Zika infection: an update

The World Health Organisation’s sudden declaration of the Zika infection as a public health emergency of international concern in early 2016 inevitably generated poorly documented and often sensational headlines. While these press articles have been relatively accurate in reporting geographical extension, route of contamination and Zika’s effects on patients, they have also partly occluded the relevant scientific facts. 

Back then, speculation relating to Zika’s potential severity was primarily based on limited epidemiological data. The numerous studies conducted over the past six months have shed new light on the transmission of the disease and its two major complications, and justify a revision of the article published here last February. 

So what is known today about this so-called new epidemic threat?

Like the dengue virus, the Zika virus is transmitted by the ubiquitous Aedes mosquitoes, which are found in tropical areas and southern parts of the western hemisphere. Associated with the cross-border movements of people potentially carrying the pathogen, the Zika infection could indeed spread in all these territories. Likewise, international travellers visiting these affected countries could be exposed to the virus and bring it back home when returning. In consideration of the risk, some scientists are urging postponement of 2016 Olympic games in Brazil, the country which has recorded the highest number of Zika cases so far. 

In fact, as of last Wednesday, the virus had been identified in 60 countries, 46 of which are experiencing the first Zika outbreaks since 2015. In the other 14 countries, virus transmission has already been active since 2007. Interestingly, four territories, which had evidenced Zika virus transmission prior to 2014, did not report any new cases for the last 18 months, a sign that the epidemics in these locations were already subsiding. 

The Zika virus was first identified in 1947 in Uganda. Besides insignificant outbreaks in Africa, Micronesia and in 2013 in French Polynesia, the recent outbreak, in comparison to other widespread and more severe infectious diseases such as influenza and dengue has induced relatively contained public health challenges among these populations. 

Two concerns however deserve continuous research and close attention, namely a foetal defect named microcephaly (a congenital brain condition where a baby’s head is much smaller than average size) and the Guillain-Barr? syndrome, a potentially (although rarely) fatal neurological disorder in adults. 

Unproven in February 2016, the cause of microcephaly of children born from pregnant women infected by the virus during the first trimester has recently been established through the identification of the virus in the newborns’ brain and imaging studies. The risk of contracting the malformation is however poorly understood and currently varies from 1 to 29 per cent of pregnancies afflicted by Zika infection during the first trimester. 

Similarly, the causality of Zika infection with regard to the occurrence of neurological disorders has also been confirmed and the risk of this complication is estimated at 2.4 cases for every 10,000 infections based on the specificities of the 2013 outbreak in French Polynesia. 

Researchers have recently suggested that the severe forms of Zika infections may be linked to co-infection with the dengue virus, which is also quite prevalent in the tropical regions. 

With regard to sexual transmission of the virus, sexual contamination has occasionally been reported among heterosexual couples and male homosexuals in the USA but is likely to remain negligible in comparison to mosquito bites.

In consideration of these new findings, the recommendations for pregnant women include travelling precautions in endemic areas, protection against mosquito bites, protected sexual relationships when the partner is infected and the monitoring of pregnancy for any women at risk. 

Finally, the change of date or location of the next Olympic games remains a controversy. The anticipated number of foreigners attending the August 2016 Rio games is estimated at half a million. This figure represents less than one per cent of all international travellers visiting Latin American countries where the outbreak is already active. While recommendations for pregnant women remain important to follow, the cancellation of the games alone would not effectively impact on the probable progression of this viral illness. 

 

DR GERARD LALANDE is managing director of CEO-Health, |which provides medical referrals for expatriates and customised |executive medical check-ups in Thailand. He can be contacted at |[email protected].