A person infected with the human immunodeficiency virus (HIV) is diagnosed with AIDS after developing one of the illnesses identified by the Centers for Disease Control as an indicator of AIDS. A person who is HIV-positive but has not had any serious illnesses can be diagnosed with AIDS based on certain blood tests (CD4+ counts).When HIV weakens the immune system, “opportunistic” infections can exploit this weakness and cause illness. A healthy immune system can easily control many of these illnesses. Being HIV-infected (being HIV-positive and having HIV antibodies in the blood) does not imply having AIDS.
Acquired immune deficiency syndrome
The first cases of acquired immune deficiency syndrome (AIDS) were reported in 1981, but it is now clear that the disease was present unnoticed for at least four years prior to its identification. The disease is distinguished by susceptibility to opportunistic pathogen infection or the occurrence of an aggressive form of Kaposi’s sarcoma or B-cell lymphoma, which is accompanied by a significant decrease in the number of CD4 T cells. Because it appeared to be spread through contact with bodily fluids, it was suspected to be caused by a new virus, and by 1983, the agent now known to be responsible for AIDS, known as the human immunodeficiency virus (HIV), had been isolated and identified. It is now clear that there are at least two types of HIV—HIV-1 and HIV-2—that are closely related.
HIV-2 is endemic in West Africa and has spread to India. The majority of AIDS cases worldwide, however, are caused by the more virulent HIV-1. Both viruses appear to have spread to humans from other primate species, with the best evidence based on sequence relationships indicating that HIV-1 has passed to humans at least three times from the chimp, Pan troglodytes, and HIV-2 from the sooty mangabey, Cercocebus atys.
Most individuals infected with HIV progress over time to AIDS
Many viruses cause a brief but severe infection that results in long-term protective immunity. Others, such as herpes viruses, establish a latent infection that is not eradicated but is adequately controlled by an adaptive immune response. Infection with HIV, on the other hand, appears to rarely, if ever, result in an immune response capable of preventing the virus’s ongoing replication. Although the immune system appears to control the initial acute infection, HIV continues to replicate and infect new cells.
The initial infection with HIV is usually caused by the transmission of body fluids from an infected person to an uninfected person. The virus is found in infected CD4 T cells, dendritic cells, and macrophages, as well as as a free virus in blood, sperm, vaginal fluid, and milk.It is most commonly transmitted through sexual contact, contaminated intravenous drug delivery needles, and the therapeutic use of infected blood or blood products, though this last route of transmission has largely been eliminated in the developed world where blood products are routinely screened for the presence of the HIV.
The transmission of a virus from an infected mother to her baby at birth or through breast milk is an important route of virus transmission. Perinatal transmission is estimated to be 25% in Africa, but it can be greatly reduced by treating infected pregnant women with the drug zidovudine (AZT) (see Section 11-23). Mothers who are newly infected and breastfeed their infants transmit HIV 40% of the time, demonstrating that HIV can also be transmitted through breast milk.
HIV is a retrovirus that infects CD4 T cells, dendritic cells, and macrophages
The ability of HIV to enter specific types of cells, known as cellular tropism, is determined by the expression of specific virus receptors on the surface of those cells. HIV enters cells via the viral envelope, which contains a complex of two noncovalently associated viral glycoproteins, gp120 and gp41. The glycoprotein complex’s gp120 component binds to the cell-surface molecule CD4 with high affinity. This glycoprotein attracts the virus to CD4 T cells, dendritic cells, and macrophages, all of which express some CD4. Before virus fusion and entry, gp120 must also bind to a co-receptor in the host cell’s membrane.
Several molecules may act as co-receptors for HIV entry, but they have all been identified as chemokine receptors. Chemokine receptors (see Chapters 2 and 10) are a G protein-coupled receptor family with seven transmembrane-spanning domains. The major co-receptors for HIV are two chemokine receptors known as CCR5, which is predominantly expressed on dendritic cells, macrophages, and CD4 T cells, and CXCR4, which is expressed on activated T cells. Following gp120 binding to the receptor and co-receptor, gp41 causes fusion of the viral envelope and the cell’s plasma membrane, allowing the viral genome and associated viral proteins to enter cytoplasm.
AIDS symptoms and signs
AIDS is a severe form of HIV infection. People with AIDS frequently develop symptoms and signs of unusual infections or cancers, owing to the immune system’s destruction of CD4 cells. When an HIV-infected person develops one of the infections or cancers, it is referred to as a “AIDS-defining condition” by medical professionals. Examples of AIDS-related conditions Significant, unexplained weight loss is another AIDS-defining symptom. Because common conditions such as cancer or other viral conditions such as infectious mononucleosis can also cause weight loss and fatigue, it is easy for a doctor to overlook the possibility of HIV/AIDS. Some of these conditions, particularly the more common infections like tuberculosis, can affect people who do not have AIDS.
Risk factors for developing AIDS
In order to develop AIDS, a person must first become infected with HIV. Among the risks of acquiring HIV infection are behaviours that result in contact with infected blood or sexual secretions, which pose the greatest risk of HIV transmission. Sexual intercourse and injection drug use are examples of these behaviours. The presence of genital sores, such as those caused by herpes, facilitates the virus’s transmission from person to person during intercourse. HIV has also been transmitted to health-care workers through unintentional needle sticks with blood from HIV-infected people, or when broken skin came into contact with infected blood or secretions.Blood products used for transfusions or injections may also spread infection, though this is extremely rare (less than one in every two million transfusions in the United States) due to HIV testing of blood donors and blood supply. Finally, infants can contract HIV from an infected mother while still in the womb, during birth, or through breastfeeding after birth.
Conclusion
A person infected with the human immunodeficiency virus (HIV) is diagnosed with AIDS after developing one of the illnesses identified by the Centers for Disease Control as an indicator of AIDS. The first cases of acquired immune deficiency syndrome (AIDS) were reported in 1981, but it is now clear that the disease was present unnoticed for at least four years prior to its identification. The disease is distinguished by susceptibility to opportunistic pathogen infection or the occurrence of an aggressive form of Kaposi’s sarcoma or B-cell lymphoma, which is accompanied by a significant decrease in the number of CD4 T cells. Many viruses cause a brief but severe infection that results in long-term protective immunity. Others, such as herpes viruses, establish a latent infection that is not eradicated but is adequately controlled by an adaptive immune response. The ability of HIV to enter specific types of cells, known as cellular tropism, is determined by the expression of specific virus receptors on the surface of those cells.