What is rabies?

Rabies is a deadly infectious viral disease. You can get rabies by being bitten by an infected animal. Currently at least 55,000 people die worldwide every year of rabies, [1]  mostly in India, Africa and South-East Asia, though rabies was once common all over the world. It is diagnosed in humans by observing the characteristic signs and by laboratory tests. Symptoms include fever, pain and extreme changes in behaviour.

Viral

Pertaining to an illness caused by a virus.

1. Wunner W.H. and Briggs D.J. (2010) Rabies in the 21 century. PLOS Neglected Tropical diseases 4:e591.

Causes

Rabies is caused by the rabies virus. It is transmitted between animals and from animals to humans, almost always through bites and rarely through other means.

The virus in the saliva of the infected animal infects the nerve cells in the bitten person, then travels from nerve cell to nerve cell until reaching the spinal cord, the brain and the salivary glands. Replication of the virus within the spinal cord and brain leads to the signs and symptoms (see below) of rabies. The replication within the salivary glands allows it to be transmitted onto others through biting. 

Animal bites

Rabies can potentially occur in any mammal. Animals known to transmit rabies include:

  • Canines (dogs, foxes, wolves, coyotes, jackals);
  • Bats;
  • Raccoons;
  • Monkeys;
  • Cats;
  • Skunks;
  • Ferrets;
  • Cows, and;
  • Goats.

Animals, from around the world, that can transmit rabies.Different animals from around the world that can be potential carriers of the rabies virus. 

Other ways of transmission

A person can, in rare cases, become infected with rabies without being bitten. Handling and skinning animal carcasses and eating raw animal meat can also transmit the virus.

Direct human-to-human transmission is very rare and occurs almost only in cases when infected donated organs, particularly corneas, are transplanted into uninfected people. It is possible to catch rabies from an infected person's saliva, so infected people are put in quarantine. There has been no well-documented case of human-to-human infection through biting. [2]

Corneas

The clear, dome-shaped structure at the front of the eye. It sits in front of the iris and pupil and helps to focus light onto the retina at the back of the eye.

Spinal cord

A bundle of nerve tissue that runs from the brain through the spinal column and connects the brain to the body, transmitting sensory and motor signals.

salivary glands

The glands in the mouth that produce saliva (spit).

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Risk factors

People who are most at risk of catching rabies are people who live in or are travelling in countries where rabies is still relatively common in animal populations, and who are also more likely to come into contact with infected animals. These can include people who are:

  • Living in areas with large bat populations;
  • Living in areas with a large wildlife population;
  • Frequent campers, and;
  • Wildlife animal handlers.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Signs and symptoms

After being bitten, there is an incubation period when symptoms do not appear. It can last from a few days to several years, but is usually about 3-12 weeks.

When symptoms appear, they can include:

  • Fever and chills;
  • Headache;
  • Sore throat;
  • Loss of appetite;
  • Vomiting;
  • Discomfort and irritability, and;
  • Pain, tingling and itching at the site of the bite.

A few days after these initial symptoms, symptoms of the nervous system can appear. These are divided into two different forms, known as furious rabies and paralytic rabies.

Furious rabies

Symptoms of furious rabies include:

  • Drooling;
  • Sweating;
  • Muscle spasms;
  • Numbness and tingling;
  • Convulsions;
  • Confusion, agitation and slow thinking;
  • Delirium and hallucinations;
  • Changes in behaviour;
  • Insomnia, and;
  • Fear of water - contact with, or even mention of, water or liquids triggers spasms.

Paralytic rabies 

Paralytic rabies appears in about 30% of rabies cases and is more difficult to diagnose correctly. [2]  Symptoms include:

  • Muscle weakness;
  • Loss of muscle control, and;
  • Paralysis, which usually first appears in the hands, then spreads to the rest of the body.

