What Causes HIV and AIDS (HIV and AIDS Facts)

Introduction of HIV

Human Immunodeficiency Virus, also known as HIV, is the causative organism. As the name acquired immunodeficiency syndrome suggests, it is a condition that weakens the immune system of the infected person and makes him or her susceptible to infections that most other humans can ward off. The disease starts to develop many years after the primary infection by the virus. By reducing the number of white blood cells, the immunity of the person keeps reducing. Since the disease does not develop any symptoms for a long duration, it is spread even more. When subclinical cases outnumber the clinical trials by a significant amount, the phenomenon is known as the iceberg phenomenon, of which AIDS is an example. People find out they are HIV positive either by chance testing or because of full-blown AIDS. This disease has a lot of stigmas attached to it, just like all the other sexually transmitted diseases, so it is essential to learn the social impact of the disease on the patient. Even though many governments around the world have implemented special laws to safeguard the rights of those who are HIV positive, social isolation continues. Even on a global scale, the WHO has implemented several programs which we will discuss in-depth in the following sections.

 

HIV AIDS

History of HIV

According to the timeline of events made by hiv.gov, the spread of disease in America started in the mid to late 1970s. The first case, however, was of a gay man, who reported shortness of breath and pneumonia-like symptoms. Even though he was given the best treatments at the National Institute of Health (NIH), he could not survive. A neoplastic condition known as Kaposi sarcoma was also found to be affecting people, with a predisposition to affecting the gay community. As information starts spreading in the gay community of the dangers of a new kind of pneumonia and cancer affecting them, more checkups and tests lead to the identification of more cases of immunodeficient individuals. Soon after, some babies of African American descent were found to have developed Kaposi sarcoma and Pneumocystis carnie pneumonia, which had now been identified to be related to each other as well as the immunodeficient state of the patients. As the spread of the disease began to enter into the population of a few hundred confirmed cases, the research of the disease also increased. Many people started to pitch in from doctors to ordinary members of the gay community to help spread awareness as well as to find out the cause of this horrible disease. The Kaposi sarcoma research and education foundation was started in San Francisco, which would later become the San Francisco AIDS Foundation. A name for the disease was finally found, Gay-related Immunodeficiency Disease (GRID). On September 24th, 1982, the disease was given its current name of Acquired Immuno Deficiency Syndrome.

Rules are made for medical personnel to follow during procedures to prevent further spread of the disease. But the disease had now found another way to spread and torment the human population, using blood transfusion. San Francisco slowly became the forefront of the war against AIDS, building the first AIDS outpatient department, dedicated to these specific patients. The guidelines used by physicians and medical personnel at the time are still being held as the gold standard in HIV and AIDs care. The first cases of female AIDS start being reported shortly thereafter, leading to widespread terror, as people previously thought this was just a disease of the gay community. The political parties are slowly cornered, by candlelight vigils and AIDS patient articles, to sanction a sum of 12 million dollars to the U.S. Department of Health and Human Services.

Meanwhile, the Pasteur Institute, one of the most legendary institutions, known to be the forefront of the war against disease, shows that a retrovirus is the cause of this debilitating condition. The discovery is made by Dr. Françoise Barré-Sinoussi and her colleagues, who were awarded the Nobel prize for her contribution along with Dr. Luc Montagnier in 2008. The Denver principles were also agreed upon at this point, leading to the establishment of the core values of the National Association of People with AIDS. As the progress was being made in the field of AIDS research, a New York physician Joseph Sonnabend was evicted by his landlord for treating AIDS patients, and this leads to the first of many AIDS discrimination lawsuits. The Margeret Heckler and colleagues concluded that AIDS was indeed caused by a retrovirus named HTLV. A diagnostic kit was also made based on the technique of ELISA. Rock Hudson was the first celebrity to confess that he had AIDS, and this confession sparked a discussion in the media about AIDS as well as its impact on society, not only the gay community, bringing AIDS into the mainstream media. The subsequent exposure to HIV given by Princess Diana and President Ronal Raegan helps to bring it to the public eye and promote its research.

