Shares of some companies that are studying potential vaccines for Ebola climbed after federal officials announced that the first case of the disease has been diagnosed in the U.S.

The Centers for Disease Control said a patient being treated at a hospital in Dallas tested positive for the disease.

Ebola is believed to have sickened more than 6,500 people in West Africa, and more than 3,000 people have died.

The World Health Organization has worked to speed up the use of some experimental vaccines and companies are ramping up testing. Earlier this month NewLink Genetics said it would start safety testing of a vaccine within a few weeks, while Inovio Pharmaceuticals said it would start human trials of a DNA-based vaccine in early 2015.

Shares of Inovio Pharmaceuticals Inc. shares rose 35 cents, or 3.6 percent, to $10.20 in aftermarket trading, while NewLink Genetics Corp. shares gained $2.68, or 12.5 percent, to $24.10. Stock of some other companies that have been involved in efforts to come up with vaccines and medications also jumped. BioCryst Pharmaceuticals Inc. added $1.26, or 13 percent, to $11.04; Sarepta Therapeutics Inc. rose $1.57, or 7.4 percent, to $22.67; and Tekmira Pharmaceuticals Corp. stock climbed $5.97, or 28 percent, to $27.11.

Ebola's symptoms can start as much as 21 days after exposure, and the disease isn't contagious until symptoms begin. It takes close contact with bodily fluids to spread.