The airline industry worked Thursday to tamp down fears that its jetliners might provide a pipeline for the lethal Ebola virus that is ravaging parts of West Africa to hop across the Atlantic to the United States.

That fear was heightened Wednesday on news that a man who flew through Washington Dulles International Airport on Sept. 20 on his way to visit family in Texas was diagnosed with the illness days after arriving in Dallas.

Airline shares dropped Wednesday, and most remained lower at midday Thursday as investors pondered the risk of Ebola.

“The big thing about this virus is that it isn’t spread by air,” said Perry Flint, spokesman for the International Air Transport Association, a trade group that represents about 240 airlines worldwide. “According to the World Heath Organization, the risk of transmission during air travel is very low.”

Flint pointed out that the man, identified by relatives as Thomas Eric Duncan, did not show symptoms of the illness until well after he landed in Dallas. He is the first person to be diagnosed with the Ebola virus in the United States.

“It’s not contagious until it’s symptomatic, and the symptoms tend to be such that typically the traveler does not feel like traveling,” Flint said. “And the symptoms tend to be recognizable.”

Ebola is spread by contact with the blood or other bodily fluids of a person sick with the illness. The early symptoms resemble an extreme case of the flu — high fever, headache, aching joints, weakness, stomach pain and loss of appetite.

On his journey from Liberia to Texas, Duncan changed planes in Brussels and at Dulles before arriving in Dallas on Sept. 20. It was not until four days later that he began experiencing abdominal pain and a fever.

Ebola “is only contagious if the person is experiencing active symptoms,” said Jean Medina, spokeswoman for the U.S. trade group Airlines for America. “There is no need for panic. There is virtually no risk to air travelers, no matter where you fly.”

Medina said the airlines receive a stream of updates from the U.S. Centers for Disease Control and Prevention and have procedures to monitor and respond to potential health risks.

The Association of Flight Attendants said it was working with crew members who had been on the two flights Duncan took inside the United States on his way to Texas.

“We’ve reached out to them to make sure that they have everything they might possibly need,” said Corey Caldwell, spokeswoman for the attendants. “This is not the first time that flight attendants have had to deal with a heightened awareness like this.”

She pointed to the swine flu pandemic in 2009 and the outbreak of severe acute respiratory syndrome, or SARS, in 2002-2003.

“Obviously, all flight attendants are aware of this,” she said. “Everybody’s talking about it, so they’re very aware, and they’re paying close attention to it. But they’re still going to work each day with that sense of responsibility that comes with the role of first responders in the aircraft.

The Federal Aviation Administration can bar U.S. carriers from flying to countries where passengers face certain risks, but the agency is unlikely to halt flights to West African nations without CDC guidance and a White House directive. Some foreign airlines — including Air France and British Airways — suspended service in August to African nations hit by Ebola.

Three of largest U.S. carriers — United Airlines, Delta Air Lines and American Airlines — serve the West African region where Ebola has surfaced, but those flights, to Lagos in Nigeria and Accra in Ghana, require connections through European cities and often involve handing off service to foreign-flag carriers not governed by FAA directives.

Delta provides direct service from Atlanta to Accra, and United flies directly from Houston to Lagos. Neither airline has announced plans to curtail its flights.

Passengers boarding flights in West Africa are being screened for elevated temperatures and other Ebola symptoms.

The Air Line Pilots Association, which represents 51,000 pilots in the United States and Canada, released a statement Thursday expressing “full confidence in the air travel procedures currently in place related to the Ebola outbreak.”

“Flight crews have guidance available and access to medical services to address a medical emergency while a flight is airborne,” ALPA said. “Should a medical emergency occur during a flight, the pilot in command, using available information and guidance, will determine the appropriate course of action with the single goal of ensuring the safety of the passengers and crew on board.”

Airlines flying to the United States are allowed to turn away passengers they fear might be carrying contagious diseases that could spread during the flight.

If a passenger falls ill with certain symptoms or dies aboard an international flight bound for the United States, the pilot is required by law to notify the CDC before the plane arrives.

According to CDC guidelines, flight crews should follow routine infection control precautions if they suspect a passenger is ill, including wearing protective garments in dealing with the passenger.

“The risk of spreading Ebola to passengers or crew on an aircraft is low because Ebola spreads by direct contact with infected body fluids. Ebola does NOT spread through the air like flu,” the CDC writes in its guidelines.

Flight crews are instructed to ask sick travelers whether they were in a country with an Ebola outbreak.

“Even if the person has been in a country with Ebola, cabin crew won’t know for certain what type of illness a sick traveler has. Therefore, cabin crew should follow routine infection control precautions for all travelers who become sick during flight, including managing travelers with respiratory illness to reduce the number of droplets released into the air,” the CDC says.

The CDC said that if an Ebola case is confirmed to have been on a flight, the agency will step in to perform an assessment and inform passengers who may have been exposed.

Flight crews also are instructed to notify cleaning crews that a sick passenger has been onboard. Baggage handlers have no risk of contracting Ebola from luggage, the CDC said, since transmission requires direct contact with an infected person.