Can pathogens be transmitted from smelling something?

Question

Long story short, when visiting neighbors the other day, a young child playing outside in the lawn stepped in some fresh animal fecal matter, and not knowing what it was, ended up taking off their shoe and put it within about 2 inches from their face to sniff it. The mother panicked, and after two calls to both poison control and the pediatrician, was told by both that as long as the child hadn’t swallowed any of the fecal matter, there was no need to worry about anything.

This made me curious. By putting something as pathogen-laden as animal fecal matter (or vomit, etc) that close to your face smelling it, wouldn’t you essentially be inhaling all kinds of bacteria, viruses, parasites, etc, assuming they were present? Or is the vacuum created by smelling something at that distance not strong enough to do this?

Answer 1

First, it is unlikely that the fecal matter was in fact pathogen-laden, but as a general statement should be treated as such. Further pathogens that would be in fecal mater are mostly transmitted through the fecal-oral route. That's why on an individual case you have little to worry about without any symptoms, but as a general case we wouldn't recommend going around taking big sniffs of feces (I'm enjoying the ad campaign for this in my head).

But you mention "vomit, etc," and it's worth pointing out there are pathogens that can infect through the respiratory tract from infectious fluids. This is mostly limited to things that can infect both your GI tract and respiratory tract, and that's not a long list (EBV is a good example). Further "smelling something" with an infectious respiratory virus (rhino, influenza, etc) can certainly cause an infection. I would highly discourage sniffing used tissues.

A bigger concern are pathogens like norovirus which are so infectious, possibly down to 10 virions to cause infection (instead of 1000s or more), that it could enter your oral tract without your even knowing it.

Even if it was infectious, there's really nothing to be done until symptoms arise that can be treated. Do feel free to discourage sniffing feces if that doesn't seem to be a self-correcting behavior.

Answer 2

Good question. The answer is no, not in this case.

In order to understand why, it will help to talk about the different ways pathogens enter the body:

• Direct contact - touching an infected person

• Indirect contact - touching something an infected person touched

• Droplet contact - infected droplets touching mucosal surfaces of eye, nose, mouth

• Airborne transmission - contact with dust/air particles containing infectious agents

• Fecal-oral transmission - ingesting contaminated water or material

• Vector-borne transmission - pathogens carried by a host animal, and transmitted through any of the above methods

Picking up the fecal matter and smelling it raises concerns about direct contact, vector transmission and airborne transmission. As Atl LED mentions, the pathogens in feces are normally transmitted through the fecal-oral route. The fecal-oral route requires that the pathogen enters the digestive tract, which won't happen by smelling. Nevertheless, it can be classified as risky behavior, and is not recommended.