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Making Sense of ... Rabies

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Rabies

What is rabies?

Rabies is a viral disease of mammals, transmitted through contact with saliva from infected animals (i.e. bites, scratches, licks on broken skin and mucous membranes). Rabies virus infects the central nervous system, causing encephalopathy and ultimately death, which usually occurs within days of the onset of symptoms.

Where is rabies usually found?

Rabies has been found in most countries of the world; it is rare in Western Europe (though it is moving westward again) and Australia, as well as the polar regions.

How common is rabies?

Estimates from the WHO suggest that there are over 50,000 deaths from human rabies each year. The vast majority of these occur in Asian countries where canine rabies is endemic. In most of Africa and Asia, the mortality data is unreliable and almost certainly under-reported.

How is rabies transmitted?

The most common mode of transmission is by a bite from an infected animal; typically dogs, but most other small mammals have been possible carriers, including bats, monkeys, foxes.

Can rabies be spread from person-to-person?

Transmission between human beings is possible through biting, scratching or other contact with infected saliva. There are several reported cases of transmission via transplanted organs, including donor corneas. There is at least one case of transplacental transmission to a baby, and others of transmission via breast milk. Transmssion is not airborne, but aerosol infection - inhalation or ingestion of saliva, or eye infection - is theoretically possible.

Who is most at risk?

People living in infected areas, and those working with infected animals or people with the disease. Higher risk groups include wildlife officers, veterinarians and people travelling overseas who expect to have contact with unvaccinated mammals that bite or scratch.

What are the symptoms of rabies?

Rabies develops in two phases:

The prodomal phase (prelude)

Symptoms may include headache and pain at bite site, often with vomiting and loss of appetite. Autonomic effects can include copious salivation and weeping.

The neurological phase

Throat spasm, and difficulty in swallowing may be followed by progeressive paralysis. The patient becomes terrified of water (hence 'hydrophobia') and becomes increasingly agitated and hyperactive.

The agitation may include aggression and biting, with confusion and delirium. Death follows.

How is rabies diagnosed?

A definitive diagnosis follows laboratory identification of the rabies virus in saliva or brain tissue. This makes diagnosis impossible during the incubation period, and means that a definitive diagnosis is usually obtained post mortem.

What is the incubation period?

The usual incubation period for rabies is three weeks to three months, but this period can vary, and periods of years have been recorded. Only one out of six bite victims (including untreated people) go on to develop symptoms.

Is there a treatment for rabies?

Once rabies is symptomatic. Only intensive care can provide support. there is no cure; many antiviral agaents have been used, none with any success.

Post-exposure prophylaxis has a role; if the animal that bit the patient is identified, it can be observed for ten days; if it develops symptoms, it can be killed and examined for the disease. If it was a wild animal, it is normally killed immediately. This can provide evidence that the bite victaim is at risk, without waiting for symptoms (which would be too late).

Rabies post-exposure prophylaxis involves wound management and immunization.

Surgical debridement of the wound is essential, and in animals has been shown to reduce the risk of disease progression. The wound is not closed, post debridement, and human rabies immunoglobulin is applied to the area (passive immunization). An intramuscular injection of the immunoglobulin is given to provide some immediate protection.

This is followed by active immunization, using human diploid cell vaccine. This is usually a course of five injections into the deltoid muscle, and 5 doses are usually given.

What is the prognosis for rabies?

While only one in six bite victims go on to contract the disease from the infected animal, rabies is 100% fatal if untreated.

What is the mortality rate for rabies?

Once symptoms have appeared, the victim usually dies in spite of subsequent immunization and treatment with rabies immunoglobulin. There are only three documented cases of patients recovering from rabies infection.

50 000 - 60 000 human deaths from rabies are estimated to occur annually, despite the existence of an effective vaccine for postexposure prophylaxis (PEP)(at least 10 million doses of rabies PEP are used annually).

In some countries, mortality is very low (for example, the USA has about one case per year)

But rabies mortality is seriously underestimated, especially in Africa. For example, Tanzania's human rabies mortality is estimated to be about 1500 deaths per year (about 5 deaths/100 000 persons), but national statistics report fewer than 200 deaths per year.

