HIV6

Chronic infection

A strong immune defense reduces the number of viral particles in the blood stream, marking the start of secondary or chronic HIV infection. The secondary stage of HIV infection can vary between two weeks and 20 years. During this phase of infection, HIV is active within lymph nodes, which typically become persistently swollen, in response to large amounts of virus that become trapped in the follicular dendritic cells (FDC) network.^[29] The surrounding tissues that are rich in CD4⁺ T cells may also become infected, and viral particles accumulate both in infected cells and as free virus. Individuals who are in this phase are still infectious. During this time, CD4⁺ CD45RO⁺ T cells carry most of the proviral load.^[30]

During this stage of infection early initiation of antiretroviral therapy significantly improves survival, as compared with deferred therapy.^[31]

AIDS

Main article: AIDS

For more details on this topic, see AIDS Diagnosis, AIDS Symptoms and WHO Disease Staging System for HIV Infection and Disease

When CD4⁺ T cell numbers decline below a critical level of 200 cells per µL, cell-mediated immunity is lost, and infections with a variety of opportunistic microbes appear. The first symptoms often include moderate and unexplained weight loss, recurring respiratory tract infections (such as sinusitis, bronchitis, otitis media, pharyngitis), prostatitis, skin rashes, and oral ulcerations.

Common opportunistic infections and tumors, most of which are normally controlled by robust CD4⁺ T cell-mediated immunity then start to affect the patient. Typically, resistance is lost early on to oral Candida species and to Mycobacterium tuberculosis, which leads to an increased susceptibility to oral candidiasis (thrush) and tuberculosis. Later, reactivation of latent herpes viruses may cause worsening recurrences of herpes simplex eruptions, shingles, Epstein-Barr virus-induced B-cell lymphomas, or Kaposi's sarcoma.

Pneumonia caused by the fungus Pneumocystis jirovecii is common and often fatal. In the final stages of AIDS, infection with cytomegalovirus (another herpes virus) or Mycobacterium avium complex is more prominent. Not all patients with AIDS get all these infections or tumors, and there are other tumors and infections that are less prominent but still significant.

Transmission

Estimated per-act risk for acquisition of HIV by exposure route^[32][33]

Exposure Route	Estimated infections per 10,000 exposures to an infected source
Blood transfusion	9,000 (90%)[34]
Mother-to-child, including pregnancy, childbirth and breastfeeding (without treatment)	2,500 (25%)[35]
Mother-to-child, including pregnancy, childbirth and breastfeeding (with optimal treatment)	100-200 (1%-2%)[35]
Needle-sharing injection drug use	67 (.67%)[36]
Percutaneous needle stick	30 (.30%)[37]
Receptive anal intercourse (2009 and 2010 studies)	170 (1.7%)‡ [30–890][38] / 143 [48-285][33]
Receptive anal intercourse (based on data of a 1992 study)	50 (.5%)[39][40]
Insertive anal intercourse for uncircumcised men (2010 study)	62 (.62%)a [7-168][33]
Insertive anal intercourse for circumcised men (2010 study)	11 (.11%)a [2–24][33]
Insertive anal intercourse (based on data of a 1992 study)	6.5(.065%)[39][40]
Low-income country female-to-male	38 (.38%)‡ [13–110][38]
Low-income country male-to-female	30 (.3%)‡ [14–63][38]
Receptive (female) penile-vaginal intercourse	10 (.1%)[39][40][41]
Insertive (male) penile-vaginal intercourse	5 (.05%)[39][40]
Fellating a man	1 (.01%)†b[40]
Man being fellated	0.5 (.005%)†b[40]
The data shown represents transmission without the use of condoms. Risk increases substantially in the presence of genital ulcers, mucosal lacerations, concurrent sexually transmitted infections, or a partner with a high viral load of HIV.[42] Commercial sex exposure and national income levels may also impact risk.[38]
Bracketed values represent 95% confidence interval † "best-guess estimate" ‡ Pooled transmission probability estimate
a Other studies found insufficient evidence that male circumcision protects against HIV infection among men who have sex with men[43][44]
b Oral trauma, sores, inflammation, concomitant sexually transmitted infections, ejaculation in the mouth, and systemic immune suppression may increase HIV transmission rate.[45]

Three main transmission routes for HIV have been identified. HIV-2 is transmitted much less frequently by the mother-to-child and sexual route than HIV-1.