Dogs I suppose are definitive hosts for rabies and though the incubation period may vary, they will finally show clinical signs and finally die. Is there a possibility of them acting as symptom less carriers?
There are different strains of rabies virus. Today, in South America (Brazil, for example), the canine strain of rabies is of rare identification. Viral strains found in dogs/cats diagnosed in Brazil are usually related to the strain found bats. Human cases in Brazil also follow this trend (a few cases are related to strains usually found in non-human primates).
The virus is kept mainly in cycles between carnivores (dogs, foxes, racoons...) and chiropteran (bats) reservoirs. The species of bats involved vary according to distribution in the globe (e.g., in South America hematophagous bats play an important role in disease dispersion, specially in cattle, from which they commonly feed). Non-hemathopagous bats are important in the disease cycle, since their behaviour change after infection (becoming more prone to contact with other mammals, thus spreading the disease).
There are further information on published articles, such as:
DOI: 10.1016/j.vaccine.2010.03.039
Evidence for repeated non-lethal natural infection in animals exist, but as far as I know, not in dogs (even for dog strains).
DOI 10.1099/vir.0.020073-0
The link between genetic variability and spatial epidemiology among the lyssaviruses gives a particularly good insight as to how viruses of wildlife can adapt and emerge into different animal populations. Rabies virus in Europe has switched host many times over the past century, adapting rapidly to new hosts as the virus expands into new species with time. Rabid bats exhibit abnormal behavior, losing their natural fear of humans and thus present a greater risk of transmission to humans
http://www.nature.com/emi/journal/v1/n12/full/emi201247a.html
Adptations is the answer, all parasite can adapt in nature when factors are not suitable for their survival.
If I understand your question correctly, a dog that is shedding rabies virus in its saliva will develop clinical signs within 10 days.
In a dog that has been infected, the virus travels from the site of inoculation to the CNS by way of peripheral nerves (incubation period), and from there spreads to other peripheral neurons and tissues (ie. salivary glands).
So infected animals can shed virus in their saliva for a few days before they show clinical signs. But if a dog had rabies virus in its saliva at the time it bit a person, clinical signs (likely coma) will be obvious by day 10.
I feel as if your fundamental question has not yet been adequately answered: "Do dogs sometimes become carriers, shedding virus without showing symptoms?"
The short answer is....well there is no short answer. Yet most prominent rabies researchers would give you one confidently, and they would say: "No!" However, they would be wrong if they said that no evidence exists to suggest carrier status in dogs. Though, the articles that do present some evidence are either disputed and their findings not widely accepted or they represent very rare occurrences. (Search Gribencha from Russia; Mshelbwala from Nigeria; Perl from USA, Fekadu from South Africa). Most authors today deny the possibility of a carrier status in dogs. Perhaps because it is so rare to have little practical significance. Certainly it does not nullify the fact that rabies can be eliminated by simply vaccinating dogs. Here are two important studies that present evidence against carrier status: 1) Tepsumethanon, 2005. Six criteria for rabies diagnosis. >1000 dogs in study. 2) Zhang, Investigate carrier status. >100 dogs in study. Zhang also points to the importance of accepting that our tests are not 100% specific. I think the important point is that if carrier status indeed exists, the high case fatality rate of rabies (approaching 100%) makes it almost insignificant.
It is important here not to confuse a few terms.
Host-adaption DOES NOT equal carrier status! Dog adapted virus are so called because they sustain epidemics in dogs. The reason for which is not due to carrier dogs but rather the ability to shed virus in the host's saliva and transmit to a new host before it dies. Here is a good article (although old) on rabies host adaption: The ecology of rabies, evidence of co-adaption, Carey 1983.
Survival following exposure (or abortive infection) DOES NOT equal carrier status! Abortive infections (although still rare) are more common. Evidence for abortive infections is mostly supported by finding antibodies in non-vaccinated populations (these are usually wildlife.) These surnames all present such studies: Carey, East, Federoff, Bell, Sallum, Munson and many more!! There are some old challenge experiments where dogs survived challenge. See Fekadu and others I can't find now. BUT, be careful not to assume that evidence of antibodies equals evidence of abortive infections! (As Ogunkoya has done.)
DO NOT confuse bat rabies ecology with dog rabies ecology. In bats survival and carrier status is a much more common occurrence. Even bat-rabies ecology is not the same for each bat and bat-virus combination.
DO NOT confuse positive serology for evidence of non-fatal infections.
Vaccinate, and you WILL get rid of rabies. It all comes down to that.
Thankyou very much for sparing your valuable time to clarify the answer in detail. I am really obliged & grateful.
Article Detection of Rabies Antigen in the Saliva and Brains of Appa...
I think that dogs can have asymptomatic manifestations, but a small percentage and, apparently, it depends on the quasispecies of the street rabies
virus.
Thank you very much for the fruitful discussion. Mass vaccination of stray dogs is a must.
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