Another U.S. intelligence official has come down with Havana Syndrome symptoms. What are they?

Asha C. Gilbert and Lindsay Schnell, USA TODAY

Another U.S. intelligence officer has been struck by Havana Syndrome symptoms, angering CIA director William Burns and resurfacing a conversation about the mysterious illness. 

Experts are in the process of verifying the officer's symptoms, which are consistent with the scores of other cases in recent years linked to Havana Syndrome, according to James Giordano, a scientist briefed on the case and others.

The officer was traveling with Burns through India this month, and an investigation is ongoing. CNN first reported the incident. There are questions about if the officer was targeted because he was traveling with the director, and U.S. officials are still trying to learn more about the illness, which started making headlines in 2016. 

"We have protocols in place for when individuals report possible anomalous health incidents that include receiving appropriate medical treatment," a CIA spokesperson told CNN. "We will keep doing everything we can to protect our officers."

The U.S. has not publicly linked the incidents to an adversary. Burns has ordered an agency-wide review of possible attacks using microwave or other directed energy.

The CIA declined to comment on the officer's case, but said in a statement that Burns “has made it a top priority to ensure officers get the care they need and that we get to the bottom of this.” Since becoming director, Burns has tripled the number of medical staff studying incidents linked to Havana Syndrome and met with agency personnel who reported cases.

So what is Havana Syndrome exactly? Read on for a primer about the affliction. 

What is Havana Syndrome? 

The name "Havana Syndrome" was coined after an illness struck people at the U.S. Embassy in Havana from 2016 to 2017, the BBC reported. Diplomats and staffers reportedly experienced hearing loss, dizziness, loss of balance and other neurological symptoms.  

Most of the people who experienced Havana Syndrome had an onset of a perceived loud noise, a sensation of intense pressure or vibration in the head, and pain in the ear or the head, according to a report by the National Academies of Sciences

For some, the symptoms subside soon, but others could have chronic symptoms like insomnia and headaches.  

Most plausible:Report finds pulsed radiofrequency likely cause of mysterious illness

What causes it? 

Different theories have circulated about what causes the illness. But in a report by the National Academies of Sciences, the researchers concluded that the symptoms were consistent with directed, pulsed radiofrequency energy.  

The committee also looked at chemical exposures, infectious diseases and psychological factors as potential culprits but found directed, pulsed RF energy as the most plausible explanation. 

The report did not say whether the energy was delivered intentionally. 

Who has had it? 

There are at least 200 cases under investigation, half of them involving intelligence personnel, including spies, diplomats, soldiers and other U.S. officials.

Cases have been suspected in Cuba, China, Europe and in the U.S. near the White House. In September, a Havana Syndrome scare delayed a trip to Vietnam by Vice President Kamala Harris. 

Contributing: The Associated Press