Delirium

A mental state caused by temporary disturbances in brain function and characterised by a host of symptoms that may include fluctuating confusion, restlessness, excitement, incoherence, illusions, anxiety, and attention deficit.

Nervous system

The extensive network of cells and structures that is responsible for activating and coordinating the body's functions, sensory input and cognition.

Paralysis

An inability to move or feel; a loss of muscle function or sensation.

Convulsions

Involuntary, abnormal contractions of muscles, leading to uncontrolled shakes and jerks of the body.

Hallucinations

A false perception of something that is not actually there. The perception can be visual or aural.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Methods for diagnosis

If a rabies infection is suspected due to an animal bite and/or the appearance of symptoms, it can be diagnosed in humans by observing the characteristic symptoms and by laboratory tests. 

Human tests

Tissue testing

Tests for the presence of the virus can be done on several tissues, including:

  • Blood;
  • Saliva;
  • Skin (taken from the back of the neck), and;
  • Spinal fluid.

Animal tests

Brain biopsy

The best places for finding the rabies virus are cells of the nervous system. However, taking samples from the nervous system can cause harm, and therefore is generally avoided in humans. To confirm or rule out a rabies diagnosis, a tissue sample can be taken from the biting animal's brain and tested for the presence of the rabies virus. This requires the animal to be put down.

Nervous system

The extensive network of cells and structures that is responsible for activating and coordinating the body's functions, sensory input and cognition.

Spinal fluid

Fluid found inside the brain and spinal column. It cushions and protects the delicate nervous tissue.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Types of treatment

Post-exposure prophylaxis

If bitten or otherwise exposed to the virus, immediate treatment (known as post-exposure prophylaxis, or PEP) is necessary in order to prevent the virus from reaching and infecting nerve cells. This can include:

  • Washing and cleaning the bite wound or scratch;
  • Vaccination, and;
  • Immunoglobulin treatment - antibodies against the rabies virus are injected into the infection site.

Milwaukee protocol

This experimental course of treatment was developed in 2004 and saved the life of an unvaccinated teenager infected with rabies. The treatment involves placing the infected person under an artificially-induced coma in order to delay the virus's advance into the brain. The Milwaukee protocol is a last-ditch resort and its chances of success are low.

Antibodies

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Coma

A state of deep and prolonged unconsciousness.

Vaccination

The practice of administering a vaccine, a solution containing a microorganism (that causes a specific disease) in a dead or weakened state, or parts of it, for the purpose of inducing immunity in a person to that microorganism.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Prognosis

Once the rabies virus is established in the body, it is almost always fatal. Some cases are reported in which people have recovered from rabies, particularly those who have been exposed to rabies from bats and other non-canine mammals. However, rabies transmitted by infected dogs, foxes and other canines appear to be more virulent and the chances of survival are very low.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link

Prevention

Vaccination

The most effective way of reducing the risks of rabies is vaccination. The original rabies vaccine was first administered in 1885 by Louis Pasteur. The vaccine is generally safe and effective. It is recommended for people who are expected to come into contact with wildlife, or are travelling to areas where rabies is found. People who have had the vaccine still need to seek immediate medical care and treatment if they are exposed to rabies.

Animal control

Another way to reduce the risk of rabies infection is to reduce the number of animals infected with the virus. Most deaths from rabies are the result of dog bites, both stray and domesticated.

Ways of reducing the risk of rabies in animals living in rabies-prone areas include:

  • Vaccinating your pet;
  • Not letting pets stray outside;
  • Avoiding contact with wild animals, particularly dogs, foxes and bats;
  • Alerting animal control authorities to any stray animals in your local area, and;
  • Carrying out public health programs to vaccinate wildlife and stray animals.

Vaccination

The practice of administering a vaccine, a solution containing a microorganism (that causes a specific disease) in a dead or weakened state, or parts of it, for the purpose of inducing immunity in a person to that microorganism.

2. Rabies. World Health Organisation. Accessed 26 June 2014 from

External link