Rabies

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Rabies

• Chapter 13

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History

• One of the oldest known diseases
• Rabies comes from rabhas which means to do
  violence
• Italian scholar Girolamo Fracastoro first
  described rabies disease in 1546 (350 years
  before Pasteur and Roux developed rabies
  vaccine).

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History

• Louis Pasteur and Emile Roux, pioneers of rabies
  vaccine
• Dried strips of spinal cords removed from rabid
  animals
• Pasteurs first vaccine testing on dogs
• 1886 First human subject injected with Pasteurs
  vaccine
• Pasteur Institute founded to treat rabies victims

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Rabies in Animals

• Disease of mammals.
• U.S., primary infectious disease of wildlife

Figure 13.2 Rabies in animals indicator status
worldwide in 2003.
Adapted from World Health Organization, 2005
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Distribution of Terrestrial Wildlife Reservoirs
of Rabies, U.S.
Adapted from the CDC, Animals and Rabies,
Rabies Just for Kids, http//www.cdc.gov/ncidod/d
vrd/kidsrabies/Animals/animals.htm.
Figure 13.3 Distribution of major terrestrial
reservoirs of rabies in the United States in 2005.
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U.S. Rabies Management Programs

• Vaccination programs to control rabies in animals
  began in the U.S. during the 1940s and 1950s
• Wildlife Services Program, part of the USDA
  distributes vaccines.
• Over 10 million oral rabies vaccine baits
  distributed in the U.S. and Canada in 2003

Figure 13.5 Biologists collect blood and other
biological samples from trapped animals to
evaluate the effectiveness of the oral rabies
vaccine.
Photos courtesy of APHIS/USDA
Figure 13.6 Merial Raboral V-RG rabies vaccine
bait.
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Rabies in Bats, U.S. 17 of all cases of rabies
in Animals
Adapted from the CDC, Animals and Rabies,
Rabies Just for Kids, http//www.cdc.gov/ncidod/d
vrd/kidsrabies/Animals/animals.htm.
Figure 13.4 Distribution of bat rabies in the
United States in 2001.
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Human Rabies

• Since 1990, over 90 of human cases in the U.S.
  were associated with bat bites.

Figure 13.7 Total number of human rabies deaths
worldwide in 2005 including imported cases in
humans and animals.
Adapted from World Health Organization, 2005
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Clinical Signs and Symptoms of Rabies

• 2 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 disease is 2-14 days
  before coma supervenes
• Death occurs on average of 18 days after onset of
  symptoms

Courtesy of CDC
Figure 13.8 Two dogs afflicted with dumb rabies.
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Stages of Human Rabies

• Incubation
• Usually 2 8 weeks
• Depends on size of inoculum, proximity of wound
  to brain, severity of wound, age and immune
  status
• Prodromal phase
• 2 10 days
• Symptoms Headache, malaise, fever, anorexia,
  nausea and vomiting

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Stages of Human Rabies

• Secondary symptoms
• Furious Rabies
• Period of excitement
• Over-reactivity (hyperexcitability)
• Biting
• Increased salivation
• Increased perspiration
• Act of swallowing precipitates a spasm at the
  throat muscles
• Patient avoids swallowing to avoid the pain
• Paralytic Rabies

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Stages of Human Rabies

• Secondary symptoms
• Paralytic Rabies
• Depressive phase
• Coma
• These symptoms also apply to animals.
• Animals that are predators show signs of furious
  rabies
• Nonpredators display paralytic or dumb rabies
  symptoms

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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 occurred.
• Rabies is present in nervous tissue
• Brain is the ideal test tissue2 or 3 samples
  tested
• Brain stem (medulla)
• Cerebellum
• Hippocampus
• dFA test is rapid (30 minutes to 4 hours)

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Rabies Diagnosis 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 2nd week of
  illness)
• Skin punch biopsies at the nape of the neck
• Rabies antigen in cutaneous nerves at the base of
  hair follicles

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Human Rabies Survivors

• 8 survivors recorded in the scientific literature
• 7 of these received pre or post exposure rabies
  passive antibodies, immune globulin or vaccine
• Half of the survivors had severe, permanent
  neurological disorders
• 2004, Jeanna Geise, Wisconsin
• Bat bite
• No post-exposure vaccine
• Was given antivirals

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Rabies Pathogenesis

• Most common route of entry - break in skin
• Bite introduces the virus into the wound
• Virus replicates in the muscle cells surrounding
  the wound
• Virus attaches to nicotinic acetylcholine
  receptors of the peripheral nerve cells and
  muscle 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.

