Rabies Virus - Lyssavirus

a detailed powerpoint on lyssaviruses using the Rabies virus as an example

1. Rabies Virus by Tanyaradzwa R Ngara

2. Introduction Rabies was called lyssa or lytta , which means frenzy or madness . They named human rabies hydrophobia Rabies is a zoonotic (transmitted from animals to human) viral infectious disease .

3. Rabies Virus A group V virus carry their genetic material in the form of negative-sense single stranded RNA of the order Mononegavirales R habdovirus , Lyssavirus genus The family Rhabdoviridae consists of more than 185 different viruses isolated from both plants and animals Susceptible to disinfectants Inactivated by drying

4. Virion properties Contain linear, single stranded and negative sense RNA genome. Virions are 45-100nm in diameter, 100-430nm long. virion has a cylindrical nucleocapsid surrounded by an envelope with large glycoprotein spikes. encode for their own RNA polymerase (RNA dependent RNA polymerase).

5. Genome features The genome encodes for 5 genes in the following order. 3’ –N-P-M-G-L- 5’ N- Nucleocapsid protein P- Phosphoprotein - cofactor of the viral polymerase M- Inner virion protein/ helps in budding of the virion . G- Glycoprotein that assists in making virion spikes L- Large protein that represents RNA dependent RNA polymerase and helps in transcription and replication

6. Genome features Linear non-segmented negative sense RNA genome Organization of genome- 3'-Leader-Virion core- Surface proteins-Polymerase-Trailer 5'. Helical nucleocapsid contains the RNA dependent RNA polymerase. The leader RNA is neither capped nor polyadenylated and is not functional as mRNA.

7. Genome features Replication occurs when the polymerase complex ignores the transcription stop signals at the 3’ end of each gene and a full-length positive-sense anti-genome is synthesized. Transcription at the gene-start site is not perfect, which leads to a gradient of mRNA abundance that decreases according to the distance from the 3’ end of the genome.

8. Rabies virus Structure

9. Viral Life Cycle

10. Viral Life Cycle After receptor binding, rabies virus enters its host cells through the endosomal transport pathway . the low pH value induces the membrane fusion process, thus enabling the viral genome to reach the cytosol . Both processes of receptor binding and membrane fusion, are catalyzed by the glycoprotein G The first step of replication involves mRNA transcription from genomic RNA using RDRP.

11. Viral life cycle cont.. For successful replication a large amount of nucleoprotein (N) and phosphoprotein (P) should be expressed. Switching of transcription to positive sense antigenome occurs after a threshold amount of N and P, which are then further used as a template for synthesis of negative stranded genomic RNA.

12. Viral life cycle… There is a single promoter site at the 3’ end of the viral genome where the polymerase attaches to the genomic RNA template and moves along the viral RNA. While moving it hits with start – stop signals at both the ends of the viral genes. Due to this only a small fraction undergoes continuous transcription process and hence this phenomenon is also known as attenuated transcription

13. Viral life cycle cont … more mRNA is produced towards the genes that are located at the 3’ end *hence producing a gradient of mRNA in the order of N>P>M>G>L. As a result of the mRNA gradient, large amount of structural protein such as nucleocapsid protein is produced as compared to L protein

14. Viral life cycle cont …. Assembly and Maturation Nucleus Cytoplasm At membrane

15. Pathogenesis mode of transmission of rabies in man is by bite of a rabid animal or the contamination of scratch wounds by virus infected saliva. Replicates at site during the incubation period Moves to nerve root endings Replicates again Spreads to the CNS Vital nerve centers infected - irritable/aggressive Direct transmission of virus occurs from cell to cell across synaptic junctions. Centrifugal spread to salivary glands, skin, etc . Secreted with saliva communicable Fatality can occur from two days to five years from the time of initial infection.

16. General Symptoms Fever Headache Weakness Discomfort * Usually exhibited for 2-10 days

17. More Severe Symptoms Insomnia Anxiety Confusion Slight or Partial Paralysis Hallucinations

18. More Severe Symptoms Excitation Agitation Hypersalivation Difficulty Swallowing Hydrophobia * Death usually occurs within days of the onset of the more severe symptoms

19. Rabies in Animals Rabid Animals By Frequency Dogs Raccoons Skunks Bats Foxes Rodents & Lagomorphs

20. Types of Exposure Bites Non-bites exposure: contamination of open wounds, abrasions, mucous membranes or, theoretically, scratches (potentially contaminated with infectious material from a rabid animal) Human to Human Transmission

21. Epidemiology Global Distribution of lyssaviruses

22. Epidemiology cont … Most of the developing countries in Asia are the victims of rabies. 55 000 deaths in Africa and Asia yearly (WHO, 2011) One Asian dies every 15 minutes where 15 % are likely to be the children under 15 years in Bangladesh also where nearly 100,000 people being bitten by dogs in 2009 and 3,000 died of rabies In India, about 15 million people are bitten by dogs every year

23. Epidemiology cont … Rabies in Africa Rabies causes at least 24,000 deaths per year in Africa (WHO, 2013) The major cause of spread of rabies in this region is urbanization In Rwanda an estimation of 127 Human dog bites was reported (Ministry of Health) Most southern African countries like; Angola, Namibia, Mozambique, Zimbabwe are also considered as high risk areas.

24. Treatment After Exposure Post exposure treatment consists of Local treatment of the wound Adminstration of rabies immunoglobins Immediate vaccination

25. Treatment.. Local Treatment of the wound Wash wounds immediately with soap & water This is the most effective way to decrease the chance of infection

26. Treatment… Patient with confirmed cases of rabies should be isolated , sedated and transferred to appropriate medical facility

27. Treatment Primary Vaccinations

28. Treatment cont ….. Primary Vaccinations Three 1.0-mL injections of HDCV or PCEC vaccine should be administered intramuscularly (deltoid area) -- one injection per day on days 0, 7, and 21 or 28

29. Treatment Passive Immunization Horse Anti Rabies serum Human Rabies immunoglobin (HRIG) Booster doses are essential whenever anti rabies serum is given with the vaccine

30. Prevention Eliminating rabies in dogs eliminating rabies in dogs through vaccination This has reduced the number of human rabies cases in most Latin America However recent increases in human rabies deaths suggest that rabies is emerging as a serious public health issue

31. Prevention cont.. prevention of human rabies through control of domestic dog rabies is a realistic goal Preventive immunization in people Safe, effective vaccines also exist for human use Pre-exposure immunization in people ( Travellers to high-risk areas in rabies affected countries, animals handlers, veterinarians in rabies affected areas

32. Prevention cont … Epidemiological surveillance Dog bites must be notifiable within national surveillance system on weekly basis Collected data should be processed and disseminated rapidly between different administrative levels Steps to be taken after reporting a dog bite Dog movement: stray or restricted dog? Circumstances around the bite: is the dog provoked or not? Dog vaccination status The offending dog should be contained and observed for 14 days

33. Applications in Gene Therapy Neuronal gene transfer To treat cardiovascular regions of CNS tissue Spinal cord regeneration

34. Thank You