RNA Virus 5

RNA VIRUS

Learning objectives

• Describe structural organization RNA virus
• Describe general characteristic of RNA virus
• List RNA viruses of medical importance
• Explain mode of transmission of RNA virus
• Explain viral replication cycle of RNA virus
• List disease caused by RNA virus
• Collect specimen which can be used to detect RNA virus

List laboratory techniques used to detect RNA viruses

Describe structural organization RNA virus

• 1. Genome Structure

RNA viruses have genomes that can be single-stranded (ssRNA) or double-stranded (dsRNA).

Single-stranded RNA viruses may be positive-sense (+ssRNA), which can directly serve as mRNA, or negative-sense (-ssRNA), which must be transcribed into a positive strand before translation.

Describe structural organization RNA virus

2. Capsid Structure – RNA genomes are enclosed within a protein shell known as the capsid, which protects the viral RNA from degradation.

3. Envelope and Surface Proteins – Many RNA viruses have a lipid envelope.

General characteristic of RNA virus

• 1. Genome is composed of ribonucleic acid (RNA) instead of DN
• Can be single-stranded (ssRNA) or double-stranded (dsRNA).
• ssRNA viruses are further classified into:

Positive-sense (+ssRNA): genome acts directly as mRNA (e.g., Picornaviruses).

Negative-sense (–ssRNA): genome must be transcribed into complementary mRNA by viral RNA-dependent RNA polymerase.

General characteristic of RNA virus cont….

2. High Mutation Rate – RNA viruses tend to have high mutation rates inside the host cell and escape the host immune system due to lack of proofreading as it is in DNA virus 3. Replication in Host Cells takes place in cytoplasm- RNA viruses typically replicate in the cytoplasm of the host cell, though some like influenza viruses, replicate in the nucleus.

3. Enveloped or non-enveloped depending on the family 4. RNA is chemically less stable than DNA – RNA viruses are generally more fragile outside the host.

General characteristic of RNA virus cont….

5. Enveloped RNA viruses are more sensitive to heat, detergents, and desiccation compared to non-enveloped ones 6. Responsible for many acute infections (e.g., influenza, measles, polio).

RNA viruses of medical importance

• Measles virus
• Mumps virus
• Hepatitis virus
• Influenza virus (H1N1).
• Dengue fever virus
• Ebola virus
• Poliovirus.
• Rabies virus.

Yellow fever virus

HIV,

• Rubella virus
• Respiratory Syncytial virus,
• Chikungunya virus
• COVID 19 virus
• Rift valley fever virus
• Enterovirus group
• Marburg
• Lassa

RNA viruses of medical importance

Mode of transmission of RNA virus

By direct contact – hepatitis B virus (STI), HIV, Marburg virus By ingestion of viruses (faecal-oral) -e.g. enteroviruses, rotaviruses, and hepatitis A virus, polio virus, Lassa virus By inhaling viral droplets – in airborne droplets or dust particle e.g. influenza viruses, measles viruses, mumps, respiratory synctial virus , polio virus, rubella, COVID 19.

By mother to child during pregnancy or birth (vertical transmission )- e.g. HIV, hepatitis, rubella virus

By saliva-e.g. rabies , mumps, measles, influenza

By indirect contact with an article- e.g. papillomavirus (wart producing virus) or towel contaminated with a virus that cause eye infection, and mumps By vector bite ( vector borne) -e.g. housefly help in the transfer of hepatitis virus from one person to another on their bodies also chikungunya and Yellow fever can be transmitted by insect bites Blood transfusion- some RNA virus such as HIV, COVID 19, hepatitis can be transmitted through transfusion of blood or blood products Mode of transmission of RNA virus

One of the RNA viral replication is HIV life cycle which consist 6 steps to complete their replication.

1. Binding – A virus consists of an outer lipid envelope , in which the glycoproteins are attached (in the case of HIV, genetic information is carried as RNA instead of DNA) .

HIV has proteins on its envelope that are strongly attracted to the CD4+ surface receptor on the outside of the T-cell, and when the viral particle binds to host cell receptors viral envelop fuses with the host cell membrane releasing the genetic materials into the host cell Viral replication cycle of RNA virus

RNA Virus 5

2. Reverse transcription – HIV's genes are carried in two strands of RNA, while the genetic material of human cells is found in DNA.

In order for the virus to infect the cell, a process called "reverse transcription" makes a DNA copy of the virus's RNA.

• This step is unique to retroviruses, this new DNA is called "proviral DNA.“

Viral replication cycle of RNA virus

RNA Virus 5

3. Integration- The HIV DNA is then carried to the cell's nucleus (center), where the cell's DNA is kept. Then, another viral enzyme called integrase hides the proviral DNA into the cell's DNA. Then, when the cell tries to make new proteins, it accidentally makes new HIVs.

