Thinking Aloud: The Worm Index and Human Development

May 6, 2015 by Darius 

According to a new study published in a science journal this week, for most of the world’s most populous countries, few factors correlate more closely with human development than the level of worm infections (!).

The study ranked the world’s 25 most populous countries based on their rates of infection from three types of worms: (1) worms that live in soil and attack the intestines, causing anemia and stunting in children, (2) snail-borne worms that cause internal bleeding and damage organs, and (3) mosquito-borne worms that cause elephantiasis.

The good news is that 10 of the world’s 25 most populous countries are entirely free of these types of infections.  The bad news is that most of the rest are projected to be among the top 10 most populous countries by 2050, depending on fertility rates.

The country with the highest rate of worm infections is the Democratic Republic of Congo, whose populace suffers from a total of 78.9 million infections by these three types of worms.  Because the DRC’s current population is only 69 million, this means that, on average, every citizen of the DRC is infected by more than one category of worm.  The DRC also has the lowest ranking of the world’s most populous countries on the UN Human Development Index.

The big countries that have the next highest rates of worm infections are Nigeria, Burma, and Ethiopia, with rates of 1.01 (more worm infections than people), 0.88, and 0.67, respectively.  Not surprisingly, these are also the populous countries with the next three lowest scores on the Human Development Index.

Rounding out the top 10 in worm infections are Indonesia, India, Bangladesh, the Philippines, Pakistan, and South Africa.  Of these, all but Burma and South Africa are projected to be among the 10 most populous countries in the world in 2050.

The so-called Worm Index is yet more proof of how China, for all of its oppressive political climate, has gotten things right: despite a population of 1.4 billion, China only has an estimated 18.5 million worm infections in the entire country, for a rate of 0.01.

Efforts to eradicate worms reap immediate and major dividends.  Worm infections are among the costliest tropical diseases in terms of disability-adjusted life years, a measure of years lost of healthy, productive life.  People afflicted with worm infections go to school less and are much less productive than their disease-free counterparts.  (One of the factors now believed to have held back educational attainment, agricultural productivity, and economic activity in the American South for much of US history, for example, was the South’s high rate of hookworm infection, which is consistent with the first type of worm infection listed above.)

Helpfully, aggressive de-worming programs are relatively cheap and can be as simple as digging and using latrines.

You can find the whole study, as well as more statistics, at

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