The usually fatal viral disease called rabies exclusively infects mammals. Humans mostly get it by being bitten by a rabid animal. In the U.S., preventative treatment is nearly 100 percent effective. Some countries have less success, with human cases up to 100 times higher than in the U.S.
An incubation period in a viral infection is the time during which the virus lays low in a person's system. The victim isn't symptomatic, and the virus can't infect others.
The typical human rabies incubation period is about one to two months. A study in India found that 90 percent of rabies cases had incubation periods of six months or less.
If the victim has suffered multiple or severe bites from an infected animal, the incubation period can be about two weeks.
Sometimes rabies has a long incubation---perhaps a half-decade---before the infected person sickens. A 2008 re-examination of a 1990 Australian case confirmed this.
Occurence of Long Incubation
Long incubation periods occur in very few cases. The Indian study demonstrated that long incubation occurs only 10 percent of the time.
Rabies infects the central nervous system. After incubation, victims might have headaches, fever and depression, and then various neurological symptoms appear. Without appropriate treatment, victims are likely to die.