HIV – Human Immunodeficiency Virus Spherical (~0.1µm Ø) Glycoprotein envelope with protein knobs on surface. Core is cone-shaped & contains RNA and the enzyme REVERSE TRANSCRIPTASE. (RNA  DNA) Virus synthesises cDNA from RNA & it incorporates into host cell chromosomes. DNA waits in host cell until activated. This is a rare type of virus called a RETROVIRUS.

Simplified Structure of HIV

Epidemiology and Transmission Transmitted by sexual contact/blood contact/mother  baby via placenta or breast milk. A person with AIDS is more likely to pass on the disease than a person who is only HIV+. Originally a “gay” disease but now widespread in heterosexual community. High risk groups: –Homosexuals –Haemophiliacs –Injecting drug abusers –Medical professionals No evidence of transmission by casual contact, saliva, “household” contact or insects.

The Disease Primary targets in blood are Macrophages and T4 Cells (T Helper Cells – a type of Lymphocyte). HIV has a great affinity for CD-4, a T4 Cell surface protein, which allows it to bind. HIV accepted into cell by endocytosis. Virus uses host cell raw materials to synthesise DNA from its RNA genome. Virus DNA migrates to nucleus and incorporates into T4 cell chromosomes. Virus genes transcribed along with T4 cell genes and many copies of virus RNA and protein coat are made. New viruses accumulate at the cell membrane and “bud” off to go and infect other cells. T4 cell usually lyses in the process.

The Disease (cont.) Eventually T4 cell count drops drastically, reducing the immune response. AIDS patient is therefore at risk of contracting and dying from any disease. Most common killers are: –A type of pneumonia caused by the protozoan Pneumocystis carinii. –Kaposi’s Sarcoma and other cancers.

HIV entering host cell Cell membrane HIV

AIDS Prevalence Worldwide

The African Problem

Treatment New in 1997 – Protease Inhibitors. Azidothymidine (AZT) But: –No cure –AZT has side effects (eg anaemia) –Protease inhibitors very expensive.

Prevention and Control Education – avoid high risk behaviour. Counselling of HIV+ patients to avoid transmittance. Treatment of injecting drug abuse/needle exchange schemes. Contact tracing (in UK)

Problems With Vaccination Retroviral genes interfere with cell division causing cancer  attenuated virus used as vaccine may also cause cancer. HIV constantly changes protein envelope. HIV has great affinity for CD-4. Antibodies produced against gp120 (recognition site) but body produces 2 nd round of a’bodies that attacks original a’bodies and CD- 4. So T4 cells that were supposed to be defended are attacked. DNA inserted into cell so: –No antigens to recognise –Can lie dormant harbouring retroviral genes Main obstacle is lack of testing models.

Problems in Developing World No particular high risk groups to target. Breast feeding by HIV+ women in west is discouraged. Advantages outweigh risk in Africa. Health education not as good. Treatment too expensive. Condoms too expensive. Can’t afford: –To screen donated blood –To discourage donors who have been exposed to virus –Needle exchange schemes