MICB 212 Rhabdovirus (Rabies)

rhabdoviridae

enveloped

helical nucleocapsid - bullet shaped

(-) ssRNA

• monopartite, linear

rhabdoviridae virus

rabies virus

RABV transmission

spreads via direct contact with infected animal’s saliva, tears or brain tissue

commonly through bites

• can be spread through scratches or exposure to eyes, nose, mouth

RABV genome

no 5’ cap and 3’ poly (A) tail

• 3’ leader (le) and 5’ trailed (tr) sequences

3’-N-P-M-G-L-5’

• junction contains

  • end (E) sequence for upstream gene

  • 2-nt intergenic (I) sequence

  • start (S) sequence for downstream gene

RABV proteins

nucleoprotein (N) protein: ~1200 copies

• covers 9 bases

matrix (M) protein: ~1800 copies

• condense nucleocapsid into tightly coiled nucleocapsid-M complex

• virus skeleton → bullet shaped

glycoprotein (G): ~300-400 spike-like projections

• G trimers (attachment & penetration)

• spans viral envelope (host cell plasma membrane-derived lipid bilayer)

RABV life cycle

1. RABV binds

   • nicotinic acetylcholine receptors

     OR

   • neuronal receptors on muscle/nerve cells

   • entry most common at neuromuscular junction after bite from infected animal

2. virus enters cell via clathrin mediated endocytosis

   • low pH in endosome triggers conformational change in G protein → envelope fusion with endosomal membrane → nucleocapsid released into cytoplasm

3. L protein transcribes (-) ssRNA → mRNAs for each viral protein

   • each gene sequentially from 3’ end with decreasing amounts of transcript made as polymerase moves along → transcription gradient

4. enough N protein made → replication begins

   • (+) ssRNA made to make new (-) ssRNA

   • N protein coats RNA as it’s being synthesized to form new nucleocapsids

5. N, P, L proteins form nucleocapsid

   • M protein links nucleocapsid with G embedded in host membrane

6. assembled virus buds from host plasma membrane → envelope forms

   • G protein ensures infectivity

RABV entry & uncoating

attachment mediated by G protein

• different receptors for different host cells

low pH of endosome results in conformational change of G → viral fusion with endomembrane → nucleocapsid released into cytoplasm

RABV gene expression

1. polymerase binds to 3’ end of genome and transcribes monocistronic mRNAs, one for each gene

   • L protein (RdRp) and P protein aid in transcription

2. L protein sometimes falls off RNA strand between genes

   • genes near 3’ end made in higher amounts while genes near 5’ end made in lower amounts

3. mRNA capped at 5’ end and polyadenylated at 3’ end

   • allows cellular recognition as normal host mRNAs

4. translation by host ribosomes

RABV: 5’ capping

L protein adds 5’ cap

methylates mRNA at N7 position (m⁷G)

RABV assembly and budding

N-P-L complex wraps (-)ssRNA genome into helical nucleocapsid

M protein interacts with

• nucleocapsid on inside

• cytoplasmic tails of G protein on inner leaflet of plasma membrane

budding releases mature & enveloped rabies virions through secretory pathway

• ER → Golgi → membrane

• M protein guides nucleocapsid to G-rich areas of membrane

• virus buds outward and captures a piece of host membrane with embedded G proteins

• virus pinches off and released in bullet shaped

RABV disease

acquired through saliva (bites/scratches) from infected animals

99% fatal following onset of symptoms

RABV animal physical symptoms

excessive drooling

difficulty swallowing

staggering

paralysis

seizures

rabies susceptibility

dogs

cats, livestock, wildlife

• bats, raccoons, skunk, fox, coyote

humans

• children

• certain groups of people

  • vet staff, wildlife workers, hunters, taxidermists

RABV animal behavioural symptoms

spread into CNS

aggression

fearfulness

depression

self mutilation

light sensitivity

lose fear of natural enemies

nocturnal animals seen during day

RABV human symptoms

fever

fatigue

headache

anxiety

irritability

numbness, itching, pain around injury site

spread to CNS

furious rabies symptoms

hyperactivity

anxiety

seizures

hallucinations

excited behaviour

agitation

hydrophobia

cardiorespiratory arrest

paralytic rabies symptoms

gradual muscle paralysis

coma

death

rabies immune evasion

evades innate immune system

RABV vaccine inventor

louis pasteur and emile roux