How worried should we be about hantaviruses?
Since a zoonotic hantavirus caused the deaths of three holidaymakers on a Dutch cruise ship in April, scientists have been trying to better understand the threat it poses to humans.
Marieke Rosenbaum, Assistant Professor, Department of Infectious Disease and Global Health, Tufts University, is researching the transmission of diseases from rodents to humans. Here, she shares some of the latest knowledge about hantaviruses.
How likely is it that the recent cruise ship hantavirus outbreak spread from rats?
At this stage, rodents remain the most likely original source of exposure. The current genomic evidence suggests that the outbreak likely began with a single zoonotic spillover event followed by subsequent human-to-human transmission.
Because this outbreak occurred in a closed, high-density environment, limited person-to-person transmission could have occurred, which is rare but has been documented with certain strains, such as Andes virus. The viral sequences obtained from different cases are remarkably similar, differing by at most a single nucleotide polymorphism, which strongly supports a common origin. This pattern is very similar to what was observed during the well-characterized 2018 Epuyén Andes virus outbreak in Argentina, where person-to-person transmission occurred.
Importantly, that does not necessarily mean rats were the source. Hantaviruses are associated with specific rodent reservoirs, and for Andes virus the primary reservoirs are wild rodents in the sigmodontine group, rather than the urban rats people commonly think of, which can carry other hantavirus strains globally.
What are the remaining knowledge gaps for scientists?
At this point, environmental investigations, including rodent trapping and testing, are still needed to identify the reservoir species and determine exactly where the initial exposure occurred. Also, the genomic data cannot completely exclude the possibility that multiple passengers were infected from the same environmental source early in the outbreak. Right now, the strongest interpretation is that there was an initial zoonotic introduction followed by at least some degree of secondary transmission between people.
How are the viruses transmitted between humans?
Most hantaviruses are not efficiently transmitted between people. Human infection classically occurs through inhalation of aerosolized virus from rodent urine, feces, or saliva in contaminated environments. However, Andes virus is a notable exception and is one of the few hantaviruses known to spread person-to-person.
Transmission is thought to occur through close contact with respiratory secretions or prolonged exposure to infected individuals, particularly during the prodromal phase of illness. The genomic similarity seen in this outbreak suggests that at least some human-to-human transmission occurred.
What diagnostic methods can be used to detect hantavirus infection?
Diagnosis relies on a combination of clinical presentation, exposure history, and laboratory testing. PCR assays can detect viral RNA during acute infection, while serologic testing can identify IgM and IgG antibodies against hantaviruses.
Genomic sequencing has become increasingly important during outbreaks because it allows investigators to identify the viral strain, compare cases genetically, and better understand transmission dynamics. Early diagnosis is critical because patients can deteriorate rapidly once pulmonary symptoms develop. In this outbreak, rapid sequencing was critical for confirming Andes virus and informing diagnostic and public health responses.
How can microbiologists contribute to disease surveillance during this outbreak?
Microbiologists are central to outbreak response. They help identify the viral strain, track mutations, and determine whether cases are linked through genomic sequencing.
Environmental and wildlife surveillance are also critical. Testing rodents and environmental samples can help identify the reservoir species and clarify how transmission occurred.
Integrating laboratory findings with epidemiologic data allows us to better understand whether we are dealing with repeated rodent-to-human spillover events or possible human-to-human spread. Those insights are essential for reconstructing transmission pathways and guiding public health interventions.
Do any other animals harbor hantaviruses?
Yes. Hantaviruses are carried by a variety of small mammals globally, including mice, rats, voles, and shrews. Different hantavirus species are associated with different reservoir hosts.
These animals generally do not become clinically ill themselves but can shed virus into the environment. Understanding reservoir ecology is critical because human risk is tightly linked to the behavior, distribution, and population dynamics of these host species.
What is the best way to mitigate the spread of the disease?
Reducing exposure to infected rodents and contaminated environments remains the most important prevention strategy. This includes rodent-proofing buildings, improving sanitation, safely cleaning areas contaminated with rodent droppings, and using appropriate personal protective equipment during cleanup or high-risk occupational exposures.
Importantly, people should avoid sweeping or vacuuming rodent droppings, which can aerosolize viral particles. In outbreaks involving Andes virus, rapid case identification, contact tracing, and infection-control precautions are also important because of the potential for person-to-person transmission.
What has your research revealed about infectious diseases in rats in Boston?
My research focuses on the ecology of infectious diseases in urban rat populations and how urban rat populations impact human health. Through the Boston Urban Rat Study, we’ve shown that rats in Boston carry a range of pathogens relevant to both human and veterinary medicine, including Leptospira, antimicrobial-resistant Staphylococcus aureus, and evidence of influenza A exposure.
Our work has also shown that rat populations in cities are highly structured geographically, which affects how pathogens spread through urban environments.
More recently, through collaboration with Steven Bradfute and his team at the University of New Mexico, we have been investigating whether Boston rats may harbor hantaviruses and other emerging pathogens. One of the major lessons from this work is that cities create complex interfaces between humans, animals, and pathogens, and understanding those interfaces is critical for predicting and preventing future outbreaks.
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