Is there a way to prevent infection?

Rabies vaccine can help to prevent rabies. People who handle or come into contact with animals that may be affected should receive a course of vaccinations.

Common sense precautions and appropriate training for professions is a much better guarantee of safety. Domestic animals and browsing or grazing animals are not considered a significant risk; but dogs, bats, monkeys and other mammals have been implicated - usually foxes in Europe.

What is the rabies vaccine?

Rabies vaccine provides immunity to rabies when administered after an exposure (postexposure prophylaxis) or for protection before an exposure occurs (preexposure prophylaxis). The effectiveness of post-exposure vaccination depends on the delay in availability, and the site of the bite

Who should get vaccinated against rabies?

Pre-exposure vaccination is recommended for people in high-risk groups, such as veterinarians, animal handlers, laboratory workers and others whose activities bring them into direct contact with rabies virus or potentially rabid bats, raccoons, skunks, cats, dogs, or other species at risk of having rabies.

Are there adverse reactions to the rabies vaccine?

There are no contraindications to post-exposure treatment. In the case of allergic reaction, alternative forms of the vaccine may be used.

There is a failure rate of about one per million post-exposure treatments. Most of these have been associated with severe lesions at or near the head, or errors in administration of the treatment.

With human diploid cell vaccines, pain, erythema and swelling or itching at the injection site occur among 30%–74% of patients. Systemic reactions involving headache, nausea, abdominal pain, muscle aches or dizziness occur in 5%–40% of vaccinees, and allergic oedema in 0.1%. Systemic allergic reactions characterized by generalized urticaria accompanied in some cases by arthralgia, angiooedema, fever, nausea and vomiting have been reported in up to 6% of persons receiving a booster dose, with onset after 2–21 days.

Purified Vero cell rabies vaccine produces local and general reaction in 10.6% of patients and complaints of mild to moderate reactions in 7%. Low-grade fever was the only significant systemic event, occurring in 8%, usually following intramuscular vaccination. Pruritus at the injection site has been the only significant local reaction.

the use of purified chick embryo cell vaccine has produced local side-effects in 16.4%, with 15.1% reporting general symptoms.

Can rabies be controlled environmentally?

Rabies contracted from canine bites accounts for more than 99% of all human rabies. Scandinavian countries eradicated rabies by environmental measures including stray dog control. The UK has relied heavily on quarantine and importation of mammals controls, but does have a program of dog control.

Local programs have included attempts to vaccinate foxes to create an immune barrier at the entrance to the Rhone Valley; Switzerland has been freed of rabies. Research continues.

Is there legal protection for workers and others?

People who contract rabies - and there families - may have a strong legal case, depending on the circumstances. many places have laws that demand vaccination of certain pets; any pet owner who fail to maintain up-to-date pet vaccination may be liable. Wild animals may be subject to quarantine or movement restrictions, and handlers who flout these laws will be liable.

On the other hand, individuals who are warned of risks and given advice on protection, and are subsequently bitten through ignoring the information, may have little right to compensation.

Legal advise should be sought, as the circumstances will always vary, and it will depend on local and national laws in your country.

What can be learned from history?

Studying cases of rabies has helped to establish how effective the vaccine can be, and who will beneift; studies of the spread of the disease across continents can enable governments to alter regulations as neede to protect the population. For example, over the past twenty years, rabies has spread westward across Western Europe, with increased incidence in Germany and France. So the UK has relaxed it's once-draconian quarantine regulations, and reduced the publicity displays at ports and airports. Go figure!

Bibliography and Further Information Sources

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 26 February 2006
Last updated: 11 March 2012
© Andrew Heenan 2006 et seq
 

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This site is not - and is not intended to be - a substitute for medical advice.

The information provided here is accurate, to the very best of our knowledge, but it is general facts, never, ever, specific to your circumstances.

If you need medical advice, you need a doctor.

If you need legal advice, you need a lawyer.

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