Rabies virus and Prion Dongli Pan Department of Medical Microbiology and Parasitology Zhejiang University School of Medicine pandongli@zju.edu.cn

Rabies virus Member of the Lyssavirus of the Rhabdoviridae

Baltimore classification DNA viruses RNA viruses Baltimore classification Fields Virology, 6th edition

1. Biological properties Has a cylindrical morphology -ssRNA enveloped virus capsid has helical symmetry Is a neurotropic virus

Negri body 内基小体 Forms round or oval acidophilic cytoplasmic inclusion bodies. Negri body in the cytoplasm of infected neuron

Rabies Transmission – by the bite of a rabid animal (commonly a dog or a cat) – the contamination of scratch wounds by virus- infected saliva. Clinical findings Incubation/prodromal period 1 to 3 months CNS infection Hydrophobia. This fear of water is the result of the pain associated with drinking. Seizures and hallucinations. Paralysis may lead to respiratory failure. Coma Mortality is >99%. Most deadly virus!

Pathogenesis

Laboratory diagnosis Animals: Animals in a rabies endemic area should beheld for 10 days for observation. If the animal is sick, kill the animal and collect samples from hippocampus tissues and look for 1) Negri bodies 2) viral antigens by immunofluorescence Human: Collect samples of saliva, serum, spinal fluid, and skin biopsies and perform RT-PCR or immunofluorescence. 海马回

Postexposure rabies prophylaxis Long incubation period is the basis of postexposure prophylaxis Local wound care Cleanse wound with soap and water. Sterilize with ethanol or iodine. Combination of passive and active immunization: Passive immunization with rabies antiserum (HRIG,given the day before or on the day of active immunization） Active immunization with antirabies vaccine (HDCV, im given on days 0, 3, 7, 14, 28).

From BSE to Prion Prion: An infectious proteinaceous particle of nonnucleic acid composition

Bovine spongiform encephalopathy (BSE) mad-cow disease

Prion protein (PrP): from PrPC to PrPSc Same amino acid sequences but different structures PrPSc (scrapie prion protein) 43% β- sheet and 30% α-helix Insoluble Resistant to protease K Pathogenic PrPC (cellular prion protein) Mainly α-helix Soluble Sensitive to protease K Has normal functions, not pathogenic

Prions aggregate extracellularly within the central nervous system to form plaques known as amyloid, which disrupt the normal tissue structure Strong resistance to autoclave, UV, regular disinfectants. Standard autoclave (121oC, 20 min) does not inactivate it. Needs 134oC, 2h

Transmissible Spongiform Encephalopathies (Prion Diseases) • Human – Kuru disease – Creutzfeldt--Jacob disease (CJD) – variant Creutzfeldt--Jacob disease (vCJD) • Animals – Scrapie of sheep and goats – Bovine spongiform encephalopathy (BSE, mad cow) Progressive neurodegenerative disease

The characteristics of Prion diseases normal

Diagnosis and Prevention Immunoblotting assay (Western blot): Treat tissue with proteinase K to digest PrPC, and then analyze with Western blot for the presence of PrPSc Immunohistochemstry: Also treat with proteinase K first Genetic analysis: For inherited mutations in the PrP gene. Prevention: quarantine of animals and complete disinfection of medical devices. No treatment.