Worm index offered as proxy for development

Recording Health_Robin Hammond_Panos
Copyright: Robin Hammond/Panos

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  • High ‘worm index’ scores, meaning more infections, relate to lower development
  • Worm infections not only occur in a setting of poverty, but also cause poverty
  • Call for the SDGs to target neglected tropical diseases such as worms

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An index based on numbers of parasitic worm infections is a robust way to measure a country’s development, according to a paper. This finding shows the importance of specifically targeting neglected tropical diseases in the Sustainable Development Goals (SDGs), say the researchers behind the measure.

The paper shows that the ‘worm index’ matches up with the levels of development indicated by the Human Development Index (HDI), a UN-approved measure encompassing life expectancy, income and education. The higher the worm index, the lower the HDI score (see chart).

worm index graph
Data from 2013 and 2014 shows that countries with a higher ‘worm index’ tend to have lower lowers of development, as indicated by the HDI. The index units are arbitrary. Credit: Peter Hotez

Because of this close association, says US doctor and lead author Peter Hotez, the SDGs should pay particular attention to neglected tropical diseases such as parasitic worms.
Unlike the Millennium Development Goals, which mentioned combating malaria and HIV/AIDS as an overarching goal, the current draft of the SDGs does not single out any diseases as a priority. But given how the index suggests worms and poverty are closely related, Hotez says, it’s good that neglected diseases in general are mentioned.

Hotez and coauthor Jennifer Herricks, both from the National School of Tropical Medicine at Baylor College of Medicine, United States, calculated the worm index using WHO data in a paper published last week (30 April) in PLOS Neglected Tropical Diseases.

“Worm infections not only occur in a setting of poverty but they also cause poverty.”

Peter Hotez

Each nation’s index is calculated based on the number of individuals requiring deworming and preventative treatments for three types of worm infection.

The three worm infections used in the measure — hookworm, schistosomiasis and lymphatic filariasis — caused a reduction of 10 million disability-adjusted life years in 2010, according to the Global Burden of Disease Study from that year.

“The Human Development Index is a complex metric that includes educational attainment and economic development. These are the two factors that worm infections are associated with,” says Hotez.

The study looks only at the correlation between the two indices and does not explore their causal relationship. But Hotez says poverty and worms are likely to affect each other.

“Worm infections not only occur in a setting of poverty but they also cause poverty,” he says. “They interfere with the intellectual and cognitive development of children and they often make adults too sick to go to work.”

Uwem Friday Ekpo, a parasitologist at the Federal University of Agriculture in Nigeria, says: “A worm index can be a useful parameter for the assessment of deworming programmes and sustainable human development — not only in developing countries but also in the developed countries, where these infections are also prevalent.”

He says it could also prove useful for measuring the outcomes of development programmes looking at poverty, sanitation, hygiene, education and primary healthcare — factors that appear to mutually affect worm prevalence.

Herricks says more research is needed to check if the index does correlate with these individual underlying factors.


Peter J. Hotez and Jennifer R. Herricks Helminth elimination in the pursuit of Sustainable Development Goals: a “worm index” for human development (PLOS Neglected Tropical Diseases, 30 April 2015)