State health officials are working on plans to prepare for a possible Zika outbreak in Texas.

Thursday, the Texas Department of State Health Services confirmed a total of ten cases of the virus, with an eleventh case reported later that afternoon, confirmed by the county but not state health department.

Seven cases are in Harris County, two in Dallas County, one in Bexar County and one, pending confirmation from the state, in Travis County.

Ten of those cases involve travelers who were infected abroad, while one involves a person infected in Texas, but not by a mosquito. According to the Dallas County Health officials, a resident there was infected through sexual contact with someone who contracted the virus in Venezuela, before returning home to Texas.

“There is a lot that we don’t know about this virus and I think that’s obviously stoking some fears as well,” said Chris Van Deusen, spokesperson for the Texas Department of State Health Services.

Health officials do know that the majority of Zika cases are transmitted by mosquitoes and that’s where they plan to focus their efforts.

As the number of people infected grows in Texas, so does the risk that the state’s mosquito population will pick up the virus.

“Not in quarantine at this point,” said Van Deusen. For now, state health officials ask those infected and any travelers who are returning from areas that have seen local transmission of the Zika virus, to continue to avoid mosquito bites.  “So that we can minimize the chance that the virus be introduced into mosquitoes here,” Van Deusen said.  

If that transmission cycle starts—human to mosquito, to human—doctors say it’s almost impossible to get the virus out of the population.

“The level of seriousness that the birth defects can cause, that really is the major concern, the effect that it can have on pregnant women and their unborn and newborn children”

Linked to an alarming number of babies born with abnormally small heads and underdeveloped brains, Zika has prompted worldwide concern.

Local transmission of Zika virus has been reported in at least 29 counties in central and South America, the Caribbean, the Pacific Islands. The World Health Organization estimates as many as 4 million people in the Americas will be infected within the next year.

“We know that it is a possibility and so that’s why we are making plans, that’s why we are talking with local health and drawing up what the right public health intervention is going to be if we do see those cases,” said Van Deusen.

At this point, officials say the state’s mosquito population has not been infected, but the type of mosquito known to be the primary carrier of Zika virus does live in Texas. The aggressive Aedes aegypti mosquito is most commonly found in the southern part of the state. The insect lives in close proximity to people, in buildings and houses and they feed during all hours of the day. 

“Dump out standing water, make sure screens are in good repair and they are not exposed to mosquitoes if they can at all avoid it and then also there is a response as far as insecticide and spraying for those mosquitoes,”  Van Deusen said.

State health officials say those tactics has helped limit the spread of dengue fever which is transmitted the same way and by the same mosquito as Zika.

Van Deusen said, “That’s sort of what our expectation is as well with Zika, we could see some limited local transmission but it’s unlikely to become as widespread as we’ve seen in other countries.”

There is no cure or vaccine for the Zika virus. Van Deusen said the best was to stop is from spreading is to stop mosquitoes.

The Centers for Disease Control and Prevention warns pregnant women should not travel to areas where Zika is circulating. The CDC also advises men who have traveled to or live in an area where the virus is locally transmitted, to abstain from sex or use condoms.

The virus stays in the blood for about a week, but the CDC is still conducting studies to determine who long the virus would remain in semen.