The most telling information at a Philadelphia Department of Public Health staff briefing about the Zika virus on Thursday was this slide: "Stay tuned: With the dynamic nature of this situation, updates . . . are expected."

Two dozen epidemiologists, mosquito-control staffers, and emergency planners got the latest on the virus, which has spread with astonishing speed through Central and South America. Every confirmed case in the continental United States has been linked to travel (or sex with someone who traveled) in the 25 affected countries. But public health officials say it's inevitable that the disease will be spread locally in parts of the country.

That's why one hot topic is how to tweak existing mosquito-control programs to target Zika.

Thursday's briefing, like past ones for related viruses such as chikungunya and dengue, was meant to prepare workers and to help them answer questions from physicians and the public.

Forty-four cases of chikungunya and 19 of dengue fever have been reported in Philadelphia over the last several years, all travel-related. No Zika has been reported.

The biggest concern is for pregnant women, because of reports linking the infection to brain damage in babies. Such women are being advised to avoid affected countries.

Early evidence of possible sexual transmission prompted the city to recommend that men use condoms and women use other forms of birth control - to prevent both transmission and pregnancy - if they or their partners have traveled and have symptoms.

Zika produces no symptoms in 80 percent of cases. Though dengue, chikungunya, and even seasonal flu produce more severe symptoms, those other viruses have not been linked to the births of children with abnormally small heads and brain damage.

Especially at this time of year, mosquito-borne viruses are unlikely in the Philadelphia region. If you feel healthy one day and really miserable with a high fever the next, you likely have influenza, said Dana Perella, who leads the department's virus monitoring efforts.

There is a vaccine against seasonal flu - and public health officials say it is worth getting - but none against Zika.

For mosquito-borne viruses, prevention is all about getting rid of mosquitoes. And while the Zika threat is new, mosquito-control efforts ramped up nearly two decades ago when West Nile virus began appearing.

That system could be the basis for controlling Zika if it arrives, with notable differences.

Catching and testing the mosquitoes that transmit West Nile involves traps set on the ground and baited to mimic where the Culex genus of mosquitoes lays its eggs: standing water sweetened with bits of hay and other materials that the insects love. Culex are most active at night.

Zika-carrying species in the Aedes genus are active during the day and behave differently. To catch them, the city would likely rely on traps that mimic human targets by releasing CO2 using dry ice or other means, said Ray Delaney, who oversees the city's vector-control program.

In the 17 years since the city expanded its mosquito-control programs for West Nile, about 30 different species have been found, he said.

The species that is spreading Zika in the tropics has never shown up in those traps. Another Aedes species is common in this region, but it is unclear if this type of mosquito is capable of causing major outbreaks of Zika. It already is targeted for eradication because it can carry dengue and chikungunya.

Beginning every April, the Health Department applies larvicide to 46,000 storm water inlets where mosquitoes may lay their eggs, Delaney said.

His office also responds to about 100 to 300 complaints a year from residents who call about standing water in old pools and other containers, usually in their neighbors' yards.

As do many suburban counties, the city sprays insecticide in areas that might harbor mosquitoes. In the city, prime targets are in and around the Wissahickon Valley and Pennypack Park.