Retroviruses: HIV

College of Medicine Microbiology
Medical Virology
Retroviruses: HIV Dr. Jawad Kadhum Tarrad
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Retro: Re=reverse tr=transcriptase
General properties:
• The virus has spherical shape.
• Genome of virus is ssRNA.
• Capsid of virus is arranged in icosahedral symmetry.
• It has envelope with spikes
Two pathogens for human;
1. human immunodeficiency virus(HIV): two types; HIV-I and HIV-II. HIV-1 is responsible for most cases of acquired immune deficiency syndrome (AIDS), whereas HIV-2 is less commonly and less virulent.
2. human T-lymphotropic virus(HTLV): two types HTLV-1 and HTLV-II . The viruses are oncogenic that responsible for T-cell leukemia/T-cell lymphoma.
Biological structure of HIV:
• Envelope: the virus is surrounding by bilayer lipid envelope that covered by projected spikes (glycoprotein: gp41, gp120)which may act as attachment sites. (N.B: HIV undergoes from high rate of antigenic variation in envelope glycoproteins).
• Capsid proteins : are arranged in icosahedra. It consist of several proteins as capsid protein(p24) and matrix protein (p17).
• Genome consist of two copies of (+)ssRNA(diploid).
Viral genome contain three main genes:
gag-which encoded for capsid protiens.
Pol.-encoded for viral enzymes ,especially polymerase.
Env.-encoded for envelope glycoproteins.
• Core protein : contain many enzymes as revers transcriptase, integrase(endonuclease), protease, ribonuclease.
Mode of transmission:
sexual contact: HIV has high affinity to semen and vaginal secretions , therefore the virus can be transmitted by anal or vaginal intercourse among homosexual and heterosexual individuals.
Parenteral transmission; it can be transmitted by blood transfusion, or by needles or syringes such as intravascular drug uses(IVDU).
Mother to child: HIV can be transmitted to neonate across placenta or during delivery or breast milk.
Other methods for transmission of HIV ; fluids of body such as urine, tear, saliva.
High risk groups:
• Homosexual men; it is believe that the virus is carried in lymphocytes of semen and enter recipient body through abrasion in rectal mucosa.
• Recipient patients blood transfusion ,especially hemophiliac patients; they are require repeat plasma clotting factor-VIII transfusion.
• Heroin addiction and drug abuser, especially IVDU who share needles and syringes