called Staphylococcus aureus. It's most common in younger children, again, largely because of the fact that children tend to touch one another more. And the key ways to reduce the risk of this, particularly if someone's got it is obsessive hand washing when they have it, not sharing things like towels, and avoiding contact where it's not necessary until it's gone away. It's relatively easy to treat, and once it's gone away, the risk is substantially reduced. So these are all relatively straightforward infections to treat, but all relatively common. Now, many times bacteria transmitted between two people and then they just sit there on the skin perfectly happily colonizing the skin, all of our skins are covered in variety of infections, but doing no harm. And then from time to time, for a variety of reasons, but usually because there's been a break in the skin, for example, with a wound or scratch or athletes foot is an example of that. And particularly in people who've got preexisting conditions like diabetes, it can then get through the skin into the layers in the skin or just below the skin and people can get infections, and a classic example of this is cellulitis. The person in this photograph has cellulitis in one of their legs. It's obvious which one. And this is an unpleasant infection. It can be quite a severe infection, until it's treated with antibiotics. So this is something which definitely does need treating. So this is not on the skin. This has now got under the skin and will make this person if it's untreated, feel extremely unwell. And indeed was very dangerous in the pre-antibiotic era. People will often need relatively prolonged antibiotic treatments for this. This will be very largely due to Streptococcus or Staphylococcus. These bacteria which specialize in being passed on between people and being on the skin and then getting in when they get a chance. Now the skin, of course, has to have certain breaks for particular reasons. And the two important ones that are built into the skin because they're necessary for temperature regulation in particular are hair and sweat glands. And these allow bacteria sometimes to get into the skin through the holes which you have in either sweat pores or in hairy parts of the body. And of course, this means not all part, for example, the palms of the hand don't have hair at all so that's not going to happen in those situations. And those can cause minor boils through to quite significant abscesses. So you get this bacteria that has managed to penetrate the infections and it's sitting in a relatively protected site within it. And the most common of these is this bacteria Staphylococcus aureus, I've talked about before. A potentially very dangerous bacteria. Minor cases, of course, resolve, all of us have had boils and things of a similar sort, but in severe cases, which are much rarer, people can go on to need a surgical release where they actually have someone actually removes the pus and antibiotics. So the majority of cases self resolve, but a few of them do go on to need minor surgery, relatively straightforward to do. Occasionally however, Staphylococcus aureus and other skin bacteria, but Staphylococcus is the most common and are most important to these, can get into the blood and cause significant infections. And in particular, Staphylococcus typically when it's off the skin can cause abscesses and it can cause these in multiple parts of the body, including the lung and the brain, but probably the most important severe one, that is reasonably common is heart valves, something called endocarditis. So this gets through the skin, into the blood and then infects the heart valves, but it can also infect bones and joints. So bones, joints, and heart valves are typical places, this bacteria goes once it's got beyond the skin. And they will need significant, long periods of antibiotics and in some cases surgery. A particular risk for getting these kinds of infections, is in fact hospital. And hospital is a very high risk environment for touch diseases. And there are several reasons for that. The first of which, is in a sense a social reason. Touching strangers is part of the process of nursing and medicine and other therapies. So there's a lot of touching of people who normally would not do so. Secondly, intravenous lines which are part of treatment for many things, both medical and surgical in hospitals, are an easy way for a bacteria to get through the skin. We have actually made access from this outside of the skin into the body a lot easier potentially for bacteria. And it's one of the reasons people need to be very careful, they change drips and look after them very carefully. And the more sick people are, the more lines they tend to have, and that would the most sick people will be in things like intensive care, where you tend to have a combination of very often immunosuppressed but certainly ill patients, so with less good immunity, with lots of lines going into them, and also an environment where lots of antibiotics are used so you'll often get lots of multi-drug resistant antibiotics. So, hospital is actually a high risk place, for getting a bacteria that's on the skin transmitted by touch, into the body and causing problems later down the line and often sometimes significant problems. So it is