Parasites, Poverty and Biodiversity

Conservationists lamenting the diminished focus on biodiversity in an increasingly ecosystem service dominated field can take succour from a study by Matthew Bonds and colleagues published in PLoS Biology.

The interesting take-home, which is actually a side event in the paper, is that the loss of biodiversity (species richness of plants, mammals, and birds), increases the burden of vector-borne parasitic diseases amongst a country’s human population, which in turn increases poverty.

The study’s principal focus was on disentangling the relationship between disease and poverty at a macro scale.

Are countries poor because they have lots of disease? Or do they have lots of disease because they’re poor? 

These relationships cannot be explored with straightforward regression models because causality is likely to flow both ways.

To circumvent this bias, the authors use a multi-layered but elegant modelling approach that makes use of additional variables that are correlated with one of disease or poverty but independent of the other – which is where they bring in biodiversity.

Links between ecosystem degradation and disease burden have been demonstrated before, but this is one of the first studies to clearly link biodiversity (in its species richness sense) to human health.

The precise mechanism of this link is not entirely clear; one hypothesis is that biodiversity puts downward pressure on parasites and non-human hosts. Important questions about the biodiversity effect on disease remain to be explored, for example, how does the effect differ between rural and urban populations and what does this mean in a rapidly urbanizing world?

The authors are reserved about the possible policy implications of their findings even though they rightly stress the importance of the question for policy.

Even with mounting evidence of a causal link between environmental degradation and human health, the nagging question for policy is whether an ecosystem approach to public health is as expedient or cost effective as other alternatives.

I suspect that in terms of direct actions it probably wouldn’t, but it does contribute very significantly to the bundle of benefits that healthy, biodiverse ecosystems provide a country.

Bonds MH, Dobson AP, Keenan DC (2012) Disease Ecology, Biodiversity, and the Latitudinal Gradient in Income. PLoS Biol 10(12): e1001456. doi:10.1371/journal.pbio.1001456  

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