It’s certainly not sick, but investors are trading heavily on companies connected to the spread and treatment of the disease after the first domestic case of Ebola was confirmed in Dallas.

The biggest drag on the broad Standard & Poor’s 500-stock index, which fell sharply Wednesday along with the Dow Jones industrial average, lately lower by over 200 points, was airline stocks.

The first U.S. patient with the deadly virus had recently traveled from Liberia on a commercial air flight. The name of the airline involved has not yet been named, which spread the share drops among top carriers.

Delta, Southwest, Spirit, American Airlines, United Continental and JetBlue stocks all took a hit. The S&P 500 Airline Index, as tracked by Bloomberg, was lately down 4%.

Delta (DAL) and United Continental Holdings (UAL) both declined, followed by American Airlines (AAL). All three airlines fly internationally, though not all operate flights to Africa. Domestic-only airlines like Southwest (LUV) were also affected by the selloff.

While airlines struggled in the wake of the first U.S. Ebola case, other companies gained even bigger from the news, helping to temper the overall losses in the S&P 500 index.

Pharmaceutical companies with Ebola vaccines or treatments in development were the biggest gainers. Shares of Tekmira Pharmaceuticals (TKMR), which has an Ebola drug in testing, soared. Tekmira’s treatment had been previously given to one of the three U.S. aid workers infected in Africa, all of whom survived the disease.

NanoViricides (NNVC), which also has an Ebola drug in development, also rose sharply, and Ebola vaccine developer NewLink Genetics (NLNK) shares were lately up over 10%.

Another big gainer was Lakeland Industries (LAKE), which makes protective work wear for the healthcare industry. Investors, who helped push its shares up over 10% at one point, hope that sales of the companies hazmat suits will boom as hospitals prepare for any more potential Ebola cases.

Read more about how everything from viral outbreaks to M&A rumors spread in this recent Fortune series “CONTAGION—How things spread.”