Zika virus and microcephaly

FlavivirusThree reports have been published that together make a compelling case that Zika virus is causing microcephaly in Brazil.

An epidemic of Zika virus infection began in Brazil in April 2015, and by the end of the year the virus had spread through 19 states, many in the northeastern part of the country. Six months after the start of the outbreak, there was a surge in the number of infants born with microcephaly. It was not known if most of the mothers had been infected with Zika virus, as results of serological tests, virus isolation, or PCR were not available.

An initial report of 35 Brazilian infants with microcephaly born to women who either resided in or traveled to areas where Zika virus is circulating revealed that 74% of mothers had a rash (one sign of Zika virus infection) in the first or second trimester. At the time of this study no laboratory confirmation of Zika infection was available, but the infants did not have other infections associated with birth defects, including syphilis, toxoplasmosis, rubella, cytomegalovirus or herpes simplex virus.

Yesterday the CDC reported on the analysis of tissues from two infants with microcephaly who died within 20 hours of birth, and two miscarriages, all from the state of Rio Grande do Norte in Brazil. The mothers all had rashes typical of Zika virus infection in the first trimester of pregnancy, but were not tested for infection.

All four specimens were positive for Zika virus RNA by polymerase chain reaction (PCR) done with primers from two different regions of the viral RNA. Staining of tissues with anti-viral antibodies revealed the presence of viral antigens in two of the four samples, in the brain of one newborn and in the placenta from one of the miscarriages.

A second report from the University of Sao Paulo documents ocular abnormalities in Brazilian infants (from the state of Bahia) with microcephaly and presumed Zika virus infection. The mothers of 23 of 29 infants (79.3%) with microcephaly reported signs of Zika virus infection (rash, fever, joint pain, headache, itch, malaise). Of these, 18 (78.3%) had symptoms during the first trimester of pregnancy, 4 (17.4%) during the second trimester, and 1 (4.3%) during the third trimester.

No laboratory results were available to confirm Zika virus infections, but toxoplasmosis, rubella, cytomegalovirus, herpes simplex virus, syphilis, and HIV were ruled out.

Abnormalities of the eye were found in 10 of 29 (34.5%) of infants with microcephaly. These included focal pigment mottling, chorioretinal atrophy, optic nerve abnormalities, displacement of the lens, or a hole in the iris.

These observations suggest that Zika virus infection may also cause lesions of the eye, although confirmation of infection needs to be done to prove causation. This uncertainty is reflected in the title of the article: “Ocular findings in infants with microcephaly associated with presumed Zika virus congenital infection in Salvador, Brazil” (italics mine).

The final paper is, in my opinion, the blockbuster. In this single case report, a 25 year old European woman working in Natal, Brazil, became pregnant in February 2015. In the 13th week of gestation she had fever, muscle and eye pain, and rash. Ultrasound in Slovenia at 14 and 20 weeks revealed a normal fetus.

At 28 weeks of gestation fetal abnormalities were detected, including microcephaly, and the pregnancy was aborted. Autopsy revealed severe brain defects, and 42 to 54 nm virus particles were detected in the brain by electron microscopy.

Infection with a variety of microbes was ruled out, but Zika virus RNA was subsequently detected in brain tissue by PCR.

Here is the clincher – the entire Zika virus genome was identified in brain tissue by next-generation sequencing! Analysis of the sequence revealed 99.7% nucleotide identity with a Zika virus strain isolated from a patient from French Polynesia in 2013, and a strain from Sao Paulo from 2015. These findings agree with the hypothesis that the current Brazilian outbreak was triggered by a virus from Asia.

Up to now there have been few data that strongly link Zika virus infection to congenital birth defects. Of these three new studies, the recovery of a full length Zika virus genome from an infant with microcephaly is the most convincing. Given the rapidity by which new data are emerging, it seems likely that additional evidence demonstrating that Zika virus can cause microcephaly will soon be forthcoming.

