Why is it that we both wash our hands after pooping and use manure for crops? Crap is crap, right? What’s the difference?
The difference is that the bacteria that are harmful to us are not harmful to dirt and/or plants.
Plus, the plants don’t care what your hands smell like.
Well, yeah, but farmers wallow in that shit all day, it ends up on the crops… isn’t it a risk if it enters the food supply?
Yes, it can be a risk if it enters the food supply, which is one of the reasons why washing vegetables is important. As I understand it, the medieval use of human waste for fertilizer was one reason that pottage and beer were so popular - if you boiled and fermented everything for days, you could be pretty sure the bacteria were dead (or, you would be sure of that if you knew what bacteria were).
Of course, bacteria that happily grow in your wet and warm colon are not going to be as happy outside where it’s (relatively) cold and dry. Likewise, they’re not as dangerous on your skin as they would be if you swallowed them.
Also, manure used for farming is not just sewage thrown onto plants. It is mixed with other ingredients (often straw) and allowed to compost (or whatever the proper term is). This is harmful to bacteria, though a city boy like me is still a little leery of the stuff.
Some modern food products are irradiated with UV to reduce the harmful bacteria present. There may be other treatment options that help.
That can be a problem if we’re talking about human shit. I don’t think, though am happy to be corrected, that we use human waste on food crops in developed countries without it having been treated first to lower the bacterial load.
On the other hand, animals like cows have completely different gut bacteria that don’t really hurt us too much if they enters the food supply.
Having shoveled my share of manure, I want to point out that farmers do wash their hands thoroughly after working. It’s not like you come in all grimy/shitty and pick up an apple with your hands and start munching.
Also, people do get sick from not washing their fruits and veggies properly. E.Coli, in particular, can be passed along this way.
It’s important to remember that the vast majority of all bacteria are harmless. This includes even most of the bacteria that live in our digestive tracks. E. coli is normally pretty tame… remember that you are infected with it right now, to the point where you have more bacteria in your gut than cells in your entire body. These bacteria are completely harmless normally, but can start some opportunistic infections. Thus they’ll cause trouble for individuals that are already sick, or immunocompromised, or if they get out of the gut and into the body cavity. But a healthy individual, encountering garden-variety bacteria, will be just fine.
Now, there are rare strains of E. coli that are pretty nasty, and these give cases of food poisoning that can be deadly. These can be found in manure, and have lead to a few outbreaks. And there are plenty of human pathogens that are specialized to spread by contact with feces, but won’t be found in the manure of other species. Any given individual won’t carry them, but if you’re talking about the entire sewage stream of a small city, you can safely assume that there are a few people there with nasty cases of food poisoning and diarrhea.
In a society where sanitation is poor, these will spread so efficiently that they’ll be everywhere. In modern germ-phobic western cultures, their spread has been pretty limited, so that the risk of picking up something nasty from sewage is relatively small. Hand-washing reduces risks and helps prevent epidemics. What might give a minor stomach cramp to the random schlub working at a fast food joint could kill the little old man who just walked in.
Well, not quite. IIRC, a number of e. coli problems in produce have been traced back to pig or cow manure.
That’s part of why you should always wash your produce - scrub your melons before cutting into them, peel off the outer layer of lettuce leaves, and give everything a good long rinse with cold-or-cool (not warm) water before cutting it or eating it. And never ever trust packaging that says something is pre-washed.
Alternately, buy frozen vegetables and nuke or boil the crap out of them before eating.
I see what you did there.
Also, there’s an interesting example of how good or bad gut bacteria can be. Normally there’s a vast array of different species living all through your intestine. In healthy individuals, this community is stable. However, after antibiotic treatments that kill the entire miniature ecosystem, some patients end up with one or two nastier species taking over the entire gut. This is the reason that many people get diarrhea after taking powerful antibiotics.
In particularly intractable infections by C. difficile, there’s a relatively new treatment that involves transplanting healthy gut flora. Which is a polite way of describing a procedure where fecal matter is taken from a healthy family member, and introduced to a patient. This is done with a feeding tube directly to the intestine to remove the squick factor and reduce the risks of opportunistic infection.
More here.
…and a new fetish is born :eek:
ETA: No, wait, 
is more like it.
Dons protective goggles and shuts mouth very, very tightly.