An elderly Utah man who died after contracting Zika from travel abroad may have spread the virus to a family contact who did not leave the country, raising troubling questions about a possible new route of transmission of the mosquito-borne virus, state and federal officials said Monday.
Officials said they are investigating how the second person became infected. One possibility is close contact between the critically ill patient and the caregiver, who has since recovered.
“This case is unusual. The individual does not have any of the known risk factors we’ve seen thus far with Zika virus,” said Gary Edwards, a health officer at the Salt Lake County Health Department, during a news conference.
Edwards said the person had not traveled to a Zika-affected country and had not had sexual contact with anyone with the virus. But the individual had “helped provide care for the deceased patient.” Citing privacy, he and other officials declined to provide additional details.
The primary mosquitoes known for carrying Zika are not present in Utah, Edwards noted. As a precaution, officials are trapping and testing mosquitoes around both persons’ homes to definitively rule out that mode of transmission.
“At this time we don’t know if the contact between the new case and the deceased patient played any role in the transmission of the disease,” Edwards said. “There is uncertainty about how this new case contracted Zika. But we do not believe that there is risk of Zika transmission among the general population in Utah based on what we know so far.”
The Centers for Disease Control and Prevention on Monday said the elderly man had traveled to a Zika-affected area and that subsequent lab tests showed he had uniquely high amounts of virus in his blood — more than 100,000 times higher than that seen in samples of other infected people.
Public health investigators in Utah are interviewing the caregiver who was infected and additional family contacts to learn more about the types of interaction they had with the patient before he died. They also are collecting samples for testing, as well as working with facilities where that patient was to determine what contacts health-care workers there had.
CDC Director Tom Frieden said in an interview that scientists are conducting genomic sequencing to determine whether there have been any mutations in the viral strain that infected the elderly man or the second person.
Researchers are looking into the possibility that an infected mosquito may have traveled from the affected region back to Utah in the clothing or luggage of the man and then bitten the second person. Frieden said such infection, while rare, has occurred with malaria cases in Queens, N.Y.
But the questions raised by the caregiver’s case illustrate how little scientists know about the virus. Until the Zika epidemic exploded in Brazil last year, researchers had never seen a situation where a mosquito-borne illness causes birth defects, Frieden said. No other similar viruses are sexually transmitted as Zika is.
“This is a unique situation,” he said. “This is the first time where there is a suspected spread of one person to another” beyond sex.
Even if such transmission is confirmed, Frieden said it would be “unusual.”
He noted that the continental United States currently has more than 1,300 travel-related cases of Zika, and if this type of transmission is not rare, “it’s likely that we would have seen this before.”