Early 2016, WHO, supported by CDC and following reports published in NEJM, concluded that Zika virus is causing microcephaly. The evidence based medecine was referring to outbreaks which occurred both in Brazil (Spring 2015) and Colombia (Fall 2015).
As of today, Zika outbreak in South America is (temporary?) over and we may start a review of the risk factors and address lessons learned:
- Zika virus has been found and localized in fetus and new born; Virus is capable to pass through placenta and brain barrier of the fetus.
- In vitro studies are reproducing nerve cells damages caused by zika virus.
- There is a close relationship between microcephaly and zika virus.
Here are some of the key points demonstrating that Zika virus is one condition leading to microcephaly; but question is to consider if it is the only one? In other words, does microcephaly resulting from a unique cause or multi-causal?
Since the beginning of the outbreak in Brazil, some Doctors and Scientists, mostly South-american, were pointing out the possible role and responsibility of a larvicide (Pyriproxyfen) used in North-East Brazil and poured in water tanks/reservoirs where water pipe system does not exist. But recently a study reported the lack of effect of Pyriproxyfen on the human being.
So, what do we need to address today by reviewing the Zika outbreak in South-America?
- to understand why North-East Brazil concentrate 90% of the entire microcephaly cases?
- to explain why there is such a discrepancy in the microcephaly cases in Colombia compared with Brazil?
Researchers also found that Dengue antibodies can initiate a specific reaction through antibody dependent enhancement (ADE) of infection with zika virus, leading to autoimmune diseases like Guillain Barre syndrome and which might be explaining pathophysiology of microcephaly.
WHO reported a study case in Martinique:Mother infected by DENV,CHIKV and ZIKV
Saying that, back to real life, in vivo, by looking at what happened in NE Brazil; starting with Dengue outbreak then followed by Zika and finishing by Chikungunya outbreak. In other words, the zika outbreak occurred on a population which was acute immunized for Dengue and a ADE might have happened in this region of Brazil explaining the discrepancy with the other regions of Brazil.
Now and looking at the numbers of microcephaly in Colombia, it is interesting to analyze prevalence of Zika related cases compared to the entire microcephalies: 60/752 = 8%.
Where are coming from the others? That means 92% of microcephaly cases are not related to zika virus but might be related to either infectious diseases including but not limited to Rubella or Cytomegalovirus. Another source might be socio-economics in these regions of NE Brazil and some locations in Colombia in link with poor resources for sanitation and poor quality of food leading to a lack of hygiene and Vitamines deficiency.
As an Health risks manager, always tracking root causes analysis and trying to understand 5 Why, I have to admit that I have not been convinced by the double statement posted by WHO & CDC on Zika virus causing microcephaly but still looking for multi-factors, multi causal including possible co-infection and ADE.