Wednesday, December 23, 2015

PAHO ZIka Week 51: And Then There Were 12

Credit PAHO



Four days ago, in Viral Creep: Zika Spreading In Central & South America, I wrote how the Zika Virus had gone from spreading locally in two countries of the Americas just 6 weeks ago, to spreading in 10.

Today, based on PAHO's latest update, you can make that 12.  A number that is certain to rise.

Like with Dengue and Chikununguya which arrived before it, Zika is finding the climate and abundance of Aedes mosquitoes highly conducive to spreading, along with a large, virologically naive population.

As a result, Brazil alone is estimating more than a half million infections over the past eight months (see Brazil Estimates 500K+ Zika Infections). 

Up until a few months ago Zika was considered a relatively minor threat, particularly when compared to the far more painful and debilitating Chikungunya and the four (occasionally) deadly strains of Dengue.  Zika infections were generally regarded as relatively mild, and self limiting.

That perception began to change, ever so slightly, after an outbreak in French Polynesia in 2013-2014, which saw a concurrent spike in Guillain–Barr√© syndrome (GBS) (see  Zika, Dengue & Unusual Rates Of Guillain Barre Syndrome In French Polynesia).

It wasn't until October of this year, five months after the Zika began to spread with earnest in Brazil, that another possible complication of Zika infection - an unprecedented surge in microcephalic birth defects - was reported in Brazil. 

While a direct link remains unproven, recent reports suggest similar (albeit smaller) increases in post-Zika epidemic birth defects were recorded in French Polynesia as well (see  Post-Zika Outbreak Spike In Congenital Abnormalities In Brazil & French Polynesia). 

The most recent epidemiological report from the Brazilian MOH indicates 2784 microcephalic births, of which more than 2500 have occurred in the past couple of months. A rate more than 100 times what would be expected in Brazil.

As maternal infection during the first (and possibly 2nd) trimester is suspected as the cause of these birth defects, they appear as a trailing indicator, only showing up months after the virus begins to spread widely in a region.

Whether it is Zika - or Zika alone - that is causing this huge surge in microcephalic births hasn't been conclusively proved, although the evidence is mounting. A recent Paper: Zika Adaptations To Humans Helped Spark Global Spread, suggests the virus may have mutated after it left Africa, increasing its pathogenicity in humans.  Additional studies are needed to confirm this, however. 

Given the profound neurological deficits often associated with microcephalic birth defects, the Brazilian MOH has declared this Microcephaly epidemic as their nation's  `Greatest Calamity’.
Meanwhile, other nations and territories in the Caribbean, South and Central America are watching nervously, and mounting a response, in hopes that a similar tragedy can be avoided in their nations.