Contents
Introduction
Rabies is a viral illness that causes encephalitis in humans and animals. It can be contracted from a bite or scratch from an infected animal. The incubation period is typically 2-3 months, but can be as short as a week, or as long as many years.
Symptoms can began as fever, myalgia, headaches and other non-specific viral symptoms, and later progress to neurological symptoms including behavioural change – which can include some unusual features – such as fear of water or fear of air – as well as altered level of consciousness or seizure.
Rabies is caused by lyssaviruses – the two most common being the rabies virus and Australia bat lyssavirus. As well as bits and scratches, saliva from an infected animal can also causes infection if it comes into contact with the eyes, mouth or nose of an individual.
Immunisation is highly effective at preventing rabies, even when given after the infective event has occurred (up to 10 days later). Rabies immunoglobulin may also be given into the wound (see Treatment below for specifics). Once neurological signs begin – there is no treatment and it is fatal.
In many developed countries, rabies has been eradicated, but be aware that in Australia it is possible to contract Bat Lyssavirus from bats. Vaccination is recommended for anyone who handles bats in Australia, and for travellers going to endemic areas.
Organism
- Rabies virus and Australia bat lyssavirus
- Viral zoonosis
- RNA rhabdovirus
- Incubation: 9-90 days
Transmission
Spread by the saliva of infected mammals – in the form of bites, contaminated scratches, or very rarely when the saliva comes into contact with the patients eyes, nose or mouth.
Risk of transmission when bitten by rabid animal is <50%
Epidemiology
- Dogs (+wolves and jackals) are main transmitters worldwide – more than 90% of cases. Other animals associated with rabies infection include:
- Bats
- Monkeys
- Foxes
- Racoons
- Skunks
- Jackals
- Mongoose
- Bats transmit in North America, parts of south America, parts of Europe and Australia
- Kills approximately 50,000 people per year worldwide
Pathogenesis
Virus multiplies in muscle and then is transmitted along nerve axons. On reaching the brain of the infected person, virus spreads along peripheral nerves to reach skin and lacrimal and salivary glands.
Clinical features
General
Paralytic form
Ascending sensorimotor neuropathy with ocular, cranial and laryngeal palsies and sphincter disturbances.
Encephalytic (furious) form
- Intermittent episodes of confusion, agitation and aggression(mania) intervened with periods of lucitidy.
- Hydrophobia (fear of water)
- Froth at mouth
- Painful spasms of throat
- +/- seizures
Complications
Death usually occurs within one week with respiratory and bulbar paralysis.
Diagnosis
- Generally on characteristic clinical picture (lymphocytes in CSF, history for dog bite, absent muscle rigidity between spasms)
- Diagnostic antibody tests do not become positive until day 8 (and difficult to interpret in vaccinated patients)
- Brain biopsy might show negri bodies.
Treatment
- Wash wound (soap and water 10-15 mins)
- If previously immunized, give vaccine on day 0 & 3
- If not unimmunized, give vaccine on days 0,3,7,14 & 28 + human rabies IgG (half given IM and half infiltrated around wound)
The Milwaukee protocol – induced coma in patients with unvaccinated rabies infections has shown some success in survival and functional outcome
Prevention
Avoid contact with animals in high risk areas.
Vaccination – Human diploid cell rabies vaccine
Prognosis
Post-exposure prophylaxis is very successful in prevention of rabies if given within ten days of infection (and is almost 100% effective if given immediately)
Unvaccinated – usually fatal once neurological symptoms have appeared
References
<ul><li>Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt</li>
<li>Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.</li><li>Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
</li></ul>