AUSTIN – Health officials confirmed a case of Zika virus in Willacy County, according to the Texas Department of State Health Services website.

The case is reported to be travel related. Zika virus cases have now been confirmed in all four counties of the Rio Grande Valley.

Zika is primarily spread through mosquitoes. Symptoms include fever, rash, joint pain and red eyes; however, most people infected don’t show symptoms or have mild symptoms. The virus has been linked to microcephaly, a birth defect where a baby’s head doesn’t fully develop.

Related Link: TexasZika.org

Early cases of the virus in the Rio Grande Valley were confirmed in September and classified as travel related. In late November, health officials said a Zika case in Cameron County was transmitted locally by a mosquito. This led to voluntary urine tests of people living in the same area as the 43-year-old woman in the case. More cases of Zika were confirmed through these tests.

As of Tuesday, the state health department listed 16 cases of Zika in Cameron County, five cases in Hidalgo County, one in Starr County and one in Willacy County. Cameron County Health Authority Dr. James Castillo said there may be plenty of others infected, but only 20 percent of people with the virus are symptomatic.

So far, the only Zika cases in the state that were locally transmitted were found in Cameron County.

As of last week, Cameron County health officials haven’t found solid proof that infected mosquitoes are in the area. None of the thousands of mosquitoes trapped throughout Brownsville have tested positive for the virus; however, testing continues.

Dr. Castillo said they are relying on health experts’ educated guess and what is known about Zika to make determinations on each case. He pointed out it’s impossible to catch every single mosquito.

CHANNEL 5 NEWS is checking on the latest confirmed case. Watch CHANNEL 5 NEWS and check back on KRGV.com for more updates.