This 2011 photo provided by Wilmot Chayee shows Thomas Eric Duncan, the first Ebola patient diagnosed in the U.S., at a wedding in Ghana. Texas Health Presbyterian Hospital Dallas, where Duncan was being treated for the disease, on Wednesday, Oct. 8, 2014 said Duncan has died. (Wilmot Chayee/AP)

THE DEATH of Thomas Duncan in Dallas from Ebola virus is a sobering reminder that we live in a world more connected and fluid than at any time in human history. The Ebola virus and other deadly pathogens can accompany people from one point on the globe to another in a matter of hours — and attempts to identify and stop carriers of the disease won’t always work, in part because of long incubation periods. Viruses and bacteria do not stop at passport control.

This does not mean that the United States or other nations should be nonchalant about screening for Ebola. While not foolproof, checks at airports, such as procedures announced Wednesday for inbound passengers to five U.S. airports, still can prove valuable if they prevent a few who are infected from spreading the virus. About 150 people a day are coming to the United States from the three nations where Ebola is epidemic. But it’s important to understand the biological realities. Ebola can incubate in a human for up to 21 days, and the infected person does not immediately show symptoms. As Mr. Duncan demonstrated, an infected person can go through multiple screenings without setting off alarms, and questionnaires don’t always single out those who either don’t know they are infected or deliberately won’t say.

The hue and cry in recent days by some Republicans to shut the border to people from West Africa is misplaced. The party’s Senate candidate in North Carolina, Thom Tillis, called Sunday for blocking such travelers from entering the United States, saying, “We need to protect the safety and the security of the American people.” Louisiana Gov. Bobby Jindal (R) floated a similar proposal.

Such extreme measures won’t stop Ebola infections from spreading outside of Africa and may cause serious disruption. The affected nations desperately need supplies, health-care workers and a lifeline to the outside world. One important aspect of the response is to keep healthy people working and normal at a time of upheaval. Stopping all flights might worsen their plight and sever trade and investment. A World Bank report released Tuesday said that the outbreak threatens “very serious” economic effects on West African nations, especially Liberia and Sierra Leone. Liberia had 27 international flights weekly at the end of August, but these were cut to only six in early September. In Sierra Leone, 31 weekly flights fell to six. Hotels are emptying out, and workers are being laid off.

Since there is no vaccine and no effective therapy available for Ebola beyond scarce, experimental drugs, the only sure way to fight the scourge is to identify those who have it, trace those with whom they came in contact and isolate the sick. The epicenter of this work is in Liberia, Sierra Leone and Guinea, where the outbreak is raging and help is desperately needed. The answer to Ebola is fighting it there, at the source, not at the U.S. border. No one is protected when a public health emergency is used for political grandstanding.