Human immunodeficiency virus (HIV) is a retrovirus that destroys CD4 T cells and is the aetiological agent of acquired immunodeficiency syndrome (AIDS). HIV is divided into 2 types, both of which cause AIDS: HIV 1, responsible for the global epidemic; and HIV 2, less pathogenic and restricted mostly to West Africa. AIDS, which usually occurs after approximately 6 to 9 years of HIV infection, is a constellation of opportunistic and other infections, conditions, or malignancies. These occur as a result of increasing immune depletion over time. 
HIV infection is a pandemic infectious disease whose impact on societies is without precedent. It is caused by a retrovirus that infects and replicates in human lymphocytes and macrophages, eroding the integrity of the human immune system over a number of years, culminating in immune deficiency and a susceptibility to a series of opportunistic and other infections as well as the development of certain malignancies.
Pregnancy in women living with HIV is complicated not only by HIV infection itself but also by the medical and psychosocial comorbidities associated with HIV. HIV infection in pregnancy poses a threat to maternal immune health and can lead to perinatal transmission of HIV in utero, intrapartum, or through breastfeeding postnatal.
The administration of antiretroviral therapy to HIV-negative people who may have been occupationally or sexually exposed to HIV. Once exposed to HIV, there may be a brief period before the infection is established, during which antiretroviral therapy may successfully prevent viral replication.
Clinical syndromes that arise as a consequence of impaired immunity in advanced stages of HIV infection. These illnesses tend to occur most often in patients who have untreated HIV infection or who fail to benefit from antiretroviral therapy. Tuberculosis, Pneumocystis jirovecii pneumonia, candidiasis, cryptococcosis, toxoplasmosis, cytomegalovirus infection, mycobacterium avium complex (MAC) infections, Herpes simplex infection, and cryptosporidiosis are among the HIV-related opportunistic infections often encountered in clinical practice.
Common opportunistic infection in people infected with HIV. It is an infection of the lung caused by the fungal organism Pneumocystis jirovecii (formerly known as Pneumocystis carinii ). Typically causes clinical disease in severely immunocompromised patients, such as HIV-positive patients with CD4 cell counts <200 cells/microlitre, bone marrow transplant patients, solid-organ transplant patients, or patients on chronic immunosuppressive therapy.
Common opportunistic infection in people infected with HIV. It is infectious disease caused by Mycobacterium tuberculosis . In many cases, M tuberculosis becomes dormant before it progresses to active TB. It most commonly involves the lungs and is communicable in this form, but may affect almost any organ system including the lymph nodes, CNS, liver, bones, genitourinary tract, and gastrointestinal tract.
Common opportunistic infection in people infected with HIV. Mycobacterium avium-intracellulare (MAI), also known as mycobacterium avium complex (MAC), consists of 2 mycobacterium species, M avium and M intracellulare . It traditionally causes 3 disease syndromes: pulmonary disease, cervical lymphadenitis, and disseminated disease.
Common opportunistic infection in people infected with HIV. Caused by the protozoan parasite Toxoplasma gondii . Cats are the definitive hosts for the parasite. Humans are intermediate hosts, and become infected by ingesting uncooked meat infected with tissue cysts (bradyzoites), from ingestion of other food or water contaminated with oocysts, or by transplacental spread of tachyzoites. Infection in humans is life-long and often asymptomatic, unless a patient becomes immunosuppressed.
Common opportunistic infection in people infected with HIV. Caused by Cryptococcus species. Cryptococcus neoformans var. grubii and Cryptococcus neoformans cause morbidity and mortality, especially in immunosuppressed populations, such as those with HIV.
Common opportunistic infection in people infected with HIV. Cytomegalovirus (CMV) is a ubiquitous beta-herpes virus that infects the majority of humans. Primary infection in individuals with normal immune function is usually asymptomatic. After primary infection, CMV establishes a state of lifelong latency in various host cells, with periodic sub-clinical re-activations that are controlled by a functioning immune system. When re-activation (or primary infection) occurs in patients with severely compromised immune function (transplant patients, or AIDS patients with CD4 count <50 cells/microlitre), uncontrolled CMV replication often ensues, which leads to the clinical manifestations characterised by fever, bone marrow suppression, and tissue-invasive disease.
Common opportunistic infection in people infected with HIV. Oral candidiasis involves a local infection of oral tissues by yeasts of the genus Candida , mostly C albicans . Although Candida are considered normal flora in the gastrointestinal and genitourinary tracts in humans, they are capable of local infection of mucous membranes (oropharyngeal candidiasis, oesophagitis, vulvovaginitis), focal invasion (endophthalmitis, meningitis, endocarditis), and dissemination (candidaemia).
The most common neoplasm arising in HIV-positive people. It is a low-grade vasoformative neoplasm associated with human herpesvirus-8 (HHV-8) or Kaposi sarcoma herpesvirus (KSHV) infection. Lesions frequently involve mucocutaneous sites, but may become more extensive to involve the lymph nodes and visceral organs. Skin lesions evolve from an early patch, to a plaque, and later to ulcerating tumour nodules.
Cutaneous manifestations often reflect immune status and may offer insight into the long-term prognosis of HIV-infected patients. The aetiologies of different diseases involving the entire spectrum of skin and HIV vary, but a useful aetiological distinction to note is that some skin diseases are fairly specific to HIV (e.g., Kaposi's sarcoma, oral hairy leukoplakia, papular pruritic eruption of HIV, HIV photodermatitis), and other skin diseases may appear in non-HIV-infected populations but have altered presentation with HIV.
Causes of altered mental status in HIV infection include both acutely presenting conditions (which often represent HIV-related opportunistic infection or associated systemic illness) and more progressive neurocognitive disease or psychological comorbidity. Neuropsychological issues arise as a direct effect of HIV infection: for example, as part of a spectrum of HIV-associated neurocognitive disorders (HAND) or as a psychiatric comorbidity (e.g., depression or alcohol/substance abuse).
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This overview has been compiled using the information in existing sub-topics.
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