Public school leaders in Boston scrambled to find new destinations for students’ spring trips after scrapping travel to nations confronted with outbreaks of the mosquito-borne Zika virus.

The director of Boston College’s international studies program fielded phone calls from nervous parents and students, facing Friday’s deadline to sign up for next semester’s travel abroad projects.

And Northeastern University e-mailed 30,000 students and staffers Thursday, warning of heightened concerns over the Zika virus in Latin America and the Caribbean.

The explosive spread of the once-obscure virus through more than two dozen countries, combined with news that Zika apparently can be spread through sexual transmission, is prompting universities and Boston’s public schools to send out alerts and reschedule travel.

“We have thousands of students in 131 countries at any one time, and some of them are traveling or will be traveling to the affected countries,’’ said Madeleine Estabrook, Northeastern’s vice president of student affairs.

Northeastern had already been sending targeted alerts to students in foreign travel programs. But with spring break looming in early March, and Zika now reported in popular spring break destinations in the Caribbean and Mexico, Estabrook said the university needed to quickly widen its message.

Concerns have grown worldwide as health authorities this week reported a case of Zika in Texas spread through sexual contact. Health officials had thought the virus was transmitted only through the bite of an infected mosquito.

Although Zika rarely causes serious illness, it has been linked to a devastating birth defect, prompting recommendations that pregnant women consider avoiding the affected areas. Further studies are planned to establish the extent of the risk to pregnant women.

“Now that there is a case that was sexually transmitted, this becomes a very different thing,’’ Estabrook said. “It starts to become important to more of our population.’’

Northeastern has not yet canceled programs in countries where Zika has been reported, but Estabrook said school officials are monitoring the rapidly changing situation.

“It could be on Monday we are sending out another message that is suggesting many more precautions,’’ Estabrook said.

At Boston College, Nick Gozik, director of the school’s international programs, said officials are studying each of the destinations in the travel program to decide whether some should be canceled or changed.

The school has eight students in Ecuador, one of the South American countries reporting Zika infections. Gozik said the risks to students studying in the mountain city of Quito, the capital of Ecuador, may not be as serious as those traveling in areas thick with mosquitoes.

“The various risks in the Amazon may be more than in Ecuador,’’ Gozik said. “A trip to the Amazon we will need to reconsider.’’

Tufts University has not made changes in its international travel programs, or sent campuswide alerts, because Zika virus has not affected any of the countries with its study abroad programs, said spokeswoman Kimberly Thurler.

“The consensus among our medical, public safety, and international travel experts was that a mass e-mail was not appropriate,’’ Thurler said. “We have a handful of other travelers in Brazil and Mexico, and we have shared appropriate information, including recommendations from the [US Centers for Disease Control and Prevention] with them.’’

Boston University also has not sent campuswide alerts, but has been posting Zika-related health and travel information on websites for its student health service and global programs, said spokesman Colin Riley.

Boston’s public schools are canceling all school-sponsored student trips to parts of the Americas with outbreaks of ­Zika, authorities said.

“At the current time, this includes Costa Rica, Dominican Republic, Ecuador, and Nicaragua,’’ stated a memo that went out Wednesday night to families and staff.

So far, six schools have had to scrap trips, Boston schools spokesman Dan O’Brien said Thursday.

“We understand the valuable learning experience these study trips provide our students,’’ the memo said. “We will work with our trip leaders and providers to find new destinations, where possible, for alternative trips.’’

Kay Lazar can be reached at Kay.Lazar@globe.com Follow her on Twitter @GlobeKayLazar.