 

Microbiology

The disease is caused by the Human Immunodeficiency Virus, which is a member of the family Retroviridae and genus Lentivirus. It is of two types, HIV-1 and HIV-2, both are antigenically and genetically distinct. There exists a similar virus, causing immunodeficiency syndrome in primates, known as the Simian Immunodeficiency Virus or SIV. Retroviruses can transform their genetic material from DNA to RNA by means of an enzyme specific to their family, known as reverse transcriptase. HIV has a spherical outer coat made from proteins and an inner core containing inside it, the genetic material as well as a few enzymes of the organism. The outer coat is made up of lipids and a trimeric envelope protein known as GP 120. The GP 120 is held at their place by another trimeric protein, known as GP 41, a transmembrane protein. The presence of envelope proteins is an indicator of the maturity of the virus. Inside the outer envelope, there exists an inner capsid composed of p17 proteins. The core lies still deeper and is made up of p24. The genetic material of the virus is composed of two single-stranded RNA molecules. There are several genes that grant HIV structural as well as functional components. These include gag, pol, and env, which all code structural components of the virus and others such as tat, rev, vif, vpx, etc., which code for other components.

HIV is a highly mutable virus and thus exhibits frequent antigenic variation, which includes variations in nucleotide sequences, cell tropism, variation in growth patterns, and cytopathology. The reason behind this is that the conversion of RNA to DNA has to take place for the functioning of the virus. Many errors may occur in this process. It was found that some strains, isolated from West Africa in 1986, reacted very weakly with type 1 antisera. They were named HIV type 2. Type 2 resembles type 1 genetically up to 40% and resembles more with simian immunodeficiency virus than to HIV 1. Thus there exist two principle types of antigenic variants of HIV, HIV-1, and HIV-2. These antigenically distinct structures allow us to identify the origin of the infection to an extent, as different types are predominant in different regions of the globe. Although HIV type 1 and related strains are prevalent all over the world, HIV type 2 is largely confined to West Africa and western and southern India. This fact can help us to make an approximate guess along with the patient’s travel history if the HIV case was indigenous or it was contracted elsewhere.

TIV 1 and 2 are then further divided into many subtypes based on the sequence of gag and env genes. There are at least ten subtypes of HIV 1 strain. Subtype A is the most commonly found virus globally, while Subtype B is prevalent in America and Europe. Subtypes vary in terms of their frequency of transmissibility by various routes like subtypes found in Asia. And Africa is more easily transmitted by heterosexual contact than American strains, which preferably transmitted by blood and homosexual intercourse.

Since HIV holds such a strong social and psychological impact on the life of an individual, before performing any laboratory investigation, written consent must be taken, and the details of all the tests to be performed must be given to the patient. Positive reports of the test should be kept confidential, and words like ‘HIV positive’ should not be mentioned. After the outcome, counseling should be done to encourage patients to talk about the disease to family and close contacts.

There exist various screening tests, like antibody detection, where the anti-HIV antibody is identified, it is one of the most important ways to diagnose the disease. ELISA(Enzyme-linked Immunosorbent assay is most commonly performed for the screening tests in blood banks and tertiary care centers. It takes about 2-3 hours to complete and thus can be used for quick results. Rapid/simple tests, however, take this a step further and require only about 30 minutes to perform the test, hence the name. They are based on principles like dot blot assays, immunochromatography, or particle agglutination assays.

Screening tests cannot, however, be assumed to be confirmatory, as they have a significant margin of error, along with many false positives and false negatives. Supplement Tests are needed for the identification of cases that are more likely to lead to. Thus they are done after screening tests to validate positive results of Screening tests. They are basically a method to detect antibodies specific to HIV. This includes western blot, which is based on the principle of the immunoblot technique. It helps in the detection of individual antibodies against various antigenic fragments of HIV.

Confirmatory tests are conducted to answer the question of the presence or absence of disease in the individual beyond a doubt. This is done by the identification of a viral structure from the blood of the patient. Viral core p24 detection is one such test in which p24 antigen is detected in the serum of the patient with 1-2 weeks of infection. The antigen usually persists for about 3-4 weeks. Viral RNA detection is the gold standard for confirmation of HIV, as it is the most specific and sensitive method among all the methods present. It is beneficial even for the detection of HIV in the window period. DNA PCR is a confirmatory test for the diagnosis of pediatric HIV. DNA PCR plays an important role as it detects the proviral DNA and also differentiates latent HIV infection from active viral transcription. Certain biomarkers even hint towards the state of the patient like the CD4 T cell count. This is done by flow cytometry, and it helps us in the detection of opportunistic infections and helps us decide whether or not to start antiretroviral therapy. CD4 T cell count below 350cubic mm indicates the need to start ART. The presence of certain abnormal proteins like neopterin, beta 2-microglobulin, and soluble IL-2 receptor also indicates disease, as they are secreted by mononuclear cells, which are stimulated by cytokinins secreted by activated helper T cells.

