So in, in this week's lectures we talked about the hosts and we talked about, quite a few mechanisms of susceptibility in the host and, in particular we covered, genetic sources of susceptibility the microbiome, nutrition among other things. And so one of the questions that was posed was is that a comprehensive list? Are there other important determinants of susceptibility that, that maybe we haven't, covered entirely in the course, or that are novel areas of research? So, [CROSSTALK] [LAUGH] exactly. So, well one thing that I'm not sure that we covered very explicitly in the lectures last week, were, or this current week, were co-infections. There was some discussion about the microbiome as this whole ecology of organisms that live within you. But, particularly, pre-existing pathogenic infection, infections with pathogenic organisms, can very much affect your susceptibility to invading infections. And, in fact, we're going to have, some videos coming up in the coming weeks, both by some case study videos by Eric Cardhell here at Penn State and Isabella Covendori are going to tell some stories about the impact of co-infections. >> Hm. >> On susceptibility to both, bact, bacterial and viral and infections, right? >> I would add that apathogenic infections,. >> can also, as Marilyn pointed out, over 90% of our infections are apathogenic and they are certainly modulating our response to the, the pathogens. And so, don't, don't forget the apathogenic infections here. And I get to tell this story because I haven't told one yet. >> [LAUGH]. >> You know it's interesting, we have been talking a bit about these unusual relationships between, between or among different microbes. And one of the coolest ones I think, are course the retroviruses, those are the viruses that I work on. >> [LAUGH]. >> But the, most of, ten percent of our genome is, is made up of these viral sequences. And, one, one way that these can, increase in frequency, at some point they have to be acquired, is because, you know, there's, there's an outbreak of a retrovirus infection going on and by chance one of them is viruses, infects the neighbor's sperm and now all prodigy will then carry the virus, it's transmitted vertically. >> Right. >> And it has the virus in all cells. But having an infectious, formally infectious, virus in your genome is one way to protect yourself from the infectious viruses. >> Mm-hm. >> So you know that's a wonderful symbiotic. >> And there's some very good examples this hasn't occurred just once but independently in sheep and mice, there's multiple, examples of that, that type of relationship occurring. >> So that behavior can be [INAUDIBLE] susceptibility. It can influence exposure, but,uh, even just scratching yourself is a form of sort of an immune response to removing fleas and ticks and things like that. That's of course, your mucus and the way you produce your mucus, particularly for [INAUDIBLE] nematodes, is a really important response and, in helping to flush out parasites and tapeworms and things like that. >> I, I think in our modern era, with modern medicine, you kind of focus on what in-the-body defenses, either from our own cells,. >> or that of the immune system, or Trudy uses some vaccine, but of course, you're right, behavior is a really crucial element there, and it's a first priority of defense. And there hasn't been that much, much study, but, but, in some cases where we have seen studies, for example the Howler monkeys, where they're trying to remove ectoparasites, what they found there was as much as 24, 24 percent, all the energy that that monkey uses. >> What? >> In a single day goes into defending- >> Against this. We see baboons, they'll use, plants, certain plants from the rainforest to get rid of schistosomiasis and they have that adapted immune system, we. You see this in ants and caterpillars. So a lot of behavior where it's ingesting a product that kills the parasite or just simply moving away or, or, or grooming these are all very useful. >> Mm. So I've got to play my card and tell a story now. But, so it, I was doing a lot of work on grass and ticks, the ticks bite the grass and give them an infection. >> And it didn't quite add up because they didn't have many ticks and yet they were all getting infected at a high rate. So I spent some time in the field just watching them and, other chicks were removing the ticks as they got on their siblings. So there was a huge amount of allopreening of their each siblings and the mother taking the ticks off when they got on. And that individual then swallowed the ticks, and when they swallowed the ticks they became infected with the virus. So, it isn't that, it's the consumption of the factor that's causing infection, not the biting of the factor, is it? >> No. >> But of course once it's been eaten it can't pass the virus on, it's dead. >> So, I would say also changes in the host behavior, ecology [COUGH] might, for example, polio in humans, right? Everybody got polio as an, as a newborn infant or a very young infant until we started cleaning up water, and then people didn't get polio until they were much older. So when you get it as a really young baby, you get lifelong immunity and you, and you never get any disease. But, when you get it when you're older, you can get poliomyelitis. Which is a, an obviously devastating disease. So, changes in host ecology really can change the susceptibility too. >> Interesting. >> And probably a timely example right now is with Ebola. And, and the role of, you know, behavioral, cultural practices in that case. >> Yes. >> In the. >> And really how difficult it is for people to change their cultural practices. That's their very deepest fear right now. >> But, again, these are, these are practices that largely affect exposure explicitly rather than susceptibility. >> Absolutely.