AIDS

General Goal: To know the major causes of this disease, how it is transmitted, and understand the basic processes that result in  the progression from HIV infection to AIDS.

Specific Educational Objectives: The student should be able to:

1. recite the most likely causes of HIV/AIDS and how this viral infection is usually acquired in the United States (modes of transmission for females and males are different).

2. describe how the virus attaches to human cells. Also know the human cell receptors that the virus attaches to (hint: M-tropic vs. T-tropic viruses).

3. describe the three different HIV/AIDS disease stages and what happens to the immune system during those disease stages.

4. describe the various means of diagnosing HIV/AIDS and when to use which test. You should also know CDC's definition for AIDS.

5. list the most common opportunistic infections that occur in HIV/AIDS patients.

5. describe the basic treatment regimen (HAART).

6. list ways of preventing HIV infections (hint: how do you prevent congenital infections?)

Reading: C.P. Conlon and D.R. Snydman, Mosby's Color Atlas and Text of Infectious Diseases. Mosby, 2000. Chapter 13, pp. 202-210.

Lecture: Dr. Neal R. Chamberlain

References: 

1. A wonderful and informative website to visit is from Johns Hopkins Medical Center Called "The Body". Go there you will learn alot!
2. Good article at Webpath on HIV and AIDS.
3. An extensive review of HIV/AIDS vaccines and the basic science findings: NIH-Funded AIDS Vaccine Research: A Critical Review by Gregg Gonsalves. For recent updates on vaccines go to http://www.niaid.nih.gov/daids/vaccine/statuslinks.htm
4. Chen RY, Kilby JM, and Saag MS. Enfuvirtide. 2002 Expert. Opin. Investig. Drugs. Dec;11(12):1837-43.

"The reality of AIDS in Botswana is so grim it is hard to grasp. In the main hospital in the capital city, Gaborone, 70% of beds in the pediatric ward are for children with complications of AIDS. The medical ward varies from 60-80%. Sometime this year, it is projected we will have 70,000 orphans, in a country with a population of 1.5 million people. One village of 30,000 people recently had 42 funerals in one weekend, with people having to choose whose funeral they would attend. Yet in that same village, a once-thriving orphan-care program struggles for funds, even for food for the children being cared for. One grandmother has lost all her siblings and their partners, leaving her with more than 20 young children to care for. This is in a society that used to care for its elderly within the extended family. True infection rates are closer to 30% (as reported in the January 17 issue of Newsweek), with most infections in the 15-49 age group. Life expectancy has dropped from 67 years to somewhere around 50 years, and is expected to drop as low as 40 years during the next ten years." (AIDS Survival News; A Letter from Africa. A First-Hand of Account of How AIDS Has Affected the People of Botswana By H. Ruth Thiessen; http://www.thebody.com/asp/apr00/africa.html)

Human immunodeficiency virus (HIV) types 1 and 2, human retroviruses, lentivirus subfamily. HIV is the  causative agent of AIDS. The most common type is HIV-1 and is the infectious agent that has led to the worldwide AIDS epidemic. HIV-2 infection is less common and less virulent, but results in AIDS as well.

EPIDEMIOLOGY

AIDS was first recognized in 1981, although retrospective studies suggest that cases occurred in Africa in the 1950's and in the U.S. by the 1970's.

Currently, two principal genetic groups of HIV-1, designated M (main) and O (outlier), have been identified. Genetic group M  is highly prevalent and is further classified into 10 established envelope subtypes, A through J. HIV-1 subtype B predominates in Europe and the Americas, whereas HIV-1 subtype C predominates sub-Saharan Africa. Mosaic forms, which combine the genetic material from two distinct subtypes, have also been identified.
 

In contrast to HIV-1 infection, which has spread through all continents, HIV-2 is primarily restricted to West Africa and to population movements from or through this region. HIV-2 strains are classified into five subtypes, A through E; only subtypes A and B viruses are predominant.

Transmission: Other inflammatory STD's enhance HIV transmission. These infections include syphilis, gonorrhea, genital herpes, etc.