 

Epidemiology of HIV

HIV was recognized as an emerging disease in the early 1980s. Evolved from a mysterious disease to a global pandemic infecting millions of people. A total of 37. 9 people globally were living with HIV by the end of 2018, which compromises adults (29.6 million-41. 7 million) and children(<15 years) counting around 1.3 million to 2. Million. Noticeable development has been seen in the past few years in global efforts to address the AIDS epidemic by improvement in access to effective medicines and specific prevention programs.

According to data, 24.5 million [21.6 million–25.5 million] people were accessing antiretroviral therapy end of June 2019. But as people diagnosed with the disease are increasing at an alarming rate as well as the number of deaths due to AIDS. According to UNAIDS 770, 000 [570 000–1.1 million] people died from AIDS-related illnesses (end 2018), particularly Eastern Europe and Central Asia.

WHO and UNAIDS defines HIV epidemics in different types.

1. Low-level epidemics:

though HIV may have existed for years, it has never spread to substantial levels in any subpopulation. Infection remains confined to high-risk populations like sex workers, male homosexuals, drug abusers. NUMERICALLY there has never been a record of HIV prevalence of more than 5%.

2. Concentrated HIV epidemics:

“HIV has spread in a particular subpopulation but is not well established in the general population. It indicates an active network of risk within sub-population. Numerically there is a consistent prevalence of over 5% in at least one defined Sub Population but not more than 1% in pregnant women in urban areas.”

3. Generalized HIV epidemics:

When HIV has been established in the generalized population. Though Subpopulation being on high-risk sexual networking in the general population helps in maintaining an epidemic independent of sub-population. The prevalence of the disease is more than 1% of pregnant women.

The spread of new infections is mostly in heterosexuals, although risk factors are a lot. 74.9 million [58.3 million–98.1 million] people have become infected with HIV since the start of the epidemic (end 2018). Since 1997 there has been a significant reduction of 40% new cases of HIV infection.

“In 2018, around 1.7 million [1.4 million–2.3 million] were newly infected with HIV, compared to 2.9 million [2.3 million–3.8 million] in 1997. Since 2010, new HIV infections have declined by an estimated 16%, from 2.1 million [1.6 million–2.7 million] to 1.7 million [1.4 million–2.3 million] in 2018.Since 2010, new HIV infections among children have declined by 41%, from 280 000 [190 000–430 000] in 2010 to 160 000 [110 000–260 000] in 2018.” (graph)

32.0 million [23.6 million–43.8 million] people have died from AIDS-related illnesses since the start of the epidemic (end 2018). These huge mortality figures are attributed to the progression of the disease because a large population, i.e., around 8.1 million people, did not know that they were living with HIV. However, 79% [67–92%] of all people living with HIV knew their HIV status. Social stigma prevents a lot of infected individuals from coming forward for therapy. This prevents an accurate estimation of the actual figures. Multiple sex partners and homosexual tendencies are linked as risk factors for the disease, making it more of a social pariah.

Despite knowing their status of the disease, only 78% [69–82%] were accessing treatment, and among people accessing treatment, 86% [72–92%] were virally suppressed.

Survival in AIDS is highly dependent on whether the patient is taking treatment or not. Certain Government organizations and the efforts of NGOs have made it possible to easily access good quality treatment to a vast majority of patients. Though the prognosis in the disease is not good if treatment is started at an early stage, then it can be beneficial. Stats issued by government authorities are quite promising, but full coverage of the patients is still a goal to achieve. As time has passed, patient coverage has significantly increased.

“In 2018, 62% [47–74%] of all people living with HIV were accessing treatment. In 2018, 23.3 million [20.5 million–24.3 million] people living with HIV were accessing antiretroviral therapy, up from 7.7 million [6.8 million–8.0 million] in 2010.”

As of the end of June 2019, 24.5 million [21.6 million–25.5 million] people were accessing antiretroviral therapy.

