Normally viruses live in reasonable harmony with their hosts, but unfortunately some are parasitic and HIV is an example of how dangerous some viruses can be. This Human Immunodeficiency Virus seeks the very cells that would normally be involved in the body’s own defence against infection from viruses, and uses their genetic material to manufacture more infectious agents leading to Acquired Immunodeficiency Syndrome (AIDS). These viruses are replicating faster and are becoming resistant to drugs, however as Professor Margaret Johnson, Director of the largest HIV AIDS clinic in the UK describes, this is a battle that medicine and modern treatment seems to be winning. The biggest threat from HIV to patients and their partners is late detection.