Infection is aided by Langerhans cells in mucosal epithelial surfaces which can become infected. Infection is also aided by the presence of other sexually transmitted diseases that can produce mucosal ulceration and inflammation. The CD4+ T-lymphocytes have surface receptors to which HIV can attach to promote entry into the cell. The infection extends to lymphoid tissues (MALT) which contain follicular dendritic cells that can become infected and provide a reservoir for continuing infection of CD4+ T-lymphocytes.

Transmission is intracellular: HIV transmission most likely requires HIV-infected cells, such as macrophages, lymphocyte or spermatozoa, which enter the body through microabrasions of the mucous membranes or through penetration of the skin with a needle.

Transmission via free virus appears to be unlikely.

Modes of transmission:

• sexual contact (heterosexual (most common means in the world) and homosexual)
• blood or blood product transfusion (before routine testing)
• transplanted tissue (before routine testing)
• IV drug use with shared needles
• transplacental (in utero) or by perinatal infection of neonates (breast milk).

About 33.4 million people are infected with HIV/AIDS, worldwide (1999). The highest rates of infection are in sub-Saharan Africa where 1 in 20 men and 1 in 20 women are estimated to be infected.

In the United States, AIDS is the 5th leading cause of death in people 25-44 years of age. 753,907 cases of AIDS have been reported since 1981; CDC). There are 120,223 patients living with HIV infection in the U.S. (2000; CDC). 311,701 people are living with AIDS in the U.S.. 438,795 people have died of AIDS in the U.S. (before 1981-2000; CDC). 21,016 new HIV infections were diagnosed in 2000 (33% female; 67% male; CDC). 43,293 new cases of AIDS were diagnosed in 2000 (CDC).

Deaths due to AIDS:
1993= 45,381
1994= 49,869
1995= 50,610
1996= 37,787
1997= 21,923
1998= 17,930
1999= 16,273

High risk populations (1999; CDC):

Geographic distribution: most AIDS cases in the U.S. occur in the most populous states and cities.

Figure 1. Female adult/adolescent annual AIDS rates per 100,000 population, for cases reported July 1999 through June 2000

Figure 1. Male adult/adolescent annual AIDS rates per 100,000 population, for cases reported July 1999 through June 2000

HIV must bind two surface proteins to infect a cell, CD4 and CXCR4 (formerly known as fusin), or CCR-5.

If CD4 and CXCR4 are used, the HIV virus is T-tropic. T-tropic viruses are transmitted via blood and blood products. They are syncytia-inducing viruses and infect T-cells.

If the HIV virus binds to CD4 and CCR-5, it is M-tropic. M-tropic viruses are transmitted via sexual contact. They are not syncytia-inducing viruses and infect macrophages and T-cells.

A pool of latently infected CD4+ T cells during the very earliest stages of acute HIV infection are infected by the virus. These infected cells are able to persist in the patient's body for extremely long periods of time (several years).

CD8+ cells promote CD4+ cell death when the T-tropic viruses start binding to CXCR4 on the CD8+ cells and with help from macrophages triggering apoptosis in CD4+ cells.

CD4+ cells are major targets for HIV, i.e., T helper lymphocytes, monocytes, neurons.

gp120: HIV recognizes and binds to the CD4 molecule via viral envelope glycoprotein gp120, and then binds to CXCR4 or CCR-5. A "schematic drawing" of gp120 binding to the receptors.

Viral reverse transcriptase produces complementary DNA using the viral RNA template.

Provirus: Viral DNA is transported into the nucleus and is integrated into the chromosome (now called a provirus), where it instigates cytopathic viral production or possibly effects programmed cell death in non-infected cells. Diagram of virus "life cycle".

Stage I: acute viral infection

• Incubation period of 1-3 weeks
• no symptoms, or any or all of the following "mononucleosis-like symptoms":
• fever, headache
• sore throat
• malaise - myalgia, arthralgia
• lymphadenopathy
• hepatosplenomegaly
• meningitis,
• encephalitis rash - small pink papules or macules over much of the body

Stage II: completely asymptomatic

Lasts for 6 or more years in 65-85% of cases.

