Parasitic Pathogens the two benefit from the relationship and the other member is actually harmed and it's it's it's really at the expense of the the other species so in in terms of a specific definition a parasite is an organism that lives on or within a host organism and the parasite gets its food from the host and it's at the expense and that that's very important to consider it is at the expanse of its host now there are several there are three major classes of parasites that cause disease one of them is protozoa one of them as helmets which we talked about is another more scientific name for worms and the third are really insects but they're called ectoparasites and we'll the next slide will discuss what those are so ectoparasites or organisms