The news story in the OP would have driven me especially batshit insane, because it’s right there in the name. ParvoVIRUS. Duh.
My definitions would revolve around disease, rather than structure or Kingdom, 'cause that’s kinda my thing:
Using small words, I’d say that amoeba are single celled oozy little organisms that move about by pushing their cell membranes out and then letting their cytoplasm follow. They do have a nucleus, I believe. They live in water, and while most do not cause disease, a few of them do. Amoebic dysentery is caused by amoebas that form in cysts and travel in poop. Wash your hands, kids.
Bacteria are single celled organisms that don’t have a nucleus. They are literally everywhere. They can live in the air, in water or on surfaces, and of course in and on people and animals. Some live in extreme hot, or extreme cold, or extreme high or low oxygen. There’s even one bacteria (C. diff) that likes to live inside the alcohol based hand sanitizer in hospitals. Some bacteria are useful, helping our bodies make or utilize vitamins, or take up space so that bad bacteria don’t have room to take hold. Other bacteria cause diseases. Many, but not all, bacteria can be killed by antibiotics, although misuse of antibiotics have caused bacteria evolution to speed up some, and now we have more and more bacteria that aren’t killed by some antibiotics their great-great-great-great-great-great-great-grandfathers were killed by just a few years ago. Antibiotics are chemicals made by bacteria, or synthetic versions of chemicals made by bacteria. Antibiotics are bacteria on bacteria warfare that we’ve appropriated for use in humans and other animals. If you counted all the cells in you, 90% of them would be bacteria. There’s more not-you in you than you. About 1/3 to 1/2 of your poop by weight is bacteria. Some of that bacteria is perfectly safe when in your gut, but can cause disease if it gets into another part of your body, like your mouth or a cut in your skin. Wash your hands, kids.
Fungi are multicellular, and closer to animals than plants. Some fungi are delicious, and we call those mushrooms. Some cause ringworm and athlete’s foot and that nasty nail fungus that inspired nightmare inducing advertisements for anti-fungal medicine. They can be hard to kill, as we don’t have a lot of medications that attack them, and they can be very hardy and hide their babies in spores until the bad stuff goes away. Spores are like little hard packets that can generally withstand high heat, poisons and pressure quite nicely, protecting the actual baby-fungus-to-be inside quite well. Fungal meningitis can be caused by a couple of different fungi, although usually it only develops in people with AIDS or other immunocompromise. A couple of years ago, though, some fungus got into medicine used for knee injections and caused an unusual outbreak of fungal meningitis in otherwise healthy people. Wash your hands, medicine makers.
Viruses don’t have even a whole cell. People have been arguing over whether they are strictly speaking “alive” for decades, and the current consensus is that we should stop worrying about it and study the hell out of them, because holy crap viruses are both cool and terrifying! A virus is evolution gone hard core - it literally only exists to make more of itself, without all that tedious mucking about with digestion and respiration and making art and posting on Facebook. Since it doesn’t have all the cell stuff it needs to make more of itself, it will hack your cells and reprogram them to make more viruses, thanks. This means they’re very good at penetrating our body’s defenses and getting into the DNA and RNA in our cells, which is awful if they cause disease, and fantastic if you’re working in genetic modification. We don’t have many good anti-virals, because the viruses go inside our cells. To get at them completely, we have to get the medicine inside our own cells, and that tends to kill them, which is not ideal. Viruses can cause all kinds of disease, including a gajillion or so which cause “the common cold”, and they can survive on surfaces for quite a while. Wash your hands, kids.
Prions are functionally much like viruses, in that they’re not whole cells, they’re just bits of stuff (proteins, to be specific) that make copies of themselves. I’ll be honest, I’m not real clear on what makes them not-viruses. But they suck, and some cause holes in your brain and we don’t have anything to treat them. Washing your hands won’t help here, although not eating brain and nerve tissue, or ground meat with brain and nerve tissue, or meat contaminated with little splatters of brain and nerve tissue can help prevent acquiring the most notorious prions that cause Creutzfeldt-Jakob Disease in humans and “Mad Cow Disease” in cows. And it’s pronounced PRY-ons.
