Introduction to the Polio Virus (Virology).pptx

Introduction and life cycle of poliovirus.

1. Poliovirus 1

2. SYNOPSIS CLASSIFICATION INTRODUCTION EPIDEMIOLOGY MORPHOLOGY TYPES OF POLIO POLIOMYELITIS PATHOGENESIS CONCLUSION 2

3. Classification of Poliovirus Group: IV (+ssRNA) Order : Picornavirales Family : Picornaviridae Genus: Enterovirus Specie: Enterovirus C Subtype: Poliovirus Human Poliovirus 3

4. What is Poliovirus ? Poliovirus is the causative agent of poliomyelitis, this disease results from Lower motor neuron damage and is characterized by Paralysis. Poliomyelitis comes from Greek polios meaning “gray” and muelos meaning “marrow”, so inflammation of the gray matter of the spinal cord. Poliovirus is 27-30 nm in diameter. Its genome size Is about 7.5 kb (7500 base pairs). Due to its short genome, it is widely regarded as the simplest significant virus. 4

5. DISCOVERY AND HISTORY In 1789,British Physician Michael Underwood provides first clinical description of the disease. In 1840,Jacob Heine describes the clinical features of the disease as well as its involvement of the spinal cord. In 1894,first outbreak of polio in epidemic form in the U.S. occurs in Vermont, with 132 cases. 5

6. ISOLATION: In 1905,Wickman first recognized that poliomyelitis was an infectious disease. Landsteiner and Poper demonstrated in 1909 that the etiological agent of poliomyelitis was a filterable virus. WHO NAMED POLIO? Throughout the 19th century it is known as “infantile paralysis. In 1909, Austrian Physicians Karl Landsteiner and Erwin Popper announced that the disease was viral and it was named “ Poliovirus ”. 6

7. EPIDEMIOLOGY Major polio epidemics were unknown before the 20th century. Localized paralytic polio epidemics began to appear in Europe and the U.S around 1900. According to WHO, there are only 3 countries in the world where polio is still categorized as endemic viral infection, Pakistan is one of them the other two are Afghanistan and Nigeria. Since the launch of the Pakistan’s polio eradication programme in 1944, there have been a massive decline in polio cases, despite this decrease in 2018 ,eight cases of polio have been reported so far; 3 from Baluchistan. 1 from Charsadda. 3 from KPK. 1 from Karachi. 7

8. Morphology of Poliovirus The Poliovirus is about 27-30nm in diameter. It is non-enveloped virus. It consist of three main components. Proteinaceous capsid. Receptors. Genome. Structure of Poliovirus 8

9. CAPSID RECEPTORS Protein shell of virus. Made up of 60 subunits each containing 4 protein chains. Each subunit contains: VP1 (302 amino acids) VP2 (272 amino acids) VP3 (238 amino acids) VP4 (68 amino acids) VP1, VP2, and VP3 particles are on the surface. VP4 particle is located inside the capsid. The capsid is icosahedral. The depressions called canyons are present on capsid. Target nerve cells of human body. They get attached to the CD155 receptor site also known as poliovirus receptor site (PVR). This receptor functions as an adhesion molecule in adherence junctions in human body. 9

10. GENOME Poliovirus genome is a single stranded positive sense RNA (7500 nucleotides long). Internal Ribosome Entry Site (IRES) is imp. for virulence. 3 subregions with 11 protein products . A viral protein known as VPg (virion protein, genome-linked) associates with the 5′-end of the genome. 10

11. Types of Poliovirus Serotypes of Poliovirus: 3 immunological types are present: Type 1 (Brunhilde) Type 2 (Lansing) Type 3 (Leon) Types based on infection severity: Abortive polio (mild symptoms like sore throat, nausea, neck stiffness, and fever). Paralytic polio (virus enters CNS and cause paralysis in arms and legs). 11

12. Types based on location : Depending on the nerves involved polio can be classified as; SPINAL POLIO : It attacks motor neurons in the spinal cord and causes paralysis in arms and legs and breathing problems. BULBAR POLIO: It affects neurons for sight, vision, and taste. BULBOSPINAL POLIO : It is a combination of both spinal and bulbar paralysis. 12

13. DISEASE POLIOMYELITIS Poliovirus is a highly contagious and acute viral infection that can lead to paralysis, breathing problems, or even death. Host range is restricted to human ,apes and monkeys. On average, post-polio syndrome occurs 35 years after the infection. Faecal-oral route and respiratory route of transmission SPREAD: with poor sanitation, contaminated faeces into the water supply, or by touch, into food . 13

14. Polio is often diagnosed by examining throat secretions, stool samples, or cerebrospinal fluid. No cure for poliomyelitis once developed,   antibiotics  for additional infections and painkillers are given. Risk factors include : travelling to polio endemic places, weak immune system, pregnant women. 14

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17. PATHOGENESIS ATTACHMENT: The poliovirus receptor is the glycoprotein CD155. CD155 is a member of immunoglobulin family of molecules with three immunoglobulin like domains. The virus attachment site is located in the outermost domain. Poliovirus binding site for CD155 are located in surface canyons. CD155 is found only in humans and some other primate species 17

