HIV infection

2 types: HIV-1 and HIV-2.
HIV-1 is more prevalent and largely responsible for the AIDS pandemic
HIV infection takes place or refers to when a person acquires the HIV virus. The initial illnes (which does not appear in all people) is a ild glandular fever like infection. There is a huge rise in virus levels.
The host's immune response controls the infection and there follows an asymptomatic period. This can last for 8-10 years depending on the host's immune status.The virus continues to multiply during this period.The antigenic makeup of the virus changes as the infection proceeds, which hampers the host's immune response to eradicate the infection.
The HIV virus requires both CD4 and either CXCR5 or CCR5 as co receptors for entry into the host's cells. During the asymptomatic period, the co receptor preference changes from CCR5 to CXCR4.
The level of CD4 cells decreases until AIDS develops. AIDS is characterized by infections with opportunistic organisms.
HIV-1 infections have a shorter asymptomatic period, a quicker progression of disease and higher rates of transmission when compared to HIV-2

Most HIV-1 strains use CCR5 as a co receptor and are known as R5 strains. HIV-1 strains that use CXCR4 as a co receptor are known as X4 strains.
There are some individuals who have had repeated exposure to HIV and not become infected. Their CCR5 genes have mutated. People with homozygous mutations express no CCR5 on their cells and are highly resistant to infection. People with heterozygous mutations have increased resistance to HIV.