The figures even vary in the different age groups receiving treatment. (As 62% [47–75%] of adults aged 15 years and older living with HIV had access to treatment, and 54% [37–73%] of children aged 0–14 years had to access to treatment. 68% [52-82%] of female adults aged 15 years and older had access to treatment. However, just 55% [41-68%] of male adults aged 15 years and older had access. Further talking about HIV in pregnancy 82% [62– >95%] of pregnant women living with HIV had access to antiretroviral medicines to prevent transmission of HIV to their child in 2018.) (graph)

When deprived of treatment, there is no chance of resolution of the disease on its own, as the virus continues to grow and divide in the macrophages and continues to weaken your immune system. Gradually virus starts destroying The helper cells, but if treatment is given at an early stage, then infection is restricted. Death due to AIDS has been reduced significantly by more than 56% since the peak in 2004. Further statistics us that the number of people dying due to this disease has decreased in the past two decades. As in 2018 around 770, 000 [570 000–1.1 million] people died due to infection of HIV as compared to 1.7 million [1.3 million–2.4 million] in 2004 and 1.2 million [860 000–1.6 million] in 2010. In terms of percentage, there has been a reduction in AIDS-related mortality by more than 33% since 2013.

 

Immune Physiology

To understand how HIV infects the human body and breaks down the immune system, we must understand how the normal immune system is built. There exist millions of cells in the human body. One of them, responsible for the immunity of the individual, is known as the white blood cell. There are many types of white blood cells, named according to the tendency to take up the stain. They are (1) Neutrophils (2) Basophils (3) Acidophils (4) Lymphocytes. All of these cells arise from the bone marrow and slowly differentiate into mature, antigenically specific white blood cells. Some lymphocytes undergo maturation and differentiation at the level of bone marrow itself. These are known as B-lymphocytes. Some of the lymphocytes move to the thymus gland and mature at that location, known as T lymphocytes. The T lymphocytes are of different types, Helper T-cell, Cytotoxic T-cell, and Suppressor T-cell. Each of these cells has different markers, and CD8+ are known as Cytotoxic T-cell, while CD4+ are known as Helper T-cell.

 

Pathology of HIV Infection

When infected by the virus, the gp120 act as anchors and attach to the cell, the rest of the virus enters the cell while the envelope sticks to the surface of the cell. The virus starts synthesizing more proteins once inside the Helper T-cell. The gp120 proteins are accumulating on the surface of the cell, and when this cell comes in contact with another Helper T-cell, it joins to it completely. The larger fused T cell formed has gp120 on is surface and keeps fusing with other helper T-cells until its size is large enough to burst, leading to the death of all the fused cells. As the number of T cells keeps fallings, the body is unable to keep a memory of the diseases it has once faced. This leads to reduced responses against each of them. Many of the commensal organisms and other organisms that are ordinarily kept at bay by our immune system then gain the upper hand and can invade the patient’s body, causing diseases.

The disease occurs in stages. The first phase is known as acute HIV disease or acute retroviral syndrome. After getting infected with HIV, it is carried to the lymph nodes and other lymphoid tissues. The virus multiplies and starts destroying the infected T cells, spilling over into the bloodstream, causing the acute mononucleosis-like syndrome. There is a significant reduction in the number of CD4 T cells during this stage. This is followed by the asymptomatic stage, which starts in one month of the infection. An optimum immune response is developed as a result of which viremia drops and CD4 count becomes normal. Though the infection becomes clinically latent, this is not microbiological latency, as immune response cannot completely clear the infection as the virus remains inside lymph nodes multiplying frequently. The latency period is not fixed and may last for ten years but varies from a few months to 30 years. When latency breaks, the disease manifests rapidly. And if therapy is not given, death occurs within two years. This is known as symptomatic HIV infection (AIDS-related complex, ARC), and it is the period in which CD4 T cells level begins to fall. Gradually patient develops symptoms such as unexplained diarrhea for more than one month, weight loss, opportunistic infection gradually leading to advance stage called AIDs characterized by a CD4 count below 200 cells/ul along with the destruction of lymphoid tissue and replacement by fibrous tissue. At this point, opportunistic infections take hold of the patient, and there is even the development of neoplasia, like Kaposi’s sarcoma.

