“I know you are concerned.” The Secretary General of the World Health Organization (WHO) wrote this last Saturday a letter to the residents of the Spanish island of Tenerife. The Dutch cruise ship MV Hondius, ravaged by the deadly Andes virus that has already claimed the lives of three passengers, would dock a day later in the port of Granadilla where more than 140 passengers could finally disembark. “I know that when you hear the word ‘outbreak’ and see a ship entering your port, it brings back memories that none of us have fully processed yet,” said WHO President Tedros Adhanom Ghebreyesus. “But the risk for you, residents of Tenerife, is low. This is the WHO’s assessment. We do not make that assessment lightly.”
The letter could not prevent the cruise ship from being met on Sunday morning by islanders with concerned texts on banners. The outbreak on the Hondius has been keeping the world busy for more than a week.
It’s difficult not to get flashbacks to the corona pandemic, but how justified is that?
Back to the Korean War
The virus that all eyes are now focused on is the Andean virus, which mainly occurs in Argentina and Chile. This pathogen is part of a much larger family of hantaviruses, of which there are more than sixty types that can make people sick. The hantavirus was first described in the 1950s, during the Korean War. Then about three hundred soldiers deployed there by the United Nations died. Another ten times as many soldiers became infected.
It wasn’t until about twenty years later, in 1978, that the source of the virus was identified: an infected fire mouse near the Hantan River in South Korea. The pathogen was therefore given the name Hantaanvirus, which later became the ‘founder’ of a much larger group of hantaviruses.
Each type of hantavirus has its own rodent host. This is the result of millions of years of co-evolution, in which the virus adapted to the specific characteristics of the host cells. The rodent’s immune system, in turn, learned to tolerate the virus without getting sick. If the virus jumps to another species, for example humans, it often causes symptoms. People can become infected through a rodent bite, but it is more common to inhale the virus particles from dried feces through the air – for example, if dust swirls in a shed or wooded area where the rodents live.
Old and new world
Depending on the type of rodent that lives somewhere, different types of hantaviruses occur in different places in the world. In Europe and Asia, mainly the so-called Old World variants are circulating. In the Netherlands, this concerns the puumala virus (in red voles), the Seoul virus (in brown rats) and the tula virus (in field mice).
For most people, such an infection goes unnoticed, or they develop mild complaints such as fever, muscle pain and headache. The infection can also become more severe, with a risk of kidney damage and bleeding. These symptoms are also called hemorrhagic (bloody) fever, a term also used for Ebola and Lassa, although these viruses are much more contagious.
The worrying mortality figures circulating about the Andean virus do not apply to the variants that occur in Europe. It is estimated that fewer than one in a hundred people will die after an infection with a European variant. 1.7 percent of all Dutch people (about 300,000 people) have antibodies against the hantavirus in their blood, it appears from research by the National Institute for Public Health and the Environment (RIVM). This indicates a previous infection. Once infected with a hantavirus, you are protected for life by generated antibodies, but only against that specific variant.
Birthday and funeral
The New World variants, which also include the Andes virus, are mainly circulating in North and South America and cause other complaints that, in severe cases, affect the heart and lungs. After a short period of general feverish complaints, the much more serious lung syndrome can suddenly develop: a high heart rate, extreme shortness of breath, low blood pressure and heart failure. People who contract the infection have a 30 to 50 percent chance of death, a mortality risk similar to that of the bubonic plague.
The lethality of the Andean virus in particular explains the large-scale and careful evacuation operation of the people on board the Hondius: every infected patient is potentially in mortal danger.
The Andean virus is spread by the long-tailed rice rat, which lives in North and South America. Outside that area, the virus has no natural host, which is important for the risk of a pandemic. The Andean virus was first found thirty years ago in Argentina. That same year, the virus also appeared in Chile. The variant is still mainly circulating in those two countries, but so far not with huge outbreaks.
A major difference with all other hantaviruses is that only the Andean virus can be transmitted from person to person. This was first demonstrated in a well-documented outbreak from 2018, in Chubut, Argentina, in the province of Patagonia. There, the first patient was probably infected with what later turned out to be the Andes virus, through (indirect) contact with a rodent. He appeared at a party with mild complaints, after which several people who had close contact with this person turned out to be infected. A number of them died from the virus, after which the chain of infection tragically continued at the funeral. A total of 34 people were infected and 11 died. After a number of months of strict isolation measures, the source of infection disappeared.