I’m amazed that a flavivirus can cause birth defects – when no flavivirus has done so before*. This is a virus spread by mosquitoes, and to which most of the world is not immune. The Zika virus outbreak will surely test our ability to respond rapidly with substantial mosquito control, diagnostics, antivirals, and a vaccine.

Update 2/11/16: A second paper has been published documenting ocular abnormalities in ten infants born to mothers in Brazil who had symptoms consistent with Zika virus infection.

Update 2/12/16: *Japanese encephalitis virus and West Nile virus have been shown to cross the placenta and infect the fetus. Such events must be rare because a larger association with birth defects has not been reported.

Comments on this entry are closed.

  • Veronica Rezelj

    Hello Vincent,
    Nice article as usual! I’ve been thinking for a while now if anyone is looking at coinfection of ZIKV with other viruses…As you said no flavivirus has done this before, and there’s many other viruses present in Brazil that do cause birth defects such as bunyaviruses. So what if it’s not Zika on its own causing microcephaly but its coinfection with other viruses?

  • Coinfections are possible, especially with dengue and chik viruses in the same areas. There is also the possibility of immune enhancement with antibodies directed against other flaviviruses. In the NEJM and JAMA studies they looked for a number of other viruses and found no evidence for other infections. But these are only a handful of cases and more will have to be looked at carefully.

  • Alan Dove

    The NEJM study is good, but I still need a little bit more to call this a real cause-effect relationship. It’s entirely possible that Zikavirus is just infecting opportunistically, and that these are cases that would have developed birth defects even without it. We also still have some disturbing inconsistencies in the epidemiology data, e.g. why are we only seeing a “surge” in microcephaly in northeastern Brazil, and why were microcephaly rates there tenfold lower than in developed countries before this? Finally, let’s not forget the lesson we all learned from the XMRV fiasco: a surprising PCR result is contaminated until definitively proven otherwise.

  • The NEJM is not PCR, it’s deep sequencing and assembly of the entire genome. Plus viral particles were seen by EM in the brain. No viral particles were ever observed in XMRV ‘infected’ prostate. I agree that there are plenty of extant questions, but the three papers do together make a compelling story. You know I’m very skeptical and yet these results ring true to me.

  • Hannah Davis

    Thanks for the update – this is really interesting stuff. The existence of the virus in the brain seems to put it in the right place to potentially cause microcephaly or other neurological defects, but I would love to see some proof that it really is the causative agent.

    Are there any examples of relatively benign viruses that get everywhere, including into a foetus, and don’t cause birth defects, or is it a pretty safe bet that the presence of any virus in the CNS of a foetus means that it caused any pathology observed?

  • Bruna Junqueira

    Thanks for updating us! According to you what would be the next step to confirm this hypothesis? I thought about transfecting any neronal cell line, is that possible? And why Colombia ins’t reporting microcephaly although they have lots of ZIKV confirmed cases in pregnant woman? Thanks!

  • Which hypothesis, that the virus can replicate in fetal brain? Infecting a neuronal cell would be a good start. As for why we don’t see an increase in microcephaly in Columbia – good question. The outbreak began there in May 2015 so we would expect to have seen microcephaly by now.

  • Bruna Junqueira

    I meant exactly what you said. That the virus can replicate in fetal brain and is responsible for microcephaly in those babies.

  • This is a good question. I don’t think we know enough to say that presence of a virus in the fetus is automatically a bad thing. We do have a virome and the fetus acquires it from the amniotic fluid. It’s mostly phages but there are likely to be animal viruses there as well. We only look for specific microbes when there are fetal problems. A lot left to learn. An important question: how many Zika infections in the first trimester result in fetal defects? For rubella virus it is 1-2 per 1,000 live births.

  • Thank you for pointing this out. Very interesting! We should not forget that we learn a great deal from non-human viruses.

