HIV

HIV explained

Human immunodeficiency virusA microbe that is only able to multiply within living cells. (HIV) is a virusA microbe that is only able to multiply within living cells. that causes weakening of the immune systemThe organs specialised to fight infection.. Infection with HIV can progress to acquired immunodeficiency syndrome (AIDS).

HIV is a type of virusA microbe that is only able to multiply within living cells. called a retrovirus; it has two strains, HIV-1 and HIV-2.[1,2]

HIV invades the cells of the body, mainly the immune cells, and particularly a type of T-cellA kind of lymphocyte, a type of white blood cell that fights infection. called a CD4 cellThe basic unit of all living organisms.. HIV uses the infected cells to produce new virusesMicrobes that are only able to multiply within living cells.. The cellThe basic unit of all living organisms. is destroyed as the new virusesMicrobes that are only able to multiply within living cells. leave it; over time, more and more CD4 cells are destroyed.[2]

The remaining level of CD4 T-cells in the body depends on the balance between how quickly the HIV destroys these cells, and how quickly the body produces new cells of this type.[1,2]

After the initial infectionInvasion by organisms that may be harmful, for example bacteria or parasites. with HIV, it takes the body around one to three months to mount an effective response to it; that is, before antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. against the virusA microbe that is only able to multiply within living cells. can be detected in the bloodstream. When they are, this is called seroconversion.[2]

Before seroconversion, the virusA microbe that is only able to multiply within living cells. is fairly unrestrained by the body's immune response and so there are high levels of HIV in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid..[3] Afterwards, the immune systemThe organs specialised to fight infection. fights back, leading to a rapid fall in the levels of the virusA microbe that is only able to multiply within living cells. (this is called the viral load).[2]

On average, people with healthy immune systems have over 1,000 CD4 cells per cubic millimetre of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.. When the CD4 count of people with HIV falls to 200 cells per cubic millimetre of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid., they become especially vulnerable to infections that would not otherwise be a problem (so-called opportunistic infections), and also to some cancers.[2]

Some medical centres define AIDS by the occurrence of 'AIDS-defining illnesses' (opportunistic infections or cancers in the presence of HIV); others by a CD4 count of 200 cells per cubic millimetre or fewer. The progression from initial HIV infectionInvasion by organisms that may be harmful, for example bacteria or parasites. to AIDS can take anything from weeks to years.[2]

Symptoms and signs

Most people develop fluA viral infection affecting the respiratory system.-like symptoms within one to three weeks of infectionInvasion by organisms that may be harmful, for example bacteria or parasites. with HIV. Symptoms may include fever, muscleTissue made up of cells that can contract to bring about movement. aches, weight loss, rash and fatigue. This is called acuteHas a sudden onset. retroviral syndrome. It lasts for one to four weeks, but often goes unrecognised.[2-5]

Damage to the immune systemThe organs specialised to fight infection. leads to the development of opportunistic infections to which most people with fully functioning immune systems would not be vulnerable.[1] These might include respiratory or urinary tract infections, for example.[4]

The cancers associated with HIV are usually those linked with other viral infections, for example, Kaposi's sarcomaCancer of the connective tissues., which is caused by human herpes virusA microbe that is only able to multiply within living cells. 8 infectionInvasion by organisms that may be harmful, for example bacteria or parasites..[1]

HIV can also damage the organs directly. In fact, it can affect every system of the body, leading to conditions such as:[1,4]

  • Fat redistribution, or lipodystrophy, which may be caused by the HIV infectionInvasion by organisms that may be harmful, for example bacteria or parasites. itself or by the drugs used to treat it. It may lead to abdominal obesityObesity centred around the abdomen, resulting in a high waist circumference., accumulation of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. over the back or the back of the neck, and reduction of subcutaneous fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body., for example, from the arms or face[4,6]
  • Insulin resistanceThe ability of a microbe, such as a type of bacteria, to resist the effects of antibiotics or other drugs. and high bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. glucoseA simple sugar that is an important source of energy in the body. levels (hyperglycaemiaA high level of glucose in the blood.)
  • Disease of the heart muscleTissue made up of cells that can contract to bring about movement. (cardiomyopathy)
  • Inflammation of the brain (encephalitisInflammation of the brain.)
  • Inflammation of one or more joints (arthritisInflammation of one or more joints of the body.)
  • Kidney problems (nephropathy)
  • Nerve damage (neuropathy).

Risk factors and prevention

HIV has three main routes of transmission:[1,5]

  • Sexual intercourse (including oral sex). The highest risk is among men who have sex with men
  • Exposure to contaminated bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. or bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. products (for example, from an unscreened bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. transfusion or needle-sharing during intravenous drug use)
  • From mother to child during pregnancy, childbirth or breastfeeding.

The people at highest risk include those with sexual partners who are HIV positive, infants born to mothers with HIV, intravenous drug users, and anyone who receives unscreened bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. products.[1]

Even if people with HIV do not experience any symptoms, they are still able to pass on the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. to others.[2]  Early diagnosisThe process of determining which condition a patient may have. may help to reduce the spread of HIV.[5]

Preventive measures may be effective after exposure to HIV. People who have been exposed to contaminated bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. products - for example, healthcare workers who have had a needlestick injury - can lower their risk of developing the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. by taking medications against HIV (antiretroviral therapy).[1] This therapy can be highly effective, particularly if taken as soon as possible after the incident. However, it is not a guarantee of protection.[7]

Antiretroviral therapy can also help to prevent HIV transmission from pregnant women with HIV to their babies during pregnancy and labour, and short courses of therapy may be given to newborn infants.[1] New mothers with HIV may be advised to avoid breastfeeding where possible, as this is another potential route of transmission.[8]

