What happened

Give them an "A" for effort: Stock markets made a valiant attempt to rally on Wednesday morning, with the Dow, Nasdaq, and S&P 500 all up more than 1% at one point. But the rally is fizzling, partly because of what have become the usual wet blanketsRoyal Caribbean (RCL 1.23%), Carnival (CCL -0.42%), and Hertz Global Holdings (HTZG.Q) were down 7.7%, 8.5%, and a staggering 11.2%, respectively, as of 1:35 p.m. EST on Wednesday.

Collage showing a cruise ship, a man in a face mask and a microbe

Image source: Getty Images.

So what

Why these stocks? I'll give you three guesses, but if you've been paying attention, you'll only need one: the SARS-CoV-2 coronavirus.

Back at the start of this month, Carnival became the symbol for the corporate risks of the dread disease when it was reported that 10 people had tested positive for COVID-19 aboard the company's Diamond Princess cruise ship.

Royal Caribbean further illustrated the extent of the danger when it began canceling cruises out of China in response to the emerging crisis.

And Hertz, yet another travel industry company in a world that seems to have suddenly locked its doors, soon became one of the latest dominoes to fall -- and falling it is today.

Now what

Anyone who thought investors had worked out all their jitters over the past two days of nonstop selling on Wall Street is getting disabused of that notion as stock indexes turn tail and give up their gains.

This crisis will pass, as so many before it already have. (Remember bird flu? We used to talk a lot about bird flu.) A cure will likely be found, regulators will likely fast-track it, and the outbreak will end.

But in the short term, and as long as this current crisis keeps escalating, it's probably best to take a cue from the vacationers who are canceling their travel plans and stay away from travel and leisure stocks for the time being.