  • C. E. Bruce

    I agree that this information is interesting but not necessary a smoking gun. Cannot understand, if the Zika Virus (discovered in the Zika Forrest of Uganda) is causing the outbreak of microephaly in Brazil, why the cases are localized, the 99.75 genetic identity, from the European woman means that it is virtually the same virus from other regions of the world – is that not correct- Then why are we not detecting the birth defect everywhere the virus exists; furthermore, a “Flavivirus” that historically has not been implicated in birth defects? This points to a localized “environmental” factor as well or a possible mutation of the virus “which is not the case with a 99.7% replication? Up to 75% of the population in other Zika epidemics have been infected which DID NOT cause birth defects. It has been reported an Larvicide Pyroproxyfen (Monsanto) was added to the water supply (to help control Mosquitoes and Dengue fever) in the area by the Brazilian Government in 2014 which the European woman may have likely drank – A group of Argentinian Doctors are questioning the use of this agent here is the link – http://www.reduas.com.ar. Any thoughts?

  • Allyn Spear

    I am still curious if the microcephaly associated with Zika could be a result of previous infection by a related virus like Dengue. We know that sequential heterotypic dengue infections can trigger hemhorragic fever, and there seems to be some antibody cross-reactivity between Dengue and Zika (at least as suggested from so many of the false positives in the Zika testing). What if that region of Brasil recently experienced a dengue outbreak from a strain that has not circulated in Columbia or other regions of the Zika outbreak, and it is actually the Dengue infection that predisposed them to more severe Zika sequelae? Just puttin’ it out there…

  • Sure, exacerbation of Zika infection by a previous flavivirus is certainly possible. At the moment we don’t have data to look at that possibility. Note that some of the cases in the above article were tested and found negative for dengue virus, so that wasn’t involved. But in other cases it’s possible.

  • We do still have this issue that Zika infection elsewhere does not seem to be causing microcephaly – but maybe that’s a reporting or other issue. I’ve heard that re-examination of the Yap Island outbreak has revealed microcephaly, but I haven’t seen those data. Other co-factors, including genetic background, other infections, environmental toxins, all seem to be involved. Of all the microcephaly reported in Brazil, we don’t know the Zika status of most of the mothers and babies. I think the above cases show that Zika *can* cause microcephaly; whether it always does, and whether many of the cases have other causes, remains to be determined. It’s not at all clear that Zika is causing all the microcephaly in Brazil.

  • Thank you for addressing this issue. I do wonder if any samples from previous “dengue” cases exist throughout Asia–or from US travelers to those countries in recent years–were retested, if any would come back positive for Zika. If the serological tests are cross-reactive, I assume there could be a significant number of false-positive dengue tests in individuals with previously unrecognized Zika infections.
    I’m also concerned about the attribution of Zika to microcephaly in Brazil for several reasons.
    1) The epidemiology is suspect; microcephaly incidence rates in Brazil prior to 2015 appear to be significantly under-reported relative to other developed countries with similar birth rates. Also, there have been reports that many of the microcephaly were incorrectly assigned. (http://www.nytimes.com/2016/02/04/world/americas/birth-defects-in-brazil-may-be-over-reported-amid-zika-fears.html)
    2) Other countries are not demonstrating simliar effects with nearly identical virus. Colombia is, perhaps, a good comparison. According to another NYT article, few microcephaly cases have been seen despite an increase in Zika akin to what Brazil has experienced. (http://www.nytimes.com/aponline/2016/02/06/world/americas/ap-zika-virus.html?_r=0)
    3) You said yourself: this is totally unexpected from a member of the Flavivirus genus.

    Might an explanation for such a significant difference between country (and even geographic regions within Brazil) be local population genetic homogeneity? I can imagine that a close-knit community with a common susceptibility would see a relatively large increase in microcephaly and other complications during a novel disease outbreak.

    Thank you again for presenting this and a wealth of other information in such clear, easily accessible terms.