Patients produce large amounts anti-HIV antibody

HIV is detectable in blood, semen, and cervical secretions.

New PCR procedures show that as many as 1 in 10 peripheral CD4+ cells are infected.

HIV-antibody-complement complexes are trapped in lymph nodes, tonsils, spleen, etc. by follicular dendritic cells (FDC).

CD4+ T cells disappear from the blood because they are sequestered in the lymph nodes (numbers are 5-10X higher than in the peripheral blood)

Follicular Dendritic Cells (FDC) facilitate HIV transmission to uninfected T cells.

When peripheral CD4+ cells number 500-200/µl, the FDC are dying and the internal structure of the lymph node is breaks down; HIV spills over into the blood.

Stage III: overt disease

Severity is directly related to the decline of CD4+ T cells, which causes diminished function by TC, B cells (hypogammaglobinemia), macrophages and NK cells, and leads to opportunistic infections and spontaneous neoplasms.

The individual has a chronic lifelong infection.

RT-PCR= Reverse Transcriptase-Polymerase Chain Reaction

1. p24 antigen= this antigen is produced early in infection and is present in the patient's bloodstream. It is useful in detecting very recent infections and in detecting HIV infection in neonates of HIV infected mothers. Serological tests can not detect recently infected individuals.
2. Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) to detect HIV RNA in plasma. To determine the presence of the HIV genome during the first 2-4 weeks of infection, when patients may be seronegative and yet are infective. It is also useful in detecting HIV infection in neonates. Now used in determining effectiveness of treatments. In concert with CD4 cell counts PCR helps in determining a patient's prognosis.

1. Enzyme Linked Immunoabsorbent Assay (ELISA) A screening test for antibody reactive with HIV proteins. ELISA for HIV-1 or HIV-2 antigens then a Western blot is performed for a definative diagnosis of HIV infection. Antibody specific for HIV gp120 or gp160 (detectable within 4-8 weeks post-exposure). However in 5% of the patients antibodies may not be detectable for 6 months or more.
2. Immunoblotting or Western blotting To determine the presence of HIV-specific antibody. To confirm positive ELISA tests.
3. Latex-agglutination assay (coated with HIV antigen) To determine the presence of HIV-specific antibody. A new screening test which is quicker than the ELISA.
4. Immunofluorescence

• fever
• malaise
• lymphadenopathy
• hepatosplenomegaly
• arthralgias

rash

AIDS-related complex (ARC)

• fever - role for TNF, IL-1
• fatigue
• diarrhea
• weight loss
• night sweats
• immunological abnormalities

• dementia
• spontaneous neoplasms

Skin. Among the earliest observed AIDS-related conditions occur as infectious or noninfectious skin eruptions.

Fungal infections: Mucosal candidiasis and Thrush (white, non-adherent plaques and erythema)

Intertriginous cutaneous candidiasis

Paronychia Dermatophytosis - Tineas: pedis, cruris, corporis; due to Trichophyton rubrum;

Onychomycosis Disseminated fungal infections showing early skin lesions

Cryptococcus neoformans - meningitis

Histoplasma capsulatum - in endemic areas; pulmonary and renal failure

Sporothrix schenckii -

Viral infections: Herpes simplex non-healing ulcers; genital, perioral, perianal; perform the Tzanck test

Varicella zoster reactivation within the dorsal root ganglion

Molluscum contagiosum (pox virus agent) - umbilicated, skin-colored papules on the face or trunk, confused with acne, sebaceous hyperplasia, disseminated cryptococcosis, and basal-cell carcinoma.

