Finding the link: Zika and microcephaly

goes behind the headlines to examine the Zika virus

It would not come as a surprise if you had only recently heard of the Zika virus. The World Health Organisation (WHO) have recently declared it’s spread an international public health emergency. Although the virus appears ‘mostly harmless’, with most of those affected suffering from mild or no symptoms. The virus has been linked with birth malfunctions, and the WHO has estimated that four million people may be infected this year! An outbreak of the virus has recently circulated the Americas after been detected in Brazil last May, having previously been limited to South- East Asia and Africa.

Image: IAEA Imagebank

Image: IAEA Imagebank

Transmitted by several Aedes mosquito species, the virus is suspected to have detrimental effects on foetuses. Last October, a steep rise in the number of babies born with a condition called microcephaly was reported in north-eastern Brazil. Microcephaly is a neurological disorder in which a baby is born with an abnormally small head in comparison to those of the same sex and age, which causes neurological defects. The timing of this steep incline was roughly around the outbreaks of Zika just months before. Since then scientists have been frantically trying to find out just how harmful the virus might be.

Although researchers are trying their best to gather evidence of the correlation between Zika and microcephaly, there is a problem. Much of the epidemiological data from Brazil is poor, largely because the abrupt rise in microcephaly cases was only suspected months after the virus had spread further afield. The surge of birth defects in Brazil is elusive and the number of suspected microcephaly cases is unclear. As of March 12, 6398 suspected cases of microcephaly and/or central nervous system malformations since November 2015 were reported by the country’s health ministry. Of this figure, only 2197 cases have been looked into, and of those, 854 have been confirmed as microcephaly. Only 97 of those cases that have been confirmed to have a link with the Zika virus.

Another issue is the lack of a reliable historical baseline for comparison. Only 147 past cases of microcephaly were reported in 2014- which is said to have been under reported. To confirmed a suspected case of microcephaly would require a baby with a head circumference of less than 33 centimetres, which should result in an estimated 600,000 suspected cases in a year. World Health Organisation recommends reduced this threshold to <31.9 cm and <31.5 cm for full-term male and female babies respectively to rule out any small, but healthy babies.

Although causational data in microcephaly is limited, an increasing number of reports on newborn babies, or stillborn or aborted foetuses that are proven to have microcephaly show Zika viral RNA within their genome. Countries other than Brazil, for example Columbia, have just seen their first few diagnoses of Zika-linked brain abnormalities and microcephaly in newborns. A rise in birth defects in two or three months’ time is therefore expected, giving time implement coping strategies.

As researchers scramble for evidence, we are slowly edging closer to finding out to what extent the Zika virus affects foetuses and how it can be prevented. With so little known, public health officials are right to urge action to protect pregnant women from mosquito bites, as a group of researchers pointed out: “Even with limited evidence linking Zika virus to neurologic disorders, the severe potential risks demand decisive, immediate action”.

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