Wednesday, 30 April 2008

'R' is for Rabies - A Killer Disease in Dogs and Man

A couple of days ago I spoke about the quarantine kennels where a rabid dog had bitten 3 people.

So I've decided to write a more technical article on the subject of rabies in dogs and people.

Rabies (Lyssa) is one of the oldest known zoonotic diseases; an animal disease transmissible to humans.
It is caused by rhabdoviruses of the genus Lyssavirus and can affect all mammals including humans.
Transmission occurs when there is direct contact to infectious saliva; via bites, scratches and broken skin. The incubation period can range between 2 weeks and 3 months depending on the site of infection, the amount of virus and the virus strain.
Due to its neurotropism rabies viruses cause neurological symptoms that may differ in animals and humans.

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.

Once symptoms of the disease develop, rabies is fatal to both animals and humans, except in very rare cases.

Clinical signs in animals

All animals exhibit certain neurological signs as a result of rabies. These symptoms may differ slightly between species.

Prodromal stage: After a certain incubation period, the onset of clinical symtoms follows. During this first stage which usually lasts for about 1-3 days minor behavioural changes can occur, e.g aggressiveness in pet animals, daytime activities in nocturnal animals, no fear of humans in wild animals or abnormalities in appetite.

Excitative (furious) phase: Eventually, the prodromal stage is followed by a period of severe agitation and aggression. The animal often bites any material. Rabid dogs, for example, may develop a typical high barking sound during furious rabies. Death may follow convulsions even before the paralysis stage.

Paralytic (dumb) phase: This stage is characterized by the inability to swallow, leading to a typical sign of foaming saliva around the mouth. Some animals may develop paralysis beginning at the hind extremities. Eventually, complete paralysis is followed by death.

Rabies is one of the most feared diseases which affects people.

Endemic canine rabies contributes to more than 99% of all human rabies cases; half of the global human population especially in the developing world lives in canine rabies-endemic areas and is considered at risk of contracting rabies.

In the developing world tens of thousands of people die from rabies every year. African and Asian countries are particularly affected by rabies. There are often insufficient controls and inadequate healthcare.

In developed countries, widespread vaccination and animal control programmes have reduced the incidence of the disease in people to low levels. Human cases are now rare in Europe, except for the Russian Federation.

Dogs are of great importance in the transmission of rabies to people, particularly in countries where there are cases of rabies in pet, feral and stray dogs.

The greatest risk of bringing rabies to the UK is either from human travellers (who are highly unlikely to pass the disease on to animals or people) or imported animals - the most important being pet dogs and cats.

Rabies has been associated with long incubation periods - that's why there is a six month quarantine for imported pets. However studies on rabies shows that incubation periods are normally between 2 and 12 weeks.

Once clinical rabies has developed, with rare exceptions, death is inevitable within a few days. There is no immune response in the incubating animal or person. The virus cannot be reliably identified in tissues before the onset of clinical signs, so there is currently no possibility of diagnosis of rabies in the incubating animal.

As well as affecting the central nervous system, rabies virus can also live in the salivary glands which allows the transmission of rabies by infected saliva through bite wounds – the usual route. Animals may pass the virus by this route before the development of clinical signs - up to 13 days in dogs.

While treatment of clinically infected animals and people is of no avail, post exposure treatment of people with vaccine and hyperimmune serum is used successfully. This remedial treatment is only partially successful in dogs and other animals.

Vaccines are used successfully against rabies and can give up to three years immunity, although vaccination does not preclude the possibility of rabies infection, as confirmed cases of rabies have occurred in previously vaccinated dogs and cats.
Nevertheless, overall, they provide a high level of protection. The protection they can offer is measured by the antibody level they stimulate.


Since 1793, the Rabies in the United Kingdom Quarantine Act has been the main control method used to keep the UK free from rabies. The result of this policy is that there have been no indigenous human cases of rabies in UK until 2002 when a bat conservationist died in Scotland., afetr being bitten by a rabid bat.
Two cases of rabies have occurred in dogs after they left quarantine so additional measures, which included vaccination against rabies on arrival, were introduced in 1972, to help avoid cross
infection in quarantine kennels. Since then, quarantine measures have been completely successful.
Import of pets through quarantine is controlled by the Rabies (Importation of Dogs, Cats and OtherMammals) Order 1974, and its amendments.

The message is clear - don't smuggle animals into the UK. Keep It Out!

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