Only two diseases have ever been completely eradicated worldwide: smallpox and rinderpest. But hopes for eradicating a third have dimmed with the World Health Organization’s announcement that the spread of polio has become a global health emergency.

After over 25 years of eradication campaigns, polio had been beaten back into only a handful of countries, and, by 2012, polio was eliminated or in sharp decline in all but three countries: Pakistan, Afghanistan, and Nigeria. But, as the virus has come roaring back, the WHO has set travel restrictions on new hotspots. Residents of Pakistan, Syria, and Cameroon are advised not to leave their countries unless they have been vaccinated against the disease and cannot carry it beyond their borders.

Pakistan is the cradle of the resurgent polio. Of the 74 cases of wild polio reported this year to date, 59 occurred in Pakistan. The increasing prevalence isn’t due to a new mutation or drug resistance; the resistance is coming from the Pakistani people, not the microorganisms that live inside them.

The vaccinators lost moral credibility when, in order to confirm the identity of Bin Laden prior to his assassination, the United States ran a fake hepatitis vaccination campaign in Abbottabad. Although doctors claimed they were going door to door to give inoculations, the blood draws they conducted were used for DNA tests discover whether any relatives of Bin Laden were living in town.

After Seal Team Six carried out their mission, some Taliban leaders banned vaccinations in the regions under their control and over a dozen vaccinators were murdered, forcing Pakistan to put its eradication campaign on hold. The doctor who conducted the operation was arrested by Pakistan’s own intelligence agency and held on charges of treason.

The doctor was accused of betraying his country to serve another government, but the United States itself came under fire for betraying the medical community and putting public health at risk. Scientific American excoriated the United States for disrupting and profaning a historically neutral and altruistic profession. Médecins Sans Frontières (Doctors without Borders) said that the CIA operation was a “grave manipulation of the medical act” and endangered the lifesaving work doctors conducted around the globe.

If doctors could be spies in disguise, how could nations welcome them in? In Syria, where polio is spreading amid the chaos of the civil war, how can vaccinators persuade Assad to let them move freely within the country, if they could be doubling as spies, assassins, or gun runners?

Ease of modern travel helps disease spread more rapidly; one sick patient in an airport or a subway hub is enough to send ripples of illness around the world. In order to check these diseases, public health officials need to be enter any country to set up quarantines and dispense inoculations. The United States has shattered the trust placed in medical workers, and polio may not be the last of the threats we face as a result.

This month, the first case of Middle East Respiratory Syndrome (MERS), a deadly respiratory infection, was identified in the United States. The CDC has been working to retrace the American Patient Zero’s steps, so they can treat and quarantine the people he exposed, before the disease can root itself in America. However, unless the illness is also checked abroad, the CDC may need to repeat these actions ad nauseum.

Along the border of Thailand and Myanmar, epidemiologists are working desperately to contain a strain of drug-resistant malaria. This strain must be eradicated, if we want to be able to continue using the current generation of anti-malarials, but one of the scientists on the project expects that the strain will nevertheless cross over to India, and, from there, the rest of the world within four years. Waiting until the disease has spread far enough to threaten us directly will mean waiting until it is too late to contain.

Combatting these diseases requires more than a team of elite commandos. Turning back a pandemic, whether of natural or human origins, requires international coordination and trust. America’s covert operations have broken that trust and put us all in danger.