Mysterious Zika spread in Utah suggests new mode of transmission

A mysterious transmission of Zika in Utah is raising alarms about whether the virus is evolving or can spread in yet another way nobody expected.

On Monday, state and federal officials said that a man who became the first person to die from the Zika virus in the continental U.S. spread it to a "family contact" who had been caring for him. Officials aren't sure how it happened, but they say it does not appear to have occurred through sexual transmission or from an infected mosquito – thus far the only known ways of spreading the virus.

Still, the Centers for Disease Control and Prevention, along with state and local health officials, are testing other family members for possible transmission and trapping mosquitoes to see whether those in the area are carrying the virus.

If there is a chance that the virus spreads through another bodily fluid or has even become airborne, then the threat would be particularly high for pregnant women, who risk giving birth to babies with birth defects if they become infected early in their pregnancy. The long-term effects of the birth defect, called microcephaly, are still being evaluated, but it causes babies to be born with abnormally small heads and possible brain damage or blindness.

RELATED: Genetically engineered mosquitos to combat Zika

Dr. Michael Bell, medical epidemiologist at the CDC's Division of Healthcare Quality Promotion, said in a call with reporters Monday that it was unlikely that the virus had become airborne but added that "in our line of work nothing is truly off the table, and we don't want to underestimate possibilities – however extremely unlikely."

The Zika virus has previously been found in urine, blood, semen, saliva, breast milk, vaginal fluid and inside the eye. CDC officials said Monday in a call with reporters that it's unclear how the caregiver became infected and would not elaborate on whether the caregiver handled some of these fluids. In one case at the University of Pittsburgh, a researcher was infected after accidentally sticking herself with a needle.

"It's early to make a statement about what might have happened," Bell said. "We are not a point to discuss the possible transmission that might have led to infection." What they find will likely influence their guidance to family members and to health care workers, he said.

Officials also aren't sure how the virus contributed to the elderly man's death. They know that the concentration of virus in his blood was uniquely high – more than 100,000 times that of other cases – but aren't sure whether his other illness compromised his immune system or whether the high concentration was the cause of his death. Zika wasn't discovered until after the patient had died in late June, and officials would not name his other illness. That person had become infected with Zika after going to an area of the world where the virus is spreading.

The caregiver who was infected recovered quickly, as do most adults who get Zika. Officials recorded only one other death on U.S. soil that occurred in an elderly man in Puerto Rico, who died after developing severe thrombocytopenia, a condition in which blood platelets are deficient. In rare cases, adults have developed symptoms similar to multiple sclerosis or have developed Guillain-Barre syndrome, a form of paralysis.

The understanding of the virus is evolving. Only last week, officials in New York City confirmed the first case of female to male sexual transmission.

As of July 13, 1,306 cases of Zika have been reported in the continental U.S., none of which have spread by mosquitoes who were present here. The vast majority of cases have occurred because people were infected when they traveled to a country where the virus was spreading.

In a statement, Dr. Erin Staples, a medical epidemiologist from the CDC on the ground in Utah called the new case a "surprise" that showed there was still more to be learned about Zika.

Copyright 2016 U.S. News & World Report