Health officials said Monday that they are investigating the case of a man in Utah who has contracted Zika virus locally through unknown means, one of the more mysterious cases of transmission yet involving the virus.
The individual, who has not been identified, recently helped care for his father, who had contracted Zika and died earlier this month. The second case had not recently traveled outside the country.
That shifts the focus of the investigation to mosquitoes and the possibility that the new case became infected while caring for his dying father. The older man had a serious illness when he contracted Zika while traveling outside the US.
Though most commonly transmitted through the bite of an infected mosquito, Zika virus can be spread through contact with body fluids from an infected person including semen and blood. The virus is also found in urine and saliva.
“The new case in Utah is a surprise, showing that we still have more to learn about Zika,” said Dr. Erin Staples, the Centers for Disease Control and Prevention’s medical epidemiologist based in Utah.
The man who died had exceptionally high levels of the Zika virus in his system at the end of his life. Health officials acknowledged the younger man was related to the man who died earlier this month but declined to provide further details; they were father and son, according to a person who was familiar with the case but who was not authorized to speak for attribution.
A statement from the CDC said the older man’s blood contained 100,000 times more virus than is normally seen in Zika infection.
It’s too soon to say whether that fact allowed for a type of transmission that hasn’t yet been seen, said Dr. Michael Bell, deputy director of the CDC’s division of health-care quality promotion.
“Currently there’s nothing specific we can say other than recognizing that a high viral load could be a different situation than we would ordinarily see,” said Bell.
“From the infection control perspective, I think it’s early to make a clear statement about what we think could have happened.”
State officials are working with the CDC to try to interview and test other people who came in contact with the man who died — additional relatives, health-care workers — to see if there were other, undetected secondary cases.
With Zika infection, as many as four out of five cases develop no symptoms; most would go undetected.
“There is a lot of uncertainty around this investigation and we’re currently exploring all avenues for possible transmission,” Dr. Angela Dunn, deputy state epidemiologist, told STAT.
“We’re exploring contact with the deceased patient [as a transmission route] as well as our mosquito trapping and testing for Aedes, the species of mosquito that is known to carry the mosquito virus as well as testing other mosquito species for the Zika virus.”
Dunn said Aedes mosquitoes are not thought to be established in Utah. Trapping efforts are underway around the residences of the man who died and his relative to try to see what types of the insect are present and whether any of them are infected with Zika.
“Our knowledge of this virus continues to evolve and our investigation is expected to help us better understand how this individual became infected,” said Dunn, who noted that based on what is currently known about the case, the health department does not believe the general public in Utah is at risk.
She acknowledged it may not be possible to find out how the new case — who has fully recovered — contracted Zika. “However, we do anticipate that this investigation will yield new information about the Zika virus.”