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  • Tianhao Xu

    Wow, this is intriguing that a virus cross placenta, and identified in brain tissues. By the time the pregnant women have the symptom of rash related to ZIKV, they should already have viremia. Well, the fetus does not have a built up immune system that virus can replicate once cross the placenta, but the latency of the birth defects is what I can’t understand.

  • Alan Dove

    The NEJM paper used RT-PCR with Zika-specific primers as well as deep sequencing (IonTorrent), which itself includes a RT-PCR step. Also, remember that because deep sequencing works by assembling fragments, we don’t actually know that there was a complete Zika genome anywhere in the tissue – just that there was a representative collection of fragments covering the complete genome. The EM definitely suggests a real infection with a virus, but of course doesn’t independently identify the virus. We have three different techniques whose flaws don’t quite cover for each other.

    I agree that the NEJM paper is the most compelling evidence so far, and I’m pretty much convinced that Zikavirus can get into fetal tissue in at least some circumstances. Now we need to nail down what those circumstances are, what other factors are involved, and whether this is really the main driver of Brazil’s apparent microcephaly outbreak.

  • Cary Rue

    low rate of fetal defects could be key to why microcephaly has only recently been linked with zika . if the brasil outbreak was the first exponential increase in infections perhaps previous levels of microcephaly were too sporadic for the connection to be made. my guess is retrospective investigations of microcephaly in countries that had zika earlier will find the virus.

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  • C.E. Bruce’s question about the reduas.ar hypothesis, that Larvicides introduced to contain mosquito populations may be causal or correlated with the incidents of microcephaly, seems important. I can see how a populist distrust of “Monsanto” might make this story to go viral for the wrong reasons, but the fact the larvicide is designed to create birth defects in mosquitos (malformations of wings etc.) and the fact similar outbreaks of Zika have not yet been associated with microcephaly makes it worth finding an answer, if there is one.

  • Rachael Tarlinton

    If you take the veterinary virus analogy further most likely the reason you don’t see lots of birth defects in areas where the virus has been present a long time is that most people will have had it (and presumably be immune to it) long before they reach reproductive age, This is what happens with other insect borne viruses that cause birth defects like Akabane and Schmallenberg – you only see large scale outbreaks of birth defects if the virus moves into an area where it hasn’t been for a long time.
    I also really don’t understand the chemical conspiracy theory – the particular chemical everyone is talking about has been tested for this (its used in flea treatments) and there is no indication that it causes birth defects in mammals. Its pretty hard to imagine it having any effect on mammals at all as it targets an insect growth hormone.

  • gabi_lisboa

    Here are some more accurate data about microcephaly in Brazil prior to 2015, the number of cases are much higher than the official reports as you suggested:

    http://www.who.int/bulletin/online_first/16-170639.pdf

  • tuxedobob

    I’m trying really hard not to drink from the conspiracy Kool-Aid on this one, but the number of diseases that can cause birth defects seems lower than the number of chemicals that can. Thinking of things like alcohol, thalidomide, and the like.

    The best thing the Zika theory has going for it is that right now, the only sites that are reporting on the larvicide theory are wacko nutjob conspiracy sites. I’m hoping some intelligent minds can come together, definitively rule something out, and get it reported on a reputable news agency such as NPR or BBC.

  • Gary J

    The article in the NEJM had nice opening and summery
    discussions.

    In the opening paragraph Suggest was used once, and Possible
    once.

    The word possible was used in the Results paragraph.

    In the summery discussion the word Potential was used twice,
    Might was used once, Possible was used twice, Characteristic was used once,
    Suggest was used twice.

    The second to last sentence of the article stated

    “Further research is needed to better understand the
    potential implications of these observations.”

