Rhabdoviridae Flashcards
Describe the morphology of Rhabdoviruses
Enveloped
Bullet shaped
Large spikes on the envelope
Helically coiled, cylindrical nucleocapsid
How many proteins are encoded by rhabdovirus RNA?
5!
Large Giraffes Need More Protein
L: large, RNA dependent RNA polymerase
G: glycoprotein for envelope spikes
N: nucleoprotein to form nucleocapsid
P: phosphoprotein mediates binding of L protein to nucleocapsid
M: matrix associates with viral nucleocapsid and lipid envelope
Describe the genome of rhabdoviridae
ssRNA, negative-sense, one molecule
Where does rhabdovirus replicate and what characterizes its maturation?
Cytoplasm
Budding from plasma membrane characterizes maturation
Which virus ‘mutant’ is formed during rhabdovirus replication?
Defective interfering virus particles that interfere with the normal replication process
What is the most important member of genus Lyssavirus?
Rabies virus, genotype-1 lyssavirus
What animals are highly susceptible to rabies?
Cats and cattle
What animals are moderately susceptible to rabies?
Dogs, sheep, goats, horses, primates, humans
How is rabies transmitted?
Between mammals mainly via bite/scratch with the virus in its saliva, not transmitted through intact skin
- Aerosol transmission has been documented in labs or bat caves
- Human vases via organ transplant?
Describe the two cycles by which rabies is maintained:
Urban: dogs are main reservoir, predominates in Africa, Asia, Central/South America
Sylvatic: Europe and N. America, usually multiple wildlife species are responsible for perpetuating a particular strain i.e. bats!
Dead end hosts: humans and most herbivores
T or F: A bat that has rabies is less likely to interact with humans than a bat that is infected with rabies
False! If a bat has rabies, it is more likely to interact with humans!
Oftentimes, asymptomatic but sometimes can be aggressive*
Which type of bat plays a major role in human and animal rabies in Mexico, Central America, and S. america?
Vampire bats
Which type of bat is capable of transmission of rabies in Australia?
Fruit bats!
Which type of bat is more likely to transmit rabies in North America?
Insectivorous bats!
Which animal is the MOST important in perpetuation of wildlife rabies in central USA?
The skunk
Which animal is the most frequently reported rabid species in the USA?
The raccoon
Describe the pathogenesis of rabies
May enter peripheral nerves directly or multiply in non-nervous tissue until there’s enough of them to reach motor/sensory nerve endings
Shed from monocytes into extracellular spaces
G protein binds to axon terminals through lipoprotein receptors
Gets into nerves
Greater degree of innervation at site of bite, shorter incubation period
T or F: Bites to the face have the greatest risk
True
If intranasal exposure occurs, how does the virus get to the CNS?
Through the trigeminal nerves and ganglia
What form of rabies happens when the virus reaches the limbic system?
Furious form
Think-emotions
What form of rabies happens when the virus reaches the neuro-cortex?
Dumb or paralytic form
T or F: first, rabies heads centrifugaly from the CNS to the peripheral nerves and then moves centripetally from the peripheral nerves to other organs
False! Opposite–first is centripetally from periphery to CNS and THEN centrifugally out bak to the peripheral nerves (salivary glands via cranial nerves–hypersalivation)
Identify pathological findings of the rabies virus, specifically in the brain
There tend not to be any! Variable inflammation and very modest histological evidence of neuronal injury
Indicates primary neuronal lesion is functional, not structural
T or F: If the bite is closer to the site of the brain, there will be a shorter incubation period
True!
Identify and describe the three general phases of the clinical course of rabies
Prodromal: virus shedding and change in temperament before obvious clinical signs are observed
Furious (acute): nervous, irritable, dilated pupils, loss of caution and fear, hydrophobia, excessive salivation, exaggerated responses to light and sound
Paralytic (dumb): fury gives way to paralysis, ataxia, muscle weakness, seizures, coma, respiratory arrest and death 2-14 days after clinical signs
*Ruminants don’t tend to exhibit fury
How do you diagnose rabies?
FAT (recommended by WHO and OIE) to look for rabies antigen
Negri bodies in the brain (not all positive brains will have these)
RT-PCR for viral RNA
Intercerebral inoculation of weanling mice for virus isolation
Mice develop encephalitis in 14 days
How do you control rabies in a rabies free country?
Quarantine involving segregation of dogs and cats in licensed premises for 6 months
What are the preexposure and post-exposure recommendations for dogs and cats?
Pre: Vaccinate at 3 months of age, revaccinate every 1 or 3 years after
Post: Unvaccinated animals are euthanized immediately, non-current vaccinated animals are evaluated on a case by case basis, and current vaccinated animals have to be revaccinated immediately and kept under owner’s control for 45 days
What are the two serotypes of the vesiculovirus?
Indiana: Fort Lupton, Alagos, Coccal
New Jersey: more virulent with the widest distribution!
T or F: the vesiculovirus can remain stable for days or weeks in cool water, soil, and on vegetation
True
What animals does vesiculovirus mostly infect?
Cattle, pigs, horses in the Americas, sometimes sheep and goats
Influenza-like disease in humans
Describe the transmission of the vesiculovirus?
Probably enters through breaks in mucosa/skin, contamination of milking machines, chewing or ingestion of contaminated fomites, arthropods via mechanical transmission! Like houseflies
Describe the pathogenesis of vesicular stomatitis
Localized infection on the epiehtlium leads to intraepithelial edema and vesicles that quickly ulcerate, common on the tongue!
Not typically a substantial systemic phase of infection
What are the clinical signs of vesicular stomatitis?
Generally self limiting with lesions that develop 1-5 days after incubation, excess salivation and fever in cattle/horses, lameness in swine, vesicles on tongue, oral mucosa, teats to ulcers
Lesions may cause salivation/anorexia, lameness, rejection of suckling calve
In horses, tongue lesions most pronounced
In swine, vesicular lesions most common on snout and coronary bands
Humans: influenza like disease
How do you diagnose vesicular stomatitis?
Vesicular lesions in horses are characteristic of only vesicular stomatitis!!
V.S. is clinically indistinguishable from other vesicular diseases of swine and cattle
Virus isolation
RT-PCR
How do you prevent V.S.?
Quarantine of affected premises Reportable in the USA! Control insect population Keep infected animals away from surface water in pastures Vaccines aren't widely used
How is bovine ephermeral fever transmitted and who are the hosts?
Transmitted via arthropods and the hosts are water buffalo and cattle
Arthropod probs Culicoides and maybe mosquitoes
T or F: bovine ephemeral fever has never been reported in the USA
True!
Describe the pathogenesis of bovine ephemeral fever
It is poorly understood, site of replication is unknown
There is an early neutrophilia with an abnormal level of immature neutrophils in the circulation
Increase in plasma fibrinogen and decrease in plasma calcium
What are the most common lesions in bovine ephemeral fever?
Polyserositis affecting the joints, pleural and peritoneal surfaces
Increase in neutrophils increases permeability!
What are the clinical features of bovine ephemeral fever?
Begins with fever followed by inappetence, excessive salivation, drooling, increased HR, stiffness, lameness, sudden decrease in milk yield
Recovery is dramatic and usually in 3 days!
Some animals are recumbent/paralyzed for 8 hours to 1 week though
How do you diagnose bovine epheremal fever?
Isolation is difficult but can be attempted by inoculation of infected buffy coat cells into cell cultures or IC inoculation of suckling mice
FA staining of blood smears
Paired serum samples
How is bovine ephemeral fever controlled?
Attenuated virus vaccines are effective BUT should only be used in endemic areas!
Vector control, duh
