Unit 3 - Rabies Virus Flashcards
What is the history of Rabies?
- One of the oldest known diseases
Earliest record of rabies from Babylon (23rd century BC)
Homer likens Hector to a “raging dog” in The Illiad (800-700 BC)
- Rabies derived from the Sanskrit word rabhas (“to do violence”) and the Latin word rabere (“to rave”)
Rabid animals often appear angry or in a rage
- Italian scholar Girolamo Fracastoro was the first to describe the true nature of rabies disease (1546)
350 years before Pasteur and Roux developed the rabies vaccine
Describe rabies in the 19th Century
- Rabies was termed hydrophobia (fear of water)
- Canine or street rabies was everywhere, especially Europe.
- The fear of rabies was almost irrational, due to the significant number of vectors and lack of any efficacious treatment
- “Mad” dog symbolized the human fear of rabies for centuries
- Suspected victims often killed themselves or were killed (shot, poisoned, suffocated) or condemned to die
- France passed law in 1810 making it illegal to murder individuals suffering from rabies, hydrophobia or any disease causing fits, convulsions, or madness
Describe the history of rabies when the vaccine was discovered.
- Louis Pasteur and Emile Roux, pioneers of rabies vaccine
Dried strips of spinal cords removed from rabid animals
Pasteur’s first vaccine tested on dogs (50/50 survived)
1886: first human subject injected with Pasteur’s vaccine; 9-yr old boy
- Pasteur’s success made him a hero
Pasteur Institute founded in 1887 to treat rabies victims
Institute widely respected for its research in microbial diseases
What is rabies in animals?
Disease in mammals:
- primarily wildlife (wild dogs, raccoons, skunks, bats, etc.)
- Less frequent in domesticated animals (cats, dogs, livestock)
What are the worldwide important Animal Rabies Reservoirs?
- Asia, Africa, South America, Mexico: wild dogs (threatening over 3 billion people)
- Europe, Canada, Alaska, former Soviet Union: foxes
- Siberia, Japan, Northern India, Europe: raccoon dogs
- Thailand: wild dogs (95% of cases)
- Caribbean Islands: mongooses
- Mexico and South America: vampire bats
What are the U.S. Rabies Management Programs?
- Vaccination programs to control rabies in animals bean in the U.S. during the 1940s and 1950s.
- Wildlife Services Program, part of the USDA distributes vaccines via hand distribution and plane distribution
- Over 10 million oral rabies vaccine baits distributed in the U.S. and Canada in 2003
What are the Oral Rabies Vaccine for wildlife?
- Raboral V-RG vaccine by Merial, Inc.
- In use in the US since 1990
- Recombinant vaccine
Attenuated vaccinia virus
Gene encoding rabies glycoprotein G
What is Human Rabies?
- 15 million post-exposure vaccinations
most common in children aged under 15
90% of human cases in the US were associated with bat bites.
- 55,000 rabies - related human deaths yearly:
dogs source of 99% human rabies death
What is involved between rabies and organ transplantation?
- Infections by corneal transplant have been reported in Thailand, India, Iran, the US, and France.
- June 2004: three organ recipients in US died from rabies transmitted in the transplanted kidneys and liver
- Donor died of brain hemorrhage/unidentified brain disorder
- February 2012: Maryland man died of rabies; received a kidney from an infected donor in 2011
How are U.S. soldiers affected by rabies?
- In August 2011 a U.S. soldier stationed at a military base in New York became ill with symptoms compatible with rabies.
- three months following active deployment in Afghanistan
- variant associated with Afghani dogs
- Soldiers returning from active duty abroad may have unreported animal exposures
What is World Rabies Day?
- Occurs each year on September 28, the anniversary of the death of Louis Pasteur
- Aims to raise awareness about the impact of rabies on humans and animals
promoting government involvement in rabies prevention and control programs
increasing the vaccination coverage of pets and community dogs
improving the educational awareness
What are the clinical signs and symptoms of rabies?
Two forms of Human Rabies
- Furious (encephalitic)
- Paralytic (or dumb)
With either form, incubation period varies
- 4 days to 6 years (rare)
- Average 18-21 days post-exposure
With either form, course of diesase 2-14 days before coma supervenes
- Death occurs on average of 18 days after onset of symptoms
What are the symptoms of rabies during the prodromal period?
(the time of onset specific symptoms)
Heachache
Malaise
Fever
Anorexia
Nausea
Vomiting
What are teh secondary symptoms of Furious Rabies?
- Hydrophobia (fear of water)
- Difficulty swallowing
- Agitation
- Anxiety
- Hallucinations
- Hypersalvation
- Bizarre behavior
- Biting
- Jerky and violent contractions of the diaphragm
What are the Secondary symptoms of Paralytic rabies?
- Lack of hydrophobia
- Lack of hyperactivity
- Lack of seizures
- weakness and ascending paralysis
- These symptoms also apply to animals:
- Animals that are predators show signs of furiuos rabies.