    Read this.

    http://www.reduas.com.ar/report-from-physicians-in-the-crop-sprayed-town-regarding-dengue-zika-microcephaly-and-massive-spraying-with-chemical-poisons/

  • Nutjob?

    techtimes.com

    Larvicide Manufactured By Sumitomo, Not Zika Virus, True Cause Of Brazil’s Microcephaly Outbreak

    A group of Argentine physicians claim that the sudden microcephaly outbreak in Brazil was not caused by the Zika virus, but by a larvicide injected into the country’s water supplies.

    According to the Physicians in Crop-Sprayed Towns (PCST), a chemical larvicide that produces malformations in mosquitoes was injected into Brazil’s water supplies in 2014 in order to stop the development of mosquito larvae in drinking water tanks.

    The chemical, which is known as Pyriproxyfen, was used in a massive government-run program tasked to control the mosquito population in the country. Pyriproxyfen is a larvicide manufactured by Sumitomo Chemical, a company associated [PDF] with Monsanto.

    “Malformations detected in thousands of children from pregnant women living in areas where the Brazilian state added pyriproxyfen to drinking water is not a coincidence,” the PCST wrote [pdf] in the report.

    For instance, the Brazilian Health Ministry had injected pyriproxyfen to reservoirs in the state of Pernambuco. In the area, the proliferation of the Aedes aegypti mosquito, which carries the Zika virus, is very high, the PCST said.

    Pernambuco is also the first state in Brazil to notice the problem. The state contains 35 percent of the total microcephaly cases in the country.

    The group of Argentine doctors points out that during past Zika epidemics, there have not been any cases of microcephaly linked with the virus. In fact, about 75 percent of the population in countries where Zika broke out had been infected by the mosquito-borne virus.

  • Dengue is why Brazil is putting larvicide into it’s water supply.

    techtimes.com

    Larvicide Manufactured By Sumitomo, Not Zika Virus, True Cause Of Brazil’s Microcephaly Outbreak

    A group of Argentine physicians claim that the sudden microcephaly outbreak in Brazil was not caused by the Zika virus, but by a larvicide injected into the country’s water supplies.

    According to the Physicians in Crop-Sprayed Towns (PCST), a chemical larvicide that produces malformations in mosquitoes was injected into Brazil’s water supplies in 2014 in order to stop the development of mosquito larvae in drinking water tanks.

    The chemical, which is known as Pyriproxyfen, was used in a massive government-run program tasked to control the mosquito population in the country. Pyriproxyfen is a larvicide manufactured by Sumitomo Chemical, a company associated [PDF] with Monsanto.

    “Malformations detected in thousands of children from pregnant women living in areas where the Brazilian state added pyriproxyfen to drinking water is not a coincidence,” the PCST wrote [pdf] in the report.

    For instance, the Brazilian Health Ministry had injected pyriproxyfen to reservoirs in the state of Pernambuco. In the area, the proliferation of the Aedes aegypti mosquito, which carries the Zika virus, is very high, the PCST said.

    Pernambuco is also the first state in Brazil to notice the problem. The state contains 35 percent of the total microcephaly cases in the country.

    The group of Argentine doctors points out that during past Zika epidemics, there have not been any cases of microcephaly linked with the virus. In fact, about 75 percent of the population in countries where Zika broke out had been infected by the mosquito-borne virus.

  • tuxedobob

    Yeah. I mean, if you look at the front page of that site, it’s just clickbait. Clickbait everywhere. Meanwhile, a lot of the other sites that showed up under the topic on Facebook are the same kinds of sites that think that vaccines cause autism or that GMOs will turn us all into mutants.

  • 1. WHO recommended the addition of the larvicide to Brazil’s water supply
    2. WHO is being very restrained about the link the ZIKA
    3. CDC isn’t being restrained but they don’t know what WHO knows
    4. previous a ZIKA outbreaks never evidenced microcephaly

    It’s not fool-proof but it certainly indicates something else afoot.

