Why hantavirus bears little resemblance to Covid-19

Fernando Simón’s reappearance in some media outlets, claiming that the risk of hantavirus is “very low” for Spain, has reminded many people of the initial public statements made by the director of Spain’s Coordination Center for Health Alerts and Emergencies (CCAES) before Covid-19 became a pandemic. While infectious diseases do have a degree of unpredictability, this situation is completely different; hantavirus bears little resemblance to SARS-CoV-2.

There are many differences between the pathogen that caused the last major global pandemic and the one that caused the outbreak on the luxury cruise ship MV Hondius, which was traveling across the Atlantic. Two key differences make the potential consequences of each very different: their origin and their transmissibility, which is much lower in the case of hantavirus.

The coronavirus jumped to humans in 2019. Until then, it was unknown. Consequently, there was little knowledge about it: how it spread, its incubation period, the symptoms it caused, or its fatality rate. That was what led to the miscalculation by virtually all global health authorities in the early months of 2020.

Initially, it was thought that SARS-CoV-2 was transmitted only through saliva droplets, leading to the hypothesis that its spread would be more controllable. However, it was soon discovered that this was not the case: it was transmitted through the air, via breathing, like a common cold. The difference was that the human immune system was unfamiliar with this new virus, and in the most vulnerable or least predisposed individuals, it wreaked havoc.

Hantavirus, although rare, has been present among humans for centuries. The hemorrhagic fevers with renal syndrome it caused were identified in the early 20th century, and in 1993, a new rodent-borne variant causing respiratory symptoms was discovered during an outbreak in the United States.

And what we know after all these years is that its transmission to humans, although possible, is much more difficult than that of Covid-19. It can jump to people through direct contact with rodents — which are its main reservoir — via their feces, in very specific contexts, and generally only through certain species.

The Andean strain — likely the one detected on the MV Hondius — can be transmitted between humans. But very close and direct contact through bodily fluids is necessary. To illustrate against the two most recent diseases that have caused global health alerts, the way hantavirus is transmitted is more similar to that of mpox (formerly called monkeypox) than to Covid-19.

Rafael Toledo, professor of parasitology at the University of Valencia, points out that in the case of Covid-19, one infected person could infect 10 others, and those could then infect another 10. “In a second generation, we already have 100 infected people. Not here. We are talking about very inefficient transmission between humans, which is linear: one person infects another, that person infects another, and so on until it stops. Either because they don’t have close enough contact for long enough, or because they die before transmitting it,” he explains.

Proof of this, Toledo insists, is that despite the fact that the conditions of a cruise ship are ideal for the spread of an infectious disease, among the nearly 150 people on board, only seven infections have been detected so far.

That’s why epidemiologists — not just Fernando Simón — are insisting that the risks of this outbreak are minimal. Knowing the pathogen, the precautionary measures to isolate and treat cases should be sufficient to prevent its spread.

“The epidemiological information may change in the coming hours, but based on what we know, our experience with previous situations and drills, this scenario would still represent a very low level of risk (the lowest of the four levels) for the Spanish population. However, it cannot be ruled out that someone on board the cruise ship may develop symptoms in the coming days and require evacuation,” Adrian Hugo Aginagalde, spokesperson for the Spanish Society of Preventive Medicine, Public Health and Healthcare Management (SEMPSPGS), told SMC Spain.

Could the virus mutate, making it more transmissible? Rafael Toledo explains that, although it is an RNA virus (like SARS-CoV-2) that can mutate easily, the number of changes that would have to occur for it to spread easily among humans is enormous and highly improbable. “The difference with the coronavirus is that it was already highly contagious between people, and small variations made it more efficient,” he points out.

Lethality and incubation

Beyond the mode of transmission, which creates a very different scenario from that of Covid-19, there are other differences with hantavirus. The latter is much more deadly. In the case of the coronavirus, in 2020 the case fatality rate was estimated at 1.7%, with enormous differences by age: 0.01% in children aged 1 to 14, 4.7% in people aged 65 to 74, 12% between 75 and 84, and 23.6% in those over 85. All of this was before vaccines and before most of the population had been exposed to the virus, when the rate dropped below 1%.

The lethality of hantavirus is highly variable. The average for the Andes strain is 18.5%: between 2013 and 2018, 598 people were infected in Argentina, of whom 111 died. However, with this type of disease, these rates can vary considerably depending on its spread and the healthcare systems where infections occur.

Another major difference is the incubation period: less than a week for SARS-CoV-2 and between one and six weeks for hantavirus. This means that observation and the possible quarantine of people who have been in contact with the virus must be longer.

The symptoms can be similar in both diseases: something like the flu, which in most cases doesn’t progress beyond that, but can become more severe.

With all this information, experts are not concerned about the ship’s potential docking in Spain. Antoni Trilla, a consultant with the Preventive Medicine and Epidemiology Service at Hospital Clínic in Barcelona, explained to SMC: “There is no risk to the general population. If the ship docks in the Canary Islands, health authorities and public health services can conduct a new health assessment of all passengers and crew and decide who should receive medical attention and/or be medically evacuated to their countries of origin, and who can remain on board and continue the scheduled voyage, properly informing them of the precautions they need to take and any potential warning signs that would require them to consult medical services.”

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