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Rabies Virus Attaches to the Nicotinic
Acetylcholine Receptors and Journeys Within
Axons of Nerves
Figure 13-11b
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Sequential Steps of Rabies Transmission
Figure 13-11a
Adapted from A. C. Jackson and W. H. Wunner, eds.
Rabies. Academic Press, 2002
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During the Course of Rabies Infection

• While in the neurons, the virus is hidden from
  the bodys immune surveillance system.
• Rabies viruses spread to many tissues via the
  peripheral nervous system
• Spread to blood, salivary glands and other
  tissues
• Virus particles predominately bud out of the
  cells of the salivary glands
• Viruses exit from the body via saliva

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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

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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

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Rabies Vaccine Shot Schedule

• Dose3 x 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

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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.

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Wound Care

• Middle of the 20th centurycauterize 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.

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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

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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.

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Postexposure Prophylaxis

• Vaccination
• 3 categories of vaccine
• Nerve tissue vaccines
• Take infected brains of sheep and goat ? infect
  individual
• Poor vaccine ? build antibodies against nervous
  tissue
• Avian embryo vaccines
• Virus grown in duck embryonated eggs
• Poor vaccine ? too many duck proteins to react to

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Postexposure Prophylaxis

• Vaccination
• 3 categories of vaccine
• Cell culture vaccines
• Example HDCV
• Virus is purified from monolayers after growth on
  human fibroblasts
• Virus is inactivated
• Very effective
• Currently used in the USA

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Vaccines

• Three vaccines used in the U.S.HDCV, RVA, PCECV

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Rabies Life CycleStructure of the Rabies virus
particle

• Unique bullet-shaped appearance
• 75 nm diameter by 180 nm in length
• Surface of the particle is covered with
  glycoprotein (G protein) spikes
• Matrix (M) protein inside of particle
• Ribonucleoprotein core (RNP)
• Genomic RNA tightly encased by N (nucleocapsid),
  P, and L (large or polymerase) proteins

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Longitudinal Section of Rabies Virus
Figure 13-13
Adapted from the CDC
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Viral Replication Genome Organization

• Genome consists of a 11,932 nucleotides
• ssRNA of negative polarity
• 5 genes and a remnant gene or pseudogene (?)

Adapted from S. J. Flint, et al. Principles of
Virology Molecular Biology, Pathogenesis, and
Control of Animal Viruses, Second Edition. ASM
Press, 2003.
Figure 13.14 Genome organization of rabies virus.
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Virus Life Cycle

• Rabies surface glycoprotein (G) attaches
• Attachment - binds to nicotinic acetylcholine
  receptors
• Entry
• Endocytosis
• Low pH dependent fusion with endosomal membranes
• Acidic interior of the endosome allows the viral
  nucleocapsid to escape into the cytoplasm
• M protein dissociates from the RNP during
  uncoating

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Virus Life Cycle

• Transcription of Viral Genes
• L (RNA dependent RNA polymerase) begins to
  transcribe the viral genome.
• A separate ssRNA transcript is generated for
  each viral gene.
• 2 ways
• Make protein
• Synthesis of new (-) RNA genome
• Replication occurs in the cytoplasm

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Virus Life Cycle

• Viral Protein Synthesis
• Viral mRNAs resemble cellular mRNAs
• N, P, M and L mRNAs translated by free ribosomes
• G mRNAs translated on membrane bound ribosomes of
  the ER
• G is posttranslationally modified (glycosylated)
  via the Golgi.

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Virus Life Cycle

• Virus Exit
• As soon as -ssRNAs, N, M, P, L proteins have
  accumulated within infected cells, assembly
  occurs
• The mature infectious particle buds through host
  cell plasma membrane

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The Life Cycle of Rabies Virus
Figure 13-15
Adapted from S. J. Flint, et al. Principles of
Virology Molecular Biology, Pathogenesis, and
Control of Animal Viruses, Second Edition. ASM
Press, 2003.