How "exactly" is Rabies transmitted?

Question

Context: I know a person which has developed a sort of "phobia" with respect to touching things that has (even the slighest) chance of being in contact with something that can transmit rabies. For instance, if something (a coin) falls on the floor of our university, said person almost cannot take it, since dogs sometimes pass around the place. This has reached a severe level which hinders this person experience in life. However, there is apparently some hope of rationalization. Specifically, the person told me that if someone can prove, for example, that the virus do not "live" long enough after dropping from the saliva of a dog to the floor in order to be transmitted to a human being, then maybe she will be more relieved. This led me to search for information on the internet, but nothing was conclusive. This takes me to my question, and sorry for the sidetracking.

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Can someone be infected by rabies by merely taking something from the ground where a infected dog may have passed by? How long does the virus "live" (or is active, I don't know the proper term) after being "exposed" to the environment? More generally, how exactly does the process of infection happen, and how can it happen?

Answer 1

This is actually far more complex a question than you probably know. The country you are writing from matters. There are some rabies virus variants that have a relatively low pathogenicity for humans (dog rabies is one of these; a relatively large innoculum is required, i.e. a bite, commonly a deep one with lots of virus-laden saliva.) The likelihood of canine-associated rabies developing from a non-bite exposure is extremely low; in fact, the exact risk is unknown.

In the US, enzootic (dog-to-dog) canine rabies virus has been virtually eliminated through vaccination and stray control programs, making wild animals (including feral cats) the primary concern. Depending on the country your friend lives in, dogs may not even be high on the list of worrisome sources.

Regarding canine-associated rabies,

Rabies control was accomplished [through dog vaccination programs, responsible pet ownership, and serious population control of stray dogs] in Europe, North America, Australia, Japan, Taiwan, Malaysia, and Singapore.

If you don't live in one of these countries/continents, dog-associated rabies is still a major concern. If you do live in the mentioned areas, you can probably dip your hand in dog saliva and not be concerned.

Rabies is usually contracted by a bite; that is most common.

The most dangerous and common route of rabies exposure is from the bite of a rabid mammal. An exposure to rabies also might occur when the virus, from saliva or other potentially infectious material (e.g., neural tissue), is introduced into fresh, open cuts in skin or onto mucous membranes (nonbite exposure). ...Exposures to bats deserve special assessment because bats can pose a greater risk for infecting humans under certain circumstances that might be considered inconsequential from a human perspective.

how exactly does the process of infection happen, and how can it happen?

The exact way it happens is not completely understood, but that answer won't help you convince your friend of anything. The virus is usually deposited in tissue near a cutaneous (peripheral) nerve. If it gains entry to the nerve, it makes its way to the brain with the typical disastrous results.

Having said all this, your friend is not going to stop worrying, because the virus is only the focus of an irrational fear. Though the foci of irrational fears are fairly stable, OCD is most likely the underlying problem, and conventional rational discourse doesn't really suffice in curing the obsession.

_{During 1990-2007, 34 bat-associated human cases of rabies were reported in the US: 6 cases reported a bat bite; 2 cases reported a probable bite; in 15 cases, physical contact was reported (e.g., the removal of a bat from the home or workplace or the presence of a bat in the room where the person had been sleeping), but no bite was documented; and in 11 cases, no bat encounter was reported, but the rabies virus was bat-specific.}

_{Any encounter with a bat, even a dead one (as stated above), must be evaluated for possible post-exposure prophylaxis.}

_{Unfortunately, in the US, animal rabies is common, and at least 23,000 persons/ year receive rabies postexposure prophylaxis (PEP). (It is probably considerably higher, as no reporting mandate exists.) With the elimination of canine rabies virus variants and enzootic transmission among dogs, human rabies is now rare in the United States, with an average of one or two cases occurring annually since 1960.}

_{In the US in 2013, of the three human cases reported, 2 were involved in organ transplants (raccoon rabies virus variant) and one was a Guatemalan (canine rabies virus variant).}

_{In 2012, one human died from an exposure to a bat. He touched a bat under a bridge. He did not report a bite to a witness. He became ill while traveling, and died in Switzerland. A number of humans exposed to his saliva (including his Swiss caregivers) received PEP.}

^*_{Some people in high-rabies areas without the illness have been documented to have developed antibodies to rabies. The mechanism is unknown.}

_{Human Rabies Prevention - United States, 2008
Pathogenesis of Rabies
A Single Amino Acid Change in Rabies Virus Glycoprotein Increases Virus Spread and Enhances Virus Pathogenicity
Human Rabies Prevention (Comment From a Canine‐Rabies‐Endemic Region)
Epidemiology of rabies post-exposure prophylaxis—United States of America, 2006–2008
Rabies surveillance in the United States during 2013
Use of a Reduced (4-Dose) Vaccine Schedule for Postexposure Prophylaxis to Prevent Human Rabies: Recommendations of the Advisory Committee on Immunization Practices}

Answer 2

The routes of transmission for rabies are concisely described on the CDC website. To summarize:

• The vast majority of cases of rabies are transmitted through the bite of a rabid animal.
• For non-bite exposures, there is potential for transmission if an infectious material (such as saliva) enters the eyes, nose, mouth, or wound of a person. There is also potential for aerosol transmission however this is only a risk to laboratory workers.
• Petting a rabid animal or contact with blood, urine, or faeces of a rabid animal does not constitute an exposure. (See the CDC guidelines for detailed information on special case contact with certain wildlife species.)

It is possible that if a person touches a fomite (such as a coin) that had very recently contacted the saliva of a rabid animal, they could be infected if that coin came in contact with an open wound or mucous membranes. Neverthless, this is extremely unlikely. Such a case has never been described. Fomites are not considered a route of transmission for rabies.

Furthermore, the rabies virus cannot survive very long in the environment. The virus will die within hours since it is very sensitive to ultraviolet light and desiccation, therefore once the saliva is dry there is no risk of transmission. This process is not instantaneous (the virus does not die as soon as it leaves the host). I was unable to find a precise length of time that the virus can survive in the environment, but this probably has not been researched because there has been no reported cases of transmission via this route. A 1974 study found that the virus in mouse brain tissue died within days at room temperature, and it is plausible that the survival in fluid exposed to the environment would be much shorter.

Most animal workers such as veterinarians receive a pre-exposure rabies vaccine but this is due to the risk of being bitten by a rabid animal.

In summary, we cannot categorically exclude transmission via a fomite, but I cannot stress enough how extremely unlikely exposure to rabies in this manner would be.