18. CD155 RECEPTOR STRUCTURE 18

19. ENTRY: Entry of the viral nucleic acid was thought to occur one of the two ways . Formation of pore in the plasma membrane. Endocytosis. ENTRY THROUGH PORE FORMATION Upon binding to receptor; poliovirus undergoes an irreversible conformational change to 135S cell entry intermediate. This transition involves the loss of VP4 and externalization of “N” terminus of VP1. The exposed terminal extension of VP1 enable the A(135S)Particle to attach to liposome. Insertion of N Terminus of VP1 may facilitate cell entry either by disrupting a membrane or by forming a pore in the membrane. Finally ,viruses release its genome into the cytoplasm and capsid remains outside. 19

20. ENTRY THROUGH ENDOCYTOSIS The Poliovirus enters the cell through receptor mediated endocytosis. The capsid penetrate into the cytoplasm, and become located inside endosome. In the endosome the acidic pH causes the conformational changes of the viral capsid protein, in particular VP1. VP1 expose hydrophobic region and interact with endosomal membrane. Consequently, a channel is formed in the capsid, from which the viral RNA is released into the cytoplasm. 20

21. ENTRY THROUGH ENDOCYTOSIS 21

22. TRANSCRIPTION AND TRANSLATION: 22 No transcription as genome is positive sense RNA. Proteins are immediately synthesized upon entry. Process of translation occurs in the cytoplasm. VP1, VP2, VP3, VP4→ Structural proteins involve in capsid formation. 2A, 3C→ Protease. 2B, 2C→ ATPase. 3A→ Protein complex formation. 3B→ makes VPg (virion protein genome-linked). 3D→ RNA dependent RNA polymerase (replicase).

23. PROCESS OF TRANSLATION : In cytoplasm IRES dependent translation The first IRES to be discovered was in polio virus RNA Vpg is cleaved upon entry Cellular proteins like pcbp and translation factors help in the binding of 40s ribosomal subunit and translation begins when complete ribosome reaches the initiation codon Uses one ORF One long polypeptide is synthesized Polypeptide is then cleaved into single proteins Up to 60 ribosomes maybe translating at a time 23

24. 24 CLEAVAGE OF POLYPEPTIDE: Cleaved by viral coded proteases. The intermediates also function as proteases. P2 and P3 segments code for non structural proteins while p1 segment codes for the structural proteins. P2 region has cis acting replication element CRE which is involved in replication process. First the 2A protein auto cleaves separating structural protein precursors from the non structural ones Some of the cleavages take place while the ribosomes are still translating , generating immediately viral proteins

25. 25 HOW VIRUS HALTS HOST’S CELLULAR FUNCTIONS: The IRES dependent translations makes cap dependent translation impossible. 2 A proteins cleaves one of the translation factors which is responsible for binding of ribosome. These cellular proteins cannot be used for the cell’s own protein synthesis. There are more ribosomes available to translate the viral RNA. Virus also causes rearrangement of cellular membrane and the creation of double membrane vesicles. These viral induced compartments and vesicles are thought to serve as a site to support virus replication.

26. GENOME REPLICATION : RNA synthesis occurs in replication complexes that contain cell proteins as well as virus proteins and RNA. Much of the RNA in the replication complexes is present as replicative intermediates (RIs). An RI is an association of RNA molecules consisting of a template RNA and several growing RNAs of varying length. These complexes are associated with the cytoplasmic surfaces of membranous vesicles of infected cells. Large numbers of vesicles formed are derived mainly from the endoplasmic reticulum. 26

27. REPLICATION COMPLEXES 27

28. The replication process involves the synthesis of a (−) strand RNA molecule from the single-stranded positive sense (+) RNA. This (−) strand serves as a template and subsequent transcription of this strand produces new copies of the (+) strand RNA. The primer for both (+) and (−) strand synthesis is the small protein VPg. Replication is initiated by the uridylylation of VPg. It is uridylylated by RNA polymerase at a cis-acting replication element (cre) located in a stem-loop in the virus genome. RNA polymerase adds UU to a VPg, using AA in cre as the template. 28

29. Uridylylation of VPg 29

30. Some of the (+) RNA molecules are used as templates for further (−) RNA synthesis, some function as mRNA for translation of more viral proteins and some are destined to be the genomes of progeny virions. It has been estimated that in a poliovirus-infected cell up to 2500 RNA molecules are synthesized per minute. The virus controls RNA synthesis in such a way that about 50 times more (+) RNA than (−) RNA is made. 30

31. ASSEMBLY : Five copies each of VP0, VP3 and VP1 assemble into a pentamer and 12 pentamers form a procapsid. Each procapsid acquires a copy of the virus genome with VPg still attached at the 5 end. At around this time the 60 copies of VP0 are cleaved into VP4 and VP2 31

32. EXIT/RELEASE: Exit through lysis after 4-6 hours of infection. Induced by viral proteins. After exiting from intestinal cell they enter the blood stream . Each cell can release up to 10,000 copies of virus. 32

33. CONCLUSIONS Poliovirus containment is a major global endeavor. The protection of children against polio is a collective responsibility of the ummah especially by its religious and political leaders. We should make people aware of polio importance through; Polio campaigns Advertisements The world polio day is celebrated on 24 th October. 33

34. 34 REFERENCES: https://www.sciencedirect.com/topics/neuroscience/cd155 https://jvi.asm.org/content/78/13/7186 http://www.endpolio.com.pk/polioin-pakistan https://www.sahealth.sa.govau/wps/wcm/connect/public+content/sa+health+internet/healthtopics/health+conditions+preventions+and+treatment https://www.ncbi.nlm.nih.gov http://www.newworldencyclopedia.org/entry/poliomyelitis

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