  • groundcontrol

    I don’t really think highly of this report for a few reasons:

    – Pyrethroid insecticides have been used for decades without any attendant spikes in microcephaly. In animal models, you don’t see abnormalities in craniofacial development until you approach the LC50 of the compound — i.e., you have to give possibly-lethal doses to see that effect. People in Brazil aren’t convulsing, drooling, or pooping their pants from pyrethrin poisoning, so I find it hard to believe that the exposure level is high enough to cause a significant spike in birth defects in humans.
    -Rather than having been disseminated in any sort of normal manner, by researchers who don’t have massive conflicts of interest, the report was published to a website by an Argentinean group of doctors who are essentially an anti-pesticide lobby, bypassing any sort of peer review. Only one of them is even named, and he is named as a “coordinator,” not an author.
    – The report ignores the possibility that other differences between Colombia and Brazil (including the medical infrastructure itself) might account for the lack of reported cases of microcephaly in Colombia.
    – The report also conveniently glosses over the available evidence supporting links between Zika and microcephaly, in favor of essentially speculating that larvicide may play a role in microcephaly without providing any concrete evidence whatsoever. Show me cases of severe microcephaly consistent with viral infection in utero, similar to the cases with demonstrable Zika infection (white matter damage, calcium deposits, ventricular dilation, etc.), but without Zika virus present. Then show me that these fetuses were exposed to larvicide. Then I’ll pay attention. Until then, these people are just rumor-mongering. I only hope that their behavior doesn’t result in a worsening of the epidemic as people become afraid to use the only tools they have for controlling the mosquito population.

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  • Snakey_Pete

    Pure speculation, could there be a chemical adjunct at play in Brazil that is altering Zika pathology?

  • Sandro Silva

    In a investigation like this it is necessary cover all variables involved in the subject and their evidences.
    1. Zica virus is not original from Brazil, so why the increasing of microcephaly was not verified in other contries?
    2. No proofs of correlation beteewn Zica and microcephaly can be found, at this moment only what we can say is that the virus was found in the babes with microcephaly, but there are other cases without the presence of Zica?
    3. In the Colombia the number of Zica infections ares very high like Brazil, but microcephaly cases not increseasing at the moment?
    4. In recent days a new component in this investigation apper: Pyriproxifen. This chemical component is being used in water for AEDS combat, and now the government are talking that no correlations between Pyriprofixen e microcephaly was confirmed. We can discard this componente from the investigations ?
    5. Why Guillain-Barré syndrome are increasing in Colombia and not in Brazil? What kind of chemical Columbia Government still using until this moment ? And there is some correlation between these chemical and Pyriproxifen?
    6. And at last but not less important, can the virus have a mutation or some change in your behavior after a interectation with Pyriproxifen?

    About Brazil
    I believe that no question can be refused without proofs and must be investigated so:
    Zica x Microcephaly
    Zica + Pyroproxifen x Microcephaly
    Zica + Aeds + Pyroproxifen x Microcephaly

    i hope to have contributed with this topic. Sorry about the english

  • Genese Sodikoff

    Thank you for this informative article and all the commentary below. The pyriproxyfen scare did make me wonder whether there is any relationship between a virus and its vector. If the vector undergoes genetic mutation over time (as with pesticide resistant mosquitos) would this have any effect on viral evolution? Or are vectors simply carriers, and host environments the main drivers of viral mutation?

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  • Rafael Guimarães

    There is a point I would like to make: Pyrethoid insecticides in Brazil are being added to the water people drink. I believe this is not the way such substance is supposed to be used.

  • Barry Atkinson

    The NEJM article does increase the likelihood of microcephaly resulting from Zika virus infection. However, it is important to remember that this is not a phenomenom unique to Zika; similar links have been found with numerous other pathogens (see below). it is likely that any infection that crosses the placenta will increase the risk of birth defects including microcephaly

    West Nile virus (http://www.ncbi.nlm.nih.gov/pubmed/16510632), chikungunya (http://www.ncbi.nlm.nih.gov/pubmed/?term=25033077), HIV (http://www.ncbi.nlm.nih.gov/pubmed/?term=25598835), rubella (http://www.ncbi.nlm.nih.gov/pubmed/?term=19911144), CMV (http://www.ncbi.nlm.nih.gov/pubmed/?term=24423639), HSV (http://www.ncbi.nlm.nih.gov/pubmed/?term=3794894) and rhinoviruses/influenza (http://www.ncbi.nlm.nih.gov/pubmed/18983582).