really important that hospital environments and healthcare environments take very seriously, trying to reduce the risk particularly of multi-drug resistant but all bacterial skin infections being passed on. And an example of this is MRSA, Methicillin-resistant Staphylococcus aureus. It's a form of a Staphylococcus aureus. This is an example of a bacteria which can be passed on relatively straightforwardly, person-to-person by touch. It's a Staphylococcus like anyone else but once it's drug resistant, if it then gets into someone, it's going to cause potential problems with treatment. And it's especially common in a hospital setting. The management of this is very straightforward. It's basic hygiene and washing hands and where appropriate, wearing gloves. And these are the key things which are necessary. And what you can see in this graph, the UK had quite a significant problem with MRSA and it hit the newspapers understandably'cause of the risk that this posed, and by doing relatively straightforward, basic hand hygiene measures in the main, the rates of MRSA both in hospital which drove this and then in the community, fell right down. And you can see that on the graphs on the right. So this is an example, of the fact that really simple things, can significantly reduce the risk of touch diseases, of which hand washing is the most important. Now we've known this for some time but this was not always accepted. And the early people who really pushed the need to reduce the risk of these touch diseases, were not appreciated by their professional colleagues. And I'll just give two examples. The first was Ignaz Semmelweis, a Hungarian physician, and he was working at a time, when puerperal sepsis that's bacterial infection, soon after birth was extremely common. And at that point in some hospitals, roughly 10% of women, who went into the hospital to have a baby, died of infection subsequently. So this is an astonishing mortality rate and that's over and above, those who died actually in childbirth itself. So, childbirth was, to remind people, an extremely hazardous thing for women, in the pre-antibiotic and pre-modern medicine era. And he thought and correctly, that much of this was passed on by doctors, who were not properly washing their hands, and in particular not washing their hands between doing autopsies on people who'd recently died, and delivering a baby. Now this is an extremely unpopular view that he put forward to people, his professional colleagues. He introduced chlorine hand washes and the result as you can see on the graph on the lower side was when he introduced this, where people had to hand wash their hands before they had to deliver babies, the rates of puerperal sepsis dropped dramatically. Despite this, this was not popular, and he became more and more frustrated by this. I'm cutting a long story short. And he was not in any way appreciated by his professional colleagues who had him committed to an asylum, by his medical peers, where he was forcibly restrained, got an infection and died two weeks later, aged 47, as secondary sepsis. So, the medical profession's resistance to change can sometimes not help anybody. The second person who pushed this was Lord Lister, Joseph Lister. And this was for surgery. Now what that allowed surgery really to take off was anesthesia. Until you had anesthetics, it was impossible to do major surgery, really for obvious reasons. It had be done extremely quickly. So the first big challenge was anesthetics. But the second one was that many people who had surgery, would then go on to die of sepsis shortly afterwards. And these again are passed on by touch. They were killed by infections. Joseph Lister introduced, following some research by Louis Pasteur, he thought, well, this might well be infection, and he introduced antisepsis. And this was to use things that killed bacteria and provided a barrier which would much reduce the risk during surgery of passing on bacteria, which would go on to kill people if they were allowed to take root. And he both had hands washed in it, he had the surgical instruments washed in it and he sprayed it on the patient during the operation. You can see this. This is a wood cut showing this. Initially Lister was mocked, but actually over time, it became really clear that this led to a significant reduction in wound sepsis and significant improvement in surgical outcomes. So, here's a big advance really which actually allowed modern surgery to develop. Modern surgery has now however moved further from antisepsis where you use an antiseptic to reduce the risk that the bacteria will cause problems to asepsis where the aim is to try and make sure the entire area is as sterile as possible, and that anything touching the wound or an exposed part of the body is sterile in some way. And this avoids contamination by touch almost completely if it's done properly. So this has led to even better surgical outcomes. Touch is also, in addition to these infections I talked about so far, which is really where touch is the principle means by which infections are transmitted. Touch may also be the main secondary route for infections transmitted by other routes, particularly the oral route, and the respiratory route. And these tend to be diseases where people might cough for example, or there might be