Cultures and Imperialism
In its last week in print, the Independent carried a piece under the headline: ‘One more thing imperialism has to answer for: dysentery.’ It’s a striking statement, but is it true?
Bacterial dysentery is caused by Shigella. There are three important kinds: dysenteriae, flexneri and sonnei. Shigella dysenteriae is the nastiest, S. flexneri is the commonest worldwide, and until a quarter of a century ago S. sonnei was a marker of children living in deprived communities in the UK (in England and Wales, 16,262 cases were recorded in 1992; the number then declined rapidly; today it is about 1000).
Genome sequencing shows that the patterns of spread and behaviour of the three kinds of Shigella are quite different. It isn’t possible to definitively determine their travels when European nations were establishing their global empires. We have no bacterial samples from those days, or even from 19th century psychiatric hospitals (‘asylum dysentery’ was a scourge). The oldest sample still alive is a Shigella flexneri strain isolated from a British soldier who died from dysentery in hospital at Wimereux on 13 March 1915.
The article in the Independent was stimulated by the publication in of a 73-author international study, which looked at 331 isolates of Shigella dysenteriae collected worldwide between 1915 and 2011. The authors concluded that its chromosome hadn’t changed much over the years and that all the strains had a common ancestor, which probably emerged at least three hundred years ago, spreading worldwide at the end of the 19th century and ‘diversifying into distinct lineages associated with the First World War, Second World War and various conflicts or natural disasters across Africa, Asia and Central America’. Another recent study focused on strains collected worldwide since the mid-20th century; it concluded that a common ancestor probably emerged in the 1920s.
Mathematical modelling plays a crucial role in this type of genealogical research. The choice of statistic is important, as are the assumptions used in the calculations, and the mathematics is sophisticated (the second study used the ‘Gaussian Markov random field skyride model assuming a lognormal relaxed clock’, for example). But there is agreement that intercontinental transfer has been happening in the second half of the 20th century. Strains in Bangladesh and the Central African Republic have a common ancestor dating from 1972; strains in Zambia and Guatemala (where a major outbreak in 1969-70 affected 100,000 people, killing more than 10,000) have a common ancestor dating from the early 1960s. Whether or not imperialism could be said to be the driving force is a semantic question.
In the case of Shigella flexneri, however, imperialism has to take some of the blame. Study No. 19 from the Institute of Medical Research in Kuala Lumpur, ‘Dysentery in the Federated Malay States’ by William Fletcher (a bacteriologist) and Margaret Jepps (a protozoologist), was published in 1924. The preface was by a Colonial Office civil servant. He wrote:
In a country like Malaya, which is so largely dependent on imported labour for the development of its vast resources, the welfare of the coolie class becomes a question which is always in evidence and demands the keenest consideration. That the Government of the Federated Malay States has not been neglectful of its responsibilities in this respect is apparent from the terms of its Labour Code … [which] ensure the provision of adequate medical aid and a sanitary standard of living. The existence of the Home for Decrepit Indians [is] further evidence of the attention given to the health and interests of this class of labour.
Jepps and Fletcher’s laboratory studies showed that most cases of dysentery were caused by S. flexneri, and that the link between its mortality rate and poverty was dramatic. The Kuala Lumpur General Hospital charged fees. It had wards of three classes: first for ‘Europeans’ (mortality negligible), second for ‘Eurasians, well-to-do Asiatics and government clerks’ (mortality 2 to 3 per cent), and third for ‘native labourers, paupers and vagrants’ (mortality about 25 per cent). The District Hospital was free and took many patients from the ‘Decrepits’ Home’ nearby. Its dysentery mortality rate was 36 per cent.
Recent fingerprinting studies show no evidence of intercontinental spread for S. flexneri. In places where human faeces continually contaminate food and drinking water, particular strains of the bacterium persist for generations. But as countries undergo economic development they disappear, to be replaced by S. sonnei. This has happened in Thailand, Malaysia, China and Vietnam, where a multidrug-resistant clade of the bacterium, known as Global III, which originated in Europe, took off in Ho Chi Minh City in the early 1980s.
Better bathrooms have done a lot to get rid of Shigella in the UK. Cheap package holidays abroad are helping to bring it back, however, and Public Health England has recently produced a poster for men who have sex with men. Its headline message is: ‘Good Session? Bad case of diarrhoea? Maybe its SHIGELLA.’