Mosquitoes on the march: how zika will spread across Europe

The saving grace for Europe and North America will be their relative affluence and greater levels of education.

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The World Health Organisation (WHO) has warned that as the weather warms this summer, the mosquitoes that host the zika virus will make their way to Europe – especially around the Mediterranean. According to analysis published in the Harvard Public Health Review in May, tourists returning home from the Olympics in Rio de Janeiro are likely to exacerbate the problem, triggering outbreaks in countries across the world.

The science on zika is advancing rapidly but the outlook remains bleak. Although a baby born with microcephaly – an under-developed head and brain – is the most widely reported possible consequence of a zika infection in pregnant women, it is not the only one. In March, the New England Journal of Medicine published a study of 88 pregnant women from Rio. Seventy-two were carrying the virus. Almost a third of those infected showed signs that their babies had been affected by growth restriction, damage to the central nervous system, or a weakened placenta; and almost 5 per cent of these cases resulted in foetal death. It is a hidden menace, too: the effect on the foetus did not depend on the intensity of the mother’s symptoms.

The European Centre for Disease Prevention and Control (ECDC) announced in April that it had recorded 359 imported cases of zika in 17 EU or European Economic Area countries. Twenty-three of these were in pregnant women. More than two dozen EU states have advised pregnant women against travelling in areas affected by zika. As the science progresses, this is likely to be extended to anyone – male or female – who wishes to become a parent in the near future. It was only in February 2015 that a paper in the journal Emerging Infectious Diseases suggested that zika could be transmitted through sex. We now know that it can be and there have been cases that prove it.

The saving grace for Europe and North America will be their relative affluence and greater levels of education. In Brazil, zika has raged through poorer districts. Not only have public health messages about avoiding mosquito bites failed to hit home, but living conditions make avoiding them almost impossible. Mosquitoes lay their eggs in any body of water they can find, whether that is a discarded food dish or an old tyre filled with rainwater. Many households that aren’t connected to internal plumbing use open containers such as disused oil drums to store water, which are perfect for female mosquitoes looking for a laying site.

Temperature is also a factor. In more affluent areas, air conditioning produces environments in which mosquitoes cannot survive. In Brazil’s poorer homes, which are often hot and humid, mosquitoes have thrived. For the same reason, zika-bearing mosquitoes are likely to thrive in southern Europe as the continent warms. Sun-seeking holidaymakers from the north may find themselves at risk and medical personnel all over Europe will have to be ready to face a variety of unusual symptoms.

European countries “need to be well prepared to protect their populations from the spread of zika virus disease and its potential neurological complications”, the WHO has urged. The ECDC is warning doctors that besides “neurological syndromes such as meningitis, meningoencephalitis and myelitis”, there could also be “potential disease complications not yet described in the scientific literature”.

So what can be done? Municipal spraying with insecticides is a difficult, labour-intensive and often unwelcome practice – again, problems that affect disadvantaged areas most. Even in affluent places such as Florida, sprays have achieved little more than 50 per cent reductions in mosquito populations.

The WHO has now recommended that zika-affected countries trial a genetic modification technology developed by Oxitec, a spin-off from Oxford University. Oxitec alters male mosquitoes in ways that make their offspring unable to survive to adulthood. In trials, the technique has been shown to reduce mosquito populations by 90 per cent. However, sustaining the effect requires that the altered males are topped up. This requires establishing local infrastructure to produce the modified mosquitoes: a significant barrier to mass deployment. Other single-release GM technologies are being developed but are yet to get out of the lab. They may take five or more years to pass stringent environmental and efficacy tests. Developing a vaccine will take a similarly long time. Zika is not going away any time soon.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article appears in the 19 May 2016 issue of the New Statesman, The Great Huckster