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Chapter Outlines

Chapter 13      Rabies

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13.1 History of Rabies Rabies also known as hydrophobia (fear of water) Louis Pasteur and Emile Roux, pioneers of rabies vaccine Dried strips of spinal cords removed from rabid animals Pasteur’s first vaccine testing on dogs 1886 first human subject injected with Pasteur’s vaccine Pasteur Institute founded to treat rabies victims 13.2 Epidemiology 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). Description of classic rabies on p. 353 19th Century and Rabies Canine or street rabies was everywhere, especially Europe. “Mad” dog symbolized mans fear of rabies for centuries. Rabies in Animals Disease of mammals. U.S., primary infectious disease of wildlife Worldwide Important Animal Rabies Reservoirs Asia, Africa, South America, Mexico dogs Europe, Canada, Alaska, former Soviet Union foxes Siberia, Japan, northern India, Europe raccoon dogs Thailand dogs (95% of cases) Caribbean Islands mongooses Mexico and South America vampire bats U.S. Rabies Management Programs Vaccination programs to control rabies in animals began in the U.S. during the 1940’s and 1950’s 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 17% of all cases of animals rabies in the United States are in bats 13.3 Human Rabies Since 1990, over 90% of human cases in the U.S. were associated with bat bites. 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 Symptoms During Prodromal Period Headache Malaise Fever Anorexia Nausea Vomiting Secondary Symptoms of Furious Rabies Hydrophobia Difficulty swallowing Agitation Anxiety Hallucinations Hypersalivation Bizarre behavior Biting Jerky and violent contractions of the diaphragm 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 furious rabies Nonpredators display paralytic or dumb rabies symptoms Rabies Diagnosis: : Rabies Diagnostic Testing in Animals Individuals who are involved in rabies testing must be vaccinated followed by regular serologic tests and get booster vaccines if needed. Rabies proficiency testing Wisconsin State Laboratory of Hygiene, Madison, WI 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 tissue - 2 or 3 samples tested Brain stem (medulla) Cerebellum Hippocampus dFA test is rapid (30 minutes to 4 hours) Rabies Diagnosis in Humans Laboratory tests are rarely done in developing countries. Several routine antemortem tests avaible 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 Human Postmortem dFA Tests Performed on brain of victim Long-needle biopsies (collect 2 or more samples) Brain stem Cerebellum dFA followed by RT-PCR, virus isolation in culture, or suckling mouse inoculation Histologic, immunocytochemstry Electron microscopy 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 Milwaukee protocol treatment (See Virus File 13-1) Animal Survivors? A few descriptions of spontaneous recovery in the literature Pasteur laboratory animals 1980 Fekadu and Baer reported two beagles recovering spontaneously Rabies Pathogenesis Most common route of entry - break in 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. Rabies Virus Attaches to the Nicotinic Acetylcholine Receptors, : Journeys Within Axons of Nerves During the Course of Rabies Infection While in the neurons, the virus is hidden from the body’s immune surveillance system. Rabies viruses spread to many tissues via the peripheral nervous system Virus particles predominately bud out of the cells of the salivary glands Viruses exit from the body via saliva 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! Fixed tissues stained with histological dyes may show the appearance of Negri bodies in the cytoplasm of brain neurons. 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 13.4 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 Rabies Vaccine Shot Schedule Dose - 3 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 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 can be captured, it will be euthanized and the head is shipped to a qualified laboratory for testing 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). Vaccination 3 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 Barre-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 Vaccines Three vaccines used in the U.S. - HDCV, RVA, PCECV 13.5 Rabies Life Cycle: Structure 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 spikes Matrix (M) protein inside of particle Ribonucleoprotein core (RNP) Genomic RNA tightly encased by N, P and L proteins Viral Replication: Genome Organization Genome consists of a 11,932 nucleotides ssRNA of negative polarity 5 genes and a remnant gene or pseudogene (?) Virus Life Cycle Rabies surface glycoprotein shares sequence homology to snake neurotoxins Attachment - binds to nicotinic acetylcholine receptors Entry - 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 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. Each viral transcript is capped and polyadenylated by the viral P protein 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. Viral Genome Replication 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, L proteins have accumulated within infected cells, assembly occurs The mature infectious particle buds through host cell plasma membrane 13.6 Genetic Variation Fixed strains Laboratory strains used in research Street strains Strains isolated from patients or rabid animals The rabies L protein does not possess RNA repair/proofreading ability. Mutation rate is 10-4 to 10-5 per nucleotide per cycle of replication