DNA Virus

DNA Viruses

Learning Objectives

• By the end of this session, students are expected to be able to:
• Describe structural organization of DNA virus
• Describe general characteristics of DNA virus
• List DNA virus of medical importance
• Explain modes of transmission of DNA virus
• Explain viral replication cycle of DNA virus
• List diseases caused by DNA virus
• Collect specimen which can be used to detect DNA virus

List laboratory techniques used to diagnose DNA virus

structural organization of DNA virus

• Genome

Can be double-stranded (dsDNA) or single-stranded (ssDNA).

Shape: Linear (e.g., Adenoviruses, Herpesviruses) or circular (e.g., Papillomaviruses, Polyomaviruses).

structural organization of DNA virus

• Capsid
• Function: Protects viral DNA and aids in host cell entry.

Symmetry Types:

• Icosahedral capsid (most DNA viruses, e.g., Adenoviridae, Papillomaviridae).
• Complex capsid (Poxviridae, with brick-shaped virions).

Capsomeres: Protein subunits forming the capsid.

structural organization of DNA virus

Envelope (Optional)

• Facilitates attachment and entry into host cells.

Lipid bilayer derived from host cell membranes, embedded with viral glycoproteins.

Associated Proteins

Structural proteins: Form capsid and envelope.

Enzymes: Some large DNA viruses carry their own polymerases (e.g., Poxviruses), while smaller ones rely on host enzymes.

Characteristics of Viruses

• They are small in size ranging from about 20 nm to about 300 nm in diameter.
• They are akaryotic particles (neither eukaryotes nor prokaryotes)

They contain either DNA or RNA and not both as their genome They exhibit living properties when inside the living cells (i.e. they are incapable of independent reproduction unless they are in the living cell) They are non motile

They can be grown in cell cultures

Classification of Viruses According to the Nucleic Acid

• Based on the nucleic acid viruses are classified into
• RNA viruses

DNA viruses

Replicative Cycle of Viruses

• Viruses are inert in the extracellular environment

They replicate only in living cells, being parasites at the genetic level The viral nucleic acid contains information necessary for programming the infected host cell to synthesize virus-specific macromolecules required for the production of viral progeny (new virus particle)

Steps in Viral Replication

• Attachment and adsorption
• Entry of the virus into the host cells

Uncoating (viral genome is injected to the host nucleus/cytoplasm) Integration of viral genome into host cell nucleus, Viruses must synthesize mRNA by using the host cell mechanisms RNA viruses produce mRNA by several different routes Viral mRNA is then translated in the host cytoplasm to produce viral proteins

Replication of viral DNA or RNA occurs in the host nucleus or the cytoplasm

Assembly of the viral proteins and genome During the replicative cycle, numerous copies of viral nucleic acid and coat proteins are produced and assembled during assembly process Release of the viral particles

This takes place on the host cell plasma membrane

DNA Viruses

• Most DNA viruses contain a single genome of linear double stranded DNA (dsDNA).
• Examples DNA viruses include;
• Varicella zoster virus
• Cytomegalovirus
• Epstein bar virus
• Human papilloma virus
• Adenovirus

Variola virus

Cytomegalovirus Virus

(cytomegalo = enlarged cell)

Cytomegalo virus (CMV) causes a number of diseases characterized by enlargement (ballooning) of the infected host cells The diseases include

• Pneumonia and hepatitis in immune-compromised patients
• Retinitis and enteritis especially in AIDS patients
• Cytomegalic inclusion body disease in infants
• Mononucleosis in transfusion recipients

Congenital abnormalities

Mode of transmission

• Through sexual contact
• Organ transplant
• Blood transfusion
• Saliva
• Breast milking

Transplacental or congenital

A table showing cmv diseases

Patient Group

• CMV-Associated Disease

Key Features

• Newborns (congenital)
• Congenital CMV
• Hearing loss, developmental delay, microcephaly
• Healthy adults
• CMV mononucleosis
• Fever, fatigue, mild hepatitis
• HIV/AIDS patients
• CMV retinitis
• Vision loss, blindness
• Transplant recipients
• CMV pneumonia, colitis, hepatitis
• Severe systemic disease
• General immunocompromised
• Disseminated CMV infection

