HIV

By - Dr. Farhan S. Nadaf

HIVHuman Immunodeficiency Virus

Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unsafe sex, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth (vertical transmission). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world.

HIV infects primarily vital cells in the human immune system such as helper T cells (to be specific, CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through three main mechanisms: First, direct viral killing of infected cells; second, increased rates of apoptosis in infected cells; and third, killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.

Classification*There are two species of HIV known to exist: HIV-1 and HIV-2.

*HIV-1 is the virus that was initially discovered and termed both LAV and HTLV-III.

It is more virulent, more infective and is the cause of the majority of HIV infections

globally.

*The lower infectivity of HIV-2 compared to HIV-1 implies that fewer of those

exposed to HIV-2 will be infected per exposure.

Comparison of HIV species

Species

HIV-1

HIV-2

Virulence

High Lower

Infectivity

High Low

Prevalence

Global

West Africa

Inferred origin

Common Chimpanzee

Sooty Mangabey

Signs and symptoms

Structure and genome

Just for illustrative purpose

gp=glycoprotein

Replication cycleEntry to the cell

Replication and transcription

Diagnosis* enzyme-linked immunosorbent assay (ELISA)

* Western blot

* Immunofluorescence assay (IFA)

* nucleic acid testing

* viral RNA or proviral DNA amplification method

* Particle agglutination assays

* Simple rapid assays

Enzyme-linked immunosorbent assay (ELISA)

Western Blot

Western Blot Binding

Western Blot

Western Blot Chemiluminescent Detection

Western Blot

Western Blot Transfer

Treatment*There is currently no publicly available vaccine or cure for HIV or AIDS.

*Current treatment for HIV infection consists of highly active antiretroviral

therapy or HAART.

*HAART neither cures the patient nor does it uniformly remove all symptoms;

high levels of HIV-1, often HAART resistant, return if treatment is stopped.

Moreover, it would take more than a lifetime for HIV infection to be cleared

using HAART.

*Despite this, many HIV-infected individuals have experienced remarkable

improvements in their general health and quality of life, which has led to a large

reduction in HIV-associated morbidity and mortality in the developed world.

*The timing for starting HIV treatment is still debated.

*There is no question that treatment should be started before the patient's CD4 count falls below 200, and most national guidelines say to start treatment once the CD4 count falls below 350.

*Anti-retroviral drugs are expensive, and the majority of the world's infected

individuals do not have access to medications and treatments for HIV and

AIDS.

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HIV At A Glance• The human immunodeficiency virus (HIV) is a type of virus called a

retrovirus, which infects humans when it comes in contact with tissues such as those that line the vagina, anal area, mouth, or eyes, or through a break in the skin.

• HIV infection is generally a slowly progressive disease in which the virus is present throughout the body at all stages of the disease.

• Three stages of HIV infection have been described:

1. The initial stage of infection (primary infection), which occurs within weeks of acquiring the virus, and often is characterized by a "flu-" or "mono-"like illness that generally resolves within weeks.

2. The stage of chronic asymptomatic infection (meaning a long duration of infection without symptoms) lasts an average of eight to 10 years.

3. The stage of symptomatic infection, in which the body's immune (or defense) system has been suppressed and complications have developed, is called the acquired immunodeficiency syndrome (AIDS). The symptoms are caused by the complications of AIDS, which include one or more unusual infections or cancers, severe loss of weight, and intellectual deterioration (called dementia).

• When HIV grows (that is, by reproducing itself), it acquires the ability to change (mutate) its own structure. This mutation enables the virus to become resistant to previously effective drug therapy.

• The goals of drug therapy are to prevent damage to the immune system by the HIV virus and to halt or delay the progress of the infection to symptomatic disease.

• Therapy for HIV includes combinations of drugs that decrease the growth of the virus to such an extent that the treatment prevents or markedly delays the development of viral resistance to the drugs.

• The best combination of drugs for HIV has not yet been defined, but one of the most important factors is that the combination be well tolerated so that it can be followed consistently without missing doses.