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Zika virus is not Ebola

Aedes aegypti mosquitoes have caused worldwide panic. Felipe Dana/AP

Just last week, the World Health Organization last week announced that the Zika virus was “spreading explosively.” Today, it declared Zika “a public health emergency of international concern.” The political pressures on the WHO to take this action have been strong. The shadow of Ebola also looms large, and the WHO seems, perhaps understandably, motivated by the worldwide conclusion that it was ineffective in responding to the Ebola epidemic in 2014, waiting to designate that disease as an “emergency” until it was far too late for this designation to matter. It did not want to make this mistake again. The problem is that Zika is not Ebola, or anything like Ebola, and declaring Zika an emergency will simply stoke fear, and even panic, in a public that deserves to have public health decisions made on the basis of facts and science, rather than on politics and fear.

Here is what we know: Zika infection produces a mild febrile illness in a minority of patients bitten by an infected Aedes mosquito. The clinical illness closely resembles related viral infections (for example, dengue) that are found in the same areas and transmitted by the same insect. The routine blood antibody test can be falsely positive in the presence or aftermath of one of these other infections. The routine blood test for Zika is also not widely available and has rarely been considered for testing patients with this mild illness by doctors in many areas that are now being declared newly Zika epidemic areas. Definitive diagnosis may require specialized tests that are available in only a few places. Thus, some of the cases previously considered to be due to widespread dengue, for example, may have, in fact, been Zika. Microcephaly appears to be increasing in some of these same areas. Zika virus has been detected in the amniotic fluid and brains of a few affected children.


What we don’t know is whether Zika has existed previously in the many newly identified outbreak areas and where we just hadn’t looked. We also don’t know whether Zika definitively causes microcephaly or brain damage, or Guillian-Barre syndrome or cerebral calcifications. If it does cause these devastating conditions, we don’t know how frequently, or whether the elevated number of cases of microcephaly have been identified using strict case-definition criteria. Of more than 700 of the originally reported Brazil cases that have been reviewed, 462 have been reclassified as not having microcephaly or due to another cause. Of the 270 caused by infection Zika was found in only six infants. One can anticipate substantial more reclassification as our diagnosis gets better and we understand the disease better.

In many ways Zika represents a form of endemic illness that is becoming more and more familiar. We can assume that Zika will eventually distribute to many of the same areas covered by dengue, chikungunya, yellow fever and West Nile virus — all of which are carried by the same mosquito. None of these diseases have the ability to spread by casual person-to-person contact, and there is no reason to believe that Zika will be spread by casual person-to-person contact either. This stands Zika in sharp contrast with SARS and Ebola, about which there was much, warranted, global concern.


All of this suggests that there is much we do not know, and that what we do know so far falls far short of justifying Zika as a public health emergency of international concern. Doing so is not without consequence. By declaring Zika a public health emergency, the WHO raises unnecessary alarm, diverts resources away from the work that needs to be done to better understand this disease, and chips away at public confidence in the ability of global authorities to discriminate between diseases that truly warrant such a label, and ones where a more judicious approach is more suited to the conditions on the ground.


So what should be done? Measures to interrupt the vector that transmits this disease are fully warranted for all of the Aedes associated arboviruses, including Zika. Prudently suggesting minimal exposure to these areas by pregnant women, given the devastating consequences is appropriate. It would also be important to double down on research to understand the burden of disease, transmission dynamics and pathogencity of Zika, and to collect reliable and rigorously obtained surveillance data. We urgently need to understand the mechanism through which Zika may be associated with neural development.

We should honestly communicate to the public what we do and do not know, and to issue reasonable, common sense, non-dramatic advice about how people should protect themselves. In the longer term we need real investment in surveillance infrastructure that can adequately monitor emerging infectious diseases so that we can reliably detect true epidemics, particularly ones that have substantial pathogenicity, and swiftly act on them.

Nonetheless, declaring a public health emergency of international concern to prevent or reduce the international spread of Zika virus will engender much fear and not meaningfully affect our ability to contain the virus. Ebola was a real international public health emergency, and declaring it as such helped to encourage governments and NGOs around the world to join in containing it. Declaring Zika an emergency, on the other hand, is crying wolf, and lessens the ability of the world to respond to a real emergency, and — better — to work in a constructive, common sense, way to try to prevent epidemics in the first place.


George Annas is a professor and director of the Center for Health Law, Ethics, and Human Rights at the Boston University School of Public Health. Dr. Sandro Galea is professor and dean of the school, and Dr. Don Thea is a professor of global health and director of the Center for Global Health and Development.