July 18, 2016 -- The CDC is investigating a Zika mystery: how a Utah resident got the virus without traveling or sexual contact.
The new case is a relative and caregiver of an elderly Zika patient who died in late June. The deceased man had traveled to an area where Zika is spreading, and lab tests showed he had high amounts of the virus in his blood -- more than 100,000 times higher than those seen in other samples of infected people, according to the CDC. He also had an underlying medical condition, which has not been disclosed. That medical condition may have contributed to the severity of his Zika infection, say officials with the Salt Lake County (Utah) Health Department.
The new patient developed mild symptoms and rapidly recovered, said CDC officials in a news conference. Neither patient was identified.
“The new case in Utah is a surprise, showing that we still have more to learn about Zika,” said Erin Staples, MD, PhD, the CDC’s medical epidemiologist on the ground in Utah, in a news release.
Doctors don’t know if the virus was passed directly from nonsexual contact with bodily fluids like saliva or urine or whether it might have been spread indirectly, through the bite of an infected mosquito. Scientists have found the Zika virus in human blood, semen, saliva, urine, breast milk, swabs from the genital tract, and in fluid in the eye.
If it was passed through a mosquito bite, it would be the first case of local transmission documented in the U.S., but that possibility seems unlikely because Utah isn’t known to have the kinds of mosquitoes that are known to carry Zika.
“Right now we’re assessing whether any other kind of transmission could be occurring,” said Michael Bell, MD, a medical epidemiologist with the CDC.
An estimated 80% of people infected with Zika don’t show symptoms. The others may have a fever, joint pain, and red eyes (known as conjunctivitis). But Zika can wreak havoc on the unborn, causing devastating birth defects including microcephaly, in which babies have unusually small heads and brain damage.
As of July 7, nine babies with birth defects linked to Zika have been reported in the U.S., according to the CDC. Six other pregnancy losses with birth defects were linked to the virus.
In a statement issued last week, Ary Faraji, PhD, manager of the Salt Lake City Mosquito Abatement District, said that neither of the two mosquito species that are known to transmit the virus have ever been found in Utah.
Casual contact seems unlikely also, Staples said. “From what we have seen with more than 1,300 travel-associated cases of Zika in the continental United States and Hawaii, non-sexual spread from one person to another does not appear to be common.”
CDC investigators are trapping mosquitoes in Utah in the communities where the family lives.
Robert Wirtz, PhD, an entomologist with the CDC, says that so far, the number of mosquitoes that have been trapped in Utah are low and they are mostly culex mosquitoes, which primarily feed on birds. Aedes aegypti and Aedes albopictus mosquitoes are believed to be the carriers in the Zika outbreak spreading through the Americas.
“As has been said, in our line of work, we never take anything off the table, but right now, we feel like transmission by aedes mosquitoes is highly unlikely,” he says.
Public health officials are interviewing the patient and other family members to learn what kind of contact they had with the deceased man. They are also collecting samples for testing from family members and others who had contact with the deceased patient to see if anyone else was infected, according to a news release from the Utah Department of Health.
“Based on what we know so far about this case, there is no evidence that there is any risk of Zika virus transmission among the general public in Utah,” says Angela Dunn, MD, deputy state epidemiologist at the Utah Department of Health.
As of July 13, 1,306 cases of Zika have been reported in the continental United States and Hawaii; none of these has been the result of local spread by mosquitoes. These cases include 14 believed to be the result of sexual transmission and one that was the result of a laboratory exposure.