The early reports of an unknown virus causing mild fever, rash, conjunctivitis and muscle ache, received at the beginning of this year from North-eastern Brazil, caused little international attention. That the responsible organism was later found to be the Zika virus, was chiefly only of scientific interest: this mosquito-borne disease was able to adopt the same transmission routes used by the much more established Dengue virus. In fact most thought of Zika as a kind of ‘Dengue-lite’ virus: still causing a deeply unpleasant flu-like illness, but not associated with the more serious bleeding abnormalities sometimes seen in severe Dengue infections. We may have been wrong to underestimate the importance of Zika, however.
The Brazilian coastal state of Pernambuco, has reported an unusually high incidence of foetal malformations this year; specifically, the occurrence of a neurological condition resulting in microcephaly. As the name suggests, this is the term given to a foetus that has a much smaller head than average, usually diagnosed by ultrasound scan. Pernambuco often reports around 10 such cases of microcephaly each year, but up until November of this year, 141 foetuses have been diagnosed. This picture has been repeated throughout Brazil, where 739 cases have so far been reported. The tragedy of the condition is that the neurological malformation that causes microcephaly is permanent, leaving the foetus (and later, the infant) with severe neurological damage profoundly affecting thought and function.
As the rapid increase of Brazilian microcephaly cases is new, and the incidence of Brazilian Zika is also new, fears have been raised that the two may be linked.
There have been several reasons to suggest that this may be the case. When the amniotic fluid bathing the microcephalic foetuses was examined, there were two cases where fluid tested positive for the presence of the virus. Further evidence that Zika may be associated with the disease came from French Polynesia. These islands also have a Zika outbreak, and also have seen an increased number of foetal malformations, noted between 2014 and 2015. These 17 incidences of foetal developmental abnormalities occurred to mothers who had been exposed to the Zika virus, but had not become unwell. The Zika infection had been demonstrated by the presence of Zika antibodies in the maternal blood.
The last piece of supporting ‘evidence’ is that patients with Zika can sometimes develop other neurological conditions in adults (such as the progressive loss of function seen with Guillain-Barre syndrome) perhaps suggesting that the virus may also be capable of the brain development abnormalities seen with microcephaly in foetuses.
There is much more work to be done at this stage, however.
It is one thing to find an association between a virus and an illness, but quite another to state that the virus causes the disease. As can be appreciated, in the context of an outbreak of an illness – when many people are infected – an association may be found which is not causative. Although ultimate proof is required, there is surely enough evidence to be concerned.
For expectant mothers, and all others at risk, the need to take bite prevention precautions is clear. Wearing clothes that will not let skin be needlessly exposed to mosquitoes is important, as is the use of DEET-containing sprays. In addition, air conditioning should be utilised where available, and sleeping under nets is advised.
Written by Dr Simon Worrell BSc MBBS MRCP, Head of Medical Communications, Healix International.
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