Understanding the Difference Between a Virus and the Stage of Disease

Electron micrograph of HIV-1 (in yellow) budding from an infected CD4+ T-cell. Credit: National Institute of Allergies and Infectious Diseases (NIAID)

HIV is the acronym for the human immunodeficiency virus. It is a type of virus classified by scientists as a retrovirus, which causes disease by infecting and killing blood cells (known as CD4 T-cells) central to the body's immune system. As these cells are progressively wiped out, the body becomes less and less able to defend itself against otherwise common illnesses.

AIDS is the acronym for acquired immunodeficiency syndrome.

It is the stage of HIV infection where a person's immune system is fully compromised, leaving the body open to a wide range of potentially deadly diseases known as opportunistic infections

As such, HIV can be considered the cause and AIDS the effect of such infection.

What is a Retrovirus?

A retrovirus is considered "retro" because it transcribes its genetic code in reverse. In most living organisms, a cell's genetic material is encoded from DNA to RNA. A retrovirus is unique in that it functions in the opposite direction, using its RNA coding to produce DNA within an infected cell.

When this occurs, the newly produced DNA is inserted into the host cell's nucleus, effectively hijacking its genetic machinery in order to create multiple copies of itself, each capable of infecting and killing a multitude of other host cells.

HIV preferentially targets white blood cells called "helper" T-cells  Chief among these are CD4 T-cells, whose job it is to trigger the body's immune response.

By systematically depleting these immune cells, HIV diminishes the body's ability to identify and neutralize the invading virus, as well as host of other agents (e.g., viral, bacterial, parasitic) it could otherwise defend itself against.

What Happens If You Are Infected With HIV?

HIV is primarily spread through sexual contact, injecting drug use, accidental blood exposure, and transmission from mother to child during pregnancy.

HIV cannot be transmitted through sweat, tears, saliva, feces, or urine.

During the initial (acute) infection, HIV replicates vigorously, infecting and destroying a substantial number of CD4 T-cells. In response, the body's innate immune defenses are actively, and the infection is gradually brought under control. 

During this chronic stage of infection, the virus doesn't disappear. Instead, it goes into a period of latency, which can last anywhere from eight to 12 years. During this time, the virus will continue to replicate silently, often with little or no signs of illness. In fact, it is often only when an opportunistic infection first appears that a person even begins to suspect that he or she may have HIV. By this time, the immune system is usually impaired, sometime severely so.

In addition to free circulating HIV, a subset of virus, called provirus, will embed itself into cells and tissues of the body called latent reservoirs. These hidden reservoirs provide HIV haven by shielding them from detection from the body's immune defenses.

Even if HIV is brought under control with the use of antiretroviral drugs, these proviral agents are able to persist, ready to re-emerge as fully formed HIV the moment that treatment fails or the immune system collapses.

What Happens If a Person Is Diagnosed With AIDS?

AIDS is not a disease per se but rather the stage of HIV infection where the body's immune system is severely compromised. Technically, AIDS is defined by either a CD4 count of under 200 cells per microliter (µL) or by the diagnosis of a so-called AIDS defining illness.

(Normal CD4 counts range on average from between 800 to 1600 cells per µL.)

If left untreated, the average survival time for a person with AIDS is between six and 19 months. By contrast, a 35-year-old started on antiretroviral therapy (ART) can achieve a life expectancy equal to that of the general population, according to research from the U.K. Collaborative HIV Cohort Study.

Ultimately, treatment is key to the avoidance of HIV-related illnesses and the restoration of immune function. Even in persons with advanced disease, the implementation of ART can suppress HIV's ability to replicate, thereby allowing CD4 T-cells to repopulate to near-normal (and in some cases, normal) levels.

Furthermore, research from the U.S.-funded Strategic Timing of Antiretroviral Treatment (START) trial concluded that the early initiation of ART conferred to a 53 percent decrease in the risk of both HIV- and non-HIV-related diseases.

As a result of these and other studies, both the World Health Organization (WHO) and the U.S. Department of Health and Human Services today advocate for the implementation of ART at the time of diagnosis, irrespective of a person's CD4 count, stage of disease, location, or income. 

Global HIV/AIDS Statistics

Since it was identified in 1981, HIV has been attributed to the deaths of over 30 million people worldwide. Globally, there are more than 35 million people living with HIV today, 69% of whom are in sub-Saharan Africa.

In the U.S., approximately 1.2 million people are infected with HIV, according to surveillance from the Centers for Disease Control and Prevention in Atlanta. Of these, 20-25% are estimated to be undiagnosed.

While expanded access to ART has profoundly lowered the rate of AIDS-related deaths, both in the U.S. and abroad, rates of new infection continue to rise in many high prevalence countries, including South Africa where the number of HIV diagnoses increased by 100,000 from 2010 to 2011 alone.

The WHO and United Nations have aimed to reverse that trend with the implementation of the 90-90-90 initiative, which targets the expansion of national treatment programs by:

  • confirming the HIV status of 90 percent of all people infected with HIV;
  • placing 90% on those confirmed on antiretroviral therapy, and;
  • ensure that 90% of those on therapy are able to achieve complete viral suppression.

By doing so, it is believed that the global infection rate could be slashed to as little as 200,000 infections by the target date of 2030.


National Institutes of Health (NIH). "Starting antiretroviral therapy early improves outcomes for HIV-infected individuals." Bethesda, Maryland; issued May 27, 2015.

May, M.; Gompels, M.; and Sabin, C. "Life expectancy of HIV-1-positive individuals approaches normal conditional on response to antiretroviral therapy: UK Collaborative HIV Cohort Study." Journal of the International AIDS Society. November 11, 2012; 15(4): 18078.

The INSIGHT START Study Group. "Initiation of Antiretroviral Therapy in Early Asymptomatic HIV Infection."New England Journal of Medicine.July 20, 2015; DOI: 10.1056/NEJMoa1506816.

Human Sciences Resource Council (HSRC). "South African National HIV Prevalence, Incidence and Behaviour Survey, 2012." Pretoria, South Africa; December 2014; accessed February 17, 2016.

United Nations Joint Programme on HIV/AIDS (UNAIDS). "Fast-Track: Ending the AIDS Epidemic by 2030. " Geneva, Switzerland; issued December 1, 2014.

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