From Miami to Berlin: a stowaway rat reveals hidden global health risks
DZIF researchers pioneer standardized pathogen screening workflow after extraordinary airplane incident
Rats of the species Rattus rattus (pictured) can transmit dangerous zoonotic pathogens such as Leptospira interrogans (leptospirosis), Streptobacillus moniliformis (rat-bite fever), Seoul orthohantavirus, and the rat hepatitis E virus.
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.
Rats, particularly the species Rattus rattus (black, ship or roof rat) and Rattus norvegicus (brown rat), are among the most successful fellow travelers in human history. For centuries, they have been traveling on ships, trains, and trucks, spreading themselves across the globe. With millions of flights each year, their chances of crossing continents as uninvited “stowaways” are also increasing. Rats can transmit dangerous zoonotic pathogens such as Leptospira interrogans (leptospirosis), Streptobacillus moniliformis (rat-bite fever), Seoul orthohantavirus, and the rat hepatitis E virus. These infections can cause severe illness in humans.
In this case, the rat was observed by passengers on the flight from Miami to Berlin, but may have been on the plane since the passenger aircraft departed from Dubai. “Rats are true globetrotters. Wherever people travel or transport goods, rats can follow—and bring their microbes with them,” explains Prof. Rainer Ulrich, DZIF scientist at FLI and senior author of the study.
Findings of a comprehensive pathogen screening
The rat was dissected in the FLI's high-containment laboratories, and samples of various tissues and blood samples were examined at the FLI and by numerous network partners. A multi-layered screening strategy was used, comprising bacterial cultures and characterization, high-throughput sequencing, and specific methods such as PCR, RT-PCR, and multiplex serology. This “all tools on deck” approach resulted in a comprehensive workflow that can serve as a model for similar cases in air and sea transport in the future.
The results were both reassuring and illuminating. None of the most feared rat-borne pathogens, such as hantaviruses, 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.
In addition, numerous other bacterial and fungal genera were discovered, including mostly harmless commensals such as intestinal bacteria of the genera Lactobacillus or Ligilactobacillus, as well as opportunistic pathogens such as Enterobacter cloacae and Klebsiella aerogenes. The team also identified four new viral genome segments of the little-studied Picobirnaviridae family.
Global spread, invisible risks
The study makes it clear that the risk lies not only in the pathogens that have been found, but also in what could be found in future cases. Whereas rats used to travel from continent to continent mainly by ship, today, thanks to global air travel, they can travel from Dubai to Berlin via Miami in less than 24 hours, potentially carrying viruses across three continents in a single trip.
“Our findings demonstrate that rats are not just urban pests. They should be regarded as active players in the global network of pathogen spread,” emphasizes Prof. Ulrich.
From incident to preparedness
The study provides the first blueprint for dealing with animals discovered on board an aircraft. The authors’ key recommendations include the immediate capture and containment of stowaway animals, in line with WHO and IATA regulations, as well as a standardized laboratory workflow for comprehensive pathogen screening. In the event of an emergency—such as a hantavirus finding—contact tracing, disinfection, and other measures could then be initiated immediately.
Looking ahead: rats as One Health indicators
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.
