HIV: How a Virus Weakens Immune Defence

HIV is a virus that targets important immune cells. Without treatment, it can gradually weaken the body's defence against infections and certain cancers. Modern antiretroviral treatment usually allows people with HIV to live long, healthy lives and prevents sexual transmission when the viral load remains undetectable.

What HIV is HIV stands for human immunodeficiency virus. It infects cells involved in coordinating immune defence, particularly CD4 T lymphocytes. The virus enters these cells and uses their internal machinery to make further copies of itself. Untreated infection gradually reduces the number and function of CD4 cells. This weakening does not usually happen all at once. HIV can remain without obvious symptoms for years while continuing to affect the immune system. HIV is a lifelong infection because some virus remains hidden within long lived cells. Current treatment controls HIV extremely effectively but does not routinely remove every infected cell from the body. HIV and AIDS are not the same HIV is the virus and the lifelong infection it causes. AIDS is not another virus and is not a synonym for HIV. AIDS stands for acquired immune deficiency syndrome. It is a clinical term for advanced HIV in which severe immune damage has allowed particular opportunistic infections, cancers or other serious conditions to develop. This progression usually follows untreated or inadequately controlled HIV. Some people first learn they have HIV only after an AIDS defining condition appears. Most people diagnosed and treated promptly in the UK do not develop AIDS. Healthcare professionals increasingly use the terms advanced HIV or late stage HIV instead. A person can live with HIV for many years without having AIDS. AIDS cannot be caught from another person. HIV is the transmissible virus. How HIV weakens immune defence CD4 cells help organise responses against infections and abnormal cells. HIV attaches to these cells, enters them and produces further virus. The CD4 count estimates the number of CD4 cells in a measured volume of blood. A falling count can indicate increasing immune damage. The viral load measures the amount of HIV genetic material in the blood. A higher viral load generally means that more virus is replicating. CD4 count and viral load answer different questions. Neither result should be interpreted alone without the person's treatment history, symptoms and wider health. When immune function becomes severely impaired, organisms that rarely cause serious disease in healthy people can produce illness. These are called opportunistic infections. The early stage of HIV infection Some people develop a short flu like illness around two to six weeks after acquiring HIV. This is sometimes called primary HIV infection or seroconversion illness. Possible features include fever, sore throat, swollen glands, rash, muscle aches, headache, diarrhoea and marked tiredness. Some people have mild symptoms or none. These features are not specific to HIV. Influenza, COVID 19, glandular fever, syphilis and many other illnesses can produce a similar pattern. Viral load can be high during early infection. A person may therefore be able to transmit HIV before knowing they have acquired it. Symptoms cannot confirm or exclude HIV. Testing is the only reliable way to establish the diagnosis. The period without obvious symptoms After the early stage, untreated HIV may cause few or no noticeable symptoms for several years. The immune system can still be sustaining gradual damage during this time. Feeling well therefore does not show that a person has not acquired HIV. Testing decisions should be based on possible exposure and clinical circumstances, not symptoms alone. Treatment during this stage suppresses viral replication, protects immune function and greatly reduces the risk of future illness. Advanced HIV and opportunistic conditions Without effective treatment, the CD4 count may eventually become very low. The body then becomes less able to control particular infections and cancers. Possible opportunistic infections include tuberculosis, Pneumocystis pneumonia, severe fungal infection and certain infections affecting the brain, eyes or digestive tract. HIV associated cancers include Kaposi sarcoma and some lymphomas. Other cancers may also become more likely or behave differently when immune function is impaired. Persistent fever, weight loss, night sweats, prolonged diarrhoea, recurrent infections, oral thrush, breathlessness or neurological symptoms can occur during advanced disease. None of these features proves HIV. They require investigation for HIV and other possible causes. How HIV is transmitted HIV transmission requires virus containing body fluid to enter another person's bloodstream or reach vulnerable tissue. Relevant fluids include blood, semen, vaginal fluid, rectal secretions and breast milk. The likelihood of transmission depends on the type of exposure, viral load and whether effective prevention is being used. Sexual transmission can occur during vaginal or anal sex when a person with HIV has a detectable viral load. Oral sex carries a much lower risk, but individual circumstances still matter. HIV can also be transmitted by sharing needles, syringes or other injecting equipment. An occupational sharps injury can create a risk, although transmission in UK healthcare settings is rare. Transmission can occur during pregnancy, birth or breastfeeding. Modern treatment and specialist maternity care reduce this risk greatly. Blood donations in the UK are screened. Acquiring