Anyone in the affected countries who gets a fever and symptoms like headache, muscle pain, vomiting, diarrhea, stomach pain or unexplained bleeding or bruising should avoid all contact with others and travel immediately by private transportation to a doctor’s office or hospital.

Consular officers from the U.S. embassies can help in finding medical services and informing family and friends, and although the State Department will not pay medical expenses, they can help transfer funds. But travelers to these regions should be aware that any country has the right to restrict exit and entry of apparently infected people, impose quarantines, and take other measures that some may view as infringements on individual rights. The government of the United States has little or no influence in such matters.

Vaccines are under development, but the soonest they will be available is in about two months, and it may take years. Some antiviral medicines have been used, but none has proved effective. In the meantime, prevention and palliative care are the only effective approaches.

The C.D.C. suggests that travelers returning from West Africa, even those without symptoms, visit a doctor when they arrive in the United States. The doctor will evaluate the traveler and consult with public health authorities to decide what further actions to take. Those who were in an area with an outbreak should monitor their health for 21 days after their return, taking their temperature daily and watching for other symptoms. Anyone with symptoms should stay away from others and call a doctor immediately.

The danger should not be exaggerated, Dr. Morse said. “The risk of infection even if you go there, unless you visit a family where there is an Ebola patient or visit a patient in a hospital, is very small. On the other hand,” he said firmly, “if you don’t have to go there, don’t.”