IF13230 — Current Hantavirus Outbreak and Considerations for Congress

Background and Current Hantavirus Outbreak Hantavirus is a zoonotic pathogen carried by rodents (e.g., mice and rats) and transmitted to humans generally from contact with their droppings, urine, and saliva. On May 2, 2026, the World Health Organization (WHO) received notification of two deaths and one critically ill passenger from an acute respiratory illness onboard the M/V Hondius cruise ship, originating from Argentina. These cases were later confirmed to be the Andes strain of the hantavirus, according to the WHO. Symptoms appeared for the initial case on the ship on April 6, 2026. Related policy issues for Congress include the nature of international coordination for outbreaks, domestic preparedness for disease outbreaks, and U.S. research and development for zoonotic diseases. As of May 13, 2026, the outbreak was ongoing; there were 11 reported cases of hantavirus linked to the cruise ship, 8 of which have been laboratory confirmed. Passengers from the M/V Hondius have been repatriated, and public health authorities have initiated contact tracing to monitor for additional spread. Additional passengers who departed the cruise ship prior to the identification of the outbreak may have been exposed to hantavirus and unknowingly exposed others. Symptoms of hantavirus from the Andes strain can appear in 4 to 42 days after exposure. The Centers for Disease Control and Prevention (CDC) has stated that the “the overall risk to the American public and travelers remains extremely low.” No U.S. hantavirus cases associated with the current outbreak have been reported as of the publication of this product. What Is Hantavirus? Hantavirus has been known to infect humans for at least several decades. The disease was first documented during the Korean War in the 1950s, the virus was isolated in 1978, and the WHO recognized the disease in 1982. Hantavirus is endemic throughout the world. Hantaviruses belong to the family Hantaviridae, with each strain typically associated with a specific rodent species. More than 40 strains of hantavirus exist in nature and are broadly divided into two categories, Old World and New World. Old World hantaviruses are endemic in Europe and Asia and can cause hemorrhagic fever with renal syndrome, a disease associated with severe bleeding and kidney failure. New World hantaviruses are more prevalent in the Americas and more commonly can cause hantavirus pulmonary syndrome (HPS), a flu-like illness that can lead to heart and lung failures. Only a limited number of hantavirus strains are known to cause human disease. Depending on the strain, hantavirus has a reported fatality rate of less than 1%-15% in Asia and Europe and up to 50% in the Americas. According to the WHO, an estimated 10,000 to over 100,000 infections occur each year, the majority in Asia and Europe. Hantavirus is known to incubate one to six weeks after exposure, which means patients can show symptoms from as early as one week to eight weeks after infection. There are no specific treatments or vaccines for New World hantaviruses; there are some vaccines for certain Old World hantaviruses. The WHO has classified hantavirus as an emerging priority because of its lethality. The Andes strain of hantavirus, a New World strain found in South America, is the only hantavirus strain known to spread person-to-person. According to the CDC, human-to-human spread is usually limited to those with direct physical contact with an infected person, including prolonged time spent in close or enclosed spaces and exposure to the infected person’s body fluids. The Andean strain was first identified in 1996 in Argentina, where evidence for human-to-human spread was first indicated. A recent outbreak occurred in Argentina in 2018-2019. Given the relatively low number of prior outbreaks, there are some unknowns about human Andes virus transmission, including the extent of contact needed and whether asymptomatic transmission occurs. Hantavirus Cases in the United States Hantavirus disease surveillance in the United States began in 1993 during an outbreak in the Southwest that killed 27 people. Since then, the CDC reported a total of 890 cases of hantavirus (35% resulted in death) in the United States from 1993 to 2023 (Figure 1). Those cases were concentrated in the western United States; 94% of cases occurred west of the Mississippi River (Figure 2). CDC has published summary data on hantavirus cases and outcomes through 2023. By reviewing CDC’s National Notifiable Diseases Surveillance System data, CRS identified 20 cases in 2024, 40 cases in 2025, and 4 cases between January 1 and May 9, 2026. Recent-year data are subject to change. U.S. Implications for the Current Outbreak. No U.S. cases of the Andes strain of hantavirus have been reported as of the publication date of this report. As of May 14, 2026, U.S. public health authorities were monitoring 41 people in the United States who may have been exposed to hantavirus related to the M/V Hondius outbreak. This includes 18 passengers from the M/V Hondius