Experts from the Centers for Disease Control and Prevention have quite the mystery on their hands: "How did a person contract the Zika virus from a relative who had an unusually high level of the virus in his blood?"

Back in June, an elderly Utah man who had visited a country that was subject to a Zika outbreak died. Lab tests showed the patient, who suffered from other medical conditions as well, had 100,000 times the amount of the virus in his blood than other samples taken from people infected with Zika.

Following his death, a family member who had cared for the patient was also discovered to be infected, prompting the current situation in which the CDC has found itself. Fortunately, the patient recovered quickly after a mild illness, but that is little solace for those who are now scratching their heads as they try to figure out how the caregiver contracted the virus at all.

Here's the problem: To date, there are only three known ways to contract Zika. The first is by being bitten by the Aedes aegypti or Aedes albopictus strain of mosquitoes, which are known to carry the virus. The second is to receive it from a partner during intercourse (a previous instance in Dallas revealed that it's possible to receive it during anal sex as well). Lastly, there is the risk of mother-to-child transmission in the womb.

However, the caregiver had none of those known risk factors: s/he had not visited an area where the virus was known to be circulating, nor had the caregiver had sexual contact with anyone known to be infected with the virus.

For what it's worth, two mosquito species capable of carrying and transmitting the Zika virus are known to be present in some tropical corners of the U.S. However, there have been no instances of an infection that has originated in the country, and no Zika-infected mosquitoes are known to have reached Utah.

"This is a very unique situation that we haven't previously seen," said Dr. Satish Pillai, who leads the CDC's Zika Response team in Utah, in a news conference Monday. "There's a lot we don't know about Zika virus and we are still doing a lot of investigation to determine whether Zika can be spread from person to person."

Zika having the potential to spread from person-to-person would change the game for epidemiologists in a big way. Of the 1,306 cases of Zika infection that have been reported in the United States, nearly all are thought to have been transmitted outside the U.S. via a mosquito bite, with 14 of them being transmitted through sexual contact.

If person-to-person transmission is possible, then that means Zika could linger in the air after an infected person has breathed, coughed or sneezed — greatly increasing the ways someone could get infected. Of course, this wouldn't be an issue if the indicators for someone being infected were more apparent, but the majority of people who are infected exhibit no symptoms, and those who do only exhibit them for about a week at most.

Unfortunately, as things stand, there are too many variables to consider in the case — such as how the deceased patient's unusually high viral load plays into all this — revealing just how little experts know about Zika.

"The new case in Utah is a surprise, showing that we still have more to learn about Zika," CDC medical epidemiologist Dr. Erin Staples said.