Science Forums 2

[mynah]

In 2007 a new strain of cold virus, an adenovirus named Ad14, infected an unknown number of people. At least 140 in the USA died of it, including young, previously healthy people, according to an article in the 6 September 2008 edition of NewScientist. By 2008, it had spread around the world – but by then the symptoms were no worse than those of any other cold.

In 2002 a coronavirus made a species jump from bats to human, resulting in SARS, causing prolonged respiratory symptoms in humans, who often died after weeks or months of suffering. By 2004 the disease had almost run its course, and those who did get infected generally suffered only mild illness.

Emerging diseases are often devastating when they first infect humans. A form of avian influenza, the Spanish flu of 1918, raged round the world, leaving millions dead in its wake before it finally subsided. Unlike most epidemic diseases, it was more likely to kill young, healthy adults in their prime than children and middle-aged sufferers.

The Spanish flu never really disappeared: Most of us have probably suffered infection, stayed in bed to recuperate for a day or two, and resumed our lives without getting too ill.

The explanation given for diminished virulence is usually that humans tend to build up antibodies and acquire at least partial immunity to new diseases, rendering infections relatively harmless. With global travel, infections spread round the world fast, but immunity is acquired at equal speed. In previous centuries, epidemics tended to be localized, but there were a few devastating exceptions: The Black Death was brought to Europe from Asia by merchant ships, Columbus and his successors decimated native Americans with European diseases (and took back syphilis as a souvenir that was much more lethal then than now), and the Spanish flu accompanied WWI soldiers to their native lands. In all cases the hapless recipients of the new germs were settlements of people who rarely traveled far from home, and whose immune systems experienced these viruses and bacteria as totally foreign.

It makes sense – but to me, it only does so to a point. I rarely get colds, and have not had one in the past two years. Does that mean that, when Ad14 rocks along, I’ll get really, really ill, or worse? If not, what confers immunity to those unaffected by the initial outbreak, and if I have been exposed, what prevented me from succumbing to severe illness the first time my body encountered the virus?