This answer summarizes
- Zika infection consequences in adults, largely mild symptoms but autoimmune Guillian-Barre syndrome in some.
- Tragic long term consequences of severe birth defects from Zika infection during pregnancy.
Evidence from both groups bolster the notion that Zika is a neurotrophic virus.
Zika Infection Consequences In Adults
While the Zika virus was first identified in 1947 and it might have triggered earlier outbreaks, the first such reports began to come out only from 2007 or so, too short a period of time to be certain of all of its long term effects.
In most Zika outbreaks, infection in adults appeared typically mild so much so that many may not have even known they got it. Overall it appears only ~20% of Zika-infected adults show clinical symptoms, relatively mild ones such as headache, joint pain (arthralgia), rash and conjunctivitis ().
In some recent Zika virus outbreaks, particularly the one in French Polynesia in 2013-2014, some Zika-infected adults were observed to develop, an autoimmune condition caused by immune system attack of the peripheral nervous system ( ).
Tragic Long Term Consequences To Newborns Of Zika Infection During Pregnancy
The 2015-2016 Zika outbreak in Brazil made clear Zika’s potentially destructive impact on the developing nervous system. Observed in the 2016-2017 Zika outbreak in Colombia as well () and now named Congenital Zika Syndrome, thus far it is the most consequential and devastating long term effect of Zika virus, outcome of infection of a pregnant woman and transplacental infection of the developing fetus (4, see below from 5). Zika infection during the first trimester and mother experiencing strong clinical signs of Zika infection appear to augur the greatest risk of CZS to fetus.
A prominent feature of CZS observed in Brazil’s Zika outbreak was, where the baby’s head is much smaller compared to babies of similar age and sex (see below from ). This outbreak witnessed a ~20-fold increase in microcephaly incidence in this region.
Even Zika-infected newborns who were apparently healthy at birth were observed to develop brain abnormalities later (see below from). This series of patients included several born with normal head circumference at birth who went on to have poor head growth later. Such infants had other neurological problems such as , , and as well.
, malformation, particularly of the hand and feet, have also been observed in CZS (see below from ).
Both microcephaly and arthrogryposis have also been observed together in CZS (see below from 4).
Brain atrophy and calcifications are some of the other brain abnormalities observed in CZS. Some CZS children born without any obvious brain abnormalities went on to develop(accumulation of cerebrospinal fluid in the brain) at 3 to 12 months of age (4, 9).
Retina and optic nerve damage have also been observed in some CZS cases (), which can occur even in the absence of microcephaly at birth ( ).
The US CDC set up the US Zika Pregnancy Registry to coordinate with state, tribal, local and territorial health departments to track Zika-related pregnancy and birth outcomes. Its most recent report () on pregnancy outcomes for 1297 pregnancies with suspected Zika infections reported from 44 states from December 2015 to December 2016 concluded ~1 in 10 lab-confirmed Zika infections resulted in Zika virus-associated birth defects.
Analyzing the data trove since the 2015 outbreak in Brazil, several groups including the CDC have concluded there’s a causality link between Zika infection and microcephaly and other birth defects (, , ), thus adding to the long list of . However, debate on the topic in the scientific literature also continues ( , , 18).
Definitive risk factors for CZS are still largely unknown (19). These include roles for co-infection withand other , genetic polymorphisms as well as differences in virulence between different Zika virus strains.
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