Pestilence is often depicted as one of the four horsemen of the Apocalypse. Colombia has largely prevented war, death and famine from spilling over from Venezuela, its perpetually troubled neighbour.

However, the fourth horseman is more persistent: Colombian health officials announced last week that the country’s first case of measles in years has arrived in its second-biggest city as health experts warn of a world-wide perfect storm of highly infectious diseases.

Declining vaccination rates in the developed world combining with vulnerable populations displaced from conflict zones ensure that diseases evade eradication.

At a press conference in Medellin, Colombia, Health Minister Alejandro Gaviria confirmed an unvaccinated 14-month-old Venezuelan boy arrived in the city from Caracas and became the first measles case since 2015.

A crippling shortage of medicines and vaccines, as well as decaying hospitals and an exodus of doctors has thrown Venezuela’s health sector into a tailspin, and its problems are spreading across its borders.

Now Colombian authorities are tracking down the 32 people who were most likely to have been exposed to the boy so they can be vaccinated.