Warts - pre-existing skin and genital warts become difficult to treat

Oral hairy leukoplakia - whitish, corrugated or hairy, adherent plaques, lateral margins of the tongue

Cytomegalovirus - nonhealing perianal or anal ulcers

Bacterial infections: Staphylococcus, Streptococcus, Haemophilus, Pseudomonas: folliculitis, impetigo, cellulitis

Syphilis - rapidly progressing to tertiary syphilis; secondary syphilis may be seronegative; test individuals showing a papulosquamous rash with RPR and/or a silver stain of a skin biopsy

Mycobacterium tuberculosis and avium-intracellulare skin lesions at the site of injections

Noninfectious inflammatory diseases: Seborrheic dermatitis - most common cutaneous manifestation; 3% of the general pop., 85% of the HIV+ pop.; often associated with Malassezia furfur

Psoriasis - exacerbation of existing conditions

Other inflammatory dermatitis - scabies, atopic dermatitis

Malignant neoplasms of the skin: Kaposi's sarcoma - pink to red to purple to brown, anywhere on skin; (1984) HHV8 also called Kaposi's sarcoma herpes virus (KSHV) has a causal role; treatment may not affect survival

Lymphoma - Hodgkin's, non-Hodgkin's, Burkett, etc

Invasive cervical cancer

Other cutaneous manifestations: Epithelioid angiomatosis - violaceous papules and nodules resembling Kaposi's sarcoma

Hair changes - greying, hairline recession

Yellow nail syndrome

Lungs: May have multiple infections.

Pneumocystis carinii: pneumocystosis - damaged alveoli with cyst production.

This airborne fungus is often acquired in childhood as evidenced by specific antibody. Latent infections are reactivated in adults with a severe T-cell deficiency or in children with a moderate T-cell deficiency. Shortness of breath, fever, weight-loss, dry non-productive cough, interstitial infiltrate in both lungs. P. carinii is identified by its characteristic morphology with a Giemsa stain of an induced sputum sample or a sample from a bronchial alveolar lavage; culture of this organism is difficult.

Cytomegalovirus: interstitial pneumonia

Cryptococcus neoformans pneumonia

Pulmonary tuberculosis

Recurrent pneumonia

Gastrointestinal tract.

Oral, anal, and esophageal inflammation

Herpes simplex virus;

Candida albicans: oral thrush and esophagitis;

Epstein-Barr virus: oral hairy leukoplakia

Severe diarrhea and malabsorption of food

Cryptosporidium (another picture of Cypto. and a fecal smear: acid fast stained)

Cytomegalovirus;

Isosporabelli

Mycobacterium avium and M. intracellulare

Lymph nodes. Lymphadenopathy or lymphadenitis

Cryptococcus

Mycobacterium spp.

Kaposi's sarcoma

Eyes. Retinitis and blindness cytomegalovirus

Brain. Toxoplasma gondii: toxoplasmosis Cryptococcus neoformans: chronic meningitis

Eradication of HIV infection cannot be achieved with currently available antiretroviral regimens therefore treatment to suppress the virus is lifelong. This is because a pool of latently infected CD4+ T cells during the very earliest stages of acute HIV infection persists with an extremely long half-life, even with prolonged suppression of plasma viremia to < 50 copies/mL. Treatment has resulted in substantial reductions in HIV-related morbidity and mortality. 

The primary goals of antiretroviral therapy are:

1. maximal and durable suppression of viral load,
2. restoration and/or preservation of immunologic function,
3. improvement of quality of life,
4. reduction of HIV-related morbidity and mortality. 

HAART (Highly Active Antiretroviral Therapy)- therapy, available since 1995, has resulted in durable antiviral responses that are being observed in an increasing number of patients. Many benefits of long term therapy are being reported. Successful HAART results in suppression of viral replication and halts damage to the immune system. It also partially restores the immune system leading to partial restoration of immune function. Clinical benefits accompanying these immunologic benefits include fewer opportunistic infections and longer life for the patients.

Conclusion: The amount of virus in the blood stream is significantly lowered and lowered for long periods of time in patients treated with all three drugs.

With the increased use of PI's the number of deaths due to AIDS can be dramatically reduced.

Classes of anti-retroviral drugs:

1. Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTI's)

NRTIs were the first group of antiretriviral drug approved for use in HIV/AIDS patients. NRTIs inhibit HIV's reverse transcriptase and can be placed within the viral DNA. When the NRTI's are placed in the viral DNA by the reverse transcriptase transcription of the viral genes is inhibited. This prevents virus multiplication and subsequent spread of the viral infection. Nucleosides require phosphorylation before they can affect reverse transcriptase activity. This phosphorylation occurs via host enzymes. The nucleotides are already phosphorylated and do not need to be activated to inhibit the viral enzyme.

2. Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI's)

These drugs also inhibit reverse transcriptase which prevents virus multiplication and spread. They do it in a slightly different fashion than NRTI's.

3. Protease Inhibitors (PI's)

HIV produces its own protease that is important in the production of infective viral particles. The protease cleaves the viral proteins to the correct sizes so that a mature viral particle can be formed (viral assembly). The protease inhibitors inhibit the retroviral protease from cleaving the viral proteins. These drugs help to slow the spread of the virus to other uninfected cells. Do not use protease inhibitors in monotherapy. HIV quickly becomes resistant to the protease inhibitors.

4. Fusion inhibitors: A new class of drugs is currently approved for use in AIDS patients. The drug Enfuvirtide [T-20, pentafuside, Fuzeon (trade name)], is a 36 amino acid peptide that mimics one section of gp41. This peptide inhibits virion-host cell fusion. Gp41 is essential in getting the HIV virion into the host cell. Refer to figure below.

With very few adverse reactions twice a day subcutaneous injections of Enfuvirtide resulted in significant reduction in viral load (about a 1 log reduction) at 24 weeks. This drug was recently (3/03) approved by the FDA for use in patients in the United States. This drug cannot be used alone it must be used with other anti-HIV drugs and is only recommended for patients with HIV-1 virus that is resistant to the other antivirals.

Another fusion inhibitor is also in the pipeline and should soon be approved by the FDA. It is a 39 amino acid peptide (T-1249) that binds to gp41 in a slightly different place than does Enfuvirtide

Click here for a list of currently approved drugs.  

The following information was taken from: Antiretroviral Therapy for HIV Infection in 1998; Updated Recommendations of the International AIDS Society–USA Panel.  ("JAMA". Vol. 280, pp. 78-86, Jul. 1, 1998.)

Early treatment of HIV infection has delayed the progression to AIDS. However, certain things should be considered as complicating this picture:

1. virologic response rates to initial therapy with a PI and 2 nucleoside reverse transcriptase inhibitors (nRTIs) range from 60% to 90% and success of initial therapy is less likely as the disease advances;
2. durability of viral suppression beyond 2 years is uncertain; however if viral titers increase studies have shown less opportunitic infections in people who remain on HAART.
3. close drug adherence is essential in preventing viral resistance, and current regimens are difficult;
4. drug interactions resulting from hepatic metabolism of PIs and nonnucleoside reverse transcriptase inhibitors (NNRTIs) increase therapeutic complexity;
5. impact of extended treatment on quality of life is a major consideration; and
6. new and long-term adverse effects are appearing, particularly with PI-containing regimens.

When Therapy should be Started:

There is growing consensus, as represented by recommendations of a Department of Health and Human Services (DHHS)-appointed panel, that early treatment initiation is associated with virologic, immunologic, and clinical benefits. The International AIDS Society–USA panel continues to recommend antiretroviral therapy for any patient with established HIV infection and a confirmed plasma HIV-1 RNA level greater than 5000 to 10,000 copies/mL who is committed to the complex, long-term therapy. Accumulating data show that viral load is a strong, independent predictor of clinical outcome. Degree and durability of virologic response correlate directly with plasma HIV RNA level and CD4+ cell count at baseline. Treatment options should be discussed with all patients with HIV infection.

Pretreatment plasma HIV RNA level and CD4+ cell count are important for evaluation of response to treatment. In general, prior to therapy initiation, 2 plasma viral load levels using the same technology and 2 CD4+ cell counts should be obtained at 2 separate visits, at which times drug therapy options, implications, and requirements are discussed and reviewed.

