Excellent question – and another one where there’s no easy answer! Since this is the infectious diseases zone, I’m going to focus on diseases that are caused by an infection (e.g. virus, bacteria, fungus) rather than conditions such as arthritis, heart disease, diabetes and so on.
Really, it depends on what you consider as dangerous – most deaths, fastest death, most contagious (easily spread),…? Luckily for us, most diseases that were once really dangerous, we now know how to identify and treat. However, before we knew about germs, sterilization of equipment and antibiotics, even the simplest cut could be fatal if it got infected – surgery would have been much, much worse. Below, I pick out a few infectious diseases, past and present, that could be called dangerous.
~ The Black Death, caused by Yersinia pestis, killed up to half of the European population and up to 200 million worldwide in the thirteenth century.
~ The 1918 influenza (flu) pandemic killed more people than died from all causes in World War I (1914-18), with estimates upwards of 50 million.
~ Human immunodefiency virus (HIV) has infected 35 million people, with around 100,000 people currently affected in the UK, and has no known cure.
~ Tuberculosis infects up to a third of the global population, with around 8 million new cases annually, and whilst not common in the UK, is increasing in frequency due to travel between here and the developing world.
~ Any microbe which has become resistant to numerous treatments (known as multi-drug resistant), as this means we’re more and more restricted in what we can use to treat it.
I think Bethany has answered this really well. I think the most consistently dangerous infectious disease in the UK is actually the flu. Bethany highlighted the 1918 flu which was a terrible disease all over the world, but even today with flu shots the fight with the flu is still an ongoing battle with several thousand people each year dying from flu.
Older people are the most at risk group and this is why the annual flu shot is targeted first at them.