diarrhea around or vomit after norovirus and people touch something, and then touch their face. Touch there particularly, touch their mouth, as a result. And they include COVID-19, flu, typhoid, norovirus and many other infections. Now, the key thing here is hands, the way in which we all explore the environment around us and actually move things from another person from another object to our face, is almost invariably hands. You don't touch things with your face unless under certain very limited set of circumstances. So if I can do a really clear commercial break here, hand washing with soap, is one of the best things we can do, both to reduce the risk of infections where touch is the principle route of transmission like the ones I've been talking about now and also the ones where it is an important secondary route of transmission for example like flu. And this can help reduce the risk of infections to ourselves and to other people. So this is the reason why hand washing is so heavily pushed by doctors, nurses and others,'cause it really does make a difference in reducing the risk of multiple infections, not just one or two. So now I'd like to move on to some really very severe diseases passed on person to person by touch. And I'm going to major in particular on Ebola. But what I say, it's also true to a large degree, of some other dangerous diseases, the viral hemorrhagic fever, Ebola, Lassa fever, and Marburg disease in particular, which have a lot, a lot in common. These are passed on by direct contact with people. So touching them, or their bodily fluids. So if they have diarrhea or if they vomit, or if you take blood, you're touching those, can also be risky. And in almost all cases, this is about touching and then touching mucus membranes but it also can be if people, for example, cut themselves whilst they're doing it. So direct touch as well. Ebola and Marburg have both led to major outbreaks, and both of them in an outbreak environment, particularly where medical services are more limited, kind of have a mortality of over 65%. So, over two thirds of people may die. Lassa has a lower mortality, but it's still significant. And for example, in the UK, we tragically had a death from Lassa in the last few weeks. They get their name from the bleeding and internal hemorrhaging, that can occur late in the disease and people become more and more infectious, the further on the disease goes and that's quite important in the management. And the biggest epidemic to date, was the large West African Ebola epidemic of 2014 to 2016, which rightly dominated the news for quite a long period in which the UK, along with many other countries assisted colleagues in particular Sierra Leone and other West African countries, because this needed an international effort, to get on top of. Now Ebola is an example of the fact that despite being relatively difficult to catch, so you've got to touch someone, to catch this disease. And despite that, it spread really quite fast and these are the maps of how quickly it spread from April to August, 2014. So, touch can still be quite an effective way to get around a community. And we knew at a relatively early stage, in particular from work by doctors and scientists in DRC, formerly Zaire who did a lot of the science on this initially, that the R-naught, the force of transmission which people have talked about a lot in the context of COVID was over one, due to three different components and all of them were driven by touch. The first was, transmission in healthcare settings. Patients passing it on to doctors and nurses who then pass it on to others. So, that was a very important part of the transmission. And because people get more and more infectious the sicker they get, the most infectious people were largely in hospital or at least being looked after by healthcare workers who might be traditional healthcare workers but professional or other healthcare workers. The second route of transmission was during funerals. In contrast to many other infections, people with Ebola, were highly infectious after they died. And then the third one was transmission in the community where it got from a funeral, got from a healthcare setting, and then was transmitting in the general community. So those were the three different environments. Now it's important to think about these'cause the way you're dealing with those, is completely different. The impact on healthcare workers was very profound. And this is true for many touch diseases. Because people are infectious, they're in hospital, and they're touched by healthcare workers, healthcare workers are often the first people to start dying of it. It was true of SARS, it was true of Ebola, for example, it's been true of Lassa, and others. So it's very high risk. And this just gives an example, from Nigeria as it happens, an imported case in this epidemic, went into Nigeria, that's case one, all of the people who are in blue in the box below, all the people that this first case infected, were healthcare workers, and all of those with a red border around them, tragically died. So this gives an impression, of quite how dangerous this is, a touch disease can be to healthcare workers. And in that epidemic, we estimated that around eight to 10% per person year of healthcare workers got infected, and of