A mathematical model that links health and economic development may have its limitations, says Philip Ball. But its consequences are too serious to ignore.
Several years ago, when Zimbabwe's agricultural industry was still successful, some farmers found that their irrigation systems weren't working properly. They eventually traced the problem to missing brass fittings, stolen from the water pipes. Why brass? Because it was so much in demand for coffin handles for those who had died from HIV/AIDS.
It is a striking metaphor for how disease disrupts the economy. Indeed, of all the deleterious effects of health problems on national productivity in African nations, few are as stark as those for HIV/AIDS. The high rate of HIV incidence in sub-Saharan Africa — mostly within the 15-49 age group that supplies the workforce — has prompted forecasts of future labour pools being depleted by 20–40% in some countries.
Figures such as this are dreadful in any context. But Matthew Bonds of the Harvard School of Public Health in Boston, Massachusetts, and his co-workers suggest in their latest study that, in the long term, the most disturbing aspect of such figures lies with the implications for economic growth1. Bonds and his colleagues have developed a theoretical model of how infectious disease interacts with economics to create 'poverty traps', in which a nation's development can be stymied indefinitely.
The team's argument relies on two-way feedback. As per capita income rises, they say, so does the level of health, thanks to better nutrition, sanitation and protection from and treatment of disease. And as health improves, so does the opportunity to increase per capita income. But within certain parameters, the researchers' model has a stable equilibrium in which the economy stagnates, held back by disease — known as a poverty trap.
One urgent question raised by the work is: how seriously should we take it? The authors make no secret of the huge simplifications such a model demands, nor of the tremendous challenges involved in trying to test and verify its predictions.
Perhaps more pertinent is the possibility that the model dictates its own predictions. Given the nonlinearities in the equations, it would be foolish to say that the appearance of poverty traps is obvious from the outset — but with the mutual dependence of income and health, it is not difficult to see how they come about.
Yet the work carries the unavoidable burden of any study that addresses such a globally important issue — if we believe the results, then the obligations they impose are huge. That, of course, is also the problem currently staring us in the face at the Copenhagen climate negotiations. And it is not to belittle the threat of climate change to say that the plight of Africa looms larger, not least because the human catastrophe there is already happening.
The question here, then — as for climate modelling — is how to evince courage in one's convictions without overselling a simplistic treatment. If we really think that a link between economics and disease is the cause of poverty traps, what are we waiting for?
However, unlike climate change, it seems like there is little to be lost even if the model proves flawed. The case for action on disease in poor countries is already overwhelming; if studies such as these add another reason by linking disease to economic development, so much the better. After all, much disease in Africa is more easily preventable than HIV/AIDS. Two-thirds of all deaths of infants below five years of age could be prevented by cheap treatments: vitamin A supplements, mosquito nets, rehydration salts. Some 200 million people are infected with debilitating intestinal worms that could be treated at a cost of US$0.25 per capita. Compared with the figures that are likely to be bandied around in Copenhagen, effective intervention here would cost very little.
It would be foolhardy to think that the answer is that simple, and Bonds and colleagues make no such suggestion. The problem in poor African nations is that the poverty traps are tangled webs of chicken-and-egg factors: corrupt or weak governance, conflict, lack of technical and social infrastructure, fragile export economies. Even for health, knowing the cure is not the same as administering it efficiently and sustainably. But this study provides another good reason to start trying.
Bonds, M. H., Keenan, D. C., Rohani, P. & Sachs, J. D. Proc. R. Soc. B advance online publication doi:10.1098/rspb.2009.1778 (2009).