The Andes hantavirus ship outbreak: Lessons from a dress rehearsal

Coming just a few years after the COVID pandemic caused widespread death and disruption, it’s no surprise that the hantavirus outbreak that began on a cruise ship last month is generating public concern. Like other American strains of hantavirus, the Andes virus that caused the outbreak has a high mortality rate, predominantly killing through respiratory collapse. Hantavirus infection is normally zoonotic. The virus usually jumps from rodents to people through aerosolized droppings, for example, when they clean a dusty shed. But on the MV Hondius, the virus instead jumped from person to person. The current outbreak is highly unlikely to morph into a replay of COVID; Andes virus is just not that good at transmitting among people. The crisis, however, is already raising serious questions about how ready we are for the next pandemic.

Patient zero appears to have been an ornithologist who had been traveling through the South America wilderness, including, potentially, areas where Andes virus can be found in the local fauna. He probably contracted a zoonotic infection before boarding the cruise ship on April 1. Though hantavirus usually has an incubation period of more than two to three weeks, his symptoms evolved in less than a week after boarding and quickly led to his death on April 11. It was not until two to three weeks later that subsequent cases appeared when his wife and the ship’s doctor, among others, fell ill.

By April 24, 30 people disembarked the ship. Unaware that they might be harboring a hantavirus infection, they travelled around the world. A few went on to develop symptoms. These included a permanent resident of the secluded South Atlantic Tristan de Cunha island, where health care literally arrived by parachute. The World Health Organization (WHO) didn’t begin evacuating passengers from the ship until May 10. Some of these evacuees were also later diagnosed with infections (two of them were symptomatic, including one in critical condition).

The situation now: A highly lethal virus that can transmit from person to person is potentially present in numerous countries. It’s infected 10, killed three, and left more than 100 people quarantining in the United States, the Netherlands, and elsewhere. Has the international response been swift and adequate? Let us see: (opens in a new tab)

First, at present, there have been no cases of infection among people who were not on the MV Hondius. Second, our limited knowledge of past outbreaks in Argentina  and Chile shows that this virus can spread among people, just not so readily as SARS-CoV-2 or measles. Third, the Andes virus’s protracted inoculation period is both a blessing and a curse. On the one hand it means that there won’t be a rapidly evolving epidemic—new cases, if they emerge, will likely do so slowly. On the other, protracted quarantines will be difficult to maintain. And there’s uncertainty about how successful virus containment will be.

Reassuring as that might be, a hard-nosed assessment of how authorities have responded to this virus scare so far turns up some reason for concern.

Did the initial diagnosis come swiftly? Let’s take patient one. It’s clear his death should have been investigated earlier as a death of special concern. A serious infection and respiratory symptoms in a person that had probably been in wild bird environments should raise suspicions. He could have had, for example, avian influenza—which might have been a far more significant pandemic threat if an efficient strain for human-to-human transmission had emerged. Were the subsequent diagnoses adequate? Yes, authorities quickly identified the type of hantavirus— Andes virus—and sequenced it. Are diagnostics easily accessible? Not at present, which could be a problem should those quarantining now or their contacts become symptomatic. The US Centers for Disease Control and Prevention (CDC) has not made a PCR test available, for example.

Was the response by international authorities swift? WHO rapidly developed new guidelines on how to define high-risk contacts and deal with suspected cases. It also adequately coordinated the evacuation of the MV Hondius, developing a plan for which country gets which passengers and under which conditions. The question now is whether countries are following WHO’s guidance?

Different countries appear to be taking different precautions.

The United Kingdom is set to release some high-risk contacts from supervised quarantines to their homes, with a suggestion for further at-home quarantine. The CDC, meanwhile, is advising high-risk contacts in the United States, where 18 patients have returned, to isolate at home and avoid sleeping in the same bed and using common items with other household members. But the agency is still allowing these contacts to have a continuous presence around potentially exposed people. Household members are allowed to come and go as they please, creating a degree of risk that they might expose others to a pathogen with 40 percent mortality rate—not something you would want near you. At the other end of the response spectrum, in the Netherlands, even health care personnel who breached the strict protocol required there for handling patient specimens are now quarantining for six weeks at home. Six weeks of quarantine is a challenge. But so are further cases of Andes virus.

Tracing people who might have been exposed remains a major challenge. We know that the roughly 30 people who had disembarked from the ship by April 24,  ignorant of their potential exposure to hantavirus, travelled to numerous countries. At least one of them developed symptoms and is hospitalized in Switzerland. Are we aware of the whereabouts and the state of health of all these individuals? Can we ensure that they have been placed in strict quarantine?

Worryingly one person who disembarked early reportedly travelled worldwide and even visited an extreme tourism conference in Vietnam, Jacqueline Sweet, an investigative journalist, reported. Imagine if this individual had ignored early symptoms and had infected other conference participants who could then return at their countries and develop symptoms weeks later.

A cornerstone of outbreak containment needs to be clear public health communication. On this score, official communication on the hantavirus raises eyebrows. The WHO head in Tenerife, for example, an island territory of Spain, disappointingly made excuses for some of the evacuees not wearing an N95 masks, saying that they might be uncomfortable for the elderly.

N95 masks, as we know from COVID, are an excellent form of first-line personal protective equipment (PPE) against a pathogen transmitting from person to person through the air. And many will recall that a lack of official clarity on whether SARS-CoV-2 was airborne or what kind of mask was effective against it during the early stages of the COVID pandemic helped sow confusion about PPE that likely hampered a rational public health response.

A counter argument would be that this disease is just not that transmissible. Extreme precaution may not be necessary. Data from the South American outbreaks published asks us to remain ambivalent on the question: Secondary cases in health care personnel have not been a consistent feature of these outbreaks, and transmission seems to occur in closed-space social gatherings or in households. But some of these outbreaks included transmission between individuals that were not in close contact. In the2018-2019 outbreak in Epuyen, Argentina, the median reproduction number, how many people an infected person infects, was 2.12 before isolation measures were implemented. Six of the 34 cases were infected by aerosol/droplets, i.e., either through larger droplets that quickly fall to the ground or small particles that can stay airborne longer.

There are many aspects of Andes virus transmission that remain unknown: How close does contact have to be for the virus to jump from one person to another? Is there the potential for pre-symptomatic transmission? We do know from another cluster of human-to-human transmission in Argentina that transmission is more efficient in the early “prodromal” phase of the disease, when an exposed individual may downplay their symptoms and not seek medical advice or isolate. Are there asymptomatic infections? It is imperative to have all passengers and crew of MV Hondius tested for antibodies to the virus, too. Do secretions in the environment remain infectious when they come from an infected human, as they do when they come from animals? Can the virus survive inside the human body for months (in semen for example, where viral genomes could be traced even seven years after infection)?

There are no vaccines available for Andes virus, nor any proven treatment, apart from supportive measures. Though a wider crisis seems unlikely with this pathogen, stopping a hantavirus outbreak or that of another pathogen will require accurate scientific information. Hantavirus disinformation has already emerged, with online posts linking its emergence to mRNA COVID vaccines, for example, or advocating ivermectin as a treatment. This is unavoidable. What is avoidable though is the inconsistency in the public messaging we’ve seen from various authorities—there’s a difference between not wanting to fear monger and being complacent.