Back in July, a 38-year-old Utah man was diagnosed with the Zika virus, even though he hadn't traveled to a Zika-affected region or had sexual contact with someone who did.
Experts were puzzled.
They knew that Zika virus was transmitted in only one of four ways: from the bite of an infected mosquito, from sexual contact with an infected person, from contact with infected blood, or from pregnant mother to fetus in the womb. They also knew that Salt Lake City, Utah is not a hospitable environment for the Aedes Aegypti mosquito, which transmits the virus easily.
The man's only contact with someone who had Zika was a hospital visit to see a 73-year-old friend with the virus ― a visit that occurred seven to 10 days before the younger man's symptoms began. Without wearing gloves, he had helped a nurse re-position his friend and had wiped the man's eyes. That was it: There was no other contact with blood or other bodily fluids.
So did he really get the virus from touching a patient? The answer appears to be yes, but there are a lot of caveats.
Tears or sweat might transmit the virus, but researchers can't be sure
In a report published in the New England Journal of Medicine, Dr. Sankar Swaminathan of the University of Utah School of Medicine concludes that the younger man likely contracted Zika virus from his older friend, who shortly died. However, Swaminathan and his fellow authors aren't sure how the transmission occurred. One possibility is that it happened because the man wasn't wearing gloves and came into contact with his friend's sweat or tears.
Swaminathan, who treated both men in Utah, emphasized that his report does not definitively implicate contact with sweat or tears as a way to contract the Zika virus.
“We can't conclude anything because we really just don't have firm evidence of how it was transmitted,” he said. “This doesn't change any recommendations from the [Centers for Disease Control and Prevention], or what the real risk factors are for people to get Zika: traveling to a Zika-endemic area or having sex with a person who has been in an area like that.”
“We just don't want to create alarm that Zika virus is easily translated from person to person,” he concluded. “We just don't think it is.”
The original patient had an unusually high viral load
The facts of the case are unusual for even more reasons. For one, the original patient, who had likely contracted the Zika virus while visiting Mexico, had an unusually high concentration of the virus in his body: Doctors measured it as about 200 million copies of the virus per millimeter of blood. Research on the typical viral load of Zika virus is still forthcoming, but to give a sense of how unusually high this concentration is, Dr. Jeffrey Klausner, an HIV and infectious diseases expert at the UCLA School of Medicine and Public Health, pointed out that someone with HIV only has about 50,000 to 100,000 copies of HIV per milliliter of blood.
The patient may have had unusually large amounts of virus in his body because he had been undergoing treatment for prostate cancer before he contracted Zika virus. The presence of cancer, his age, and the radiation and hormone therapies he underwent may have all worked together to make his Zika infection unusually virulent, resulting in his rapid deterioration and death, said Klausner. In fact, his death in and of itself is unusual, as the disease is typically mild or even symptomless for most people.
This high viral load may have resulted in the presence of the virus in bodily fluids where it usually isn't present, leading to the other man's subsequent infection. Patient 2 did not have any underlying medical conditions and was not immunocompromised in any way, Swaminathan said.
“We know the amount of virus in the original patient was extremely high, so it's not surprising that perhaps with such a high amount of virus, body fluids not generally considered to be high risk for spreading infection could be infectious,” Klausner concluded. “It does just speak to a need to routinely employ universal precautions when being potentially exposed to any potentially infectious material.”
What this means for the rest of us: probably nothing
The young man's case is remarkable because of how unusual it is, but it probably doesn't have any further implications for transmission in other parts of the world, said Klausner, who was not involved with the case but did review Swaminathan's report.
Klausner expressed dismay that the man didn't take standard precautions, such as wearing gloves or face masks, when visiting his infectious friend in the hospital. But he also pointed out that the event is extremely rare, and that there is no need for the general public to be alarmed that Zika virus could be spread through casual physical contact.
As for the rest of us, we can prevent the spread of Zika virus by not traveling to regions where Zika virus is spreading locally, and by making sure that our properties don't harbor standing water that could invite or nurture a mosquito infestation. If we do live or travel in an area affected by Zika virus, preventing mosquito bites and using condoms consistently and correctly during each sexual encounter can limit the risk of getting or transmitting the disease.
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