Traffic on the bridge between Dandong and Sinuiju has decreased noticeably since North Korea imposed strict measures against Ebola, local businessmen say. (Anna Fifield/The Washington Post)

When it comes to North Korea, there is no end to the conspiracy theories.

The world had barely finished speculating about Kim Jong Un’s prolonged absence from the public eye last summer — Was it gout? Too much cheese? Broken ankles? A coup d’etat? — before Pyongyang provided more fodder for speculation by dramatically closing its borders in response to the Ebola outbreak last fall.

Surely this couldn’t actually be about Ebola, breaking out half a world away, some North Korea watchers said, espousing a range of theories from domestic political instability to a desire to further shield North Koreans from outside information — and especially from the highly critical U.N. reports on Pyongyang’s human rights abuses.

Now, even as the West African countries where the outbreak began return to a relatively normal footing, the “hermit kingdom” of North Korea has stepped up its measures to guard against the disease.

[Read: North Korea wasn’t kidding about Ebola]

In addition to strictly enforcing a 21-day quarantine for anyone who has been out of the country, Kim’s regime has canceled the Arirang mass gymnastics performance scheduled for April — a jaw-dropping display of children acting as robots that brings in thousands of tourist dollars — and has banned foreign runners from the Pyongyang marathon that was also set for April. The race has historically attracted some competitors from Africa — in 2013, the men’s winner was Ethiopian.

Rumors are circulating among foreign residents in Pyongyang that the so-called “Non-Standing National Emergency Prevention Committee/Anti-Epidemic Committee” will also cancel an international trade fair scheduled for May.

Here in Dandong, China’s commercial gateway to North Korea, business people say the Ebola measures have had a noticeable impact on cross-border trade, which already was suffering amid a downturn in global commodity prices.

All North Koreans who enter China are put into quarantine when they return, even though it’s just a bridge away, and are held in one of three quarantine zones — in Pyongyang, in North Pyongan province and in Sinuiju, the city on the other side of the Yalu river from Dandong. North Koreans can be overheard in restaurants here talking about the quarantine and saying they won’t go back until it’s lifted.

“The medical system in North Korea is so poor that one person becoming sick can shake up the whole country, cause the whole country to collapse,” said one Chinese businessman in Dandong, who spoke on the condition of anonymity to protect his trade. “North Korea is taking precautionary measures because Chinese people travel around the world, and they don’t know where these Chinese people have been.”

[Watch: China holds Ebola drills]

At a customs center in Sinuiju, sacks have been laid on the floor and covered with a powder that all vehicles must drive through, and the contents of the trucks are fumigated, businessmen here said in interviews last week.

North Korean drivers who deliver the truckloads of goods that can be seen crossing the bridge into China every morning are not allowed to go home but are made to stay in an inn in Sinuiju, they say. Traffic on the bridge has reportedly halved.

Some businessmen have found ways around the measures.

“We send goods to a warehouse near the port in North Korea, and then the North Korea partner comes to collect the goods and deliver them to places in North Korea, like Pyongyang,” said Li Yunlong, an agent for a chemical exporting company. “They go through the quarantine. We don’t have to deal with it.”

No such luck for those working in the tourism industry.

Dandong attracts 20 million visitors a year because of its proximity to North Korea. Chinese people of a certain age in particular like to take boat tours on the river that separates the two countries and reminisce about the old communist days.

But day trips to Sinuiju for Chinese tourists have been canceled as a result of the Ebola measures, and locals report that fewer visitors are coming here as a result.

And, this being about North Korea, there are still some conspiracy theories, of course. Almost all of them center on the political chill between Beijing and Pyongyang since Kim took power three years ago.

[Read: North Korea says U.S. created the Ebola outbreak]

“It is all about politics,” said the owner of a souvenir shop. “Why is North Korea taking quarantine measures? They are targeting China. They are doing this to block Chinese people just because relations between the two states have become bad.”

A travel agent who gave his name as Li also thought the Ebola measures were political.

“Usually by this time, North Korea would have opened up its border already. But now it is still closed,” he said. “It is all about politics. The relationship between our two countries is not as good as before.”

Hallie Gu contributed to this report.