The World Health Organization has declared an international public health emergency from the "extraordinary" spread of polio to new countries. It wants residents of Pakistan, Afghanistan and other countries where the dangerous and highly infectious disease is spreading to be vaccinated and carry proof of treatment before being allowed into any other country.

This reflects a big setback to the ambitious international campaign to eradicate polio by 2018 to which more than $1 billion has been dedicated. It is also a sign that deadly attacks by Islamist militants on public health personnel administering oral polio vaccine to children in Pakistan have been distressingly effective.

According to the United Nations health agency, until now the anti-polio campaign had been making slow but impressive headway. The average annual number of cases fell from over 1,300 in the 1990s to around 1,100 in the first decade of this century. In the past three years the average has been around 400, a sign of real progress.

The number of new cases being reported in Asia is still relatively small, although in the first three months of 2014 the rate was triple that reported a year earlier. But the ability of the disease to spread rapidly among untreated children is real cause for concern.

The most troubling aspect of the new outbreaks is not just that the number of polio cases worldwide is now increasing, bucking a decades-long downtrend. It is that a life-saving public health campaign has become the target of terrorists who want to eradicate all forms of modern civilization. In parts of Africa they are bringing back slavery.

In Pakistan they are bringing back polio.