Immunity

Immunity and the problem of infectious disease

There has recently been an increased awareness of the problem posed by infectious diseases with the emergence of antibiotic resistant bacteria. Bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile have become well known. However, we live in a world full of microorganisms and some of these have the potential to cause disease.

Throughout human history infectious disease has been a constant threat. The Bible describes the plague of Ashod. This occurred in what is the modern day Gaza Strip around 1100 BC, probably killing many thousands of people. Black Death arose in 14th century England and killed an estimated 100,000 people. Bubonic plague in 1665 killed at least 68,000 people in London alone. Cholera epidemics in England during the 1850s also killed thousands of people. Between 1568 and 1620 the indigenous population of Mexico fell from 30 million to 1.6 million, largely due to infectious disease introduced by European invaders, to which the local people had no immunity. Influenza killed between 20 to 40 million people in 1919; it is likely that such a pandemic will strike us again. Smallpox killed 300 million people in the 20th century before it was eradicated. In many poorer areas of the world, 70-80% of deaths are caused by infections. Children under five are often extensively affected; diarrhoea and vomiting is still the most common cause of death in the world's children. Simple bacterial chest infections also kill many children every year.

Over 3000 children die from malaria in Africa every day. At the time of writing 33 million people are infected with the human immunodeficiency virus (HIV) and over 2 million die each year from acquired immunodeficiency syndrome (AIDS).