From Miami to Berlin: a stowaway rat reveals hidden global health risks

09/09/2025 - In 2017, a Miami–Berlin flight took an unexpected turn when passengers spotted a rat on board. After landing, the rat was captured and handed over to scientists at the Friedrich-Loeffler-Institut (FLI). There, it was not only seen as a nuisance, but also as an opportunity to examine it as a potential carrier of pathogens. Investigations by scientists from the German Center for Infection Research (DZIF), in collaboration with many other scientists from the “Rodent-borne pathogens network (NaÜPa-net)”, revealed only a few zoonotic and non-zoonotic pathogens. However, the incident underscored how easily pathogens can spread across continents—and why standardized testing of animal stowaways is so important. The findings were recently published in the journal Scientific Reports. The results were both reassuring and illuminating. None of the most feared rat-borne pathogens, such as hantavirus, Leptospira bacteria, or rat hepatitis E virus, were found. This implies that the risk of infection for passengers and crew during the flight was very low. However, the detection of a methicillin-susceptible Staphylococcus aureus (MSSA) strain in the rat’s nose and intestines was somewhat concerning. Whole-genome sequencing revealed that the strain was nearly identical to those found in humans in Europe and North America. This strain carried human-specific immune evasion genes, suggesting that it had adapted to humans before ending up in the rat. Its presence implies recent transmission from people to rats and potentially the reverse. “The surprising part was not what we didn’t find, but what we did find: a Staphylococcus aureus strain that is nearly identical to human variants. This shows that rats can pick up pathogens from us and potentially pass them back,” says Prof. Ulrich, a former member of the DZIF research area Emerging Infections. The researchers see rats as important indicators of ecosystem health in the future. The plan is to trace the origin of such animals through genetic analysis. In this case, mitochondrial DNA analysis showed that the rat belonged to a global line of black rats. However, it remained unclear whether it had boarded in Miami or Dubai. “This was a wake-up call,” says Prof. Ulrich. “It showed how vulnerable our interconnected world is to the spread of hidden pathogens. But it also showed that science can provide practical solutions.” The study was conducted by a consortium involving the FLI, the Robert Koch Institute, University Medicine Greifswald, the University of Leipzig, the Universitätsmedizin Göttingen, and other partners, and was supported by the DZIF.