Most of us in our youth have thrilled to the miraculous delivery of Jerusalem as described so vividly by Byron:
The Assyrian came down like the wolf from the fold,
And his cohorts were gleaming in silver and gold;
And the sheen of their spears was like stars on the sea,
When the blue wave rolls nightly on deep Galilee.
Of course, you remember what happened next as the Assyrians lay sleeping outside the walls of the city on the night before the great battle. Byron has it that:
The Angel of Death spread his wings on the blast,
And breathed in the face of the foe as he passed.
Isaiah, in the Old Testament, tells the story in more detail: "Behold, the angel of the Lord went out and slew in the camp of the Assyrians one hundred and eighty five thousand. And Sennacherib, the king of the Assyrians, departed and returned and dwelt in Ninive."
There is a body of opinion that believes that, in this instance, the angel of the Lord took the form of an outbreak of malaria, since the disease was once rampant throughout much of southern Europe and the Middle East. The name of the disease, mal' aria, meaning "bad air", recalls the fact that it was supposed in ancient times to be caused by noxious gases exuded by a marsh. Nowadays, however, we know that malaria is caused by a microscopic organism called plas- modium, that resides in the saliva of certain species of mosquito called anopheles.
Climate affects the spread of malaria in several ways. Still, stagnant water, for example, is essential for anopheles to lay their eggs and breed successfully; if these breeding grounds dry out, the eggs do not survive. Provided, however, there is sufficient rainfall to provide the breeding sites, then the higher the average temperature the greater the reproductive success of the mosquito, and the more widely the malarial infection can be spread. Plasmodium, too, enjoys the heat,and thrives in regions where the average temperature is up to 25 Celsius.
One of the many concerns about the possible effects of global warming is that a change in certain regions to a wetter, warmer climate could allow malaria to become more widespread. Predictions from the climate models suggest that a doubling of carbon dioxide in the atmosphere could increase the theoretical range of the disease by 30 per cent - or 17 million square kilometres - and that in this part of the world it could again become endemic in continental Europe, southern Britain and perhaps, for all we know, in parts of Ireland.