About Rabies

What strikes first to your mind when you hear ‘rabies’? A dog bite that leads to death – most of us have the same thought. Ever wonder how these happy and innocent animals can transmit such a fatal disease? Well, let us understand better by learning about the disease.

What is Rabies?

Rabies is a deadly disease caused by rabies virus, which mainly affects the animals. This disease can be transmitted to humans through the infected saliva of the animals via bites or scratches. The virus infects the central nervous system of the mammals and causes various symptoms. If the person is not treated immediately, the disease can spread to the brain and cause death. However, this disease can be prevented by vaccines.

Transmission of rabies to humans:

The infection spreads when an infected animal bites or scratches a human being. However, the infection is not spread by touching or feeding the animal, or when the animal licks. A majority of the rabies cases are caused by dog bites. But other animals like cats, monkeys, bats, wolves, and jackals can also transmit the disease.

Rarely, the infection can spread when the saliva contacts an open wound or the mucous membranes, like the eyes or mouth. This may happen when an animal licks an open cut on the skin.

How will I know if I have rabies?

After the virus enters the human body, it should travel to the brain to produce any symptoms. This time between the exposure and the presentation of symptoms is called the incubation period, which may last from a few days to months.

Sometimes, the infection may produce early signs that indicate the onset of a disease, even before the diagnostically specific signs and symptoms develop. These signs include:

• Pain and/or itching at the site of bite
• Fever
• Nausea and vomiting
• Sensitivity to changes in temperature

Rabies can occur in two different forms – ‘furious’ rabies and ‘paralytic’ rabies.

Furious rabies accounts for nearly 70-80% cases. It is presented as hyperactivity, hydrophobia (fear of water) and sometimes aerophobia (fear of air currents or of fresh air). This type of rabies results in death in a few days due to cardio-respiratory arrest.

Paralytic rabies comprises of around 20-30% cases. This type of disease manifests as a gradual paralysis of muscles, beginning at the site of bite or scratch, which progresses towards the central nervous system. Ultimately, the patient suffers from coma, followed by death. Such patients can survive for 1 to 2 weeks or longer.

Diagnosing Rabies

Unfortunately, till date there is no single test available to diagnose human rabies infection. However, there are several tests that can help indicate rabies before death in humans. Tests are performed by collecting various samples like the saliva, serum, spinal fluid, and skin biopsies of hair follicles at the nape:

• Saliva is tested by virus isolation or reverse transcription - polymerase chain reaction (RT-PCR).
• Antibodies against the rabies virus are examined in the serum and spinal fluid sample.
• The rabies antigen in the cutaneous nerves at the base of hair follicles can be detected by examination of skin biopsy specimens.

There is no way to know if the animal has transmitted the rabies virus to you when the animal bites. Thus, the prevention of rabies infection is the first step taken, even if there is a slight possibility of being exposed to the virus.

How is rabies treated?

Rabies is usually fatal as there's no effective treatment for this disease. Hence, it is very important to seek immediate medical attention when an animal bites or scratches you or you think you've been exposed to rabies; you may receive a series of vaccine shots to prevent the infection.

Rabies can be prevented by rabies vaccine, made from killed (attenuated) rabies virus. This vaccine is given after considering various factors, including:

• The circumstance of the bite - provoked or unprovoked
• The type of animal – wild or domestic
• History of animal vaccination
• Information regarding the circumstance surrounding the bite from local health authorities

If the animal that has bitten you is known to have rabies, the rabies vaccine is given. But, if the animal cannot be found, it is safe to assume that the animal has rabies and begin the treatment.

It is always advisable to

There are two types of rabies shots, which include:

• Rabies immune globulin, a fast-acting shot is given to prevent the virus from infecting you. This injection may be given near the spot where the animal bit.
• A series of rabies vaccines are given to help fight against the rabies virus.

Rabies vaccine can be given pre-exposure or post-exposure; however, the immunization schedule differs.

