By Peggy O'Hare

The federal Centers for Disease Control and Prevention issued an alert Wednesday urging pregnant women to consider postponing any travels to Brownsville because five people there have become infected with the Zika virus through mosquito bites.

The virus poses special risks for pregnant women because it can cause microcephaly and other severe brain defects in unborn babies. This can occur even if expectant mothers don't suffer any symptoms of the illness.

Pregnant women living in Brownsville or traveling to the city are being advised to take strict precautions to prevent mosquito bites. They are also being cautioned to consistently use condoms during sex or to abstain from sex during their pregnancies because the virus is also spread through sexual transmission.

"Temperatures in the region are still conducive to mosquito-borne transmission. ... Pregnant women in the area are at some risk for Zika virus infection," said the CDC alert issued Wednesday.

The five cases surfaced within a single city block spanning less than a half-mile on the east side of Brownsville, Mayor Tony Martinez said. The first case was reported Nov. 28. Four more surfaced Friday.

None of those patients are pregnant, Martinez said.

"Everybody is on high alert. ... It's a situation that we take very seriously," Martinez told the San Antonio Express-News late Wednesday.

"It's really a very confined area of exposure," he said of the block where the cases occurred. "But by the same token, we are first and foremost concerned that everybody takes all the precautionary measures."

The four additional cases reported Friday were identified through door-to-door surveillance conducted by the Cameron County Department of Health and Human Services. Martinez said the city block where the infections occurred is a mixed-use area, but is more residential than commercial.

Authorities have declined to publicly identify the street where the cases surfaced because they want to protect the patients' privacy.

Esmeralda Guajardo, health administrator at Cameron County Department of Health and Human Services, said she would not be surprised if more cases turn up.

"We've had a lot of patients show up at our county health clinics," Guajardo said late Wednesday. "And they've called whenever they felt that they possibly could have Zika. A lot of providers call and reach out to us because they understand that we're taking the lead.

"We had a lot of individuals within the community asking, calling for some direction in terms of their health care -- and not necessarily to say that they were pregnant, but just women as a whole that were considering getting pregnant. So we have a call center that we started as soon as we saw the increase of calls. And we're going to continue doing that tomorrow. And that's going to be manned by some of our clinical staff members."

Four of five people infected by the Zika virus won't show any symptoms. Those who do exhibit only mild discomfort, such as rash, joint pain, aching muscles, headache, low-grade fever and red eyes. Those symptoms usually go away within a week.

But the virus is much more insidious for unborn babies. They can be infected before or during birth.

As of Nov. 30, 32 babies exposed to the Zika virus had been born with birth defects in the continental United States, CDC statistics show. Five other infants who did not survive due to miscarriages, stillbirths or terminated pregnancies also showed evidence of birth defects, the CDC reported.

The CDC alert just released advises pregnant women living in Brownsville -- or who traveled to the city on or after Oct. 29 -- to get tested for the Zika virus.

Pregnant women who did not use condoms while having sexual contact with anyone living in Brownsville or with anyone who traveled there on or after Oct. 29 also are urged to get tested.

"We really need women to take care of themselves and make those appointments with their medical providers and ask them about Zika to reduce the risks of getting it," Guajardo said. "That's crucial. People need to be a little bit more proactive in making sure that they minimize that risk."

The border separating Texas from Mexico passes through Cameron County. Patients have also been infected with the Zika virus through mosquito bites that occurred in Mexico near the U.S. border. Because of that, the CDC issued a bulletin last year urging pregnant women not to travel to any area of Mexico below 6,500 feet.

No vaccine to prevent the infection exists.

(c)2016 the San Antonio Express-News