Difference between revisions of "Rhabdoviridae"

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

Latest revision as of 13:51, 21 May 2010