Scientists set critical 'date to watch' for new wave of hantavirus spread - as woman in 'serious' condition after testing positive for disease

Health experts have set a crucial "date to watch" for when scientists will know if the hantavirus outbreak has spread beyond the MV Hondius cruise ship.

Dr Steven Quay, a US physician-scientist, has worked out that third-generation cases should start appearing around this date if the virus has jumped from ship passengers to people they encountered after disembarking.

His calculation is based on a roughly three-week incubation period seen with the Andes strain.

"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," Dr Quay said.

So far, all 10 confirmed infections came aboard the vessel, with no evidence yet of a wider spread.

But worries centre on 30 passengers who stepped off the ship on Saint Helena on April 24 - before anyone realised they might be carrying a deadly illness.

Among them was Miriam Schilperoord, 69 - the wife of patient zero, Leo Schilperoord, 70.

She became so unwell by the time she reached South Africa that KLM refused to let her board a flight.

She later died from the virus.

Meanwhile, a French woman is in a "serious condition" in hospital after testing positive for hantavirus, French health authorities have confirmed.

The country's Health Minister Stephanie Rist said the unnamed woman fell ill on Sunday night on her repatriation flight back to France and was later found to be carrying the disease.

Ms Rist added that her symptoms "worsened overnight" and she remains in hospital under careful supervision.

While experts have said public risk remains low because the virus typically spreads only through close contact like kissing or sharing drinks, there are troubling signs the Andes strain might transmit more easily than thought.

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Professor Joseph Allen of Harvard University has been in touch with a doctor aboard the MV Hondius who raised concerns that some infected passengers hadn't had close contact with patient zero.

Instead, they had simply crossed paths in dining rooms or lecture areas, hinting at a possible airborne transmission.

One person reportedly caught the virus after merely saying hello to a symptomatic individual at a birthday party, while others at the same gathering became infected despite sitting at separate tables up to six feet apart.

Two British passengers who left at Saint Helena have returned to the UK and are now self-isolating - though neither has shown symptoms yet - but they will have encountered others during their journey home.

Meanwhile, around 20 Britons from the cruise are being held at Arrowe Park Hospital on the Wirral for 72 hours after flying into Manchester Airport on Sunday evening.

If May 19 passes without any third-generation infections emerging, the next crucial milestone becomes June 21.

That's when the incubation period will have fully elapsed, meaning no further cases could possibly stem from this initial outbreak.

Only once that date passes with no new infections can health officials declare the outbreak over.

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