Rabies

From MicrobeWiki, the student-edited microbiology resource
"Rhabdoviridae" Tranmission electron microscope picture of the viruses outer envolope. From: ppdictionary.com [1]

Taxonomy

| Order = Mononegavirales | Family = Rhabdoviridae | Genus = Lyssavirus | species = Rabies Virus|

NCBI: [4] Genome: Rabies Virus [5]

Description

Rabies (derived from Latin word Rabere, meaning 'Rage') is a viral disease caused by Lyssavirus rabies virus. It is a neurotropic virus, capable of invasive infection of the central nervous system. The disease is extremely lethal to those unfortunate enough to show symptoms of the infection. The primary transmission of the virus to humans occurs through dog bites and scratches. The numbers vary widely form country to country, however, it is estimated that 55,000 people die per year from the rabies virus in Asia and Africa . The disease can be dramatic in its appearance as with many animals the disease is known to cause hyperactivity and sporadic behavior while becoming aggressive to things around them and eventually succumbing to paralysis of muscles.

History and Impact

"middle ages rabid dog" A woodcut from the Middle Ages showing a rabid dog. From: Wikipedia.com [2]

Rabies is a very old disease having originated before much of written history. The relationship between dogs and humans is shaped and altered greatly by the this disease originating from mad and crazed animals. Some of the oldest texts that are linked to rabies come from 2300 BC Eshunna, a Babylonian city, known for heavily fining people who's dogs bit others and lead to their death. Through out the Greek and Roman Empires rabies was well known and even widespread. The Greek philosophers even wrote that "dogs suffer from the madness." (Aristotle 400B.C.). It was the Romans who first described the saliva from rabid dogs as 'virus' which is Latin for poison. A Roman physician by the name of Celsus had a treatment for wounds caused by rabid animals that remained widely accepted from 45 A.D. till the 1900's. Many physicians in history have described the symptoms of rabies, came up with cures and temporary ailments for the sick. The first case of rabies reported in the Americas was in Mexico by a priest in 1703. The disease swept the entire world slowly over centuries until it was noted on every continent on the globe except Antartica.

In 1804 a German scientist by the name of Zinke begins conducting experiments using infected saliva on various animals, confirming that the disease does come from other infected animals. The key turning point in history for rabies comes in the 1880's when Louis Pasteur, a chemist, and his assistant, scientist, and physician, Emile Roux begin research for a cure to rabies. By 1883, the two have created was is to be the first vaccine against the disease, but the real test to prove to the public that it works comes in 1885 when a nine year old Joseph Meister is bitten by a rabid dog and brought to Pasteur who puts his career on the line by testing the new vaccine for the first time. The vaccine was a success and young Joseph Meister became the first person to be successfully treated for the disease. Pasteur being a chemist not a doctor is given immediate praise and hailed as a hero. This new vaccine is still used to this day and is still the standard treatment of rabies to this day. The vaccine also works towards animals such as dogs leading to the campaigns of vaccinating pets to prevent the spread of disease.

Virology

Pathogenisis

Transmission

Infection to humans usually occurs through a bite or scratch from an infected animal. Saliva from infected animals, as well as humans, can cause rabies when in contact with mucous tissues or recent skin wounds. Inhalation of aerosols containing virus particles as well as transplant of viral infected tissues have also been documented as possible forms of transmission. Many animals have the potential to carry the virus, but the most common source is dogs. Bats are a common source in the Americas. Other animals known to carry the disease include foxes, raccoons, skunks, jackals, and mongooses. Human to human infection through bite or scratch is hypothetically possible, but has never been confirmed.

Incubation

The rabies virus has a fairly long incubation period in comparison to many other viruses. Average time from inoculation to symptoms is approximately 1-3 months, however, cases have been reported of symptoms showing in as little as 1 week, and as long as 6 years.

Epidemiology

Virulance Factors

Diagnosis

No tests are currently available prior to symptoms to test for the viruses presence. The Virus can be confirmed via intra vitam and post mortem procedures that detect the virus as a whole, the viral antigens from host production, or the nucleic acids of the virus from infected tissues. Examples of these detection methods include reverse transcription polymerase chain reaction (RT PCR) test kits, negri bodies found in neuron cells, use of florescent tagged antibodies in infected tissues, live viral culturing (including WI-38, BHK-21, or CER), and several serological tests (including MNT, RFFIT, and EIA). Some of the tests can even be combined such as using IF on live tissue cultures to test for presence of rabies antigens.

Treatment

Post-Exposure Prophylaxis is the main course of action needed to prevent rabies from causing disease. The type of interaction with a suspected infected animals dictates the specific action necessary for treatment and is generally understood in three categories.

(1) Touching, Feeding, and licking on skin require no PEP.

(2) Nibbling of uncovered skin, minor scratches with no bleeding may require immediate local treatment of wound and vaccination is recommended as a precautionary measure to prevent the disease.

(3) 1 or more trans-dermal bites or scratches or lick on broken skin, as well as contact of mucous membrane with saliva will require local treatment of wound(s), vaccination, and likely use of rabies immunoglobulin to prevent and counteract to virus.

Physical and chemical methods of cleaning wounds are recommended as effective methods of removal of the virus. Some examples of these methods include Rinsing the wound with water, soap, detergent, and providone iodine.

Prevention

"Rabies Distribution" Data from the World Health Organization (WHO) 2012. From: nathnac.org [3]

Eliminating Rabies in Dogs

The disease is absolutely preventable with the use of the vaccine. Do to the cost of health care, the best way to prevent the spread of rabies to humans is by eliminating rabies in animal (especially dog) populations. Rabies has been completely eradicated from a few countries, but there have been recent increases of the disease in Asia, Africa, and Latin America suggesting that the virus is becoming a re-emerging pathogen. By preventing rabies in animals such as dogs, the number of people needing Post-exposure prophylaxis treatment is significantly diminished.

Preventative Immunizations in People

Rabies in animals

Dogs

Bats

Opossums

Foxes

Wolves

Other animals

Host Immune Response

References