For individuals who have not received rabies vaccine previously, postexposure prophylaxis includes administration of human rabies immune globulin (RIG) and rabies vaccine. Immunoglobulins (RIGs) are infiltrated at the site of the wound & rabies vaccine is administered as series of shots.

People who travel to regions where rabies is widespread, who work with rabies in laboratory settings, pet owners can have pre-exposure vaccine. This is given on the days 0, 7 and 21 or 28.

Despite pre-exposure vaccination, additional therapy after a rabies exposure is required. However, it eliminates the need for rabies immune globulin and reduces the number of doses of vaccine. This type of vaccination is important for individuals who are travelling to regions where immunizing products may not be available or where the biologics used may be of lesser quality; this would in-turn increase the risk of adverse events.

Safety of the rabies vaccine

Rabies vaccine is safe, and the risk of any serious harm is very less. However, it is associated with typical, mild problems such as:

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  Soreness

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  Redness

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  Swelling

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  Itching

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  Headache

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  Nausea

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  Abdominal pain

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  Muscle aches

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  Dizziness

Rarely, the vaccine can cause the following moderate to severe side effects:

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  Hives

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  Joint pain

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  Fever

Some individuals may have allergic to the rabies vaccines. Signs of a severe allergic reaction are:

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  Difficulty breathing

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  Hoarseness or wheezing

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  Hives

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  Paleness

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  Weakness

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  Rapid heartbeat

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  Dizziness

If you have any of these side effects, call you doctor immediately.

Usually, after injecting the vaccine, the patient is asked to wait in the doctor’s office or emergency room for 30 minutes to observe if any allergic reaction will occur.

Can rabies be prevented?

Yes, rabies can be prevented by taking some precautions:

• Vaccinate the pets: Pets like dogs and cats can be vaccinated against rabies. You veterinarian will tell you how often they should be vaccinated.
• Protect your pets: Keep your pets confined and monitor them when outside. Protect the smaller ones from predators and rabid animals.
• Seal your home: Keep bats away from home; seal any gaps or cracks through which bats can enter.
• Get vaccinated if travelling: Before travelling to any country or region where rabies is a common condition, talk to your doctor if you can get vaccinated. You may receive the vaccine if you are planning to stay there for an extended period, or if the region lacks medical facilities.

Vaccination

Rabies vaccine is an active immunizing agent made of killed rabies virus. This vaccine protects the human body against infection of the rabies virus. This vaccine is given to individuals who have been exposed to the virus or who are at risk of the infection, before actually being exposed.

The rabies vaccine is manufactured from inactivated strains of rabies virus. When the vaccine is administered, the rabies antigen (the inactivated virus) induces production of antibodies against the rabies virus. These antibodies provide immunity against the virus.

Rabies vaccine can be administered in two ways –

Post-exposure prophylaxis:

Individuals who have been exposed to the rabies vaccine by an animal bite or scratch that is known or thought to have rabies. This is also known as post-exposure prophylaxis.

This type of vaccination is typically given as an intramuscular injection on days 0, 3, 7, 14 and 28. Human rabies immune globulin is given on day 0, unless the patient has received rabies vaccination previously. Recently, intramuscular inoculation of the vaccine has been replaced with intradermal injections.

According to the National Guidelines on Rabies Prophylaxis provided by National Centre for Disease Control, India, anti-rabies neutralizing antibody titre of 0.5 IU/ml or more in serum is effective for protecting the human body against the rabies virus. This protection is obtained by day 14 of a post-exposure prophylaxis in most healthy individuals. This can be achieved irrespective of the simultaneous administration of rabies immune globulin.

Pre-exposure prophylaxis:

Individuals who are at high risk of getting infected with rabies virus can be administered with rabies vaccine. This is known as pre-exposure prophylaxis. This type of vaccination consists of intramuscular injection of 1 ml vaccine on days 0, 7, 21 and 28. Based on the vaccine manufacturer, booster doses can be recommended at 3–5-year intervals.

However, the current treatment standard fails to prevent patient death once the rabies virus enters the central nervous system. This inability to treat these cases is attributed to the absence of effective anti-viral agents specific for rabies.