Passengers from the hantavirus-stricken cruise ship MV Hondius. Photo / Getty Images
May 19 could prove critical in the hantavirus outbreak.
Currently, no cases have been confirmed in people who were not on board the MV Hondius, so there is no evidence the virus has spread beyond the confines of the ship.
But the long incubation period of the virus means it is impossible to know whether passengers who left the ship early on April 24 have passed on the disease.
Dr Steven Quay has calculated that all generation-two cases – those involving people who developed symptoms after contact with “patient zero”, Leo Schilperoord, 70 – took an average of 22 days to become ill.
The US physician-scientist estimates that generation-three cases – involving anyone who contracts the infection from the holidaymakers – should start showing up around May 19, if the same incubation period of about three weeks holds true.
In previous outbreaks of the Andes strain of hantavirus in Argentina, the peak time for symptom onset was 22 to 28 days.
“We now have 10 hantavirus cases, one apparent patient zero and nine human-to-human generation two cases,” he said.
“May 19 is a good date to watch for... if cases continue beyond that point they will probably be generation two to generation three cases.”
Some 29 passengers left the ship at Saint Helena before the outbreak was identified, including Miriam Schilperoord, 69, the wife of patient zero, and a Swiss passenger who is in hospital with the virus.
Schilperoord was so ill by the time she arrived in South Africa that she was refused a flight by KLM, and later died from the virus. An air hostess was initially thought to have contracted the virus from Schilperoord but has since been cleared of infection.
A British national who left the MV Hondius at the British Overseas Territory of Tristan da Cunha, in the South Atlantic, is also suspected of having the virus.
All 30 left the ship before it was clear that they could have been carrying a lethal illness, and are likely to have come into contact with hundreds of people in the past fortnight.
It is now all but proven that the virus can be passed from person to person via bodily fluids, which can harbour infectious particles.
Experts have said that there is little risk to the public, because the virus spreads only through close contact, such as kissing or sharing food or drinks.
Ship passengers have been sent a questionnaire asking whether they shared a kiss or hug with anyone who was sick or died, or were within 1.8m of an infected person for at least an hour cumulatively.
They have also been asked whether they shared sexual contact, touched soiled bedding or clothing, shared a bed, slept in the same room, shared a bathroom, shared a toothbrush, cigarette or vape, or came into contact with bodily fluids.
However, there are worrying signs that the Andes strain may be even more contagious than previously believed.
Professor Joseph Allen, of Harvard University, said he had been in contact with a doctor on the MV Hondius, who was concerned that some of those infected had not had close contact with patient zero. They only crossed paths in dining rooms or lecture areas.
If that is the case, it suggests that the Andes strain could spread through airborne transmission.
In a previous outbreak of the strain in Chubut Province, Argentina, it was reported that one person had become infected after saying “hello” in passing to a symptomatic person at a birthday party.
Others were infected at the same party despite sitting at different tables, up to 1.8m apart.
In the same outbreak, two patients admitted to hospital were placed in rooms with hantavirus patients and later contracted the virus despite there being no close contact.
A French citizen and a man from the US who were evacuated from the ship tested positive for the virus this week, bringing the total number of suspected cases to 10.
If all caught the virus from patient zero, then the reproduction rate – the number of people each person infects – is nine. This is as high as the Covid-19 Omicron variant, although the confinement of the ship will have driven it much higher than would be expected in the wider environment.
But it means that Andes strain may transmit to people more easily than first thought, and anyone who crossed paths with those travelling back from the MV Hondius could be at risk.
Two Britons were among those who left the ship at Saint Helena and travelled back early, and are now self-isolating in the UK. Neither has developed symptoms yet, but they will have crossed paths with others on their journey home.
Meanwhile, some 20 Britons who were on the cruise ship are isolating at Arrowe Park Hospital on the Wirral for 72 hours, after being flown into Manchester Airport on Sunday night.
If May 19 and the subsequent days pass without third-generation infections, then the next date to look out for will be June 21.
That is when the incubation period will have run its course and there is no chance that anyone else could be infected from the first outbreak.
Only if we reach that date with no further cases will the outbreak be over.
The world will have to hold its breath until then.
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