Gregg Zoroya, and Liz Szabo

USA TODAY

At least 11 U.S. troops have been infected with the Zika virus since January, nearly all of whom traveled to countries where the mosquito-born illness is prevalent, a Pentagon health report published Friday disclosed.

In addition, four dependents of servicemembers — which can include spouses and children — and two military retirees contracted the illness, according to the report. It underscored the risks to military personnel of child-bearing age exposed to the virus during deployments.

A fetus infected with the Zika virus during the first three months of pregnancy has about a 1% to 13% chance of developing microcephaly, an abnormally small head usually caused by incomplete brain development, according to the Centers for Disease Control and Prevention.

Among the 17 infected are four women, though none were pregnant, said Dr. Jose Sanchez, deputy chief of Armed Forces Health Surveillance Branch.

Troops suffering from the Zika were four soldiers, three Airmen, a Marine and three members of the Coast Guard, according to Sanchez. The first confirmed case was diagnosed in late January, the report said.

Fifteen of the 17 had traveled to South America or the Caribbean. They included four who visited Columbia, three who went to the Dominican Republic and three who visited Puerto Rico. One person had traveled to Brazil, which is dealing with a Zika epidemic.

"It is a fair assumption that the military is at higher risk for mosquito-borne infections," said Amesh Adalja, a senior associate the Center for Health Security at the University of Pittsburgh Medical Center. "The military is stationed all over the world and often have prolonged outdoor exposure, enhancing the likelihood they will be bitten."

The military should make sure that servicemembers and their families "are made completely aware of the risks and the measures required to protect themselves from both mosquito and sexual transmission," Adalja said. "Mosquito repellents for troops in active Zika zones will be essential, as will minimizing standing water mosquito breeding sites on military bases.

The Pentagon in March ordered heightened monitoring for certain mosquito species at military installations in 27 states and the District of Columbia in response to the Zika virus crisis, according to Air Force Maj. Benjamin Sakrisson, a Pentagon spokesman. The Defense Department called for expanded monitoring, trapping, testing and eliminating water sources as breeding grounds, the newspaper reported.

"The Department has been providing information about the Zika virus and prevention of mosquito-borne illnesses to service members and their families through all available channels," said Sakrisson, adding that military doctors brief families about "avoidance of unprotected sex and repellent use while in risk areas."

The Pentagon also offered to relocate family members of active-duty personnel and civilian Defense Department employees assigned to regions at higher risk for infecting people with the virus, Military Times reported.

More than 600 people in the continental U.S. have been infected with Zika, including 195 pregnant women. All of those cases were related to travel. More than 1,100 cases of Zika, including 146 involving pregnant women, have been detected in the U.S. territories of Puerto Rico, American Samoa and the U.S. Virgin Islands, where the disease is spreading among local mosquitoes, according to the Centers for Disease Control and Prevention.

The true number of Zika cases could be much higher. Only about 20% of people infected with Zika have symptoms, which can include fever, rash, joint pain, pink eye and headache.

Zika is spread by the Aedes aegypti mosquito species, found in much of the southern U.S., as well as the Americas, Africa and Asia. Scientists say it's possible that Zika also may be spread by the Aedes albopictus, whose range stretches as far north as New England, according to the CDC.

The people at highest risk from the Zika virus are pregnant women because the virus can cause devastating birth defects in fetuses, according to CDC director Thomas Frieden. The CDC encourages pregnant women to avoid traveling to areas with Zika outbreaks.

Infected men also can spread Zika through vaginal, oral or anal sex, according to the CDC. It’s not known if infected women can pass the virus to men.

The CDC has issued guidance to help reduce the risk of sexual transmission.

If a man has had a possible Zika exposure and has a pregnant partner, he should wear condoms or abstain from sex for the duration of the woman’s pregnancy, according to the CDC.

If a man has had symptoms of Zika, he should consider using condoms or abstaining from sex for six months, according to the CDC.

Men who have traveled to a Zika-affected area, but who have not had symptoms, should consider using condoms or abstaining from sex for eight weeks, according to the CDC.

Women who’ve traveled to Zika-affected areas should delay trying to get pregnant until eight weeks after their symptoms start; if they don’t have symptoms, they should avoid trying to conceive for eight weeks after being exposed.