BIG had a comment about aerosol transmission of rabies to spelunkers from
bat guano and whether that was inconsistent with what's known about rabies.
In fact, it should have been possible to predict that this could occur.
Some bats can harbor rabies for a long time and given enough time, it's not
inconceivable that rabies could end up in feces.  In most mammals, rabies
kills so quickly that I doubt this could ever happen.  (Humans can also
harbor rabies for a very long time--up to six years in some case reports!
Conceivably, infected humans could transmit rabies, too, but I haven't seen
this documented.)
 
Aerosolozed droppings or saliva could infect the olfactory nerve, which is
only an inch or so away from the brain.  This is probably the worst place to
be infected because the virus would go immediately to the brain.
Post-exposure treatment may not even be effective in such cases.  I've also
heard of cases of swimmers being infected with amoebae through the olfactory
nerve.  Cerebral amoebiasis is *extremely* nasty and difficult or impossible
to treat.  Rabies has also been documented to be transmitted through the
mucous membranes of the eyelids although it's pretty rare.  So, the
take-home message is that you don't need to be bitten to get it.  In fact, I
believe that more than half of all cases of rabies in humans in the U.S.
and Canada are cases of unknown transmission in which there is no known or
remembered bite or scratch.
 
This doesn't have much impact on the dynamics of rabies spread, however.
Olfactory and other non-bite transmissions of rabies are so uncommon that
they usually get written up as case reports in medical journals.  I
certainly wouldn't want people to get paranoid about every aerosol droplet
they're exposed to.  If a ferret, dog, or even a cow sneezes in your face,
it's not a valid reason to be given the post-exposure treatment for rabies
or demand that the animal be tested.  Whereas rabies *can* be transmitted
this way, it appears to be inefficient (for the virus) and rare...*nothing*
like true airborne viruses such as influenza or foot and mouth disease.
 
--Jeff Johnston
[Posted in FML issue 1620]