FREETOWN, SIERRA LEONE – The airport worker pointed the infrared thermometer gun at my forehead and squeezed.

It was impossible not to be anxious. Whatever the thermometer’s green digital readout declared would determine whether I’d be allowed to board a plane out of Sierra Leone and take flight from the world’s first Ebola epidemic. Behind me, dozens of other travelers waited for their date with the thermometer gun.

Temperature checks for travelers in West Africa have emerged as the favored front-line, last-ditch defense for containing the spread of Ebola, which has ravaged Guinea, Liberia and Sierra Leone. Congo and Nigeria are facing smaller outbreaks.

But there are doubts about how effective these screenings are, and questions about whether they do anything other than make people feel more confident about travel — but there’s utility in that, too.

Some nations, such as South Africa, have opted to close their borders to people from Ebola-afflicted countries. Many airlines have stopped flying to these places, too. Just last week, Air France halted flights to Liberia and Sierra Leone. Brussels Air stopped and then restarted flights. British Airways announced a brief moratorium on its flights to the region last month, then decided not to fly again until at least 2015.

But groups such as the World Health Organization have urged airlines and countries to maintain their connections to nations dealing with Ebola. Cutting them off will only worsen the epidemic, making it more difficult to transport needed people and supplies, the organization said.

So temperature checks have been added to the list of measures to be taken at airports, seaports and border crossings for travelers arriving from West Africa.

Fever is one of the earliest signs of Ebola, a virus without cure and at best a 50 percent chance of survival. But part of the problem is that it can take two to 21 days for symptoms of the virus to occur, although median onset is eight to 10 days. And a person is not contagious until they show symptoms. So it would be possible to be infected and yet not sick.

At the airport in Sierra Leone, one thing was clear: This was one test on which people didn’t want to score high.

The airport worker wore a white lab coat and a surgical mask. She held my official health declaration form, which I’d filled out moments before, listing details of my stay in the country and asking me a series of Ebola-related health questions. Had I had a fever now or in the past two days? Headache? Vomiting or nausea? Diarrhea? Intense pain? Ten questions in all.

I checked off “no” to each.

The final entry on the form was left to the health worker. My temperature.

Anything higher than 38 degrees Celsius, or 100.4 Fahrenheit, was trouble. A fever. There are lots of relatively mundane causes for fevers – malaria, common ailments and infections. In normal times, a fever is not a barrier to climbing aboard a plane. But not anymore.

The health worker jotted down my number: 36.8.

Not being good with Celsius conversions, I asked her, “Is that okay?”

“Yes,” she said, smiling. “Okay.”

That translated into 98.25. Normal.

I could continue on my way. But that wasn’t the final temperature check at Lungi International Airport, a small facility reachable by a 30-minute water taxi ride from the capital city of Freetown. After going through passport control and getting my boarding pass for the 4:10 a.m. flight on Royal Air Maroc to Casablanca, Morocco, passengers were probed again for fever just before leaving the terminal.

Passengers compared temperatures on the short bus ride to the plane. I’d scored the same 36.8. An American doctor, forced to leave the country by the aid group she worked for, joked about her 33.4-degree temperature – a little low. A man standing next to her with a guitar slung over his shoulder had scored 36.8.

Fever checks at airports have been done during other outbreaks. In 2003, when the world was alarmed by the spread of severe acute respiratory syndrome (SARS), many Asian airports used thermometers to help stop its spread. Airports have checked temperatures in outbreaks of dengue fever and the H1N1 flu virus, as well.

A study of the 2009 H1N1 flu pandemic showed that entry screening policies delayed local transmission by seven to 12 days.

In 2003-04, Taiwan began screening passengers’ temperatures at two major airports. They were looking for SARS, but found the test “is an effective means of identifying imported dengue cases,” while health questionnaires were essentially useless.

It’s not clear what will happen with this Ebola epidemic. Ebola is not an airborne virus, like SARS or the flu. But it can be spread by contact with infected blood, saliva and sweat.

So far, there has been only one documented case of someone with Ebola making it onto a flight. That was in July, before the airport screening protocols were in place, when a man, who apparently knew he was infected, flew from Liberia to Nigeria. He apparently didn’t infect anyone on the plane, but he did infect staff and hospital workers in Lagos.

After we got off the Royal Air Maroc flight in Casablanca, passengers were greeted by another screening: a thermal imaging camera.

My next flight was to Dakkar, Senegal, a country that shares a border with Guinea, where this Ebola epidemic began. Senegal recently recorded its first Ebola case: a student from Guinea. At the Dakkar airport, we were again met by a thermometer gun.

The last leg of my convoluted journey was from Dakkar to Washington Dulles International Airport.

Only there, no one was waiting to take our temperatures.

As the worst Ebola outbreak in history unfolds in West Africa, The Post's Joel Achenbach explains how the deadly virus wreaks havoc on the human body. (Davin Coburn/The Washington Post)