Rabies is a viral disease that affects the central nervous system and is almost always fatal once symptoms appear. It is primarily spread through the bite or scratch of an infected animal, most commonly dogs, bats, raccoons, skunks and foxes. Rabies has an incubation period that can vary greatly, ranging from about 3 weeks to several months or even years. This leads to the key question: is it possible to develop rabies months after being bitten or exposed to a rabid animal?
Quick Answer
Yes, it is possible to get rabies months after exposure, though rare. The rabies virus has an incubation period that varies from about 3 weeks to 6 months. There have been exceptional cases where rabies developed 1 year or longer after exposure. This is why it is critical to receive post-exposure treatment if bitten or scratched by an animal that could have rabies, even if months have passed.
Typical Incubation Period
In humans, the typical incubation period for rabies is 1-3 months after exposure. This is the time from the initial bite/exposure to onset of initial symptoms.
Most cases occur within 1-3 months:
- About 80% of rabies cases appear within 1 month after exposure
- 95% of cases occur within 3 months
Factors that influence the incubation period include:
- Site of virus entry – Shorter incubation with bites to highly innervated areas like the face
- Viral load in the inoculum
- Severity of bite – Deeper wounds and lacerations have shorter incubation
- Age and health status of exposed person
In rare cases, the incubation period may be under 20 days or exceed 6 months. When onset occurs more than 6 months after exposure, it is termed “prolonged incubation rabies.”
Maximum Incubation Period
While most rabies cases have an incubation under 3 months, in very rare cases the incubation period has exceeded 1 year. Some of the longest documented incubation periods include:
- 19 months – bitten by a dog in the Philippines
- 2.5 years – infected in Iran
- 6 years – bitten by a dog in India
- 8 years – bitten by a dog in the former USSR
There has also been a report of rabies developing after 30 years, but very extensive exposure to rabid animals over years may have been involved in some prolonged cases like this.
Nonetheless, these cases illustrate that it is possible, though very rare, for rabies to develop over a year after a bite from a rabid animal.
Rabies Post-Exposure Treatment
The possibility of prolonged incubation periods is one reason why post-exposure rabies treatment is recommended anytime there is possible exposure to rabies virus, even if months or over a year have passed.
Treatment after a bite, scratch or exposure involves:
- Wound cleaning/flushing – Thoroughly washing the wound with soap and water to lower virus levels
- Rabies vaccine – A series of 4 vaccine shots over 14 days
- Rabies immune globulin (RIG) – Injection of antibodies to help neutralize rabies virus
This combination of wound care, rabies vaccine, and rabies immunoglobulin is highly effective in preventing the development of rabies in exposed patients, even with prolonged incubation periods.
Getting appropriate post-exposure prophylaxis promptly, even if up to a year or more has passed since the exposure, is crucial for preventing this fatal disease.
Symptoms
The first symptoms of rabies may be nonspecific and flu-like. As the disease progresses and the virus spreads to the brain, symptoms become more severe.
Early symptoms can include:
- Fever
- Chills
- General feeling of unease or discomfort
- Fatigue
- Loss of appetite
- Headache
- Nausea
As the disease advances, neurological symptoms appear like:
- Increased anxiety, agitation, confusion
- Abnormal behavior
- Hallucinations
- Insomnia
- Loss of muscle coordination
- Paralysis
- Seizures
- Hydrophobia (fear of water)
Once clinical symptoms develop, rabies is nearly always fatal. This highlights the importance of preventing infection by promptly receiving post-exposure treatment after any potential rabies exposure, even if exposure was months prior.
Rabies Transmission
Rabies virus is spread through the saliva or nervous tissue of an infected animal. The main routes of rabies exposure are:
- Animal bites – Most rabies cases result from the bite of an infected animal. The virus is present in saliva.
- Scratches – Scratches can also transmit rabies virus if saliva from an infected animal enters the scratch wound.
- Mucous membranes – Exposure of eyes, nose, mouth to saliva or nerve tissue containing virus.
In the U.S., wild animals like raccoons, skunks, foxes and bats are the most common transmitters. Rabid bats especially pose a risk, as their bites may not be noticed.