those, over 70% died. This was initially until we worked out how to deal with that. So what this makes clear, is that it's absolutely critical to do really rigorous, healthcare protection, for everyone's benefit but obviously in the first instance healthcare workers and everyone they might subsequently infect. And this is about making sure they cannot touch, anything from either the body or any secretions. And this was highly effective. Once this took hold, and people did all the routines and had the kit, the rates of transmission went right, right down in healthcare settings. So that was the first one, that's a very classical bit of public health in hospital settings. But we knew that that was not going to be enough. And there was an exponential curve of increasing rates. And what we knew is that the longer we delayed intervening in wider ways, the bigger this epidemic was going to get and the wider it was likely to spread. So it was absolutely critical to get a move on, in helping to support colleagues in Sierra Leone. So the next component was reducing transmission from funerals and other peri-death rituals. It is absolutely normal in every society that people want to care for the sick, particularly their own family and friends. And that they want to celebrate their life and mourn after they die. So that is absolute. Every society does in different ways, but that's universal. And local burials here involved washing and touching the body. That was normal procedure for, in a dignified and respectful way mourning and celebrating the person. Now we know perfectly well how to do a medically safe burial. It's a touch disease. It's about avoiding basically touching the person who's recently died, and what they did. The challenge, and this is a really key point here, was a social one, how to do it in a socially acceptable way, so that the family and a community could mourn their family member or their friend or leader or a charismatic individual. And this is where the social sciences became extremely important. Working with local leaders to understand what was a respectful way of doing this that was still safe, and then moving to those kind of approaches. But not doing so in a way that actually interfered with the fact that people wanted rightly to mark the passing of someone they loved or cared about. And this was really important because several of the funerals, particularly a very high charisma people, including for example, to high charisma people, could lead to over 100 people, for example getting infected with Ebola, with a very high mortality rate. So this was a very major part of the transmission rate. And sadly many very, very important doctors died, including Dr. Umar Khan who's one of the Sierra Leonean leaders in this area along with many others. And of course people wanted rightly to give proper respect, but to do so in a safe way. And then the third component, was increasing social distancing in the community. It's relatively difficult to catch in the community but the key was to make it less so. So, simple things like how could you do a respectful greeting that didn't involve a handshake, which is obviously a high risk in this environment. And this is a demonstration of religious leaders from different faiths, demonstrating respectful greetings, that don't actually require physical touch. But again, the key is to make it acceptable socially. And many of the things we had to do of course had serious downsides, closing schools, roads, markets, what in recent terms we would've termed here lockdown, was necessary to get on top of this. And alongside that, was trying to make sure that the people who had symptoms of Ebola, which were very similar to lots of other things, isolated very early on. And then later in the disease when we had rapid diagnostic tests, that we could find all their contacts, and isolate them as well. And that way we actually were able to get on top of, when I say we, I mean the general medical community, led by Sierra Leonean doctors and Sierra Leone government, able to get on top of this, by reducing little by little the number of people that someone came in contact with physically, and therefore the number they passed it onto.'Cause if you can reduce it down from a situation where every person was infecting, more than one person to a situation where every person is infecting less than one person, then the disease goes away. But we were then able, to move over time from a purely social model of public health which is all about isolating people, to a much more medical model, as we developed new scientific tools. And as with COVID the most important to these was a vaccine or vaccines. So although this particular outbreak, was ended almost entirely using social public health, distancing, straightforward ways of preventing touch between infected and uninfected people, initially including the whole society and then as we got more testing, are able to concentrate on those who had actually got infection. Once we got later in the epidemic, initially two, and then subsequently more, Ebola vaccines were developed, over 80% effective. And we can move over to a situation where they can do most of the work. So rather than actually having a situation where it's all done socially, we move increasingly over to a situation where it's all done medically