HIV infection is caused by the HIV virus. In Ireland, most cases of HIV happen when someone who does not know they have HIV and is not on treatment has sex without a condom.
They can pass the virus on even if they do not have any symptoms of infection.
The chances of passing on the virus are higher in the first few weeks after getting HIV. This is because the amount of virus in your body is very high.
Effective treatment stops someone with HIV from passing it on.
If you think you may have HIV, you should get tested and start treatment if needed.
How HIV spreads
HIV does not pass easily from 1 person to another. The virus does not spread through the air like cold and flu viruses.
HIV lives in the blood and in some body fluids. To get HIV, 1 of these fluids from someone with untreated HIV has to get into your body.
The body fluids that contain enough HIV to cause infection are:
- semen
- vaginal fluids, including menstrual blood
- breast milk
- blood
- anal fluids
Other body fluids, like saliva, sweat or urine, do not contain enough of the virus to pass to another person.
How HIV does not spread
You cannot get HIV from:
- kissing, touching or hugging
- coughing or sneezing
- sharing a glass, cup, cutlery or other utensils
- contact with saliva, sweat or urine
- sharing a public toilet or swimming pool
- having sex with someone living with HIV on effective treatment
The chance of getting HIV from oral sex is very low. This is regardless of whether the person with HIV is on treatment or not.
How HIV gets into your body
The virus usually enters the body through the thin lining on or inside the anus, vagina and genitals.
Less commonly, it enters the body through:
- the thin lining of the mouth and eyes
- cuts and sores in the skin
It can also get into your blood if you share needles or other injecting equipment with someone who has untreated HIV.
Babies can get HIV during pregnancy, delivery or breastfeeding if their mother is not on HIV treatment.
What HIV can do to your body
HIV infects the immune system. The virus attaches itself to cells in your immune system called CD4 lymphocyte cells. These cells protect your body against some bacteria, viruses and other germs.
The virus enters the CD4 cells and uses them to make more viruses. These virus copies then leave the CD4 cells, killing them in the process.
If left untreated
If left untreated, HIV continues to destroy your cells and damage your immune system.
The number of CD4 cells in your blood drops so low that your immune system stops working. You are no longer able to fight infections. This can take up to 10 years. During this time you may feel and appear well.
The number of CD4 cells in your blood is also called your CD4 count.
If HIV is untreated, it also means there are more virus copies in your body. This could result in HIV being passed on to your sexual or drug-using partners.
Risk factors for HIV
Anyone can get HIV.
You may be at risk of HIV if your sexual partner or previous sexual partner has untreated HIV.
This risk may increase the more sexual partners you have without using a condom.
It is a good idea to talk about HIV status with new sexual partners and consider having an HIV test.
You may be at risk of HIV if you share drug-injecting equipment with people who have untreated HIV.