The deadly MERS virus makes its first leap from person to person in the US

So far, public-health officials know of two people in the United States who have brought over a case of the deadly MERS virus from Saudi Arabia. And now it seems one of them spread it to someone else.

That third person, a resident of Illinois, never needed medical care, is no longer infected, and is doing fine.

At the moment, this doesn’t look like anything to panic about, though public-health officials are watching the situation closely.

Here’s our full explainer on MERS, or Middle East respiratory syndrome. The disease was first discovered in 2012 and has a surprisingly high death rate. There have already been 572 confirmed cases and 173 deaths, mostly in the Arabian Peninsula.

Public health experts are keeping a close eye on the MERS virus, which is a cousin of SARS, to see if it becomes more easily transmissible. If it does, it would have the necessary features to possibly become a global pandemic.

Yet this recent spread in the US doesn’t necessarily suggest that MERS is getting any worse. So far, the virus has generally only been transmitted from close contact such as within families and healthcare settings — and not from casual environments like being on the same airplane flight.

Officials had been closely monitoring the Illinois resident, along with dozens of other people connected to the first two US cases. They’ll now be tracking down his contacts, too.

It’s possible that these investigations will turn up other cases similar to this one — people who had it and never knew it and didn’t get sick and now don’t have it anymore. It’s not uncommon for a disease that jumps from animals to people to cause less severe illness with each further leap. MERS’ origins are still mysterious, but it’s also been found in camels and bats.

Right now, we only know of one person in the US who has the MERS virus in his body: the patient in Florida. The other two people have cleared the virus from their systems and shouldn’t be infectious.