Any potential exposure to a bat or wild carnivore should be treated by a medical provider to assess rabies risk and provide post-exposure treatment if warranted. Even if exposure occurred months prior, it should still be evaluated for treatment.
Diagnosis
Rabies can be difficult to diagnose, especially in the early stages before neurological symptoms appear. No specific clinical or laboratory tests can readily identify rabies before symptoms arise.
Some techniques used to diagnose rabies include:
- Virus detection – Testing saliva, spinal fluid, skin samples for presence of rabies virus RNA or antigen. Only works after symptoms appear.
- Serology testing – Looking for antibody evidence of rabies virus exposure in blood serum or cerebrospinal fluid.
- Brain biopsy – Microscopic analysis of brain tissue from fatal cases for evidence of rabies virus.
These direct testing methods may fail to detect rabies virus, especially early in the course of disease. This delayed diagnosis possibility is another reason prompt post-exposure treatment is advocated after any potential rabies exposure.
Can Rabies Be Cured?
Unfortunately, once clinical rabies symptoms develop, there is no effective treatment. Rabies has one of the highest fatality rates of any infectious disease – over 99% of diagnosed human rabies cases are fatal.
Intensive medical care focuses on comforting the patient and controlling symptoms to ease suffering in the disease’s final stages. Sedatives and pain medications may be used. Paralysis and seizures are treated with drugs as able. Nutrition and fluids are provided intravenously. But no specific anti-rabies treatments have proven successful at this stage.
The Milwaukee protocol, an experimental approach using an induced coma and antiviral drugs, has been applied in some desperate cases. However, it has failed more often than succeeded and is not recommended as standard care.
Prevention remains the key due to rabies’ exceptionally high mortality once symptomatic. Receiving fast medical assessment and post-exposure treatment after potential rabies contact, even months later, offers the only way to prevent this deadly outcome.
Prevention
The most effective ways to prevent rabies include:
Avoiding Exposure
Stay away from all wild mammals and stray or unattended animals to prevent bites and contact with rabies virus. Monitor children’s activities and teach them to avoid approaching unknown animals. Reduce potential attraction of wild animals to yards with measures like securing garbage in closed containers. Call animal control to have stray animals removed from the area.
Animal Vaccination
In the U.S., most documented rabies cases in domestic animals now occur in unvaccinated pets. Vaccinating dogs, cats, ferrets, horses and valuable livestock protects these animals and reduces the overall rabies risk. Rabies vaccine is typically administered in an initial series of 2-3 injections, then boosted every 1-3 years depending on the animal, its age and vaccine type.
Bite Prevention
Closely supervise all interactions between unfamiliar animals and children. Seek professional animal training if a household pet develops aggressive behavior. Teach children to be calm and avoid sudden movements when approached by unfamiliar animals. Report stray or aggressive animals to animal control for removal.
Post-Exposure Treatment
If bitten or scratched by an unknown, potentially rabid animal, or if saliva, nervous tissue or other infectious material contacts broken skin or mucous membranes, immediately wash wounds thoroughly with soap and water. Then seek urgent medical care for evaluation and possible post-exposure rabies treatment, even if the exposure was months ago. Rabies post-exposure prophylaxis is highly effective in preventing disease when administered promptly after viral contact.
Conclusion
Rabies remains a concerning, fatal infectious disease spread by animal bites and contact with infected saliva. While its incubation period typically ranges from 2-8 weeks, rabies has rarely developed over a year after exposure in exceptional cases. That is why thorough washing of contact wounds, vaccination and immunoglobulin shots are recommended following any potential rabies virus exposure, even if months have passed since the initial risk incident. Though prolonged incubation rabies is very uncommon, prompt post-exposure prophylaxis offers the only chance to prevent this deadly neurological disease. By avoiding high-risk contacts with wild mammals and following guidelines for prophylactic treatment after possible exposures, people can protect themselves against this fatal infectious disease.
| Incubation Period | Time from Exposure to Symptom Onset |
|---|---|
| Typical | 2-8 weeks |
| Usual range | 2 weeks to 3 months |
| Maximum reported | 6 years |