 

Clinical Diagnosis: Since HIV can have a wide array of symptoms, it becomes very difficult to pinpoint the development of the disease in the individual. This made it imperative to develop a set of parameters for classification in the people as having or not having AIDS. One of the most accepted classifications given was the CDC classification system. Based on the clinical examination of the patient as well as the current CD4 T cell count, the patients were classified into three categories, A, B, and C. The division into various categories was based on the presence or absence of a set of symptoms along with HIV positivity on tests. If an HIV positive subject was asymptomatic, had persistent lymphadenopathy all over the body or had a history of acute HIV infection and no other symptom, he/she was classified as category A. Category B subjects have symptoms of a weakened immune system with diseases like bacillary angiomatosis, candidiasis – oropharyngeal or vulvovaginal, herpes zoster or listeriosis. Such diseases are not found in people with competent immune systems, rather limited to these individuals. They can also present with noninfectious diseases like fever or diarrhea for more than a month, idiopathic thrombocytopenic purpura, pelvic inflammatory disease, or peripheral neuropathy. Symptoms of neoplastic and dysplastic conditions such as cervical dysplasia or cervical carcinoma in situ can also be found in such patients. Category C contained most of the diseases that constitute the AIDs related complex, which include a wide array of diseases that assure us of the complete incapacitation of the immune system of an individual. A detailed list of these conditions is beyond the scope of this article.

The World Health Organisation also recognized the lack of a guideline to diagnose AIDs patients and developed a detailed classification fo both adults as well as children. The classification is made such that it is solely based on the clinical evaluation of the patient, allowing facilities lacking in proper cell counting units to be able to diagnose and classify the disease. The patients are classified into four categories based on the clinical examination, which are Clinical stage 1, 2, 3, and 4.

 

Clinical stage 1: For both adult as well as young patients, this phase represents an asymptomatic period, accompanied by generalized lymphadenopathy in some individuals.

 

Clinical stage 2: For adults, this stage represents a condition where the individual faces weight loss without any attempt to do so, along with an array of skin and mucosal diseases. A list of these skin-related diseases includes herpes zoster, angular cheilitis, papular pruritic eruption, fungal nail infections, and seborrhoeic dermatitis. The mucosa of the individual is also infected, leading to diseases such as recurrent oral ulceration, sinusitis, tonsillitis, otitis media, and pharyngitis. For children, the weight loss criteria are replaced by idiopathic hepatosplenomegaly, and a few skin and mucosal diseases are added to the diagnostic parameters. These include linear gingival erythema, extensive wart virus infection, and molluscum contagiosum. The child may also present with idiopathic parotid enlargement.

 

Clinical stage 3: This stage shows similar patterns in both adults and children with minor differences. The diseases found in both the adult and child affected by this stage are persistent oral candidiasis, oral hairy leukoplakia, pulmonary tuberculosis, severe bacterial infections and acute necrotizing ulcerative stomatitis, idiopathic chronic diarrhea for more than a month(for adults) or 14 days (for children), idiopathic fever for more than a month, unexplained anemia, thrombocytopenia, and neutropenia. The specific findings in adults are unexplained weight loss (>10% body weight), giving the disease a nickname, Slim’s disease. The specific findings in children include unexplained refractory malnutrition, lymph node tuberculosis, symptomatic lymphoid interstitial pneumonitis, and HIV associated bronchiectasis.

 

Clinical stage 4: Similar to stage 3, most of the symptoms are shared between adults and children. The symptoms are, HIV wasting syndrome, pneumocystis pneumonia, recurrent severe bacterial, chronic herpes simplex infection, oesophageal candidiasis, extrapulmonary tuberculosis, Kaposi’s sarcoma, cytomegalovirus infection, central nervous system toxoplasmosis, HIV encephalopathy, progressive multifocal leukoencephalopathy, extrapulmonary cryptococcosis, chronic cryptosporidiosis, disseminated nontuberculous mycobacterial infection, chronic isosporiasis, disseminated mycosis, lymphoma (cerebral or B-cell non-Hodgkin), etc. This stage is known as Full-blown AIDs. 

 

Pharmacological Management of HIV

The pharmacological management of AIDs is by the use of antiretroviral therapy, known as ART. Since the advent of this therapy, it has become possible for people living with HIV to able to live virtually symptom-free lives. This is the reason for the call to widen the distribution of the drugs and to do so at the lowest prices possible. The new developments in the field of pharmacology have paved the path for the completion of this goal. The study of drugs, along with an in-depth analysis of the adverse reactions that the drugs are capable of producing, has led to the new and comprehensive dosing regimen.