    Most of these viruses have multiple reports rather than just the one cited here

  • groundcontrol

    There are definitely issues in general with pesticide usage in South America. However. there isn’t any actual evidence, besides correlation in time, that addition of larvicide is related to microcephaly (that time frame also correlates to Zika virus coming to this hemisphere). Meanwhile, we’ve got stronger (but still not ideal) evidence linking the virus to microcephaly: it’s seen in fetal brain, and the clinical manifestations of damage look more like they are viral in origin than they look like the result of chemical teratogen exposure.

    I think it’s definitely possible that factors like environmental toxins can play a role in the high rate of microcephaly in Brazil as compared to other countries. But I think it’s really irresponsible to decide that larvicide is to blame with no concrete evidence, and to then stop treating the water, in a country with an ongoing dengue epidemic and a new and terrifying epidemic that has evidence linking it to devastating birth defects. I am very afraid that we will get data from Rio Grande do Sul showing that larvicide was not to blame, in a few months’ time after stopping larvicide causes a spike in new infections.

  • Cam McDermaid

    An interesting array of information and more coming all the time. A recent WHO bulletin adds some more information about the background rate of microcephaly http://www.who.int/bulletin/online_first/16-170639.pdf which is much higher than expected.

    It would be interesting to examine foetal tissue controls from the same geographic area to see if the presence of the Zika fragments is incidental. From a precautionary principle the furor around Zika virus seems reasonable. It just seems premature to attribute an apparent increase in microcephaly to it as yet.

  • Nmit

    You realize that PCR-based testing would only indicate a concurrent infection by Dengue/Zika? If the DENV antibodies were leading to enhancement of Zika infection or permeabilization of the placental membrane, that would only require that the mother be infected at *some point* in the past few years by Dengue, and she would have presumably cleared the Dengue infection a long time before. What would really need to be done is a Dengue antibody test on the maternal serum.

  • dcpattie

    Should the US consider travel bans for Zika endemic zones? Ironically, all the travel ban hysteria displayed for Ebola might have been better saved for this emerging disease. I’m only raising the question, not suggesting we actually impose travel bans but some considerations. (1) Zika virus is a Flavivirus – same as Yellow Fever virus and before the Yellow Fever vaccine, quarantine was an effective countermeasure (that’s all we had then and basically all we have now for controlling Zika); (2) this is urban cycle transmission so humans are the reservoir (i.e., limit the reservoir and you may prevent sustained transmission). I’m guessing our trump card – and why we are not calling for travel bans from Zika endemic zones – is that we believe our ability to control mosquito populations is “good enough” and therefore mitigates the risk of endemic Zika in the SE United States? But then again West Nile virus became entrenched across the country fairly quickly.

    Or is it that its coming, we cannot stop it, and we just need to deal with the consequences?

  • disqus779

    How can it be that Columbia has reported 3177 cases of pregnant women with Zika virus, but no Microcephaly? Is the Columbia report faulty?

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  • Paul Richards

    The cdc is being extremely irresponsible by definitely suggesting zika is the cause of the micro-cephalic babies. From the WHO report, 85%+ of all the cases of microcephaly had NO ZIKA VIRUS present in either the mother or the baby. The correlation is minimal at best. Approximately 1 in 8 babies had zika, 7 in 8 didn’t. This means zika cannot be the culprit. Something else is at work here. Also correlation is not causation. STD cases can be statistically correlated to the increase in McDonalds but any reasonable person will say the one doesn’t affect the other.