In 2016, the World Health Organization triumphantly declared the Americas to be the first region on the globe to eradicate measles. One year later, a measles outbreak erupted in Venezuela.

"And consequently, since June of 2017 we've seen upwards of almost 6,500 cases [in Venezuela]," says Robert Linkins from the U.S. Centers for Disease Control and Prevention. Linkins is the branch chief of Accelerated Disease Control and Vaccine Preventable Disease Surveillance at the CDC, and in that role he's the CDC's top person on measles globally.

"Do not travel to Haiti due to crime and civil unrest," the U.S. State Department says, urging Americans to avoid the country that is wracked with violent protests against President Jovenel Moise. The State Department is pulling all nonemergency U.S. personnel and their family members from the country.

Public health officials grappling with record-high syphilis rates around the nation have pinpointed what appears to be a major risk factor: drug use.

“Two major public health issues are colliding,” said Dr. Sarah Kidd, a medical officer at the Centers for Disease Control and Prevention and lead author of a new report issued Thursday on the link between drugs and syphilis.

A Senate Democrat on Thursday filed a proposal that would allow public schools to buy a type of drug that is used to treat people who have overdosed on opioids. 

Updated at 6:15 p.m. ET

Calling it "a great thing to do," President Trump declared a national emergency on Friday in order to help finance a long-promised wall on the U.S.-Mexico border. It's a highly unusual move from an unconventional president.