HIV through a UK blood transfusion is therefore extremely unlikely. Everyday contact does not transmit HIV HIV is not spread through hugging, shaking hands, sharing a home or sitting beside someone. It is not spread through toilet seats, bedding, swimming pools, crockery, cutlery, food or drinks. Saliva, sweat and tears do not transmit HIV during ordinary social contact. HIV is not spread through coughing, sneezing, ordinary kissing or food prepared by someone living with HIV. Mosquitoes and other biting insects do not transmit HIV. The virus cannot reproduce within them, and they do not inject another person's blood when they bite. People living with HIV do not need isolation at work, school, home or in social settings. Standard precautions for blood apply to everyone, regardless of known HIV status. Fear of casual transmission is scientifically unfounded and contributes directly to stigma and discrimination. Undetectable equals untransmittable Antiretroviral treatment can reduce the viral load until routine laboratory tests cannot detect it. This is described as an undetectable viral load. A person taking effective treatment who maintains a sustained undetectable viral load has zero risk of transmitting HIV through sex. This is known as undetectable equals untransmittable, or U=U. Undetectable does not mean that HIV has been cured or completely removed. Treatment must continue, and viral load monitoring confirms that suppression is being maintained. U=U applies specifically to sexual transmission. It should not automatically be extended to sharing injecting equipment, pregnancy, birth or breastfeeding, where separate specialist guidance applies. U=U does not prevent other sexually transmitted infections or pregnancy. Condoms may still be chosen for those purposes. HIV testing HIV testing may use a laboratory blood sample, a finger prick sample or an approved oral fluid self test. Different tests detect antibodies, viral antigens or genetic material. A screening result described as reactive or positive does not complete the diagnosis by itself. Further laboratory testing confirms whether HIV is present and distinguishes between possible false reactive results. A negative result means that the test found no evidence of HIV at that time. A very recent infection may still be within the test's window period. The window period is the interval after exposure before a particular test can detect infection reliably. It varies according to the test and whether PEP or PrEP has been used. A clinician may advise repeat testing after a recent exposure. Someone who may need PEP should not wait for the window period or for symptoms before seeking help. Testing is confidential HIV tests are confidential. Sexual health clinics provide free and confidential testing, and NICE advises that anonymous testing can be discussed when confidentiality remains a concern. Testing requires informed consent, as with other medical investigations. A person should understand why the test is being offered and how the result will be communicated. A positive diagnosis leads to prompt referral to a specialist HIV service. Staff provide treatment information, emotional support and help with notifying partners who may benefit from testing. Partner notification can often be arranged without revealing the diagnosed person's identity. The aim is to offer testing and prevention, not to assign blame. Pregnant people are routinely offered HIV testing as part of antenatal screening. HIV testing may also be recommended for certain illnesses, possible exposures and groups with an increased likelihood of undiagnosed infection. Modern antiretroviral treatment HIV is treated using antiretroviral therapy, known as ART. BHIVA recommends ART for everyone living with HIV. ART combines medicines that block different stages of the virus's life cycle. Combination treatment suppresses replication more reliably and reduces the risk of resistance. Many modern regimens are taken once daily, sometimes with several medicines combined into one tablet. Selected people may use long acting injectable treatment after specialist assessment. Treatment is normally lifelong. Stopping ART allows viral load to rise again and can permit further immune damage or transmission. Most people achieve an undetectable viral load within months. Immune recovery can continue for longer, particularly when treatment began with a low CD4 count. Treatment choice considers resistance results, kidney and liver function, pregnancy, other medicines, hepatitis infection, side effects and individual preference. Why consistent treatment matters Taking ART as agreed keeps drug levels sufficient to suppress viral replication. Repeated treatment gaps can allow the viral load to rebound. Depending on the regimen, ongoing replication during inadequate treatment can select resistant virus. Resistant HIV may require a different combination of medicines. Difficulties taking treatment may result from side effects, mental health problems, unstable housing, stigma, cost pressures, shift work, privacy concerns or medicine interactions. These difficulties require practical support rather than judgement. HIV teams can adjust regimens, provide reminders, address interactions and coordinate psychological or social support. Someone should not stop or share HIV medicines without specialist advice. Vomiting, inability to swallow tablets or a prolonged interruption should be discussed promptly with the HIV team. Monitoring treatment and immune health Viral load is the main measure of how effectively ART is suppressing HIV. A rising