1) Define what is clinically understood by the term 'microcephaly'. Besides Zika virus, what other maternal infections can also cause microcephaly?

2. How likely is a baby whose mother is infected with Zika virus to develop microcephaly? Should Zika infection be the only concern?

3. How might the data collected on the incidence of microcephaly be an underestimate of the severity of Zika infection during gestation?

 

(1). Microcephaly is a birth defect where a baby's head is smaller than expected when compared to babies of the same sex and age. Babies with microcephaly often have smaller brains that might not have developed properly. Other maternal infections besides Ziko virus that can cause microcephaly include; Craniosynostosis as a result of premature fusing of the joints between the bony plates that form an infant skull keeps the brain growing .Treating craniosynostosis usually means your infant needs surgery to separate the fused bones. Other cause of Microcephaly is Chromosomal abnormalities, Down syndrome and other conditions may result in microcephaly. Other causes include infections passed to the fetus during pregnancy; These include toxoplasmosis, cytomegalovirus, German measles (rubella), chickenpox (varicella). Cerebral anoxia is also a major cause of microcephaly as a result of decreased oxygen to the fetal brain. Uncontrolled phenylketonuria in mothers is also a major cause as it hampers the body ability to break down the amino acid phenylalanine.

(2) Reported estimate incidence of microcephaly has wide variation due to the differences in the definition and target population.Overall, about 5% of fetuses and infants born to women with laboratory evidence of recent possible Zika virus infection in the U.S. territories had possible Zika-associated birth defects, the same as the percentage reported in the 50 U.S. states during 2016. Possible Zika-associated birth defects including brain abnormalities or microcephaly were reported following Zika virus infection during every trimester of pregnancy. Among completed pregnancies with positive nucleic acid tests confirming Zika virus infection identified in the first, second, and third trimesters, the percentages of fetuses or infants with possible Zika-associated birth defects was 8%, 5%, and 4%, respectively.

The Ziko virus also should not be the only concern since other studies showed earlier that the risk of birth defect did not depend on the presence or severity of Zika-related symptoms. chief author Dr. Bruno Hoen of the University Medical Center of Guadeloupe told Reuters Health by email.

(3)The actual number of infants who had Zika virus testing and postnatal screening might be underestimated because of delay in reporting results to medical records and change of clinical guidance. Misclassification of microcephaly might occur because of imprecise measurement of head circumference at at birth and difficulties with consistent surveillance for microcephaly could result to under ascertainment. Underestimate of the severity of Zika infection during gestation can also result from failure to assess other potential etiologies for these birth in the analysis Lack of postnatal neuroimaging also may led underascertaining brain abnormalities