The Centers for Disease Control and Prevention (CDC) on Friday issued more travel notices about the Zika virus, warning travelers about the potential risks of the mosquito-borne illness.

The notices were issued one week after the CDC advised pregnant women who were planning to travel to 14 countries and territories where outbreaks of the virus were occurring to consider postponing their trips while scientists probe a potential tie between Zika and a rare birth defect.

The notices issued Friday added eight additional countries or territories to the list, bringing the total to 22. The warnings are spread throughout the globe and include places in South America, the Caribbean, Central America, Polynesia and more.

Travelers heading to those areas are asked to “practice enhanced precautions” to prevent mosquito bites, which is how the virus is spread. Pregnant women are advised to rethink their travel plans because of Zika’s potential impact on their unborn children.

Last week, the Hawaii Department of Health announced a child born with microcephaly — a birth defect marked by a smaller-than-usual head — had previously been infected with Zika. The department said his mother likely contracted the virus when she was living in Brazil last May.

The Brazilian Ministry of Health reports that there have been 3,893 cases of microcephaly in the country since the virus arrived in May. The country used to see fewer than 200 cases per year.

Children with microcephaly can develop seizures, vision problems and have developmental delays, the CDC says, but it only occurs in 2 to 12 out of every 10,000 births in the United States.

Scientists are still trying to find a conclusive link between Zika and microcephaly, which can be caused by several other factors. Last week, Dr. Lyle Petersen, the director of CDC’s division of vector-borne diseases, told a news briefing the CDC had “the strongest scientific evidence to date” of a link between Zika and “poor pregnancy outcomes,” though more tests were needed.

Still, the warnings and advice for pregnant women continue. Earlier this week, the CDC issued new guidelines about how healthcare providers in the United States should care for pregnant women who had traveled or were planning to travel to areas where Zika was being transmitted.

Only about 1 in 5 people infected with the virus display any signs of illness, the CDC says, and symptoms are generally mild. They include fever, rash and joint pain, and most people recover within a week. The illness is seldom severe and rarely requires hospitalization.

There haven’t been any reports of people contracting the virus in the United States, the CDC says, though there have been some instances where travelers got bit by infected mosquitos overseas and returned home. The mosquitos that transmit Zika are found in the United States, though Dr. Petersen told the news briefing it’s unclear exactly how or if the virus may spread here.

He told reporters the country has seen improvements in anti-mosquito measures, like using air conditioning and window and door screens, which have helped reduce the spread of other mosquito-borne illnesses, like dengue and malaria, in the past. The CDC encourages all travelers to Zika-prone areas to sleep in screened or air-conditioned rooms, as well as wear long clothing and insect repellant, as there is no vaccine or medicine that can currently prevent an infection.

Countries and territories where the CDC has issued travel notices for Zika include Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Suriname, Venezuela, Barbados, Guadeloupe, Haiti, Martinique, Saint Martin, Samoa, Cape Verde, El Salvador, Guatemala, Honduras, Panama, Mexico and Puerto Rico.