FORT WORTH, Texas (CBSDFW.COM/AP) – An American doctor who contracted the Ebola virus felt a deep calling to work in Liberia and was exhausted after months of treating patients with the deadly disease.

Kent Brantly’s mother, Jan Brantly, says her 33-year-old son’s “heart is in Africa.” She says he comes from a long line of physicians and missionaries.

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The director of maternal-child health at JPS Health Network where Brantly completed his residency just months before heading to West Africa has been in touch by phone and email.

Dr. David Mcray says Brantly had been working for months when he contracted the disease. Mcray says Brantly has told him he is “terrified.”

Mcray says Brantly’s prognosis is grave. The doctor is suffering fever, headache and abdominal pain in an isolation unit for Ebola patients on the outskirts of Liberia’s capital.

He spoke with friends there on Monday, who relayed this message.

“Thank you for all the prayers and messages of encouragement. I’m praying fervently that God will help me survive this disease. Please continue to pray along with me, and pray for my friend Nancy who is also very sick… Thank you all so much.”

Brantly’s wife and two children were already back in Texas for a planned trip to attend a wedding when he began displaying symptoms.  Doctors say patients are only contagious when they have symptoms.  As such, they believe his family has not been exposed.  However, according to the CDC, they are under a 21 day “fever watch” as a precaution.

With the news of Brantly’s condition, there are a lot of questions, including if the outbreak could spread to the U.S.

While there are no flights originating in West Africa that land at DFW Airport, passengers are still free to travel. The CDC is urging caution, and increased vigilance.

“We realize that there is no border that separates viruses,” said Zachary Thompson, Director of Dallas County Health and Human Services.

Thompson says the CDC is watching the situation closely as Ebola is very aggressive, highly contagious, and most often fatal.

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“They’re asking the medical community to be on alert to look around for any possible cases that could happen here. Not been any to date. But, it’s always a concern.”

According to the CDC, patients are typically not contagious until they show symptoms-and the disease cannot be spread by casual contact.

“There is very strict regulation,” said Dr. Darrin D’Agostino at the UNT Health Science Center. “So the chances of it coming to Texas are very, very small.”

The Ebola outbreak in Africa has spread through at least three countries in the region.

More than 670 people have died and officials in Sierra Leone say the virus is getting worse.

In Liberia, they are closing some borders — and instituting strict quarantines in communities affected by the outbreak.

Ebola spreads through bodily fluids. There is no known cure for the virus.

(©2014 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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