Multi-organ involvement, potentially fatal

Laboratory Diagnosis for Cytomegalovirus Virus

Clinical Situation

Specimen Collected

Diagnostic Method

• Congenital CMV (newborn)
• Urine, saliva
• , culture
• Systemic CMV (transplant/HIV)
• Blood
• PCR, serology
• CNS involvement
• CSF
• PCR
• CMV pneumonia
• BAL fluid
• PCR, culture
• CMV hepatitis/colitis
• Tissue biopsy
• Histology
• CMV retinitis
• Vitreous/aqueous fluid

PCR

Laboratory Diagnosis for Cytomegalovirus Virus cont

• Diagnostic features in cell culture
• Cytopathic effect in tissue culture (cell enlargement)
• “Owl's eye” nuclear inclusions are seen in cell culture
• Treatment
• Ganciclovir
• Valganciclovir

Cidofovir

Inclusion bodies of CMV in cells

Epstein Bar Virus (EBV)

• Diseases caused by Epstein bar virus are
• Burkitts lymphoma in East African children (occurs as a tumor of the face and jaw)

Infectious mononucleosis

Mode of transmission

• Saliva ( kissing , sharing drinks ,
• Oral secretions
• Blood transfusion

Organ transplant

Laboratory Diagnosis

• Tumor aspirates
• Full blood picture
• Drug of Choice

No effective drugs is available

Burkitt lymphoma

Varicella Zoster Virus

• It is a member of Herpesviridae family
• They are dsDNA viruses, enveloped, icosahedral in shape

Transmitted through inhalation

Causes cytopathic effect in cell culture (after being infected, cells dies, and the died cells may clamp together and form inclusion bodies, cells may be lysed or mutated)

Disease caused by varicella zoster

Chickenpox (Varicella)

• Acute, highly contagious infection, usually in children.
• Symptoms: Fever, malaise, itchy vesicular rash .
• Transmission: Respiratory droplets or direct contact with lesions.

Prevention: Varicella vaccine is highly effective

Diseases Caused by Varicella Zoster Virus

• Shingles (Herpes Zoster) affecting eye
• Painful rash on forehead/eyelid
• Keratitis
• ,uveitis,
• possible vision loss
• Reactivation of latent VZV in sensory nerve ganglia, often decades after chickenpox.
• Symptoms: Painful, localized vesicular rash
• Prevention: Shingles vaccine (recommended for older adults

Note: Both diseases are caused by the same virus

Herpes zoster

Cytomegalovirus Retinitis

• Caused by cytomegalovirus
• Features:
• Pizza pie retinal appearance(hemorrhage+ necrosis)
• Blurred vision , floaters
• Technique
• Smear to see multinucleated cells (Tzanck cells)
• Serological test for Antigen or viral DNA detection
• Drug of Choice

Acyclovir

Adenovirus

Disease caused

Adenovirus infection is a contagious viral disease, commonly resulting in a respiratory tract infection.

• The diseases includes
• Respiratory tract infection
• Eye infection
• Gastrointestinal infections
• Urinary tract infection

Myocarditis

Adenoviridae family

• Epidemir

Diagnosis

Infection is diagnosed by signs and symptoms, and a laboratory test is not usually required Treatment

Most adenovirus infections get better without any treatment

Variola virus

• Disease caused
• Variola virus belongs to family poxviridae
• Having double stranded DNA and enveloped
• Disease caused
• Small pox – transmitted through inhalation of airborne Variola virus.
• Direct contact with lesions or contaminated objects
• Diagnosis –
• serological test
• Polymerase chain reaction (PCR).

Enzyme linked Immunosorbent assays (ELISA),

Small pox disease

Treatment

• Cidofovir – therapeutic agent administered intravenously

Brincidofovir

Human papilloma virus

• Disease caused

Warts

HPV infection of the skin in the genital area (Genital warts) is the most common sexually transmitted infection worldwide

Genital warts

Genital warts

Treatment for genital warts

Trichloroacetic acid: Topical acid solution that is applied to remove a genital or anal wart Cryotherapy: Procedure in which a genital wart is gradually removed with liquid nitrogen Electrocautery: Procedure that uses electricity to burn away warts.

Surgery: Removal of a genital wart using a scalpel, scissors, surgical shaver, or a spoon-like cutting device called a curette.

Evaluation questions

• Mention 5 diseases caused by DNA virus
• Mention two laboratory diagnosis of CMV
• Write down two management procedures for disease caused by HPV

Mention the mode of transmission of HPV