- Nonpredators display paralytic or dumb rabies symptoms
What is U.S. rabies testing in animals?
- Gold Standard is direct fluorescent antibody test (dFA)
Post-mortem test
done on animals behaving abnormally or show consistent rabies signs if human or other animal exposure have occured
- Rabies is present in nervous tissue
Brain is the ideal test tissue: 2 or 3 samples tested
- Brain stem (medulla)
- Cerebellum
- Hippocampus
What is Direct Fluorescent Antibody Test (dFA)?
- Ideal tissue to test for rabies antigen is brain.
- Fluorescently labeled antibodies directed against the viral nucleoprotein.
- dFA test is rapid (30 minutes to 4 hours)
How is rabies diagnosed in humans?
- Laboratory tests are rarely done in developing countries.
- Several routine antemortem tests available in the U.S.
Virus isolation
RT-PCR to detect viral RNA
Saliva
Tears
CSF
- Serum
Antibodies to rabies (appear in second week of illness)
- Skin punch biopsies at the nape of the neck
Rabies antigen in cutaneous nerves at the base of hair follicles
What is Human Postmortem dFA tests?
- Performed on brain of victim
- Long-needle biopsies (collect 2 or more samples)
Brain Stem
Cerebellum
- Followed by RT-PCR, virus isolation in cluture, or suckling mous inoculation
Histologic, immunnocytochemistry
Electron mircroscopy
Who are included in Human Rabies Surviviors?
- Seven survivors recorded in the scientific literature before use of the Milwaukee Protocol
- All 7 received pre- or post-exposure rabies passive antibodies, immunoglobulin, or vaccine
- Half of the survivors had severe, permanent neurological disorders.
- 2004: Jeanna Geise, Wisconsin, Milwaukee Protocol Survivor
- Bat bite
- No post-exposure vaccine
- Milwaukee protocol treatment (see Virus File 13-1)
What is the Milwaukee protocol?
- Experimental course of treatment of an acute infection of rabies in a human being
- Patient into a chemically induced coma (ketamine, midazolam, & phenobarbital)
Most rabies deaths are caused by temporary brain dysfunction with little to no damage occurring to the brain
- Antiviral drugs ribavirin and amantidine
- Aggressive supportive care
- 15 yr-old Jeanna Giese (2004; Virus File 13-1)
Contracted rabies from bat bite; hospitalized 1 month after bite
Brought out of coma once signs of immune response were detected
Declared virus free after 31 days
Discharged from hospital 76th day after rehabilitation
Remarkable recovery; graduated college in 2011
Why did the Girl Deise Survive?
- To date, the success of the initial Milwaukee Protocol has been difficult to replicate.
- 4 survivors out of 35 patients
- Patients in the United States, Thailand, Germany, and India all died after administration of this protocol.
- Did she get exposed to an attenuated bat strain of rabies?
- No virus was recovered from Geise’s bodily fluids to test this hypothesis.
- Potential animal research
- Apply Milwaukee protocol to rabid animals and systematically test what parts of the protocol are critical.
- Vet schools have not permitted these studies.
- Concerns over rabid animals in their ICUs.
Are there animal surivivors?
A few descriptions of “spontaneous recovery” in the literature
- Pasteur laboratory animals
- 1980: Fekadu and Baer reported two beagles recovering spontaneously after experimental infection
What is the pathogenesis of Rabies?
- Most common route of entry is a break in the skin.
- Virus replicates in the muscle cells surrounding the wound.
- Virus attaches to nicotinic acid receptors of the peripheral nerve cells of the neuromuscular junction.
- Virus journeys within axons of nerves at a rate of 0.5 to 15 inches per day.
- It may take weeks before the virus reaches the spinal cord motor neurons of the CNS.
- This is why post-exposure vaccination is possible.
- Antibodies prevent the spread of the virus to the CNS, stopping the disease.
What are the sequential steps of rabies transmission?
Rabies Virus attaches to the nicotinic acetylcholine receptors and journeys within axons of nerves.
Virus hidden from immune surveillance while in neurons
What happens during the course of rabies infection?
- Rabies viruses spread to many tissues via the peripheral nervous system.
Cardiac muscle, kidney, pancreas, cornea, salvary glands
- Virus particles predominately bud out of the cells of the salivary glands.
Viruses exit from the body via saliva.
Intermittent shedding
What are the results of an autopsy?
- Little evidence of brain damage even though fluorescent antibody labeling and electron microscopic analysis of brain tissues show all the neurons are infected.
Neural dysfunction through inhibition of neurotransmitters?
- Fixed tissues stained with histological dyes may show the appearance of Negri bodies in the cytoplasm of brain neurons.
What are Negri Bodies?
- Inclusion bodies found in cytoplasm of nerve cells.
- Contain ribonuclear proteins produced by virus.
What is the immunity?