The dosing regimen followed currently consists of a combination of many types of drugs:

1) Nucleoside Reverse Transcriptase Inhibitors (NRTI): Drugs that contain nucleosides that inhibit the enzyme Reverse Transcriptase and prevent the replication of the virus. These are Abacavir, Emtricitabine, Lamivudine, Tenofovir Disproxil Fumarate, and Zidovudine. Each of these drugs has an abbreviated form, which is used regularly in clinical practice as well as scientific publications. Abacavir – ABC, Emtricitabine – FTC, Lamivudine – 3TC, Tenofovir Disoproxil Fumarate – TDF, Zidovudine – AZT, ZDV.

2) Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI): Drugs that contain proteins that inhibit reverse transcriptase enzyme by binding to it and preventing its binding to the single-stranded RNA molecule. These drugs include Doravirine – DOR, Efavirenz – EFV, Etravirine – ETV, Nevirapine – NVP, Rilpivirine – RPV.

3) Protease Inhibitors (PI): It includes drugs that inhibit the protease enzyme responsible for the construction of the protein coat of the core of the virus. These are Atazanavir – ATV, Darunavir – DRV, Fosamprenavir – FPV, Ritonavir – RTV, Saquinavir – SVQ, Tipranavir – TPV.

4) Fusion Inhibitors (FI): This drug prevents the fusion of the virus and the T- helper cells. Only one drug constitutes this class, Enfuvirtide – T-20.

5) CCR5 antagonists: These drugs block the function of CCR5, which are receptors that are needed for the proper fusion of the virus with the CD-4 +ve helper T cells. This class also only has one drug, Maraviroc – MVC.

6) Integrase inhibitors: Integrase is an enzyme responsible for the binding of the DNA strand, formed from the RNA strand after the action of reverse transcriptase, to the DNA of the helper T cell. Its presence is important for the replication of viral DNA. These drugs include Doltugravir – DTG, and Raltegravir – RAL.

7) Post attachment inhibitors: These are monoclonal antibodies which bind to receptors present on the surface of CD4 helper T cells and inhibits the fusion of two cells together.

These drugs are given in various combinations and regimens, which are beyond the scope of this article as there are many intricacies to the actual prescription to keep in mind.

 

Prevention of HIV

Even though we have come a long way towards making this debilitating disease a treatable one, it remains one of the foremost threats humanity faces today. The drugs may help to keep the individual asymptomatic, but they do take a toll on the patients’ health. Thus still in this day and age, we have to follow the age-old adage of “prevention is better than cure”. The prevention of HIV is based on the principle that exposure to HIV positive blood or body fluids is the main cause of transmission, other than the parent to child transmission. Thus to prevent HIV, we must prevent the exposure of HIV positive bodily fluids, like blood, semen, vaginal secretions, etc. This can be done by the use of condoms, preventing the use of intravenous drugs, checking for contamination in donated blood, preventing exposure to multiple sexual partners, etc.

For prevention of HIV infection, providing sex and health education to students, drivers, sex-workers, and all common people is necessary. One should avoid indiscriminate sex, and the use of condoms and femidoms should be encouraged. People should be guided to follow healthy habits like not share personal things like Razors, toothbrushes, towels, and undergarments. Both clinicians and patients/ addicts should avoid the sharing of needles and syringes. Women suffering from AIDS and those who are at high risk should avoid pregnancy as the newborn may also acquire the infection from mother.

One of the major ways of transmission of infection is Blood and sperm donation and also the body tissue and organ transplantations. So, proper sterilization methods are needed to prevent the infection, eg.

  1. ALL blood should be screened for HIV 1 and HIV 2 infection before transfusion.
  2. Hemophiliacs can be prevented from infection by introducing heat treatment of factor 8 and 9.

In the end, all sources of communication and media should be actively involved in educating the people about HIV infection, its nature, mode of transmission, and its methods of prevention.

 

References

German Advisory Committee Blood (Arbeitskreis Blut), Subgroup’ Assessment of Pathogens Transmissible by Blood’ (2016). Human Immunodeficiency Virus (HIV).

 

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