`Mrs Pat" would not have brooked El Nino. Mrs Pat, those of you above a certain age will certainly remember, was the actress Mrs Patrick Campbell, once affectionately described by Hilton Edwards as "a fiend in what may once have been a human shape". And it was Mrs Pat herself who famously remarked - maybe, for all we know, by way of reciprocity - "My dear, I don't care what they do, so long as they don't do it in the street and frighten the horses." Horses, it now seems, have every reason to be frightened of El Nino.
African horse disease, or AHD, is an infectious ailment with mortality rates of up to 95 per cent. It appears occasionally in Europe and in Asia, but major epizootics, which is what you call an epidemic among animals, occur in southern Africa every 10 to 15 years. Until recently, no one could detect any pattern to these irregular recurrences, but now, in the scientific journal Nature, Baylis et al, as they say in academic circles, report a strong association with El Nino.
Since 1803 there have been 14 very noteworthy AHD epizootics in South Africa - in 1819, 1837, 1854, 1862, 1877, 1887, 1891, 1913, 1918, 1923, 1925, 1940, 1953, and 1996. And during the same period the years in which El Nino has been particularly strong were 1819, 1837 - and, yes, you've guessed it - 1854, and so on up to 1996. The odds against this happening by chance are about 1 in 300; the only question now, it seems, is why?
El Nino, as of course you know, is a marked warming of the surface waters of the Pacific Ocean that occurs every three to seven years, and which has come to be associated with many of the worst excesses of the elements in widely separated areas of the world.
It brings drought to Indonesia, and storms and landslides to the normally arid coastal regions of Peru and Ecuador; in South Africa a drought occurs, and is often followed by exceptionally heavy rains.
The theory is that these El Nino conditions may be very favourable for Culicoides imicola, the insect by which AHD is spread. This vector breeds in damp soil, and its population can increase 200-fold in years of heavy rain. Moreover, a statistical analysis of the years listed above showed that they had one feature in common: an El Nino induced pattern of pronounced drought in the period from January to March, followed by heavy rains from April through to June.
These, it would seem, are the conditions that the breeding Culicoides imicola finds irresistible.