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So there was a case in India, where a man developed rabies 25 yrs after the dog bite. Source: https://www.google.co.in/amp/s/m.timesofindia.com/city/goa/25-yrs-after-dog-bite-man-gets-dies-of-rabies/amp_articleshow/16415870.cms I have the following questions: 1) what are the reasons behind such a long incubation pd?

2) in such cases, can vaccines taken years after the dog bite save the person? (Even though it’s advised to take it immediately)

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  • $\begingroup$ I think the article described that the virus was sequested in the tissue, and that is why it did not spread. Also I think one can do treatment after exposured although 25 years sound long. I think it depends on if the patient had been vaccinated previously as well. source: academic.oup.com/cid/article/30/1/4/323391 $\endgroup$ – Ro Siv Apr 15 '18 at 15:34
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This question may not be particularly answerable.

The only available information about this specific case is in the original article (Shankar et al. Ann Indian Acad Neurol. 2012 Jul-Sep; 15(3): 221–223. doi: 10.4103/0972-2327.99728); they say only:

The anatomical site of viral latency and the mechanism of reactivation of rabies, a neurotropic virus, remains an enigma to be unraveled.

Other reports in the literature of long incubation periods (>7 years, the previously reported maximum seems to be 14 years) are scattered/old/speculative, e.g. Gavrila et al. Ann. Inst. Pasteur 1967 Vol.112 No.4 pp.504-15:

Discussing these cases of prolonged incubation periods, the authors point out that in rabies the incubation period can vary within very wide limits and that it is possible in areas where the disease is enzootic that, in very exceptional cases, the disease can develop after an incubation period which may sometimes greatly exceed the maximal limits now admitted, and that, as for example in cats [this Bulletin, 1965, v. 62, (1106)], stress conditions and so forth may lead to the generalization of the virus until then quiescent at the point of entry.

Plotkin 2000 Clinical Inf Dis 30:1 says

the reasons for this long latency are unknown ... in the absence of specific prophylaxis, the virus becomes hidden, only to invade the CNS weeks, months, or years later. Where is the virus during this period? There is some evidence for slow replication in muscle cells and for latency in macrophages, but there is no certainty that these account for the long incubation periods.

There has been an experimental study on skunks (Charlton et al. Acta Neuropathologica June 1997, Volume 94, Issue 1, pp 73–77) that suggests there is some infection of muscle cells at the injection site, but otherwise not much is known about the mechanism.

I would guess that vaccination would be effective if it were administered soon enough, but it will probably be hard in these surprising cases to identify the disease soon enough.

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The incubation period for the rabies virus is typically not that long - usually under 1 month. The reasons for longer incubation period include site of virus entry (where on body the infection occurs) and the viral load (how much virus enters at the infected site). Although there are examples of very long incubation (many months or years), reasons for this are unknown. You may find the link below helpful - see under "symptoms".

http://www.who.int/mediacentre/factsheets/fs099/en/

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