Saturday 9 January 2016

Zika virus in amniotic fluid...but is that enough?

A report published this month provides background of an investigation of two women described as being part of the 'microcephaly cluster' in Brazil.

The study describes ZIKV detection in the amniotic fluids of the two women; the first laboratory confirmed detections of vertical transmission (from mother to embryo/foetus/baby) of Zika virus (ZIKV; genotyped as "Asian" strains).[1] Transmission around the time of birth (perinatal transmission) has been reported before.[2]

Interestingly, neither mother had ZIKV RNA detected by RT-PCR suggesting they were not acutely infected at the time of the investigations. The authors were not clear whether viral culture was attempted nor whether antibody studies were conducted on the mothers. There is no real time frame for when the mothers were infected beyond a comment that they had relevant symptoms. The authors also do not describe investigations for any other infectious agents or environmental factors nor anything about the deliveries.

Investigation #1...

Foetal ultrasound was conducted at 30.1 weeks' gestation and revealed anomalies including:
  • unusually small head circumference
  • low weight
  • brain atrophy
  • coarse calcifications of the frontal lobe

Investigation #2...

Foetal ultrasound 29.2 weeks' gestation and revealed anomalies including:
  • unusually small head circumference
  • low weight
  • a range of brain anomalies
  • some calcifications
  • cataracts in both eyes and one eye was smaller than the other
Around the same time in the same State (Paraiba)....
  • 6 children borne with small head circumference were diagnosed with ZIKV (lab confirmed?) and born (without complication?) to mothers reporting symptoms during pregnancy
The authors noted that the lack of cases of vertical ZIKV transmission found in over 65 preceding years may be because cases have not been sought, not been reported or were just rare until now. This lack of data may also relate to levels of local immunity which may act to moderate ZIKV infection among people in areas of endemic transmission, or perhaps because the virus has changed and this is a new trick it has acquired..because of the M word. In short, we don;t know if microcephaly and central nervous system developmental interference is a new or an old-but-unknown feature of Zika virus disease (ZVD). Or if it is even related to ZIKV at all.

The authors conclude by warning that if investigations in other states of Brazil find people with ZIKV antibodies, that this is a severe health threat. However they make no mention of the importance of seeking other culprits - likely or not - in the search for understanding of why cases of microcephaly in Brazil have risen so rapidly. Differential diagnosis can be a complex beast in the mosquito-borne virus world.

In a 1 December Pan American Health Organization (PAHO)/World Health Organization (WHO) epidemiological alert,[3] data up to 30 November 2015 listed 1,248 cases of microcephaly (99.7 / 100,000 live births), including 7 deaths, in 14 states of Brazil. By comparison, in 2000, the prevalence was 5.5 cases / 100,000 live births and 5.7 cases / 100,000 live births in 2010.[3] 

More recently the Brazil Ministry of Health tabulated all microcephaly cases. From an average of 156 cases in each of the preceding 5 years, the number has jumped to 3,174 cases in 2015

Both data sets describe a 20-fold increase in cases in just a year.[4]

Whether ZIKV is to blame, or something else, the urgency with which this outbreak of microcephaly is now being investigated in Brazil is clearly warranted. 


  1. Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg?
    A. S. Oliveira Melo, G. Malinger, R. Ximenes, P. O. Szejnfeld, S. Alves Sampaio and A. M. Bispo de Filippis

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