who were transferred for monitoring to the National Quarantine Unit in Omaha, NE, where they are encouraged to stay. The other 23 people under monitoring include passengers who left the ship before the outbreak was identified and other individuals who may have been exposed to ship passengers. According to the CDC guidance, those with high-risk exposures (e.g., passengers of the M/V Hondius) may have the option for home-based management or facility-based management at the National Quarantine Unit or in a location identified by a health department of each person’s jurisdiction. In all cases public health agencies are to conduct daily monitoring, according to the CDC. Figure 1. Reported Hantavirus Cases in the United States, 1993-2023 / Source: Chart generated by CRS with data from CDC. Figure 2. Hantavirus Cases by State, 1993-2023 / Source: Map generated by CRS with data from CDC. Considerations for Congress The identification of the Andean strain in the recent hantavirus outbreak highlights the potential risk of human-to-human transmission of this particular virus. Outbreaks of hantavirus and other zoonotic diseases (e.g., avian influenza) frequently occur globally and can spread to the United States by humans and animals via transportation networks (e.g., aircraft, ships, cars) and wildlife corridors (e.g., bird flyways). International Coordination. The WHO and other international organizations attempt to coordinate countries to enhance monitoring, reporting, and response to infectious disease threats. The United States withdrew from the WHO in 2026. Despite withdrawal from the WHO, the United States is still party to the International Health Regulations, through which CDC has received notifications from international partners about this outbreak. The CDC says it has worked closely with other federal agencies and international partners to bring Americans on the M/V Hondius home as quickly as possible. Congress may conduct oversight on U.S. coordination with international partners in this outbreak in light of the recent U.S. withdrawal from the WHO. Congress may also consider whether the United States’ ability to coordinate monitoring and responses to future zoonotic disease outbreaks with other countries is sufficient. Scientific Research and Development. Zoonotic diseases are expected to increase due to greater human incursions into wild areas, ecosystem alterations, and broadening transportation networks. Many scientists contend that scientific research into zoonotic diseases is important for increasing preparedness to address outbreaks, enabling early detection of outbreaks, and improving the development of treatments and vaccines. Others suggest that certain types of zoonotic disease research introduce potential risk and should be limited or banned. There are many unknowns about hantaviruses and other pathogens that cause zoonotic diseases, including information about their emergence, spread, and transmission. The federal government conducts research on zoonotic diseases and supports other research through grants. Some of this research is aligned with a One Health approach, which recognizes the interconnectedness of human, animal, and environmental health to predict and mitigate zoonotic and panzootic diseases. Congress might consider whether levels of funding and agency priorities are appropriate for answering scientific questions and developing new products that could help contain the current outbreak and prevent future ones caused by hantavirus or other pathogens. U.S. Domestic Response. No U.S. hantavirus cases associated with the current outbreak have been reported as of the date of the publication of this report. Many U.S. laboratories can test for hantavirus; currently, only the Nebraska Public Health Laboratory can conduct diagnostic testing for the Andes virus strain. State and local public health agencies receive ongoing CDC grant funding that can support infectious disease containment activities. The CDC also has access to an Infectious Disease Rapid Response Reserve Fund with a balance of over $500 million that could support enhanced response. Congress may choose to review federal public health agencies’ efforts to contain this outbreak, whether such efforts are sufficient, and whether existing resources at the federal, state, and local level can support the response to the current outbreak and to future zoonotic threats. The COVID-19 pandemic and recent outbreaks of hantavirus, avian influenza, and measles demonstrated how communication from and trust in public officials can influence how the public responds to a disease outbreak, including whether recommended procedures to combat or slow the spread of a disease are adopted by the public at large or at-risk individuals. Through its oversight authorities, Congress may choose to examine whether federal resources for public health and science agencies are sufficient to address how the U.S. government would respond to emerging infectious diseases and garner trust with the public about the risk of these diseases.

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