The recent report of an outbreak of hantavirus on a cruise ship gave feelings of double déjà vu to those of us in the infectious diseases field. The first déjà vu moment is that of the Covid-19 outbreak on the cruise ship the Diamond Princess, which was the first such SARS-CoV-2 outbreak of its nature and resulted in the ship being bounced around, and finally allowed to dock and discharge its beleaguered passengers after two weeks of quarantine. The second déjà vu moment is the hantavirus infection that claimed the lives of classical pianist Betsy Arakawa and, by extension, her husband Gene Hackman in their New Mexico home just over a year ago. Betsy had apparently contracted hantavirus pulmonary syndrome from rodent nests found around their house and subsequently died at home, while Gene Hackman, who had advanced Alzheimer’s, was unable to call for help and died of heart failure.

As of writing, the current outbreak on the cruise ship MV Hondius has already killed three people, and at least five others have fallen ill. Six of the eight cases have tested positive for the Andes hantavirus on genomic sequencing. The rest of the sick patients are presumed to have hantavirus infection until they can be properly tested, since they are showing symptoms consistent with the disease. The ship is currently docked off the coast of Praia in Cape Verde, and some of the sick passengers have been evacuated. The rest of the passengers and crew are likely going to be quarantined either onboard or transferred to a facility for this purpose. The MV Hondius originated from Argentina, where hantavirus is endemic, particularly the Andes virus, which is the only hantavirus that has been documented to be capable of human-to-human transmission. According to reports, the cruise ship also stopped in Uruguay and Chile, where there have been periodic outbreaks of hantavirus. Authorities in these countries are racing to find the potential source and contain any local infections as well.

What is hantavirus? Hantavirus is a family of viruses that can cause two distinct deadly syndromes: hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). Hantavirus disease usually starts off with a flu-like illness characterized by fever, malaise, muscle pain, and headaches, and can easily be mistaken for more common illnesses. Patients who progress to HPS end up with shortness of breath that can progress to severe respiratory failure and death. If they survive, recovery can be prolonged for up to six months. Patients who progress to HFRS have symptoms that are very similar to leptospirosis, with decreased urine output, bleeding in the urine and the stool, and potentially bleeding in the lungs as well. Low platelets can be found in both syndromes, and so hantavirus infection can be mistaken for dengue fever.

Hantavirus is a zoonosis, which is an infectious disease transmitted from animals. The natural host of hantaviruses is rodents, and humans are infected when they inhale aerosolized dried rodent feces, urine, or saliva. Rodents do not manifest signs or symptoms of disease, and so these serve as persistent reservoirs of infection. Hantaviruses are found all over the world.

Hantaan virus was the very first hantavirus to be described and gave the virus family its name. It was discovered during the Korean War when it caused an outbreak of HFRS among soldiers stationed along the Hantan River. Hantaviruses in the Americas (New World hantavirus), such as Sin Nombre and Andes, can cause HPS, which has a 30 to 60 percent mortality. Old World hantaviruses include Hantaan, Seoul, Puumala, and Dubrava-Belgrade viruses, and these cause the relatively milder HFRS with a mortality rate of one to 15 percent. Puumanla and Dubrava-Berlgrade viruses cause less severe disease than Hantaan and Seoul.

There are no effective antivirals for any of the hantaviruses. Supportive care for HPS is the mainstay of treatment, including the use of ventilators and high-flow oxygen to support recovery of lung function. For HFRS, hydration and management of electrolytes are crucial. In case of renal failure, dialysis may be necessary either as a temporary measure if the kidneys recover or as an ongoing measure until a renal transplant can be performed. There is no widely available vaccine for hantavirus. Some inactivated vaccines have been developed in China and Korea and seem effective for preventing HFRS, although the duration of protection is unclear. Other vaccines are in development, including DNA, protein, and virus-like particle formats, and preliminary results are promising.

Prevention of infection starts with good pest control to minimize exposure to aerosolized mouse droppings. Wearing protective equipment, such as masks, when cleaning out rodent nests, especially those with dried mouse droppings, can decrease the risk of exposure and infection. It is still unclear how human-to-human transmission occurs with the Andes virus. Previous reports suggest close contact, but at least one transmission event occurred with only transient contact between the infected case and the subsequent victim.

The transmission pattern on the MV Hondius remains unclear. The victims could have all been exposed to rat droppings at the same time and manifested disease at different times. The incubation period of the Andes virus can take up to six weeks, and so there is a possibility of a single exposure. However, the previous documentation of human-to-human transmission for this specific hantavirus also makes it possible that some of the infected patients were subsequently exposed on board to the sick passengers. Active investigation is ongoing, and contact tracing for those passengers who were able to leave before the vessel was quarantined is being done.

One of the most important questions I get asked a lot is whether there is a chance this could turn into another pandemic. The World Health Organization (WHO) has already stated that this is unlikely. While the current outbreak seems to involve human-to-human transmission, this usually occurs only with prolonged and close contact. The period in which a patient is contagious is very short and only happens when he or she has a fever. The fever typically lasts only one day, although the other symptoms can persist. Finally, the long incubation period means that proper contact tracing and quarantine can interrupt transmission. Hantavirus can be controlled and contained. The most important thing is that we remain vigilant and listen to properly vetted advice from trustworthy sources like WHO and the Department of Health.