A mysterious and extreme case of Zika in the US has shown that we still have a lot to learn when it comes to the virus – and suggests the virus may be capable of being spread by physical contact.
Earlier this year health authorities in Utah were baffled when a patient contracted Zika – but not via any of the usual channels through which the virus is known to spread.
But a new study, led by researchers from the University of Utah, has examined the Utah episode, and concludes that Zika virus – at least in this very peculiar case – appears to have been spread through physical contact alone.
Not only that, but the virus could be deadlier than we first thought, because while the patient in this scenario was elderly, he was otherwise healthy when he contracted the virus, but died soon after in hospital.
While Zika has been known to kill adults before – in very rare instances – usually such fatalities occur when people have compromised immune systems, which wasn't the case here.
"This rare case is helping us to understand the full spectrum of the disease, and the precautions we may need to take to avoid passing the virus from one person to another in specific situations," says infectious disease specialist Sankar Swaminathan.
"This type of information could help us improve treatments for Zika as the virus continues to spread across the world and within our country."
The circumstances of the case began when the elderly patient, a 73-year-old Salt Lake City resident, visited Mexico in May last year. During his trip, he was bitten by mosquitoes, which is the most likely explanation for how he contracted Zika.
Upon returning from his trip, he went to hospital experiencing inflammation, watery eyes, and a rapid heart rate.
With his condition deteriorating, the man's 38-year-old son visited him in the hospital, and comforted his father, helping to reposition him in bed and wiping away his tears.
The father later died in hospital, and tests after his death confirmed he had Zika. But only a week after the father passed away, Swaminathan happened to notice that the son also had watery eyes – a common Zika symptom – and tests confirmed he too had contracted the virus.
What baffled the researchers was that the son – unlike the father – had not travelled to a Zika-infected area, nor had sex with anybody who was infected (or who had travelled to a Zika area). And Utah doesn't have Aedes aegypti mosquitoes.
So how did he catch Zika?
In these circumstances, the researchers conclude "infectious levels of virus may have been present in [the father's] sweat or tears, both of which [the son] contacted without gloves."
While there's no precedent for this hypothesised channel of Zika transmission, it could be that the virus was able to spread due to the other perplexing anomaly of this case: an extraordinarily high concentration of virus in the father's blood, at 200 million particles per millilitre.
"I couldn't believe it," says Swaminathan. "The viral load was 100,000 times higher than what had been reported in other Zika cases, and was an unusually high amount for any infection."
In light of this extreme viral load, the researchers think it may have been what enabled both the deadliness of Zika in this instance (killing the father), and its previously undocumented ability to spread purely by physical contact (infecting the son).
The son later recovered from his comparatively mild case of Zika, but while it's an otherwise sad and somewhat disturbing story, the good news is that this strange episode tells us more about how Zika might be able to function – and it's better to be prepared than not.
"This case expands our appreciation for how Zika virus can potentially spread from an infected patient to a non-infected patient without sexual contact or a mosquito vector," says one of the team, Marc Couturier from the University of Utah's ARUP Laboratories.
"This and any future cases will force the medical community to critically re-evaluate established triage processes for determining which patients receive Zika testing and which do not."
As for Swaminathan, he says the questions raised by this unusual Utah infection will require further research to clear up – although there's no guarantee on when such an extreme viral load may show up again.
"We may never see another case like this one," says Swaminathan. "But one thing this case shows us is that we still have a lot to learn about Zika."
The paper is published in The New England Journal of Medicine.