with vaccines and drugs which is much less socially disruptive. Again, as we've seen with COVID. We weren't able to vaccinate the whole population. There weren't the vaccines available to do that. And so the method that was used which was effective in the environment of this particular touch disease would work as well in something like COVID, was something called ring vaccination. You find the person who's infected, and then you vaccinate all the people who they've come into contact with, and indeed, ideally all the people that they've come into contact with. And therefore you make sure that there's a ring around them, that isn't a physical barrier, but is one where actually those people are immune and therefore the disease doesn't pass out from around this. So it's something developed originally for eliminating and then eradicating smallpox. So those are some very serious diseases, passed on human to human. Although the initial case for Ebola was probably, a child touching a bat. So it was actually originally jumping species. And I'd just like to talk briefly about some infections inquired by humans touching animals. There are quite a lot of these. And just as you can catch infections from humans by touching them, you can catch infections from animals by touching them. Some common ones include something called orf, something you can catch for example by touching goats. It's not dangerous, but can be unsightly as you can see on this finger on the top left. Anthrax of the skin which is one of the less dangerous forms of anthrax, but you also can catch by touching animals or animal hides. And an important one historically for several reasons was cowpox. You get this from, milkmaids got this from milking cows, that were infected on their hands. And this is important both'cause it was an important disease for quite a long time, but also because it was the origin of vaccination. So taking the sample of cowpox from a milkmaid, a lady called Sarah Nelmes, and transferring that onto a child, protected them from smallpox which was a much more dangerous disease. And that was the initial step along vaccination done by Edward Jenner. But we can also, pass on relatively straightforward to bacteria. So you can actually pass on for example multidrug resistant bacteria to companion animals and pets, by touching them and potentially also vice versa. So touching, you can actually pass on things between species, relatively straightforwardly. Some human parasites and other infections have however evolved to specialize in transmission indirectly, from touching soil, sand or mud or swimming in fresh water. And many of the places you can actually, catch these things are extremely beautiful to look at, and enjoyable to spend time on beaches, and swimming in fresh water lakes for example, are two of the ways, this can happen. Start off with some worms, which have evolved, to use soil to transmit by touch. And the two most important ones of human ones, are hookworms, and a infection called Strongyloides, but they're passed on in broadly the same way. And hookworm on the right, show the life cycle. It's really quite a complicated life cycle. It's evolved to do this, because this is an effective way of passing on. People who are infected excrete eggs of the hookworm, in their feces. And if that gets into the soil, then the larvae come out in the soil or sand and then if someone walks over or it or lies on it or touches the sand or soil, that gets through the skin. So it's evolved to get through the skin. It then goes up through the lungs, is a very complicated life cycle, and back to the gut, at which point it starts to excrete eggs and the cycle repeats. So this is a parasite evolved incredibly effectively, to use the fact that we defecate outside, and then touch sand or soil, to use touch to be transmitted and Strongyloides, is relatively similar. Some slightly more dangerous actually disease. Although hookworm in a heavy infection can cause anemia and various other problems. There are also, and these people who've laying on beaches may well be aware of this, dog and cat hookworms can do some of this. They can actually penetrate the skin but then they essentially get lost. But they cause a big inflammatory response. And you get what you see here, which is something called cutaneous lava migrans. So you're lying on the beach one day and then a few days later or sometime later, you get this itching and you can sometimes see these worms moving very slowly. You can't actually see them racing, very slowly, day-to-day they move, as they move through your skin. Eventually they'll die. They can't go anywhere'cause they're not designed for humans but this is an example, where the parasite is kind of got halfway there. Then there are other infections which actually also use sand or soil. Here's one example, jigger fleas. Got a number of other names but that's the normal colloquial one. Eggs are hatched in the sand. They're fleas, they can move around, jump in some cases. They get into the skin, they penetrate the skin, the female penetrates the skin, then swells up, the male mates with the female who's in the right place, and then she has eggs and they break out and the cycle continues. And they can really quite right painful for people. And you can see this person. You can actually