Utah’s mystery Zika case has been solved, and the answer, as with so many revelations about Zika, is something never before seen with this virus. Someone seems to have gotten Zika through only casual physical contact with an infected person—the first such case that’s been documented.
In July, after a 73-year-old patient who’d contracted Zika while traveling to Mexico died (a rare occurrence in itself), a second person came down with the virus. The second patient had visited the first man in the hospital, but had not traveled to any Zika-infected areas or had sex with anyone who had. So with the two known methods of transmission—mosquito bites and sexual transmission—out of the running, it was unclear just how this second person had managed to get infected.
In a new paper published in the New England Journal of Medicine, the patients’ physicians from the University of Utah describe just what happened with these cases:
Patient 2 reported having assisted a nurse in repositioning Patient 1 in bed without using gloves. Patient 2 also reported having wiped Patient 1’s eyes during the hospitalization but reported having had no other overt contact with blood or other body fluids, including splashes or mucous membrane exposure.
The only fluids the second patient could have come in contact with are sweat and tears. A previous study detected traces of the virus in the tears of infected mice; there hasn’t been any similar research on sweat. The second patient probably either had a cut somewhere on his skin, or he inadvertently touched his eyes, nose, or mouth, and the virus entered his body. “It should not be able to pass through unbroken skin,” says Sankar Swaminathan, the chief of infections disease at University of Utah Health Care, and first author on the paper.
But a big part of why this transmission likely occurred has to do with the uniqueness of the first patient’s case. It’s very rare for people to die of Zika—in this outbreak so far, there have been only 13 fatal cases in adults (not counting deaths from Zika-related Guillain-Barré). When Zika patients die, Swaminathan says, in many cases they also have a preexisting condition like leukemia that compromises the immune system. In this case, the first patient, while elderly, was not immunocompromised. But his infection was extremely severe. His blood had 200 million copies of the virus per milliliter—with a typical infection, Swaminathan says, you’d expect to see hundreds of thousands, and one million would be considered high.
It’s not clear why this man suffered so intensely from what is typically a very mild virus. He’d had dengue in the past; it’s possible that remaining antibodies from that somehow worsened this infection. This can sometimes happen when people get two different strains of dengue—the second dengue infection will be worse. Swaminathan also speculates that the man may have had a genetic immune deficiency that just happened to be very specific to this virus.
With infectious diseases, “there’s some people we find who get very unusual manifestations of infections that 99.99 percent of people never get,” Swaminathan says. It could be that these people, though not otherwise immunocompromised, have specific weaknesses to particular pathogens.
Whatever the reason, the patient ended up with an abnormally high viral load, which led to shock, respiratory failure, and eventually death. (The second patient came down with a less intense, more ordinary version of Zika.) The extent to which the virus can be spread through bodily fluids like this is a question the authors suggest needs more research, but Swaminathan suspects that it may be the high viral load that led the virus to be present in the first patient’s sweat or tears. Mosquitoes and sexual transmission are still the main worries—“For the general public, this doesn’t really change very much,” Swaminathan says—but this case is yet another surprise pulled from Zika’s seemingly endless playbook.