It's easy to test for malaria, if you actually think to test for malaria. In the 90s, we used to hear wild stories from people we knew who would come down with malaria shortly after returning to the USA and doctors and nurses would freak out not knowing what to do about it, and the medication would be expensive to obtain, so the conventional wisdom was also to remember to take a few pills with you on the plane back to the USA!
It's sad but unsurprising that no one was able to treat these German workers in time. When I was a child, there was already talk of strains developing resistance, and this has gotten worse in the 21st century, and the airport workers caught the most deadly strain:
https://www.theguardian.com/world/2026/aug/27/malaria-outbre...