Traveling in Patagonia
Apart from that one outbreak, hardly any significant clusters of infections have been observed. For several years now, the Argentine Ministry of Health has reported a handful of cases per year. However, there appears to have been an increase in the past year: from 57 infections last epidemiological year (which runs from June to June) to 101 cases in the past year. All those infections mainly occur in the north of Argentina (Salta and Jujuy), the center (Buenos Aires, Santa Fe and Entre Ríos), the northeast (Misiones) and in Patagonia (Neuquén, Río Negro and Chubut).
However, three infections with the Andean virus were reported in Chubut last month, all in one family. But since 1996, no Andean virus has been detected in the more southern province of Tierra del Fuego. There is the port of Ushuaia, where the passengers boarded the Hondius. A health official there mentioned it last week during a press conference “very unlikely” that the infections were acquired on the cruise ship in the port city.
How the virus ended up on the ship is still being investigated. Argentine officials last week pointed to a scrap yard in Ushuaia known as a hotspot for bird watchers. The most likely explanation was that the deceased Dutch couple would have been there before they boarded the Hondius. The Argentine government said it would catch rats and mice in that area to investigate whether the animals carry the virus.
It is now increasingly less certain whether this actually happened. It has never been confirmed that the couple visited the dump. A local guide said against it The Sunday Times that he showed other passengers of the Hondius around there, including a French couple, a British man and an American woman. The Dutch couple traveled around Argentina, among other places, for months, just like some other people on board the Hondius. The Dutch man who died first on April 11 was never tested. His wife later tested positive for the hantavirus and also died. The count now stands at three deaths and ten confirmed infections. More may follow, given the long incubation period of the Andean virus.
Will this be the new corona pandemic?
No, virologists and doctors say for now. The WHO also calls for calm. „The proof of the pudding is in the eating“, says Martin Grobusch, head of the Center for Tropical Medicine and Travel Medicine at Amsterdam UMC. “But if we look at how this outbreak is developing, it is exactly in line with what we can expect from this virus: low transmissibility. Otherwise everyone who was on that ship would have been sick by now.” In view of the long incubation period, he expects a handful of new positive tests in the coming days, but no large new clusters.
The Andean virus has a number of properties that differ in crucial ways from viruses such as SARS-CoV-2. Although human-to-human transmission is possible, this is a lot more difficult than with Covid-19. “The Andes virus mainly settles in the lower respiratory tract,” says Grobusch. “With Covid-19 or influenza, the virus multiplies high, in the throat and deep in the nasal cavity. With the Andes virus, this happens mainly deep in the lungs, so that the virus particles are only coughed up in case of severe complaints. In that sense, it is not a typical respiratory virus that spreads easily.”
It is not without reason that most clusters of infections with the Andean virus have so far been identified in family circles: infection appears to require intensive contact, such as exchanging saliva or close contact in an enclosed or poorly ventilated space. Several people on board the Hondius said that they held the hand of the widow of the Dutch man who died or hugged her to comfort her. The passengers shared small sleeping cabins with each other for weeks and sat at the buffet in varying compositions.
A major difference with Covid-19 is that people without complaints do not or hardly appear to be contagious. “With Andes virus is correct at the peak of the complaints the amount of virus particles is highest,” says Grobusch.
The Andean virus is also genetically quite stable. That is, since the virus was discovered thirty years ago, it appears to have barely mutated. This is in contrast to Covid-19, where the high mutation rate was a cause for concern. If a virus mutates quickly, it can adapt in such a way that it spreads better and better between people.
From the 2018 tragedy, experts conclude that strict isolation measures can effectively contain an outbreak with the Andean virus. But that outbreak was limited to a village in Argentina. Now it is about a cruise ship with passengers from more than twenty countries. Some of them disembarked unknowingly, including on St. Helena, when it was not yet known that a deadly virus was circulating on the ship. They came into contact with the local population and boarded commercial flights to all corners of the world.
Now it comes down to how well health authorities get a picture of these people, how willing they are to go into quarantine as a precaution and whether they will report and be tested if they have symptoms. “I am impressed by the epidemiological research that has been conducted internationally in recent days,” says Grobusch. “It is impressive how many people have already been traced within a few days. We probably already know who was at risk for almost everyone, and how high that risk was.”
The Dutch cruise ship Hondius upon arrival in the port of Tenerife.
Photo Ramon from Flymen/ANP
