A biologist displays Aedes aegypti mosquito cells inoculated with the Zika virus in a laboratory in Campinas, Brazil. (Paulo Whitaker/Reuters)

Update: New details are emerging about the mysterious Zika case in Utah where a son caring for his sick father became infected with the virus. The father's death in June was the first related to Zika in the continental United States. His son's infection was unusual because, unlike all other known adult cases, he had not traveled to a Zika-infected region or had sex with a partner who had done so.

Instead, he had remained at his father's side in the hospital.

In a case study published Wednesday in The New England Journal of Medicine, the medical team who cared for both patients said it's likely the younger man contracted the virus through his father's sweat or tears. The older man had an unusually high level of virus in his blood, more than 100,000 times higher than that seen in samples of other infected people.

The son had contact with his father's skin and wiped his eyes, "both without gloves," said Sankar Swaminathan, an infectious disease specialist at the University of Utah's School of Medicine who treated the two patients.

No other family members or health care workers who had contact with the 73-year-old man reported a Zika infection.

Swaminathan said the case offers critical new information for health care providers and researchers. In rare cases, when patients have severe Zika infections, "the levels of virus may very well be unprecedented, and the implication is that such cases may present increased risk for transmission through bodily fluids," he said.

There only have been nine other Zika-related adult deaths in the Americas that have not been linked to Guillain-Barré syndrome, a rare nervous system illness that causes muscle weakness and sometimes paralysis. Some of those nine individuals had serious underlying medical conditions or very weak immune systems, Swaminathan said.

But that was not the case for the Utah man. The father had been treated for prostate cancer but did not have a severely weakened immune system when he became ill with Zika.

However, he had previously been infected with dengue, a related virus. Some research in animals has suggested that previous dengue infections may worsen a subsequent Zika infection. It's possible that could have happened in this patient's case, triggering his severe infection, Swaminathan said.

The father had traveled to the southwest coast of Mexico, where he got bitten by mosquitoes. After returning home, he became sick and was admitted to the hospital in shock, respiratory distress, a sore throat and conjunctivitis, or inflammation of the eyes.

Swaminathan said most doctors treating someone with those symptoms might suspect illnesses such as pneumonia or sepsis, a complication from a life-threatening response to infection. But not Zika.

"What this case tells me is that doctors should think about Zika when they see someone who is severely ill and might have been exposed," he said. "It now expands the spectrum of illness."

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Everything you ever wanted to know about the Zika virus and its spread across North and South America. (Daron Taylor,Claritza Jimenez/The Washington Post)

Original post from Sept. 13: As Congress debates emergency Zika funding for the third time this year, new findings from a mysterious Utah case suggest that the virus may spread through contact with bodily fluids, a worrisome new possible route of transmission.

Until now, scientists have said that Zika is spread primarily through the bite of an infected mosquito. It can also be spread through sex as well as blood transfusions, and a pregnant woman can pass the virus to her fetus.

But information released Tuesday by federal and state health officials suggest that contact with bodily fluids, such as tears, discharge from infected eyes, saliva, vomit, urine or stool, could have been how a Utah man became infected after caring for his elderly father. The father died in June after contracting Zika from travel abroad. The father’s blood had a level of infectious virus 100,000 times as high as the average level reported in people infected with Zika, according to a report released Tuesday by the Centers for Disease Control and Prevention.

The son recovered fully.

Health officials are recommending that family contacts and close friends caring for Zika patients who are very sick avoid contact with the patient’s bodily fluids and use good hand hygiene, said Angela Dunn, deputy state epidemiologist in Utah. Health-care workers are urged to continue to apply standard precautions while caring for all patients, including those who might have Zika virus disease. Such measures include wearing gloves, masks and other personal protective equipment.

People may often be lulled into a false sense of security about the way Zika spreads, thinking it may just be through mosquitoes or sex.

Although local, state and federal officials cannot say definitively how the son became sick, the Utah case suggests that the way the virus was transmitted “doesn’t appear to be one of the modes we’ve seen before,” said Alexander Kallen, a CDC medical officer.

“It does raise the possibility that there was potential exposure to the blood and bodily fluids of the index patient, and that could have led to transmission of the second case,” Kallen said.

Earlier this summer, the Food and Drug Administration asked blood centers in two Florida counties to immediately stop collection because of possible local transmission of the Zika virus. The CDC has since issued travel advisories warning pregnant women from heading to Miami Beach and an area north of downtown Miami known as Wynwood where the virus is being spread locally by mosquitoes.

As part of the investigation in Utah, health officials interviewed and tested 18 other family members, and none were positive for the virus. They also identified medical workers who cared for the elderly man and surveyed 238 households living within a 200-meter radius of the two homes in which the father lived before becoming hospitalized. Eighty-six medical workers and the community residents who agreed to provide blood or urine specimens were tested. No one else has tested positive. Nor have officials found any evidence of either mosquito species that transmit the virus, Dunn said.

Dunn said investigators don’t know which bodily fluid could be the culprit. Zika has been detected in blood, urine, semen, saliva and breast milk. It has also been found in genital-tract swabs and fluid inside the eye.

Most people who get Zika infections show no symptoms or have only mild illnesses. But in some cases when patients are very sick, “they often have a lot of diarrhea” and the virus could have spread through that exposure, Dunn said. The son reported hugging and kissing his father and helped hospital personnel hold him while he was being cleaned, the report said.

Although it’s perplexing that no one else developed an infection, officials say, it’s hard for a retrospective investigation to fully capture all aspects of the son’s exposure.

“We don’t know if there may have been some unrecognized contact with mucous membranes, or whether it was just bad luck that he came in contact with infected fluid,” Kallen said.

Because the father had such a high level of the virus in his body — one of the highest scientists have seen — it’s also likely that the virus showed up in more places in his body, increasing the risk of transmission.

Read more:

Newest superbug found in a Connecticut toddler

Zika is spreading and remains global emergency, WHO says

U.S. will run out of money to fight Zika in September

Lifelong heartache, care for babies born with Zika in the U.S