A small cluster of hantavirus infections linked to a recent cruise ship voyage is under investigation by international health authorities, with confirmed and suspected cases reported across multiple countries.
According to the World Health Organization, the event involves infections consistent with the Andes strain of hantavirus, a pathogen responsible for a severe respiratory disease with a high case fatality rate in the Americas. There is no approved antiviral therapy that can cure hantavirus infection.
Current reports indicate approximately seven individuals classified as confirmed or suspected cases, including at least three deaths. Cases involve both passengers and potentially crew members, with epidemiological investigations ongoing to determine the timing and nature of exposure during the voyage.
Passengers who had been traveling in Argentina before boarding the cruise ship are believed to be the most likely source of the Andes hantavirus outbreak, according to Bobbi S. Pritt, MD, MSc, FCAP, professor of Laboratory Medicine and Pathology and chair of the Division of Clinical Microbiology at Mayo Clinic, during a May 12 press briefing hosted by the College of American Pathologists (CAP). Pritt added that similar outbreaks have occurred in Argentina before, noting that the sequencing data released so far from other countries has not shown concerning mutations in the current strain.
At least 17 US citizens are among those aboard the ship, who have been identified for follow-up or repatriation to the US. The vessel is currently on route to Spain, under coordinated port and public health oversight. Authorities are continuing to track disembarked individuals across multiple jurisdictions.
Given the unusual setting of a cruise ship outbreak and the involvement of a high-consequence pathogen, the situation is being closely monitored by public health agencies across the world.
Today's Clinical Lab spoke with Mara Jana Broadhurst, MD, PhD, DTMH, FCAP, associate professor in the University of Nebraska Medical Center’s Department of Pathology, Microbiology, and Immunology, and an expert in BSL-4 pathogens, about what we know so far about the outbreak, how such cases are investigated, and what challenges laboratories may face in confirming and tracking infection in real time:
How is hantavirus typically diagnosed?
Broadhurst: Hantavirus infections are most commonly diagnosed using serologic tests that detect antibodies generated by the immune system in response to the virus. These tests are generally reliable once symptoms have developed, but antibodies may not yet be detectable early in infection or before symptom onset. Hantavirus infection can also be diagnosed by detecting viral RNA in blood using PCR-based testing.
What makes early detection challenging?
B: Molecular tests may be more sensitive during the earliest stages of infection and can sometimes identify infection before symptoms or antibodies are detectable. However, these tests are specialized, not widely available, and are typically performed only in select public health or reference laboratories. Early detection can be challenging because the initial symptoms of hantavirus infection such as fever, fatigue, headache, and muscle aches are nonspecific and overlap with many other viral illnesses.
What do we know about transmission risk in close-quarters environments like cruise ships?
B: Most hantavirus infections occur after exposure to infected rodents or their excreta, particularly through inhalation of aerosolized particles from rodent urine or droppings.
In the case of Andes hantavirus, limited person-to-person transmission has been documented, but it appears to require close and prolonged contact. Reported exposures associated with transmission have included sleeping in the same bed, intimate contact, or providing direct care to an infected individual.
Andes virus has been detected in body fluids including blood, saliva, urine, and semen. However, the precise mechanism of transmission between people has not been definitively established.
Cruise ships can facilitate the spread of infectious diseases because they involve prolonged close contact among passengers and crew in shared indoor environments. However, Andes hantavirus is not considered highly contagious, and there is currently no evidence that it spreads efficiently through casual contact in the way that respiratory viruses such as COVID-19 or influenza do.
Why is the Andes strain of hantavirus being closely watched by health authorities?
B: Andes hantavirus is the most common hantavirus causing human infection in South America. Like Sin Nombre virus, which is the primary hantavirus found in the US, Andes hantavirus can cause hantavirus cardiopulmonary syndrome (HCPS), a severe respiratory illness with a mortality rate of approximately 40%.
What makes Andes hantavirus distinct is that it is the only hantavirus species for which person-to-person transmission has been clearly documented. Although this type of transmission appears to be uncommon and generally requires close and prolonged contact, it raises important public health concerns that warrant careful monitoring and contact tracing during outbreaks.
Importantly, Andes hantavirus is not considered highly contagious in the way that viruses such as COVID-19 or influenza are. Documented person-to-person transmission has been relatively limited and has generally occurred in settings involving sustained close contact, rather than casual community exposure.
The situation remains under active investigation as health authorities refine case definitions and continue monitoring exposed passengers. A flight attendant previously evaluated has tested negative for hantavirus, narrowing the focus to confirmed and suspected passenger cases.
According to a CDC official, arrangements are underway for passengers to be met in the Canary Islands and transferred to Nebraska for further evaluation and quarantine, with additional updates expected as laboratory and epidemiological findings continue to emerge.
The Nebraska National Quarantine Unit—a federally designated facility for monitoring and caring for people exposed to high-consequence pathogens—will remain available throughout the incubation period, said Broadhurst during a May 12 CAP press briefing. She added that decisions on whether exposed individuals are monitored in the facility or at home will depend on balancing clinical oversight with practical considerations and are still being evaluated.
So far, preliminary data indicates the strain is similar to those seen in prior outbreaks in Argentina and Chile, said Broadhurst.
“While I haven’t seen the sequencing data yet,” said Benjamin Bradley, MD, PhD, FCAP, medical director of high consequence pathogen response, virology, and molecular infectious disease at ARUP Laboratories, during a May 12 CAP press briefing, “with access to next-generation sequencing, we are able to genotype these viruses in near real time and share that public health data.” Sequencing and modelling is underway, he said, and is likely to be published in the scientific literature soon.
Editorial Note: This article was updated on May 12 to include details from a College of American Pathologists press briefing with Mara Jana Broadhurst, MD, PhD, FCAP; Bobbi S. Pritt, MD, MSc, FCAP; and Benjamin Bradley, MD, PhD, FCAP.