pull, you can actually cut them, well, push them out, but they can be quite unpleasant if people got a lot of them. If they're in the wrong place it can be quite painful to have. And there are other parasites that are specialized in slightly different methods with touch for example, tumbu flies, are something which lays eggs on wet clothing. And if you then wear that clothing they put a little, the maggots actually penetrate your skin and they develop in your skin. So, there are a variety of parasites sort of actually specialized, in using your skin as the place that they develop certain parts of their life cycle. So those are ones from land or objects. Then there are some parasites which have evolved to penetrate the skin from fresh water. And the most important to these is schistosomiasis. Has a very complicated life cycle but again, the simple version, is that people either pee out eggs, or comes out in their stool, depends on which type of schistosomiasis it is. That gets into fresh water, the eggs hatch, and they get some little miracidia and these little parasites, swim and penetrate your skin, get into the body, into the bit of the body they live in. Different ones live in different parts of the body. Girl meets boy, mate, produce eggs, and the cycle repeats. So these ones have developed a way of getting through the skin very, very specifically. And they do this via some snails where they have to actually use on the left are the three different snails which go with three different forms of schistosomiasis, in different parts of the world. So, this particular method is used by different forms of schistosomiasis in different parts of the world. Other animals also have, different sorts of schistosomiasis but these are ones that affect humans. So those are parasites. There are also fungal infections which you get from touching soil or plants. Unlike the parasites I just talked about, this is probably in a sense, incidental. It's not a key part of their life cycle but they can still cause very significant problems. Fungal diseases are particularly dangerous in people who are immunosuppressed. Severe AIDS, have got other problems, but they can affect people, who've actually got normal immunity. Which fungus, we're talking about that you can catch by contact, particularly with soil or vegetable matter, depends on where in the world you are. So for example sporotrichosis is known as a rose garden's disease, quite well known in parts of the USA, Madura foot which is demonstrated in this photograph here, a really quite dangerous, fungal infection you can get in parts of Africa, Asia, or Latin America. So, which fungus you get depends where in the world you are but what's common to them, is touching. And the foot ones, the best way probably to prevent them is wearing shoes. Finally I'd like to just talk about two very severe diseases, where the infection is only passed on when there is a puncture to the skin, and it's achieved by different routes. The first is tetanus. And this follows a wound or a prick, and is caused by a nerve toxin which causes very severe spasms, illustrated here, in a soldier with tetanus in the previous era. It's an extraordinarily distressing disease to have. And with a high mortality, even with fairly good treatment. Historically, what happens, it lives in soil or animal dung, it's its principle root. And so it's dirty wounds which tend to cause this but you may not actually see the dirt but they've got soil or dung usually on them. And classically the kind of places people tend to get them through different environments, agriculture, where people are constantly among soil and can take cuts and nicks and not really notice them particularly. War, classical place to get tetanus, in the previous era, and childbirth in non-sterile settings and unclean surgery. These are all routes by which, tetanus can get in. It forms a little small abscess, often not noticed, not very of use, not really a particularly big deal, but it produces an incredibly potent toxin and that's the dangerous part. So the tetanus toxin, once it's circulating in the blood, often tiny amounts, gets into the muscle, and then moves up the motor nerves, up to the central spinal column. At that point it binds irreversibly to the bit of the system that stops you spasming. So, your whole body is in permanent situation where the movement you make, you can just stop it exactly where you want, because it's always in balance. And what tetanus does is it turns off the thing which allows you to stop it at the particular point and people go into uncontrollable spasms. These are very painful and can compromise people's breathing very badly, and the mortality can be extremely high, in severe cases, where treatments aren't available up to 80% in adults and up to 100% in neonates who catch this. So it's a very dangerous infection. Neonatal tetanus in particular, has an extremely high mortality. And in rural communities without expert midwifery, this led to a high proportion of neonates dying. Up to 50% have been recorded and higher than that in some places including, photograph of the top, top right here, St Kilda, the most remote part of the British House, where the majority of children at various points in history, would die of tetanus, after childbirth because of getting probably soil