4. Transcription- Once HIV's genetic material is inside the host cell's nucleus; it directs the cell to produce viral proteins . The strands of viral DNA in the nucleus separate, and special enzymes create a complementary strand of genetic material called messenger RNA or mRNA which enter the cytoplasm for translation.

Viral replication cycle of RNA virus

RNA Virus 5

5.Translation- The mRNA carries instructions for making new viral proteins from the nucleus to a kind of workshop in the cell.

As each mRNA strand is processed, a corresponding string of proteins is made. This process continues until the mRNA strand has been transformed or "translated" into new viral proteins needed to make a new viral particle.

Viral replication cycle of RNA virus

RNA Virus 5

6. viral assembly, maturation and release- The final step begins with the assembly of new virus. Long strings of proteins are cut up by a viral enzyme called protease into smaller proteins. These proteins serve a variety of functions; some become structural elements of new HIV, while others become enzymes, such as reverse transcriptase.

Once the new viral particles are assembled, they bud off the host cell, and create a new virus. The virus then enters the maturation stage, which involves the processing of viral proteins. Maturation is the final step in the process and is required for the virus to become infectious.

With viral assembly and maturation completed, the virus is able to infect new cells. Each infected cell can produce a lot of new viruses.

Viral replication cycle of RNA virus

Disease caused by RNA virus

• Severe Acute Respiratory Syndrome (SARS)
• influenza,
• common cold,
• Hepatitis B and C
• Pneumonia
• Mumps
• Dengue( break-bone fever)

Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF)

Polio infects person’s spinal cord

HIV does not cause one disease condition but associated with a group of diseases and conditions. Main effect of HIV in the human is that it weakens the immune system hence rendering it incapable of fighting against diseases.

• Chikungunya
• Rift valley fever
• Yellow fever
• Rubella
• Marburg hemorrhagic fever

Disease caused by RNA virus

Disease caused by RNA virus

Disease caused by RNA virus

Chikungunga virus causes chikungunya through bite of mosquitoes

Disease caused by RNA virus

Disease caused by RNA virus

Poliovirus

A single stranded RNA virus which is transmitted through fecal oral route as the virus are shed out in feaces Positive sense ssRNA virus

• Belongs to picornaviridae family
• Genus –enterovirus

Causes polio (nerve system infection )

Disease caused by RNA virus

• Polio damages the motor neurons in the spinal cord, leading to
• Muscle weakness
• Paralysis ( often of the legs )
• Permanent limb deformities

Difficult walking which require crutches or braces

Laboratory diagnosis

• Specimen
• Stool
• Throat swab/Nosal pharyngeal swab
• Blood
• Cerebral spinal fluid
• Diagnosis technique
• Specimen grown in cell culture to observe cytopathic effect
• Serological technique
• Complete blood count

Molecular test

Disease caused by RNA virus

Disease caused by RNA virus

Disease caused by RNA virus

Specimen which can be used to detect RNA virus

• Nasopharyngeal swab/ throat swab
• Nasal aspirate/wash( sample fluid from the nose)
• Buccal swab(between the cheek and teeth is obtains generous amount of saliva)
• Serum or plasma
• Blood or other tissue sample
• Stool
• CSF
• DBS (dried blood spot)

Urine

Laboratory techniques used to detect RNA viruses

• Serological test
• PCR( polymerase chain reaction)
• ELISA
• Western blot

Cell culture.

REFERENCE

Becker, F.J. & Silverton, R.E. (1985). Introduction to Medical Laboratory Technology(6th ed.). Butterworth London.

• Cook, G. (2000). Manson’s Tropical Diseases. (22th ed.). London: WB Saunders

Company Ltd.

Greenwood, D. Richard, C.B.S., & John, F.P. (1992). Medical Microbiology (4th ed.). Hong Kong: ELBS with Churchill Livingstone, Medical Division of Longman Group, UK Ltd.

Jawetz, Melnick, & Adelberg's. (2007). Medical Microbiology (24th ed.) USA: The McGraw-Hill Companies, Inc.

Levinson, W. (2004). Medical Microbiology and Immunology (8th Ed.). Examination & Board. New York: International Edition Lange Medical Books /McGraw Hill Medical Publishing & Davson.

Monica, C. (1987). Medical Laboratory Manual for Tropical Countries (2nd ed.) Volume1 Oxford: ELBS Butterworth, Heinemann Ltd.

Monica, C. (1998). District Laboratory Practice in Tropical Countries. Part 1. Tropical