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
× Rhabdovirus, 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.

8. 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.

9. Rabies virus Structure

10. Viral Life Cycle

11. 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.

12. 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.

13. 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

14. 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

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

16. 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.

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

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

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

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

23. 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

24. Epidemiology
Global Distribution of lyssaviruses

25. 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

26. 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.

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

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

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

31. Treatment
Primary Vaccinations

32. 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

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

34. 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

35. 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

36. 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

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

38. Thank You