02.02.161:20 PM ET

The More We Know About the Zika Virus, the More Confusing It Gets

Does it cause birth defects? Can it be sexually transmitted? Why new outbreaks usually stump the experts.

The deepening Zika virus outbreak has entered a too-familiar phase: total confusion. Once a simple (though hair-raising) story about a mosquito, a virus, and a devastating birth defect, Zika now is a chaotic mess of conflicting data. As new facts and fears have piled up, it has become just about impossible to tell exactly which way is up.

Two new events have added to the din. First, the World Health Organization held a press conference yesterday to proclaim the most alarming birth defect—microcephaly—to be an official global disaster, or in WHO-speak, a “Public Health Emergency of International Concern.” This designation frees up resources and focuses appropriate attention on the problem.

What the WHO did not proclaim was a “Zika virus” crisis. That’s because Zika infection among those not pregnant is a nuisance, albeit with a small risk of Guillain-Barre paralysis—but that’s all. The public health problem, rather, is the apparent risk to a fetus of maternal infection. Yet the data still does not crisply establish a cause and effect relationship between the virus and microcephaly.

This lawyerly sidestep allows the WHO to focus on the disease and not the putative cause, thereby avoiding (they hope) future criticism that they waffled too long.

Which is fine—public health is hard, especially when the economic future of an entire country or region hangs in the balance. And the reason for their bureaucratic caution was brought home by the second noteworthy Zika event of the week (and it’s only Tuesday!)

In Scientific American, a report of Zika in Colombia, which shares a border with Brazil, describes over 2,000 cases of Zika in pregnant women but no microcephaly in the offspring. Confused yet?

The preliminary information from Colombia flies in the face of a re-look at a previous Zika outbreak from 2013 that affected 28,000 people in French Polynesia. Initial descriptions did not identify microcephaly but, according to WHO comments yesterday, more recent scrutiny of the aftermath of the epidemic has demonstrated an increase in this birth defect similar to what is being seen in Brazil.

So why is it so difficult to know what exactly is going on? It’s the same problem that affects every outbreak of a new virus, something we have learned and relearned as the wheel turns and out comes SARS then MERS then Chikungunya then Ebola and all the rest.

Here is the skinny: When a new virus appears, an accurate diagnostic test is never available, much less a vaccine or treatment. This means that the public health investigators thrown into an emergency situation have no way to distinguish actual cases from things that look like and sound like actual cases but are not. So, estimates of disease frequency are all over the place, ranging from the shrug-able to the oh-my-god.

Further complicating the issue for Zika is that the worrisome infection occurs months before the birth of the affected infant (if indeed Zika causes the problem). Right now, the thinking is that the first and perhaps second trimesters are when acquisition of Zika virus results in severe birth defects. So by the time the baby is born five or six months after infection, the Zika virus has come and gone from both mom and baby, making diagnosis ever more difficult. And this presupposes that a reliable test is drawn by a lab that can process, store, and send specimens to a regional reference lab in a timely fashion. Good luck with that.

Surely there have been some affected babies with detectable Zika but some without. Ditto for moms. And the promise of results from a cohort of CDC-studied pregnancies and newborns remains due any day now so we may have clearer answers. But mostly we are in the midst of a standard issue outbreak witnessed in real time, complete with panic, uncertainty, and finger pointing.

And given all that is at stake—infants, pregnancy, the future of regional tourism, and the Summer Olympics—that depends on this collection of still evolving tests and concepts, the entire mess is likely to get decidedly messier before it all begins to settle down.