viral load may reflect missed treatment, interactions, absorption problems or resistance. CD4 count helps estimate immune strength and the risk of some opportunistic infections. It may be checked less often once treatment is stable and immune recovery is established. Other monitoring can include kidney function, liver function, blood counts, cholesterol, glucose and screening for hepatitis or sexually transmitted infections. HIV care also includes vaccination, cancer screening, reproductive health, mental health and assessment of cardiovascular, bone and kidney health. A person living with HIV should receive ordinary primary and preventive healthcare as well as specialist HIV care. Pre exposure prophylaxis Pre exposure prophylaxis, called PrEP, is HIV medicine taken by a person who does not have HIV before possible exposure. When used correctly, it is highly effective at preventing HIV acquisition. PrEP is usually provided through sexual health services. Most people use tablets, while some eligible people may be offered long acting injectable PrEP. The appropriate schedule depends on anatomy, the type and timing of exposure, hepatitis B status and individual circumstances. Event based dosing is not suitable for everyone. HIV testing is required before PrEP begins because PrEP alone is not adequate treatment for established HIV. Regular follow up usually includes repeat HIV tests, kidney monitoring and screening for other sexually transmitted infections. PrEP does not prevent gonorrhoea, chlamydia, syphilis or pregnancy. Condoms remain useful where protection from these is wanted. Post exposure prophylaxis Post exposure prophylaxis, called PEP, is emergency antiretroviral treatment used after a significant possible HIV exposure. PEP should be started as soon as possible, ideally within 24 hours and no later than 72 hours after the exposure. It is normally taken for 28 days. PEP is available from sexual health or HIV clinics and from A&E when specialist clinics are closed. It is not normally issued through routine GP services. A clinician assesses the exposure type, timing, source information and any known viral load. PEP is not usually needed after sexual contact with a person whose sustained undetectable viral load is confirmed. Baseline and follow up HIV testing are required. PEP is highly effective when prescribed appropriately and taken correctly, but it cannot guarantee prevention. PEP does not prevent other sexually transmitted infections or pregnancy. The consultation may therefore include additional testing, emergency contraception, hepatitis prevention and safeguarding support. Condoms and safer injecting Condoms reduce the risk of HIV when a partner's viral load is detectable or unknown. They also reduce several other sexually transmitted infections. Water based or silicone based lubricant reduces condom breakage and tissue injury. Oil based products can damage latex condoms. Needles, syringes and other injecting equipment should never be shared. Needle and syringe programmes provide sterile equipment and support without judgement. PrEP, PEP, condoms, sterile injecting equipment, regular testing and effective ART are complementary prevention methods rather than competing choices. HIV during pregnancy and infant feeding Routine antenatal HIV testing allows treatment to begin promptly when needed. A pregnant person already taking ART should remain under specialist HIV and maternity care. Suppressing viral load greatly reduces transmission during pregnancy and birth. The delivery plan and medicine choices depend on viral load, treatment history and obstetric circumstances. U=U is proven for sexual transmission. It should not be used to assume zero transmission during pregnancy, birth or breastfeeding. Infant feeding decisions require individual discussion with the specialist team. The plan considers viral suppression, available feeding options, monitoring and the person's informed preferences. Babies born to people living with HIV receive a specialist prevention and testing plan. Early treatment for a child diagnosed with HIV protects growth, development and immune function. Living well with HIV With effective treatment, most people living with HIV can expect a long and healthy life. They can work, study, have relationships, have sex and become parents. HIV status does not determine someone's character, sexuality, behaviour or value. Anyone can acquire HIV when a biologically possible exposure occurs. Stigma can delay testing, disrupt treatment and cause psychological harm. Accurate information about transmission and U=U is therefore part of medical care. People living with HIV may choose carefully who they tell. Confidential support from the HIV team can help with relationships, disclosure, fertility, employment and mental wellbeing. What this lesson should not be used for This lesson cannot determine HIV status from symptoms, appearance, sexuality, nationality or a partner's history. Only appropriate testing can diagnose HIV. It should not be used to calculate an exposure risk, choose PrEP or PEP, interpret a reactive result, or change antiretroviral treatment without professional advice. Seek urgent advice immediately after a possible exposure because PEP must begin within 72 hours and works best when started earlier.

HIV is the virus that gradually weakens immune defence when untreated. AIDS is advanced HIV with specific serious opportunistic conditions, not another name for every HIV infection. Modern ART protects health, and a sustained undetectable viral load means zero risk of sexual transmission.