Zika and microcephaly: Causation, correlation, or coincidence?

“Although the mechanisms of Zika virus pathogenesis appear to fall in line with the requirements for centrosome abnormalities, there is as of yet no evidence to prove culpability.”

From the Jan. 14 issue of Microbes and Infection:

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6 thoughts on “Zika and microcephaly: Causation, correlation, or coincidence?”

  1. Microcephaly is rare, occurring from 1 per 6200 to 8500 births. Brazil had approximately 3M births in 2014. Given the microcephaly frequency in a normal population one would expect between 353 and 484 as background. Just for argumentsbsake, if you annualize this and apply it to the numbers reported to the WHO anything above 500 would seem to be abnormal. With 3200, really abnormal. Something going on. Zika causation?

  2. Thanks Vic,

    The Brazillians are revising their numbers as the cases are being re-examined, and they are now up to 404 confirmed cases of microcephaly and 709 discarded. This is a report dated 2 February from the Braziloian Ministry of Health:


    So, it looks like less than half of the original 4700 (or so) cases will turn out to be microcephaly – let’s say 2,000 confirmed cases.

    The report also mentions 17 with respect to Zika virus, but my Google-translate of the Braziillian report makes it hard to know what they mean by “with respect to”. One paragraph which has been translated understandably states 76 deaths from microcephaly. Of these, 15 were investigated and confirmed for microcephaly and / or alteration of the central nervous system, and five had identification of Zika virus in fetal tissue. Another 56 are still under investigation and five have already been discarded.

    On the whole, still a very small number of cases compared to what is known about the prevalence of microcephaly in countries with well developed monitoring and reporting (i.e. the US). Added to the fact that Zika virus is already widespread and – for the most part – almost asymptomatic in adults and so exposure is likely to be quite high.

    A long way to go before there is evidence for a link.

  3. I would really appreciate some links to the actual numbers here. I saw one news article that stated the rate of microcephaly cases in Brazil are only now approaching the – otherwise considered normal – rates in the US. This suggests to me that all we are seeing is increased surveillance and therefore increased detection – not an actual increase in the number of cases.

    The problem is the source of these numbers (newspaper article, that sis not seem to understand the point) and I have been trying to find something concrete from a reputable source. All I get from WHO and CDC are scare stories based on “we cannot definitively rule out a link”. Given the virus is endemic in Africa, what is the microcephaly rate there? Anyone know?

    This paper gives no numbers and the first link (to the Brazillian Health Ministry) only gives numbers of cases not rates and refers to only two cases where RNA could be detected from affected patients. 399 cases is unpleasant, but what is the population in these states? It is telling that the state with the highest number is the state where they first “noticed the increase” and where there has been monitoring for the longest time. It is a commonly observed effect that rates of rare diseases increase with attention and to read these numbers as evidence of an increase in occurrence (not just an increase in observation) is skating on thin ice.

  4. The link between the zika virus and microcephaly has not been established. It is curious that so many microcephaly cases have been discovered in the most backward parts of Brazil. The virus causes no problems apparently in Asia. Getting rid of the aedes aegypti mosquito because it also brings dengue and other diseases is a good idea. The aedes aegypti virus is an invasive species, not native to Brazil. But is a crash program to create a vaccine a good use of funds to fight what may turn out to be a harmless virus? Is the current mass hysteria warranted? Could the cause of microcephaly in tropic areas be poor sanitation and poverty?

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