and dung into wounds or on the care of the umbilical stump. So once neonates have got tetanus, mortality is essentially 100%. Was very common in rural UK and USA as well as the rest of the world, prior to vaccination. But the two things that have transformed this, are modern midwifery and clean birthing practice, and tetanus vaccination. And as vaccination of women who are pregnant or who are likely to become pregnant, has expanded. Neonatal tetanus has essentially gone away. So it's vaccination of mum, either prior to or during pregnancy, which has got rid of this really serious problem for newborns. So, the vaccine for tetanus has transformed the risk. The tetanus vaccine is to the toxin, it's not to the infection. You can still get the infection. And it means that you don't then get, any form of likely tetanus spasming, but because it's not against the infection, it's against the toxin. If you are vaccinated that protects you but it doesn't actually protect anyone else. This is an infection from the soil, and there's no form of herd effect. And to be clear, herd effect only really in my view refers, to a situation like this where there's widespread vaccination. So it is very important to vaccinate mothers to protect their newborns, as well as doing proper birthing practice. And tetanus is now given to children and at various other points, usually with two other very serious infections, diptheria and pertussis. But those are not touch diseases. The final infection that I'd like to talk about is rabies. And this, again, this is a touch disease, but it has to get through the skin. And it does this by the bite of an animal. Up to 99% of human cases are from dog bites. And it's still a very serious problem. Rabies once someone has got rabies the disease, so if they're not vaccinated, is 100% fatal. And it is an extraordinarily unpleasant way to die. Of all the ways I've seen to die of an infection it is the worst. People die in terror. Usually within 10 days. And the way that rabies achieves this, is that the animals which have it, are extraordinarily irritable and aggressive, they salivate very heavily, they find it very difficult to swallow, and they snap at anything. So, a dog which has got rabies, a rabbit dog, will basically bite anything around it. This would include dogs, which normally would be very placid. So the infection, as part of the way it transmits, is to get the dog to puncture the skin, while salivating and the saliva then, that's injected into the skin by touch, will then cause rabies in the victim. Rabies fortunately is becoming rarer but it is still a significant part of the problem in many parts of the world. The key thing with this, three things with this, three ways we use vaccination. The first, and probably important actually, is vaccinating dogs and other domestic animals but particularly dogs. The second is to vaccinate wild animals, which might pass on rabies such as foxes. And this has been done by baiting, putting vaccine on bait like chicken heads, spreading them around and then the wild animals get vaccinated, whilst they munch their chicken bones. And the third is in humans. You can both get vaccine prophylaxis, particularly if you're going to a place, a long way from medical help or where you are dealing with many animals, and post vaccination. If you get someone fast enough, the vaccine is effective in the first few days, and will prevent it developing. So the vaccine has been transformational. And rabies is going down but it is still a very significant problem. And this really just demonstrates, once you vaccinate dogs, then the rate of rabies in dogs goes down, and then the rate of rabies in humans goes down as a secondary result of that. So, the key is actually, in this case vaccinating the animal. So in summary, several ways in which infections are passed on principally by touch, skin-to-skin infections such as viral warts and scabies, several bacterial skin infections, some of which can then, if they get into the body can be really quite significant, particularly Staphylococcus aureus. Hospital-acquired infections is a high risk environment if people are not obsessional, with their hand hygiene. It's also a secondary route for respiratory and oral infections. And then finally in terms of to human-to-human direct contact, you have these very severe diseases such as Ebola or Lassa, which are also passed on by touch. And with all of these, social things we should avoid, touching multiple strangers and hand washing are part of the way that we reduce the risk of transmission in the community. And then you get infections from touching animals. And then infections from particular quite specialized often infections from touching soils, sand, or fresh water. And these are used by several parasites, fungi and bacteria. And finally, there are some infections which in sense are specialized at puncturing the skin for their transmission, including tetanus and rabies. So, touch is a very important route of transmission. And a lot of the ways you need to think about how you reduce to this, is as much in the social sphere, and using the social sciences as it is in the biological ones. But vaccines have certainly transformed the risk of some of the most dangerous touch diseases including rabies, tetanus, and Ebola. Thank you very much.