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Redirected page to Category:Rhabdoviridae
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#REDIRECT[[:Category:Rhabdoviridae]]
 
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{{toplink
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|linkpage =Viruses
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|linktext =VIRUSES
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|pagetype=Bugs
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}}
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<br>
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=Introduction=
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Rabies is a neurological killer that has evolved a fool-proof technique of transmission, and it cleverly evades the species barrier to present a potent threat to mammalian life.  While the simplicity of the virus ensures its transmission, it also contributes to its weakness: its monoclonal antigenicity means that a single vaccination covers all strains of the disease.  Though rabies is considered endemic in parts of the developed and undeveloped world, vaccination schemes have rendered the disease controllable to a satisfactory degree.  Nonetheless, infection is still largely fatal and the disease should not be taken lightly.
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=Morphology=
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*Large, enveloped, negative-sense RNA virus
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*'''Bullet-shaped''' with short glycoprotein spikes
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=Types and Subtypes=
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Two Genera:
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#Lyssaviruses: 7 genotypes
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##'''Genotype 1''' is '''classical rabies'''
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##Genotypes 2-7 more limited in distribution
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##Genotype 4 infects '''insectivorous bats'''
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#Vesiculoviruses are all '''exotic''' to the UK:
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##Vesicular Stomatitis Virus
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##Ephemeral Fever
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##Fish Rhabdoviruses, such as viral hemorrhagic syndrome and infectious haematopoetic necrosis virus
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=Virulence and Pathogenesis=
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*Rabies is moderately resistant: it can survive well in dark places at low temperatures for several days
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*Infection occurs through a '''penetrating bite''' in which virus is transmitted via '''saliva'''
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*'''Incubation''' period is variable but can be long (10 days to 12 months), and increases with distance of the bite to the CNS
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**80% show signs within 4 months
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*Primary replication of the virus occurs in the '''muscle'''
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*The virus gains access to nervous tissue and travels toward the '''brain''', where it continues to replicate
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*It then migrates down cranial nerves to infect salivary glands and the cornea
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*Virus is shed in '''saliva''' and '''tears''' and can be shed BEFORE the onset of classical signs
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*The onset of clinical signs in dogs and cats includes:
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**Behavioral changes
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**Pyrexia
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**Salivation
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**Dilation of pupils
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*Two forms of the virus exist:
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**'''Furious''' form:
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***Common to cats and dogs
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***Abnormal aggression, salivation, and attack without provocation
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***Disordered wandering, "copulatory" movements.
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***Incoordination, convulsions, coma and death within 3-10 days
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**'''Dumb''' form
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***May or may not follow Furious form
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***Common to ruminants and horses
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***Ruminal tympany, tenesmus, diarrhoea
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***Paralysis of lower jaw, drooling saliva, tremors and progressive paralysis
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***In dogs, a change in voice may be observed (bellowing)
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*Human infection is characterized by '''hydrophobia'''
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=Epidemiology=
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*Rabies is a '''NOTIFIABLE''' zoonosis
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*Rabies is found worldwide, though currently considered exotic to the UK and Australia
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Host Range:
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*All mammals are susceptible
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**Very susceptible: foxes, jackals, wolves
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**Susceptible (10,000x virus necessary to infect): cats, rodents, bats, skunks, cattle, mongooses
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**Moderately susceptible (100,000x virus necessary to infect): dogs, sheep, goats, horses, primates
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*Isolates can show to some species specificity in their reservoir host
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Reservoir species by region:
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{| style="width:60%; height:200px" border="1" align=center
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!'''Region'''
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!'''Reservoir Species'''
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|-
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|Europe
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|Red fox
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|-
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|Russia, Turkey, Middle East
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|Dog, Raccoon
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|-
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|USA
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|Raccoon, Fox, Skunk
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|-
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|Africa
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|Dog, Jackal, Mongoose
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|-
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|Asia
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|Dog, Mongoose
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|-
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|South America
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|Dog, Vampire bat
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|-
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|Worldwide
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|Insectivorous Bats
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|}
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*The current position of DEFRA holds bat lyssaviruses to be present in the UK
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*Human infection and death an occur after infection with bat rabies
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**Nocturnal bat bites account for 50% of human cases in the USA
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*Humans develop disease but excrete little virus
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*Immune recovered animals are rare, but are not shown to be infections
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=Diagnosis=
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*'''Isolate''' and monitor for clinical signs
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*In the field:
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**Remove brain core sample via straw through occipital foramen in the direction of an eye
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**Place contents in a 50% glyerol/PBS for FAT or virus isolation, or in 10% formaldehyde for histology
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**Whole head can also be removed and sent to lab
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*In the lab:
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**'''Fluorescent Antibody Test (FAT)''' on smears or frozen sections of hippocampus or cerebellum should show presence of Negri bodies
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***Being replaced by testing for monoclonal antibodies to nucleoprotein
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**Histological detection of Negri bodies using Mann's or silver stains
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**Intracerebral inoculation of mice followed by FAT testing of brain smears of affected mice
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**RT-PCR on brain or saliva can be performed to determine genotype
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=Rabies Control=
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For countries where rabies is considered exotic:
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*6 month quarantine of carnivores and ruminants (Norway, Sweden, Portugal, Australia, New Zealand)
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*In the UK, this has been replaced by the '''Pet Travel Scheme''' ([http://www.defra.gov.uk/animalh/quarantine/index.htm PETS])
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For virus-endemic countries:
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#Control in pets:
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#*Annual Vaccination:
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#**Antigenicity allows a single antigenic type to vaccinate
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#**'''Inactivated virus''' or '''canarypox''' recombinant viruses
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#*Control of stray population
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#*Muzzling in public
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#Control of wildlife reservoir hosts:
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#*Feeding vaccinated bait
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#*Secondary consequence of increasing reservoir host population (eg European foxes)
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#Control in humans
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##Prevention by vaccination with a single booster if bitten
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##*The current vaccine is grown in human diploid cells (HDCV) and is BPL-inactivated, and therefore costly
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##*Developing countries utilize older vaccines passaged from a 1939 case ("Flury" vaccines)
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##If bitten and unvaccinated:
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##*Clean and disinfect wound
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##*Human '''anti-rabies immunoglobulin''' administered around bite
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##*Intramuscular vaccination program: 2 dose-1 dose-1 dose at 0, 7, and 14 days post-bite
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For more on Rabies control in Europe, see [http://www.who-rabies-bulletin.org/About_Rabies/Control.aspx here]
 
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