SONIA SHAH is a science journalist and author. Her book Pandemic: Tracking Contagions From Cholera to Ebola and Beyond will be published in February 2016.
A cholera outbreak that began in Iraq in mid-September has spread into war-torn Syria. From there, a massive flow of desperate refugees  could carry the disease deep into the Middle East and even into southern Europe.
Humanitarian aid physicians working in Syria report that three cases have been confirmed in two cities controlled by the self-proclaimed Islamic State (also known as ISIS): Deir ez-Zor, in eastern Syria; and Aleppo, in the northwestern part of the country. Undoubtedly, these cases are just the tip of the iceberg. Under the best conditions, clinicians usually diagnose only 30 percent of the cholera cases that occur during epidemics ; in Syria, where hospitals and clinics have been destroyed by air strikes, they’re likely diagnosing far fewer.
This outbreak was predictable. Cholera is caused by a bacterial pathogen that passes between people via human waste and is easily spread through contaminated food and water. If introduced into crowded refugee camps with rudimentary sanitation, the pathogen can rapidly explode. Millions of people are internally displaced in Syria, and supplies to disinfect drinking water have been cut off outside government-controlled areas. Eight months ago, the World Health Organization (WHO) noted the country’s vulnerability to cholera. And then two months ago, the pathogen struck in neighboring Iraq, where 15 of 18 provinces are now infected . With a porous border and a mass exodus of Syrians, Iraqis, and others under way, cholera’s arrival in Syria was just a matter of time.
Predictable and preventable cholera epidemics have reached historic proportions in recent years. In October 2010, ten months after a magnitude seven earthquake shattered the country, cholera arrived in Haiti, most likely for the first time in over 100 years . The U.S. Army Corps of Engineers had predicted as far back as 1999 that the country was ripe for an outbreak of waterborne diseases such as cholera, a warning echoed by aid nongovernmental organizations after the earthquake. The UN nevertheless ferried soldiers directly from cholera-struck Kathmandu, Nepal, into the country that October without