Studies suggest that male circumcision reduces the incidenceThe number of new episodes of a condition arising in a certain group of people over a specified period of time. of HIV amongst men.[9] Other preventive measures include safer sex practices, access to sterile needles and screening of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. and bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. products for transfusion. Education on the potential routes of transmission of HIV may help to reduce the risk of infectionInvasion by organisms that may be harmful, for example bacteria or parasites..[5]

Tests and diagnosis

HIV may be diagnosed by the presence of antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. against HIV in the bloodstream. Because it takes a while for the body to produce antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. to HIV following initial infectionInvasion by organisms that may be harmful, for example bacteria or parasites., however, HIV tests that rely on the presence of antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. may be negative in the early stage of infectionInvasion by organisms that may be harmful, for example bacteria or parasites.. If this is the case, the test may need to be repeated at a later date. A high viral load would also confirm the diagnosisThe process of determining which condition a patient may have..[5]

Monitoring someone's viral load and CD4 T-cellA kind of lymphocyte, a type of white blood cell that fights infection. counts is the best way to monitor HIV infectionInvasion by organisms that may be harmful, for example bacteria or parasites. and predict the progression to AIDS. People with lower CD4 counts and higher viral loads have a greater risk of progressing to AIDS within a shorter time frame. Monitoring the percentage of lymphocytes that are CD4 cells may also be useful.[1,10]

Tests can be done to determine whether the virusA microbe that is only able to multiply within living cells. is resistantA microbe, such as a type of bacteria, that is able to resist the effects of antibiotics or other drugs. to any medications. This can be useful before someone starts antiretroviral therapy, or if they have responded poorly to treatment.[11]

Choosing treatments

The best treatment available for HIV is the use of combination antiretroviral therapy, which brings about improvements in the person's immune function as well as reducing the viral load.[1]

Early treatment with antiretrovirals is now routine in developed countries, and this approach is also being adopted in places with limited resources, where possible.[12]

A number of different types (classes) of antiretroviral therapy exist, and new classes are always under development. The current groups are:[1,2,13]

  • Nucleoside analogue reverse transcriptase inhibitors (NRTIs)
  • Non-nucleoside reverse transcriptase inhibitors (NNRTIs)
  • Protease inhibitors
  • Fusion inhibitors
  • CCR5 blockers.

NRTIs are similar to the building blocks of DNAThe building blocks of the genes in almost all living organisms - spelt out in full as deoxyribonucleic acid., and so enter the DNAThe building blocks of the genes in almost all living organisms - spelt out in full as deoxyribonucleic acid. of virusesMicrobes that are only able to multiply within living cells. present in cells and help to prevent the virusA microbe that is only able to multiply within living cells. from replicating. NNRTIs and protease inhibitors also inhibit viral replicationThe process by which DNA makes copies of itself when a cell divides.. Fusion inhibitors prevent HIV from entering cells.[2]

The HIV virusA microbe that is only able to multiply within living cells. gains access to human cells by two main receptors, CCR5 and CXCR4. The virusA microbe that is only able to multiply within living cells. that uses CXCR4 generally causes more harm than that using CCR5. Most HIV uses CCR5.[1] CCR5 blockers prevent the entry of HIV into cells by means of the CCR5 receptor. However, there are concerns that therapy can encourage the virusA microbe that is only able to multiply within living cells. to switch from using CCR5 to CXCR4, which may accelerate the progression of the disease.[13]

The side-effects of antiretroviral therapy can make it difficult for some people to continue with their medications. These effects may include bloating, nausea and diarrhoeaWhen bowel evacuation happens more often than usual, or where the faeces are abnormally liquid., fatigue, headaches and nightmares. More serious adverse effectsUndesirable side-effects of medication. may include lipodystrophy and low levels of certain cells in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. (cytopenia).[1,6,14] These side-effects vary from drug to drug and from person to person; this makes tailoring treatment to the individual all the more important.

Drug resistanceThe ability of a microbe, such as a type of bacteria, to resist the effects of antibiotics or other drugs. may also emerge; resistanceThe ability of a microbe, such as a type of bacteria, to resist the effects of antibiotics or other drugs. to one drug often means some level of resistanceThe ability of a microbe, such as a type of bacteria, to resist the effects of antibiotics or other drugs. to other drugs in the same class.[1]

People who have severe suppression of the immune systemThe organs specialised to fight infection. may benefit from taking long-term antibiotic medicines to protect against conditions such as pneumocystis carinii pneumoniaInflammation of one or both lungs..[1]

Outlook and living with HIV

A number of sources of information are available for people with HIV, including advice from healthcare professionals, information hotlines, websites and public health departments.[5,15]

Counselling can offer information on the disease process and reducing the risk of transmission, and provide psychological support.[16] Available programmes may also include family and relationship counselling, telephone counselling and support groups.[17]

Safer sex practices such as using a male condom continue to be important for people with HIV, to prevent the further spread of the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. and to protect against other sexually transmitted diseases.[18] Furthermore, some reports suggest that people who have HIV may become infected with a different strain of HIV, and that this 'super infectionInvasion by organisms that may be harmful, for example bacteria or parasites.' can accelerate the progression of HIV to AIDS.[19]

As outlined above, the time period from infectionInvasion by organisms that may be harmful, for example bacteria or parasites. with HIV to development of AIDS can be highly variable from person to person. In a small proportion, this progression takes a matter of weeks.[2] At the other end of the spectrum, some people who are HIV positive do not develop AIDS for a decade or more, even without taking antiretroviral therapy. These people are referred to as 'long-term non-progressors'. People who have a very low viral load at the time of diagnosisThe process of determining which condition a patient may have. of HIV infectionInvasion by organisms that may be harmful, for example bacteria or parasites. are more likely to fall within this group.[20]

References: 
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