DETROIT (WWJ) – Four cases of the Zika virus have been confirmed in Michigan, according to a U.S. Centers for Disease Control report Friday.

Michigan Department of Health and Human Services Spokesperson Jennifer Eisner said none of the cases are in pregnant women, and all of them are believed to be travel-related — meaning the virus was not contracted locally.

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Details, including who these patients are and where they live, have not been released.

There are 544 confirmed cases in the U.S., according to the CDC.

Zika is a disease spread through the bite of an infected mosquito in tropical climates that leads to flu-like symptoms including fever, rash, red eyes and muscle pain. It is usually mild and lasts several days to a week.

Many people who are infected will not experience symptoms; and CBS News Medical Contributor Dr. Holly Phillips says 80 percent of people who contract the Zika virus never know it.

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In pregnant mothers, the virus has been linked to brain damage and abnormally small heads among their babies.

The number of pregnant women in the U.S. infected in Zika virus has tripled because the government has changed the way it counts cases.  There are now 157 pregnant women infected in 50 states, and another 122 in US territories, according to the CDC.

Zika is primarily spread by mosquito, although it can also be spread through sexual contact with an infected partner.

There is neither a vaccine to prevent nor medication to treat Zika.

The CDC recommends that international travelers protect themselves from mosquito bites by wearing long-sleeved shirts and pants to reduce exposed skin; using insect repellent that contains 20 percent or more DEET or Picaridin; and staying in screened or air-conditioned rooms. In addition, the CDC recommends that sexual partners protect themselves by using condoms to prevent sexually transmitted infections.

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For more information about protecting yourself from Zika, call the Detroit Medical Center’s hotline for travelers at 1-888-DMC-3370 or go to the CDC’s travel website,www.cdc.gov/travel.