AIDS is a retroviral disease characterized by profound immuno suppression that leads to opportunistic infections, secondary neoplasms and neurological manifestations.
Prevalence: Currently AIDS affects more than 40 million people all over the world and more than 90 % of the infections prevail in developing countries. Currently, the sub- Saharan Africa in general and South Africa, Ethiopia and Nigeria in particular shoulder the greatest burden of this pan endemic.
Mostly affected individuals are those aged between 15 and 49 years of age however, the epidemiology is quite different in children less than 13 years. Close to 2 % of all AIDS, occur in this age group presently where more than 90 % of this transmission results from transmission of the virus from the mother to the child. Women are more vulnerable than men
Receptive sexual partners
• Uterine, cervical and vaginal conditions that promote HIV transmission easily include cervical erosion, cervical ectopy, sexually transmitted diseases (STD), and cervical cancer.
• STD often goes unnoticed due to inaccessible anatomic locations.
• Menstruation: May make the transmission of HIV easier just before, during or after menstruation. It results in a large raw exposed area in the inner uterine lining to the virus
• Those with very low socio-economic backgrounds are vulnerable to sex trade (HIV is said to be” the holocaust of the poor”).
• Age of earlier sexual contact where the very young female genital linings are vulnerable to easy lacerations.
Modes of transmission
- Sexual activities 75% of all world-wide transmission is heterosexual transmission.
- Parenteral transmission In intravenous drug abusers, hemophiliacs who received factor viii concentrates and random recipients of blood transfusion
- Mother to child transmission. About 25 –30% HIV, positive mother will transmit HIV to their infants. About 60% of this infection is transmitted during child- birth 25% during pregnancy and 15% during breastfeeding.
- Needle Pricking: Accidental needle struck injury or exposure to non-intact skin to-infected blood in laboratories accounts for about 0.3% risk of stereo-vision as compared to a 30% risk of accidental exposure to hepatitis B infected blood.
HIV causes AIDS and HIV is a non-transforming retrovirus belonging to Lentivirus family. The retrovirus undergoes an unusual biologic process in which the genetic material in form of a single stranded RNA, can be converted to double stranded DNA by the effect of reverse transcriptase.
Two type of HIV viruses
HIV – 1 – USA, EUROPE, East and central Africa·
HIV – 2 – West Africa
HIV genome consists of a single stranded RNA enclosed within a core of viral proteins. The core is in-turn enveloped by a phospholipids bilayer deprived from the host cell membrane. The Envelop contains glycoproteins such as gp 120 and GP 41, GP 24.
- Targets of HIV infections are: The immune system and Central nervous system
- Target cells are those having CD4 receptors includeCD4 + T helper cells, Monocytes /macrophages, tissue cells such as dendritic cells present in genital tracts and anorectal region, certain brain cells (glial cells) and some other cells as well
- CD4 – Receptor molecule is a high affinity receptor for HIV. This explains for the selective tropism of the virus to aforementioned cells.
- Initial binding of gp 120 to CD4 molecule leads to conformational change for the new recognition site on gp120 for the co receptors CCR5 or CXCR4.
- The second conformational change in gp41 results in insertion of a fusion peptide into the cell membrane of the target T-cells or macrophages.
- After fusion, the viral core containing the HIV genome enters the cytoplasm of the cell(internalization).
How a latent HIV infection is transformed into productive infection?
- Antigen or mutagen-induced activation of T-cells is associated with transcription of genes encoding the cytokine IL-2 and its receptor (IL-2R) and after some steps induction of nuclear factor- KB (NF– KB) activates the transcription of HIV provirus DNA and leads ultimately to the production of virons and to cell lysis.
- Cellular activation, by antigens or cytokines (e.g. TNF-∞, IL-1, IL-2) induces cytoplasmic kinases that translocate NF-KB from the cytoplasm to the nucleous. In the nucleous, NF-KB binds to the enhancer sequence within the promoter region and similarly long terminal repeats (LTR) have KB sites. Thus, induction of NF-KB activates the transcription of HIV pro-viral DNA and leads ultimately to the production of virons and to cell lysis.
- Furthermore, TNF-∞, also leads to transcriptional activation of HIV –m RNA by production of nuclear factors of that bind to KB enhancer elements of HIV
Case definition of AIDS according to Centre for disease control (CDC)
Any HIV infected person with fewer than 200 CD4 + T-cells /μl + is considered to have AIDS. HIV infection progress to AIDS within 7 to 10 years in most cases, however exceptions to this typical course also occur:
- Long term non progresses : Those who stay symptomatic for 10 years or more with stable CD4 + T-cells count and low plasma viremia
- Rapid Progresses: Groups of patients with the middle chronic phase is telescoped to 2-3 years after primary infection