Medical authorities are warning that the Zika virus may already be spreading through Texas, California, Arizona and other parts of the U.S. where the summer weather fosters an inviting habitat for mosquitoes. Outbreaks may remain hidden until mothers begin giving birth to afflicted babies, reports the Dallas News in its coverage.

Although over 900 people have been diagnosed with Zika in the United States, according to the Centers for Disease Control and Prevention (CDC), the majority of them contracted the infection while traveling in South America or the Caribbean. The CDC has also identified 13 cases where Zika was sexually transmitted in the U.S.

So far the CDC has reported no locally acquired mosquito-borne cases in the continental U.S. But a number of health experts are expressing concern over disease-carrying Aedes aegypti mosquitoes that could migrate north as summer temperatures provide a more conducive environment for them.

A study in the journal PLOS Current Outbreaks says that this summer, mosquito populations might proliferate in at least 50 U.S. cities, including Dallas, Houston, Los Angeles, New York City, and Washington, D.C. "Meteorological conditions are suitable for Aedes aegypti across all fifty cities during peak summer months (July-September)," note the authors.

Peter Hotez, M.D., a professor and dean at the Baylor College of Medicine, writes in Momentum that Aedes aegypti mosquitoes may already be transmitting Zika to people living in the at-risk areas of Arizona, southern California and the Gulf Coast. Infections may not have come to light yet as the symptoms of Zika are mild and may not motivate victims to get a diagnosis.

In an NPR interview, journalist Donald G. McNeil, Jr. warns that the time is ripe for Zika to strike hard in the United States. Author of the book "Zika: The Emerging Epidemic," McNeil says that Americans are particularly vulnerable in 2016 because Zika is still an unfamiliar virus.

"Nobody is immune to it, nobody has antibodies to it," declares McNeil, though he offers a silver lining: "After this year, a fair number of people will be immune, and each year immunity will grow."