When HIV and Aids burst into the public consciousness in the Eighties as a new, deadly global disease, it was accompanied by a mythology of misinformation. And, inevitably, teaching about it involved dispelling the host of terrifying untruths: you couldn't catch it from sitting on a toilet seat, it was not a "gay plague" confined to homosexual men, and you couldn't become infected by using the cutlery of someone who had the disease or by shaking their hand.
Yet many myths persist today, and much more work is needed if we are to combat prejudice against HIV-positive people and promote the worldwide vaccination programme.
At the start of the 21st century, few in developing countries had access to HIV treatment, mainly due to the very high cost of antiretroviral drugs and international patents that stopped them being manufactured at cheaper prices. In 2006, the World Health Organisation (WHO) set a 2010 target of universal access to HIV treatment, prevention and care. The target was missed. This year, however, the international community has made a fresh commitment - to achieve universal access by 2015.
Globally, an estimated 33 million people have HIV and up to 90,000 people in the UK are HIV positive, a quarter of them unaware that they are infected. Between 1981 and 2007, around 25 million people died as a result of HIV, making it one of the most destructive pandemics ever.
But some people still fear those who are infected with HIV, and as a consequence they are treated as if they have leprosy - another much- misunderstood disease. As a child, I recall being read passages from the Bible about lepers and believing - wrongly - that leprosy rotted flesh and that fingers and toes would ultimately just "drop off". It was, I thought, very infectious and I believed lepers rang a bell as they walked, shouting "unclean". I pictured it as a variation on the cart-pushing undertakers in plague-ridden Britain, who stalked the streets calling "Bring out your dead!" Leprosy, of course, is only mildly contagious, and if detected early can be successfully treated. Most people are immune to the bacterium that causes it, and the bell of my childhood memory was used simply to attract attention while begging for money.
A WHO programme is in place to eradicate leprosy, and many countries that had high incidences are now reporting that the disease is no longer a national threat, defined as no more than one case per 10,000 people reported each year - although some countries such as Brazil, India and a few in central Africa still have some way to go before they can make this claim.
Smallpox, however, is a complete success story in humanity's battle against deadly diseases. It killed millions, including Queen Mary II, 17th-century consort of William III, but global eradication had been achieved by the 1980s. Edward Jenner is credited with developing the vaccination against smallpox in 1796, though treatments for it existed in ancient China and Turkey.
Jenner took pus from a sufferer of a related disease, cowpox, and scratched it into the arm of nine-year-old James Phipps, who developed immunity against smallpox as a result. Today Jenner would be chastised by the General Medical Council for unprofessional conduct and no doubt struck off the medical register. Yet his discovery has, over the centuries, saved millions of lives.
Good questions to discuss with pupils on World Aids Day, then, are "How do scientists combat killer diseases?" and "Why is the cost of drugs a major issue?"
In the UK, about pound;4.5 billion is invested each year in new drug research, yet the media often reports stories of "vital" drug treatments denied to patients as the cost of providing the drugs outweighs the benefits of providing a few extra weeks of life. The tricky moral and ethical question to grapple with is how to measure the cost against the likely benefits. Drug companies want to see large profits in return for the investment they make in research and development.
Not all drugs make it through the testing stage. In 2006, six participants in a clinical trial suffered catastrophic organ failure after taking a new drug being developed to treat arthritis, multiple sclerosis and leukaemia. Compensation costs ran into millions and the company that developed the drug collapsed.
But talking about issues like this in schools is vital if we are to avoid perpetrating myths about diseases and extend pupils' understanding of the moral, ethical and social implications of developing, testing and trialling new drugs.
Discussing HIV and Aids, as well as other epidemics and pandemics, can provide useful learning opportunities in science - for example, the difference between bacterial and viral infections, how vaccination is essential to stop the spread of disease, and why antibiotics cannot kill viruses.
Widen the discussion by looking at historical accounts of epidemics and the geographical spread of diseases, while considering the economics of the research and design of new drugs. Many academic subjects can also be linked to ongoing health issues in the real world. World Aids Day is not only an opportunity to educate pupils, but also to unite in the fight against HIV and show support for people who continue to live with the condition.
James Williams is a lecturer in science education in the school of education and social work at Sussex University. His latest book is "How Science Works: teaching and learning in the science classroom"
Resources covering citizenship, PSHE, whole school and science:
Key stage 1 World Aids Day Assembly, shared by foxedup80. A resource to help inform and educate pupils about the day.
Key stage 2 HIV: Kishe's Story, shared by Hamilton Trust.
A story about a young orphan to encourage reflection on the impact of HIV across generations.
Key stage 3 How Diseases Can Spread, shared by Claire-bear 88.
A biology lesson that includes starters, main activities and links to video clips.
Key stage 4 A Cry in the Darkness resource pack, shared by The Salvation Army.
Includes assembly and lesson ideas.
Key stage 5post-16 Alcohol, Drugs, Health and Sex Education worksheets, shared by axis-education. Designed to help pupils make informed decisions on sex, smoking and drugs.
Find all resources and links at www.tes.co.ukresources011.
Original headline: Price and prejudice