For asymptomatic patients with low plasma HIV RNA level (eg, <5000-10,000 copies/mL) and high CD4+ cell count (eg, >0.35-0.50 × 10⁹/L [350-500/µL]) deferral of therapy with close follow-up may be appropriate given treatment complexities, risk of adverse effects, consequences of resistance, and the possibility that such persons may fall into the category broadly described as long-term nonprogressor. For those with low HIV RNA level (eg, <5000-10,000 copies/mL) and low CD4+ cell count (eg, <0.50 × 10⁹/L and particularly <0.35 × 10⁹/L), therapy initiation is recommended, given independent prognostic significance of CD4+ cell count and clinical trial data support.

Another approach is to treat symptomatic patients and patients in category 3 (CD4+ cell count <200/ul). Encourage treatment for asymptomatic patients in category 2 and wait to treat asymptomatic patients in category 1.

Treatment guidelines can be obtained by clicking here.
 

Initial Antiretroviral Regimens:

The goal of antiretroviral therapy is to improve survival and decrease morbidity via continuous
maximum suppression of HIV replication. 

There are currently three types of combination regimens employed as initial treatment (no prior anti-retroviral therapy: 

1. NNRTI-based regimens (one NNRTI and 2 nRTIs) that are PI sparing (ex. efavirenz + zidovudine + lamivudine). A recent study, ACTG 384, indicates that certain combinations of these drugs are better in patients with no prior HIV treatment (Robbins GK et al. Comparison of sequential three-drug regimens as initial therapy for HIV-1 infection. N Engl J Med. 2003;349:2293-2303). Researchers in this study found that efavirenz (EFV) + zidovudine (AZT) + lamivudine (3TC) were the best at preventing treatment failure.
2. PI-based regimens that are NNRTI sparing (1 or 2 PIs + 2 or 3 nRTIs; ex. )
3. Triple nRTI regimens that are both PI- and NNRTI-sparing (ex. lopinavir/ritonavir + lamivudine + zidovudine)

Use of potent therapy has resulted in remarkable declines in hospitalization rates, morbidity, and mortality where the drugs are available. Furthermore, protease inhibitor (PI)-containing regimens can be cost-effective.

There are 20 approved antiretroviral drugs so far:

1. 8 nRTIs [abacavir, emtricitabine (FTC), zidovudine (AZT), didanosine (DDI), zalcitabine (DDC), lamivudine (3TC), tenofovir (disoproxil fumarate), and stavudine (D4T)]
2. 3 NNRTIs (efavirenz (EFV), nevirapine and delavirdine)
3. 8 potent PIs (amprenavir, atazanavir, fosamprenavir, ritonavir, indinavir, lopinavir/ritonavir, nelfinavir (NFV), and saquinavir [soft-gel capsule])
4. Fusion inhibitor (Enfuvirtide)

Monitoring Response to Therapy:

Plasma viremia is a strong prognostic indicator in HIV infection. The higher the levels of HIV RNA in the patient's bloodstream the worse their prognosis. HAART often leads to increases in the CD4+ T cell count of 100-200 cells/ml or more. CD4+ T cell responses are generally related to the degree of viral load suppression

Plasma HIV RNA assays of increased sensitivity, which have a dynamic range of about 20 to 50 to about 50,000 copies/mL of plasma should be used to determine success of treatment and treatment failures. Every 2 months plasma HIV RNA levels and CD4+ cell counts should be obtained. When CD4+ cell count decline occurs in concert with a rising HIV RNA level in an adherent patient, there is no question that treatment failure has occurred.

Treatment to reduce transmission of HIV-1 to infants born to pregnant women infected by HIV-1.

If a single dose of Nevirapine is given to mother during labor and a single dose of Nevirapine is given to the neonates after delivery in addition to the ZDV treatment above the rate of transmission of HIV to the infant decreased to about 1 percent (ZDV plus Nevirapine) verses around 6 percent (ZDV only). (Lallemant et. al. 2004. Single-dose perinatal nevirapine plus standard zidovudine to prevent mother-to-child transmission of HIV-1 in Thailand. N. Engl. J. Med. Jul 15;351(3):217-28).

Vaccines: No vaccine is currently approved by FDA. Clinical trials are currently being conducted with a number of different vaccines.