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HIV and AIDS

Dr Tom Leach

Introduction

Human immunodeficiency virus (HIV) was first identified in 1983. Left untreated, it causes Acquired Immunodeficiency Syndrome (AIDS). In the developed world its spread is relatively limited, and modern treatment means that life expectancy is almost the same as that of non-sufferers. But in the developing world, in Africa and Asia in particular, it is still a growing and widespread problem.
The HIV virus binds to CD4 receptors, which exist on T-cells, monocytes, macrophages and neural cells. Soon after infection, the HIV virus replicates rapidly, but by about 6-8 weeks, the host immune system responds, and thereafter there exists an equilibrium between viral replication and immune response. AIDS develops when the function of the immune system is impaired to such an extent that it can no longer perform its normal functions in fighting off other infections, and is classically defined as a CD4 T-cell count of <200 x 106 / L, although in the UK and Australia, this strict definition is not always used in the presence of AIDS defining infections.
Antiretroviral therapy (ART) has revolutionised treatment and prevents most patients with HIV from progressing to AIDS. As such, some now consider that managing HIV is like managing any other chronic disease. Patients should start ART as soon as possible after diagnosis.
Some countries and facilities now refer to AIDS as “late-stage HIV”. The viral load (number of circulating viruses) can predict the progression to AIDS.
Most patients with HIV require life-long daily antiretroviral drugs to keep the infection under control.

Epidemiology

Transmission

Pathology

HIV is a single stranded RNA retrovirus. The virus is incorporated into a host cell, whereby, the viral enzyme transcriptase will begin transcription of the RNA to DNA. Then, the viral enzyme integrase will integrate the DNA into the host’s.

Infection of cells – These new virions can now infect new cells. They are capable of entering any cell that expresses the CD4 receptor. The virus will bind to CD4 receptors with the gp120 glycoprotein. Susceptible cells include:

CD4+ T cells will migrate to lymphoid tissue, and release millions of virons, ready to infect new cells.
As the infection progresses, destruction of CD4+ cells leads to reduced efficacy of the host immune system.  

HIV Virion

Clinical features

HIV infection can be divided into stages:

Seroconversion – typically occurs 2-6 weeks after exposure. Is often asymptomatic, but in about 50% of cases there may be a period of fever, malaise, myalgia, pharygnitis and maculopapular rash.

Asymptomatic infection – typically, after the initial phase, patients enter a long asymptomatic period. This can last for years – typically around 5 years or more.

AIDS related complex (ARC) – aka – symptomatic infectionthis is a set of prodromal symptoms that precedes the onset of AIDS. It can include:

AIDS

Diagnosis

HIV antibody testing is typically a 2-step process. The antigen-antibody (ELISA) test is used a screening test, and if positive, diagnosis is confirmed by a secondary test (e.g. Western Blot test).

Other tests associated with HIV:

HIV and TB – often co-exist, and can be a real problem.

Once diagnosis is confirmed, patients should also be tested for:

Monitoring

The following should be measured every 3 months:

HIV RNA levels (viral load)– strongly predicts the progression to AIDS, regardless of the CD4 count!

CD4 count

Management

Sensitive and sympathetic discussion is typically appropriate in the first consultation(s) after diagnosis. In asymptomatic patients in particular, try to avoid technical discussions about treatment regimens.

ART – antiretroviral therapy (formerly known as HAART – highly active anti-retroviral therapy) is the mainstay of medical treatment.

 

Principles of therapy

Typically 3+ drugs are used in combination
Start treatment as early as possible – i.e. before CD4 count <200, ideally as soon as diagnosis is confirmed.

Exact treatment regimens vary locally. Involve a specialist (sexual health physician) as soon as the diagnosis is made. Below is an overview of some of the classes of medications used.

NRTI’s – e.g. Zidovudine, Didanosine, Lamivudine, Emtricitabine, Tenofovir, Abacavir

Protease Inhibitors – e.g. Indinavir, Ritonavir, Saquinavir, Lopinavir

NNRTI’s e.g. Nevirapine, Efavirenz

Prevention

PEP – post-exposure prophylaxis – anti HIV drugs can be taken as prophylaxis, if taken within 72 hours of exposure to HIV. This exposure could be in the form of sexual contact (including oral, vaginal, anal), or blood products contact.
Needlestick injuries
Prevention of vertical transmission

15% risk of vertical transmission (higher in Africa)
Methods of prevention of vertical transmission:
All HIV positive mothers should              

Counseling for HIV testing

It is very important to remember that before you perform an HIV test you need to tell the patient about the implications of a positive result. You should:
Determine the level of risk (e.g. unprotected sex, number of partners, sex overseas)
Discuss the benefits of knowing if test is positive:

Ask about major concerns e.g.:

Post-term counseling

References

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