Dear Baya,

        I’m just recovering from a bad attack of ‘flu, which seems a good time to write to you about disease. Is it true that millions died of influenza in about 1917 – a disease which I easily get over? And is it true that influenza is caused by a virus which could only have developed when population began to get dense on earth only a few thousand years ago?

             I really know too little about disease in different cultures and periods, even though my mum is a nurse and tells me a bit. I can’t understand why it took so long for certain societies to deal with,, and why millions still die of, easily preventable diseases.

      What are the worst diseases on earth? Are they AIDS, malaria and dysentery, as I would guess? How do diseases work, along what chains of cause? How was it that some of the great diseases, like plague and malaria, were eradicated in certain areas of the world in the past?

      Are we going to face new diseases, the Ebola virus or SARS, which could threaten all humans? Is it inevitable that in the end the viruses and bacteria will overcome all our defences? Can multi-resistant strains like MRSA which my mum talks about in her hospital, be dealt with?

     I know you have some odd theories about what are the most important medicines on earth – wasn’t one of them the humble cup of tea? It would be great if you could simply and shortly (no heavy science please!) explain the general outlines of how we live in a world where a very minor shift in the balances between us and microbes can lead to so much suffering.

Lots of love,

P.S. Writing this has made me feel a little less sorry for myself and grateful for all the medical attention I’ve had.