- No antibody responses detected during the incubation period of rabies virus infection.
- Antibodies appear in serum and later in CSF after symptoms appear.
- Some patients (who experience encephalitic furious rabies) mount a cell-mediated response.
- Virus can inhibit type I and II interferon responses
What is the management of Human Rabies?
All high-risk individuals should be vaccinated against rabies virus:
- Veterinarians
- Animal handlers (e.g., zookeepers)
- Dog catchers
- Mail carriers
- Speleologists
- Trappers and hunters in rabies endemic areas
- Laboratory workers who work with rabies virus
- Individuals who are involved in the production of rabies vaccines
- Peace Corps workers
- International travelers who go to places that have endemic dog rabies
What is the Rabies Vaccine shot schedule?
- Dose: 3× 1-mL shots injected intramuscularly into the forearm or shoulder on:
Days 0, 7, 21, or 28
Usually takes 7–14 days to induce immunity
Immunity lasts approximately 2 years
- Individuals who are at high-risk (e.g., vets) must be tested every six months for rabies antibodies.
- A booster will be administered if necessary.
What is involved in the wound care?
- Middle of the 20th century: cauterize wounds caused by rabid animals
- Today:
- Wounds washed thoroughly with 20% soap, 70% ethanol, or 2% benzalkonium chloride
- Also irrigated with a virucidal agent such as povidone-iodine
What should you do if you are bitten by an animal?
Provide the following information to a physician:
- Animal involved
- Whether the bite was provoked or unprovoked
- Vaccination status of the animal (if known)
- Whether the animal can be safely captured for rabies testing
- Geographic location of the incident
If the animal shows signs of rabies and can be captured, it will be euthanized and the head shipped to a qualified laboratory for testing.
What is Postexposure Prophylaxis?
Human Rabies Immune Globulin (HRIG, Hyperab)
- Provides passive immunity until active antibodies are induced by the vaccine
- Unvaccinated individuals who experience a bite from a rabid animal will receive immune globulin and a shot of vaccine on day 0.
- HRIG is expensive and not available in all countries.
- Many countries use ERIG (of equine or horse origin).
- It is considerably cheaper.
- Highly purified and safe (serum sickness rare)
What else is involved in Postexposure Prophylaxis?
- Vaccination
- Three categories of vaccine
- Nerve tissue vaccines
- Avian embryo vaccines
- Cell culture vaccines
- Early vaccines made of nerve tissues
Produced serious side effects such as Guillian Barré-like syndrome, paralysis, CNS disease, meningoencephalitis
Semple vaccine—1 in 200 recipients experience serious side effects, up to 14% of recipients die
Nerve tissue vaccines are still being used in Asia, South America, and Africa
What are the vaccines?
Three Vaccines used in the U.S.
- HDCV
- RVA
- PCECV
What is the Rabies Life Cycle?
(structure of the Rabies Virus Particle)
- Unique bullet-shaped appearance
- 75 nm diameter by 180 nm in length
- Negative strand RNA virus
- Enveloped; surface covered with glycoprotein spikes
- Matrix (M) protein inside of particle
- Ribonucleoprotein core (RNP)
- Genomic RNA tightly encased by N, P, and L proteins
What is the viral replciation of the genome organization?
Genome consists of a 11,932 nucleotides
Negative strand ssRNA
Five genes
What is the Virus Life Cycle?
- Rabies surface glycoprotein shares sequence homology to snake neurotoxins
- Attachment—binds to nicotinic acetylcholine receptors
Co-receptors?
- Entry—low pH dependent fusion with endosomal membranes
- Clathrin-coated pits
- Acidic interior of the endosome allows the viral nucleocapsid to escape into the cytoplasm
- M protein dissociates from the RNP during uncoating
What is involved in the transcription of Viral Genes?
Negative sense ssRNA
- Pre-packaged L and P proteins responsible for transcription
- L (RNA dependent RNA polymerase) begins to transcribe the viral genome.
- A separate +ssRNA transcript is generated for each viral gene.
- Each viral transcript is capped and polyadenylated by the viral L protein.
What is Viral Genome Replciation?
- After N is synthesized, it binds to leader region of viral RNA genomes.
- Full-length +ssRNA copies of the viral genome are made from N-encapsidated viral RNAs.
Termed anti-genome RNA
Anti-genome RNA serves as a template for progeny (–ssRNA) genomes which will be packaged into the viral particle
- Virus exit
As soon as –ssRNAs, N, M, P, and L proteins have accumulated within infected cells, assembly occurs.
The mature infectious particle buds through host cell plasma membrane.
What are the genetic variations involved in rabies viruses?
- Fixed strains
Laboratory strains used in research
- Street (wild) strains
Strains isolated from patients or rabid animals
- The rabies L protein does not possess RNA repair/proofreading ability.
High frequency of mutations
Mutation rate is 10–4 to 10–5 per nucleotide per cycle of replication
