Hey everybody, Dr. O. In this video I want to talk about ID-50 and LD-50. So ID-50 is the Infectious Dose-50. Which is the dose, the number of organisms, that it would take to cause an infection in 50% of people. So it’s a good measure of how virulent a microbe is, how easy, how easily it can cause infection. The LD-50, now just so you know, I generally only think of toxins when I think of the LD-50, so it’s the Lethal Dose-50, but technically it would be, you know, how many viruses, how many bacteria or how many toxins would it take to kill 50% of infected people. So, but for me, I think Infectious Dose I think of how easily something can cause an infection, Lethal Dose I’m generally thinking of toxin, so to me it’s the best way to measure how potent a toxin is. So here we see just a picture that kind of shows the general idea, this isn’t any specific organism, but you see how many organisms it takes to cause mortality in 50% of people. So that’s how you figure these out. So I think it’s super important as we move on here to a list to understand that these are medium values which means that if you have a very strong immune system, you’re very healthy, a lot of stomach acid, whatever factor might come into play, it would take a much higher number for you, but someone that’s malnourished and has other problems, the number would be a lot lower. So, this is not an exact number by any means, it’s a great way to compare one organism to another. The other thing that’s worth noting here, let me show you an example would be, oh I two mouse arrow there. So, you have like, let’s see, Salmonella enterica serovar Typhi there it takes about a thousand organisms to, uh, to cause an infection, but the mortality rate of this typhoid fever that can be caused by this is about 10% whereas right below it, the Salmonella enterica serovar Typhimurium, this is going to lead to just your more quote unquote “basic Salmonellosis” which has a mortality rate of around 1%, especially people that are getting treatment. So, you notice that the Infection Dose really has nothing to do with how dangerous an organism would be. Alright, so just a couple of examples there and I apologize for that arrow there, must have been there when I took the screenshot of this. You’ll see the viruses are generally going to be pretty low, but look at like the difference between the different types of E. coli, so your E. coli 0157:H7, you know, one of the most potentially dangerous forms of E. coli, the Infectious Dose is pretty low, this says ten to one hundred, I’ve seen some studies that put that Infectious Dose between, like, four and five organisms so very very small numbers, whereas look at some of these other strains like enterotoxigenic strains of E. coli takes between, what is that, ten million and ten billion organisms to actually cause an infection. So, the Infectious Dose basically tells you how many organisms do you have to be exposed to before you have a problem. See, like cholera down there at the bottom, that’s going to be about a million so a much higher number than some of these other ones. Okay, uhm, one more thing to think about here with Infectious Does is the way in, the portal of entry, so here’s an example of an organism, Bacillus anthracis, which causes anthrax, that has a different Infectious Dose depending on the portal of entry. So it takes ten to fifty endospores to cause cutaneous anthrax with skin, when they come into contact with your skin. Inhalation anthrax, which is generally what we think of, especially with being used as a biological weapon, ten to twenty thousand endospores. And then ingestion anthrax would be two hundred and fifty thousand to a million endospores. So the portal of entry matters. Just a couple more numbers here with the Lethal Dose, just as a comparison. So, again, it tells you how toxic a toxin is, right, how potent a toxin is or needs to be to actually lead to death or serious illness. So you see here that like Botulinum toxin only take .03 nanograms per kilogram whereas the Shiga toxin, which is what E. coli 0157:H7, the enterohemorrhagic E. coli’s would release two hundred and fifty nanograms per kilogram and then Staphylococcal enterotoxin takes one thousand three hundred and fifty nanograms per kilogram. So you’re looking at a massive difference in how much of a toxin it takes to be lethal. Alright, so that is the ID-50, the Infectious Dose-50, and the LD-50, the Lethal Dose-50. I hope this helps, have a wonderful day. Be blessed.