Rabies

Rabies, or 'hydrophobia', is known as a disease that makes dogs sick and mad. Consequently, all dogs in many northern European countries are vaccinated against it. However, it can affect all warmblooded creatures, including man.

Rabies is caused by a virus, which, among other things, attacks the nervous system and is excreted later in the saliva. When an animal gets sick, it may start to bite.

People are most often infected by the bite of a dog, bat or monkey. In Europe the virus is mainly carried by the fox.

Rabies is rightly feared. By the time the symptoms appear, the disease can no longer be cured and almost always ends in death.

Fortunately, rabies can be prevented with a vaccine and, if you have been bitten, there is every chance that you can be treated before the symptoms develop.

What causes rabies?

The virus that causes rabies is the lyssa virus, and it is one of the few in that particular group which can cause illness in man.

The rabies virus is good at 'hiding' from the immune system. As a result, no immune response really develops, so the body finds it hard to combat.

After a bite, when the virus has travelled from the nerve pathways of the muscles into the central nervous system (CNS), it replicates quickly and spreads into many parts of the brain. The brain becomes inflamed and many functions of the CNS are affected.

The virus spreads via the nervous system to many of the tissues of the body, including the skin, mucous membranes and salivary glands.

How is rabies transmitted?

Rabies is a classic 'zoonosis', which means that it is an illness that is passed directly from animal to animal and from animal to human.

The effect on the brain also causes aggressive behaviour, which can make the animal attack and bite without provocation. This is how the virus spreads from the animal's saliva to the tissue of the bitten animal or person.

It then seems to make its way into the muscle cells. In theory, saliva on mucous membranes and small open cuts may also be the route of entry for the rabies virus. Cats can also pass the disease on by scratching a person or other animal.

In principle, all warmblooded animals can be infected, but the disease is found most commonly in dogs, foxes, cats and monkeys.

Bats are the main source of infection in countries where domestic animals are vaccinated and the fox population is tightly controlled.

Where does rabies occur?

Rabies is prevalent in all the continental regions of Asia, America and Africa. Greenland and many countries in Europe have rabies in their animal populations.

The virus has reached as far as Southern Jutland in Denmark, although the rest of Scandinavia, as well as the British Isles, are rabies-free. This is also true of Japan, Australia and New Zealand.

Understandably, these countries are very keen to maintain their rabies-free status. As a result there are regulations on importing animals.

From a global point of view, the WHO estimates that 10 million people a year are treated after exposure to rabies. Some 40,000 to 70,000 people are thought to die of the disease each year, many in India.

What are the symptoms of the disease?

Normally between three weeks and three months can pass between infection and the onset of symptoms (incubation period). But in individual instances, it may be as much as several years.

In spite of being bitten by an animal with rabies, it is not certain that you have been infected. Only one out of six people who have been bitten develop symptoms - even if they have not been treated.

If you get rabies and do not manage to be treated in time, the disease evolves in two phases:

The prodomal phase (prelude)

In this phase, the patient may have a fever, vomiting and loss of appetite, headache and pain at the site of the original bite.

The autonomic nervous system is affected. This manifests itself as copious salivation and weeping.

The neurological phase

Paralysis may occur in this phase. In particular, there are spasms in the throat, making swallowing difficult.

The person affected becomes terrified of water (which is why it's also called 'hydrophobia') and becomes anxious and hyperactive.

It is in this phase that animals become mad and bite. Symptoms such as those seen in encephalitis are also present, along with increasingly uncontrolled movement, confusion and delirium.

Prospects

Once visible symptoms have developed, the mortality rate is almost 100 per cent. Very few people are known to have survived a rabies infection.

The suspicion of infection can be allayed by observing whether the animal fails to develop signs of the disease over 10 days.

The disease does not develop if appropriate treatment is applied in time.

What can you do to avoid infection?

In developing countries, avoid stray dogs. In general, you should not pick sick animals up. At home, it can be tempting for a child to pick up a poor little bat, flapping about wildly on the ground.

If an animal bites you, don't despair. Administer normal first aid. It is vital to wash the wound thoroughly with copious amounts of water, and, if at all possible, use a 20 per cent dilution of soap.

If the animal may be infected with rabies, the wound must be treated by a doctor, even if you have been vaccinated. You should also see a doctor for cuts and scratches

You should also think about whether you are adequately protected against tetanus.

Vaccination

The vaccine is administered as an injection of killed rabies virus. It is now much improved and no longer consists of painful injections into the stomach!

A total of three injections are needed: the first two with an interval of one week and the last one three weeks later. The injection can be given into the skin (intradermal) at a tenth of the dose of the intramuscular injection. The vaccination provides protection for three years.

The vaccination is recommended for people who live in areas where there is a steady incidence of rabies virus. In particular, if you intend to spend time in areas where there is no immediate access to preventive treatment, you should be vaccinated.

Should you be bitten, you will need the rabies vaccine regardless of whether you had a pre-travel rabies vaccination. However, if you have received the pre-travel vaccine you will not need to have the rabies immunoglobulin injection as well.

How is the disease diagnosed?

In developing countries, the disease is often diagnosed on the basis of what the patient's family can relate and the characteristic disease picture.

In developed countries, the doctor will confirm the diagnosis by sending tissue samples to a laboratory, where the virus can be detected. In animals, the diagnosis is made by detecting the virus in samples of brain tissue from the dead animal.

How is rabies treated?

As soon as a bite has been sustained, immediate first aid is vital.

The likelihood of infection is determined by the extent of rabies in the area, the species of the attacking animal and whether the attack was unprovoked.

The closer a bite is to the face, the greater the risk, since the virus has a shorter distance to travel to the brain.

Preventive treatment after exposure to infection is the only way to stop the fatal disease developing. Treatment is both by giving specific immunoglobulin (passive immunisation) and by administration of a normal vaccination (active immunisation).

The disease usually takes long enough to develop in humans to allow the body's immune response to be stimulated by the vaccination, before the symptoms of rabies manifest themselves.

Preventive treatment with immunoglobulin

It is possible to administer specific antibodies (immunoglobulins) against the rabies virus as a type of antidote. It is the same principle as the antidote to snake bite.

The immunoglobulins act by binding themselves to their target, in this case the rabies virus, and preventing the virus from penetrating into the cells, so that the immune system has time to react and destroy them.

The immunoglobulins are broken down in the body after a while and, as a result, this type of vaccination does not provide lasting protection, because the immune system itself has not learnt to recognise the virus. The latter is achieved by active immunisation with rabies vaccine.