According to the Centers for Disease Control and Prevention (CDC), HIV is the human immunodeficiency virus. It’s the virus that can lead to acquired immune deficiency syndrome or AIDS.
WebMD said HIV attacks and destroys CD4 cells which are white blood cells whose main function is fighting diseases. When CD4 cells get low, people are more susceptible to illness.
AIDS is the final stage of HIV infection. CDC said at this point the immune system is so severely damaged, it has difficulty fighting diseases and certain cancers.
The Mayo Clinic wrote that scientists believe a virus similar to the human immunodeficiency virus first occurred in some populations of chimps and monkeys in Africa, where they're hunted for food. Contact with an infected monkey's blood during butchering or cooking may have allowed the virus to cross into humans and become HIV.
AVERT, an international HIV and AIDS charity, said that HIV is found in the blood, sexual fluids and breast milk of infected people. Transmission occurs when a sufficient amount of these fluids get into another's bloodstream.
The Mayo Clinic stated that the virus can enter the body through mouth sores or small tears that sometimes develop in the rectum or vagina during sexual activity. Pregnant women with the virus can transmit HIV to babies during pregnancy, delivery and breastfeeding.
The CDC said that sharing needles or other equipment used with intravenous drugs can spread HIV. WebMD added that the virus may be transmitted by dirty needles used in tattooing or body piercing.
The Mayo Clinic says the virus may also be transmitted through blood transfusions. However American hospitals and blood banks now screen for HIV antibodies, so this risk is very small.
The CDC stressed that HIV cannot reproduce outside the human body. It isn’t spread by air or water, insects, including mosquitoes, saliva, tears, or sweat> It is not passed on through casual contact like shaking hands, sharing dishes or closed-mouth kissing.
AVERT said that while some people have no symptoms, others experience a flu-like illness that last for a brief period soon after becoming infected with HIV.