The incubation period
The incubation period is the time that it takes for symptoms to develop after a person is infected with a virus. The incubation period for rabies is usually between three and 12 weeks, although it can be as short as four days or as long as 19 years. However, it would be highly unusual for an incubation period to last for more than a year.
The length of the incubation period is important because this is the only period in which the rabies vaccine can prevent a rabies infection.
The closer the bite is to your brain, the shorter the incubation period. For example, a bite to your face, head or neck will have a shorter incubation period than a bite to your arm or leg.
Initial symptoms
The initial symptoms of rabies are often non-specific, and it can be easy to mistake them for other, less serious types of infection. They include:
- a high temperature (fever) of 38ºC (100.4ºF) or above
- chills
- a general feeling of uneasiness – ‘feeling out of sorts’
- fatigue (extreme tiredness)
- insomnia – problems sleeping
- lack of appetite
- headache
- irritability
- anxiety
- sore throat
- vomiting (being sick)
Around half of people will also experience pain, itchiness and a tingling sensation at the site of the bite.
Advanced symptoms
The initial symptoms of rabies last for two to 10 days, before more severe symptoms start to develop. There are two types of advanced rabies symptoms. They are known as:
- furious rabies, which account for 4 out of 5 cases
- dumb rabies, which accounts for the remaining cases
Furious rabies
Furious rabies is characterised by episodes of increasingly bizarre and hyperactive behaviour, separated by periods of relative calm. During these episodes, a person may have some, or all, of the following signs and symptoms:
- aggressive behaviour, such as thrashing out or biting
- agitation
- hallucinations – seeing or hearing things that are not real
- delusions – believing things that are obviously untrue
- excessive production of saliva
- high temperature (fever)
- excessive sweating
- the hair on their skin stands up
- a sustained erection (in men)
Around 50-80% of people with furious rabies will also develop hydrophobia (a fear of water). This initially begins as a pain in the throat or difficulty swallowing. On attempting to swallow, the muscles in the throat go into a brief spasm that lasts for about five to 15 seconds. Subsequently, the sight, sound or even the mention of water (or any other liquid) will trigger further spasms.
The affected person will then fall into a coma before dying, usually within 12 days, as a result of heart or lung failure.
Dumb rabies
Dumb rabies is characterised by increasing muscle weakness, loss of sensation and paralysis (an inability to move one or more muscles). This usually begins in the hands and feet before spreading throughout the body.
Hydrophobia is unusual in cases of dumb rabies, although muscles other than those in the throat may go into spasm. As with furious rabies, someone with dumb rabies will fall into a coma and eventually die from heart or lung failure.
When to seek medical advice
If you are in a part of the world that is known to be affected by rabies, always seek medical advice as soon as possible if you are bitten or scratched by an animal, particularly a dog.
In England, there has not been a case of rabies from an animal born in England for over 100 years. However, always seek medical attention if you are bitten by a bat (although this situation is rare), or if you suspect that someone in your care who is unable to report a bite may have been bitten. For example, if you find a bat in a young child’s room.
Symptoms of rabies in an animal
As with humans, the symptoms of rabies in an animal follow a number of stages.
The first stage is marked by initial non-specific symptoms, such as:
- loss of appetite
- high temperature
- change in normal behaviour, such as appearing unusually tame around strangers
The second stage is known as the ‘mad dog’ stage and usually lasts for two to four days. It is characterised by very aggressive and erratic behaviour, such as:
- constantly barking or growling
- no fear of normal, natural enemies
- attempting to attack and bite anything that comes near, including inanimate objects
The final stage, known as the ‘paralytic’ stage, lasts for two to four days and is characterised by symptoms such as:
- the animal appearing to be choking
- foaming at the mouth
- the dropping of the lower jaw (in dogs)
- paralysis of the jaw, mouth and throat muscles
