NEW YORK (Reuters) - U.S. stocks tumbled Wednesday as caution rose following the first diagnosis of a patient in the United States with Ebola. Airline stocks fell sharply on concerns the disease could curb air travel, with several numbering among the biggest decliners on the S&P 500.

The Dow Jones Industrial Average fell 238.19 points (1.40 per cent) to 16,804.71. The broad-based S&P 500 fell 26.13 (1.32 per cent) to 1,946.16, while the tech-rich Nasdaq Composite Index sank 71.30 (1.59 per cent) to 4,422.09.

Delta Air Lines lost 3.5 per cent to US$34.90 while Southwest Airlines was off 2.8 per cent at US$32.83. The NYSE Arca Airline index fell 2.1 percent. "African travel isn't a huge part of the travel industry, but it does seem like some parts of the industry are likely to be disrupted from this," said Mitch Rubin, chief investment officer at RiverPark Advisors in New York.

Drug companies with Ebola treatments in their pipelines rallied in heavy trading. U.S. shares of Tekmira Pharmaceuticals jumped 17 per cent to US$24.91 and was the Nasdaq's most active name. Sarepta Therapeutics rose 4.8 per cent to US$22.11 while BioCryst Pharmaceuticals added 4.7 per cent to US$10.23.

In a positive reading on the economy, a report showed private employers added 213,000 jobs in September, more than expected, although August's number was revised down by 2,000 jobs. The stronger-than-expected September data could raise expectations for the closely watched non-farm payroll report released tomorrow.