Human Immunodeficiency Virus

Dr. Suhail Naser

Human Immunodeficiency Virus (HIV) is the causative agent of Acquired Immune Deficiency Syndrome (AIDS).

HIV-2 was isolated in 1986 in West Africa

HIV-1 was isolated in 1983 in France and USA

Human Immunodeficiency Virus•Belong to the lentivirus subfamily of the retroviridae

•Enveloped RNA virus, 120nm in diameter

•HIV-2 shares 40% nucleotide homology with HIV-1

•Genome consists of 9200 nucleotides (HIV-1):

•gag core proteins - p15, p17 and p24

•pol - p16 (protease), p31 (integrase/endonuclease)

•env - gp160 (gp120:outer membrane part, gp41: transmembrane part)

•Other regulatory genes ie. tat, rev, vif, nef, vpr and vpu

STRUCTURE OF HIV

HIV particles

HIV Genes

• Three basic genes– gag – encodes matrix, capsid, nucleic acid

binding proteins– pol – encodes reverse transcriptase– env - encodes surface glycoproteins,

transmembrane proteins

HIV Antigens

• Major surface/envelope glycoproteins– gp120– gp41 anchors gp120 to virus

• Major capsid proteins– p24– P18

• Other minor surface & structural proteins– p55

Replication

• The first step of infection is the binding of gp120 to the CD4 receptor of the cell, which is followed by penetration and uncoating.

• The RNA genome is then reverse transcribed into a DNA provirus which is integrated into the cell genome.

• This is followed by the synthesis and maturation of virus progeny.

CO-RECEPTORS

• HIV infects and ultimately destroys CD4+ ,CCR5+ or CXCR4+ are the co-receptors necessary for attachment.

Schematic of HIV Replication

CELLS WHICH ARE INFECTED BY HIV

All cells which have CD4 receptors on their surface.

• T4 (Helper/inducer) lymphocytes

• 5-10% B lymphocytes.

• 10-20% Monocytes & Macrophages.

• Glial cells and microglia in CNS.

MODE OF TRANSMISSION OF HIV

•Sexual contact

•Intravenous drug use

•Transfusion of blood and infusion of blood products

•Mother to foetus-Perinatal

•Others

MODES OF ACCQUIRING HIV.• Sexual Contact = 0.1 -1.0 %• Transfusion of blood and blood products = > 90%• Tissues and organ donation = 50 -90%• Injections and injuries, unsterile needles = 0.5 -1.0%• Mother to baby (transplacental) = 30%• SECRETIONS WHICH HAVE HIV • Blood• Lymphocytes.• Semen • Saliva• Urine • Tears• Breast milk.

Others (not specified)

Injectable Drug use

Blood and blood products

Perinatal

Sexual

85.7 %

6.8 %

2.2 %2.6 %

2.7

MODES OF SPREAD OF HIV

• HIV infects and destroys an important type of cell in the body’s immune system known as the T-helper (TH) cell, also known as the CD4 cell

How does HIV cause AIDS?

• CD4 cells direct and coordinate other cells in the immune system to battle infections

• When CD4 cells are destroyed, the body loses its ability to fight off infections

How does HIV cause AIDS?

CD4 Cells

4-8 Weeks Up to 12 Years 2-3 Years

CD

4 Cell C

ount

1,000

500

Asymptomatic HIV Infection AIDS

Acute Infection

HIV Infection is characterized by a steady decline in the number of CD4

cells

Time

200

CD4 cell count

4-8 Weeks Up to 12 Years 2-3 Years

CD

4 C

ell C

oun

t (c

ells

/mm

³)

1,000

500

Asymptomatic HIV Infection AIDS

Acute Infection

HIV Infection is characterized by a steady decline in the number of CD4

cells

Time

200

high risk of opportunistic infections

Clinical Features

1. Seroconversion illness - seen in 10% of individuals a few weeks after exposure and coincides with seroconversion. Presents with an infectious mononucleosis like illness.

2. Incubation period - this is the period when the patient is completely asymptomatic and may vary from a few months to a more than 10 years. The median incubation period is 8-10 years.

3. AIDS-(CD 4 Count less than 200/cc)related complex or persistent generalized lymphadenopathy.

4. Full-blown AIDS.

Opportunistic Infections

Protozoal pneumocystis carinii (now thought to be a fungi),

toxoplasmosis, crytosporidosis

Fungal candidiasis, crytococcosis

histoplasmosis, coccidiodomycosis

Bacterial Mycobacterium avium complex, MTB

atypical mycobacterial disease

salmonella septicaemia

multiple or recurrent pyogenic bacterial infection

Viral Cytomegalovirus, HerpesSimplexVirus,

Varicella Zoster Virus, JCV

Opportunistic Tumours

• The most frequent opportunistic tumour, Kaposi's sarcoma, is observed in 20% of patients with AIDS.

• KS is observed mostly in homosexuals and its relative incidence is declining. It is now associated with a human herpes virus 8 (HHV-8).

• Malignant lymphomas are also frequently seen in AIDS patients.

What is the “Viral Load”?

• The HIV viral load is simply a measure of the quantity of HIV in a drop (mL) of a patient’s blood, and it is usually measured in copies/mL

• In general, the higher the viral load, the faster CD4 cells are destroyed

Laboratory Diagnosis

Test Serology

ELISA Latex Agglutination Western Blot Immunofluorescence

Virion RNA, RT-PCR P24 antigen Isolation of virus

Lymphocyte CD4:CD8 T cell ratio

Objective

Initial ScreeningInitial ScreeningConfirmatory testConfirmatory test

Detection of virus in bloodEarly marker of infectionTest not readily available

Correlate of HIV Disease

SPECIMENS FOR DIAGNOSIS OF HIV INFECTION

SerumVenous blood drawn using syringes and collection tubes (e.g. vacutainers), and serum separated from blood by centrifugation

Most common testing media for all kinds of tests

•Time consuming•Staff with a higher level of training required•Costly•Risk of occupational exposure

Whole Blood from finger prick •easy to perform, •require minimal equipment•can be carried out by the appropriately trained counsellor•Less costly•risk of occupational exposure is substantially reduced

SPECIMENS FOR DIAGNOSIS OF HIV INFECTION

Saliva and Urine

•Collection-simple, safe, non-invasive, inexpensive, and the sample can be stored at room temperature

•Can be collected in groups•Safer to collect than blood (less infectious)•Eliminates the risk of accidental exposure through needle stick or test tube breakage

•Can be collected from persons unwilling to giving blood•Useful for testing hard-to-reach populations such as sex workers and at sites where blood collection may be difficult, such as remote clinics or point-of-care facilities.

•Cost-effective-minimal training, no equipment for collection

However, the quality of these assays as compared to conventional serological tests needs to be assessed

Laboratory tests for diagnosis of HIV infection

Screening tests

Supplemental tests

Confirmatory tests

ELISA Western Blot Virus isolation

Rapid tests- Latex agglutination

- Dot blot assay

Immuno-fluorescence

Detection of viral nucleic acid - In situ hybridization

- PCR

Simple tests- Particle agglutination

Detection of p24 antigen

-Non-specific tests for HIV

• Blood counts– Leucopenia– Lymphocyte count less

than 400/cmm– Thrombocytopenia

• T-cell subset assay– CD4 count below

200/cmm– Normal CD4:CD8 ratio

2:1. Reversed in AIDS to 0.5:1.

• Hypergammaglobulinaemia

• Diminished CMI – Candidial, tuberculin tests.

• Lab diagnosis of opportunistic infections

• Malignancies