London School of Hygiene & Tropical Medicine

The recent cluster of microcephaly cases and other neurological disorders in Brazil and French Polynesia have been declared a Public Health Emergency of International Concern (PHEIC) by a World Health Organization (WHO) emergency committee, chaired by the School's Professor David Heymann.

Microcephaly is a condition in which babies are born with small heads, and can be due to abnormal brain development. There have been approximately 4,000 suspected cases of microcephaly in Brazil. Though not scientifically proven, it is suspected that the steep rise in cases may be caused by Zika virus infection during pregnancy.

Transmitted by Aedes aegypti mosquitoes, Zika virus usually only causes mild illness in the general population, with symptoms including malaise, fever and a rash. WHO has estimated that there could be 3 - 4 million cases of Zika virus infection in the Americas over the next 12 months, with the risk that the virus could also spread to other countries.

The WHO emergency committee of 18 experts and advisers agreed that the situation merits PHEIC status as an 'extraordinary event' thought to constitute a public health risk to other states through the international spread of disease, and requiring a coordinated international response. The committee urged that steps must be made to improve surveillance of Zika virus infection and control of mosquito vector populations, while the development of diagnostic tests and vaccines are a priority.

David Heymann, Professor of Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, and chair of the WHO emergency committee, said: "It was a very difficult decision to discern between what is a Public Health Emergency of International Concern, and what should be precautionary measures because of possible relations between Zika and these clusters. But the PHEIC was called regarding the clusters of microcephaly and neurological disorders, and there were two major recommendations.

"These were that surveillance for microcephaly and other neurological disorders needs to be standardised particularly in areas where transmission of Zika virus is occurring. At the same time there needs to be intensified research of new clusters of microcephaly and neurological disorders to determine whether there is a causative link to Zika virus and other factors. The PHEIC has to do with proving that these clusters are or are not linked to the Zika virus."

Commenting on the announcement Prof Peter Piot, the School's Director, said: "The WHO's announcement is welcome news. It will draw worldwide attention to Zika, encourage international collaboration and allow holidaymakers and travellers to make informed decisions. It will also release funds to intensify research efforts. This is crucial as there is no vaccine, no known cure or good diagnostic test for Zika.

"We need to be clear - Zika is not Ebola and the risk to the general population is low. Only about one in five cases show any symptoms at all, which are normally very mild - malaise, rash, low fever, itching and red eyes. However, this outbreak in South and Central America is unprecedented and, coupled with this potential link with microcephaly, it is right that this should be treated as a public health emergency.

"There is a danger of Zika spreading to countries with less developed healthcare systems, including in Africa. This could have serious financial and health implications in some of the poorest parts of the world. The WHO's decision could help prevent this happening. When it comes to Zika, we need to be ahead of the game."

*Update - 3 February 2016*

The World Health Organization has urged European countries to prepare themselves for cases of Zika virus, as it warns that every country in which Aedes mosquitoes are present can be at risk.

Commenting on the announcement, Jimmy Whitworth, Professor of International Public Health at the London School of Hygiene & Tropical Medicine, said: "While Aedes aegypti is not present in western Europe, a related mosquito, Aedes albopictus does occur in the southern parts of western Europe. This mosquito is a competent vector for Zika virus, as well as for chikungunya and dengue.

"Aedes albopictus is already found in Spain and in southern France during the summer and seems to be steadily increasing its spread northwards. Outbreaks of chikungunya occurred in Spain and France (in the Carmargue) last summer. It is possible that Zika virus could be introduced into European Aedes albopictus and cause similar outbreaks in the future.

"It is important that Spain and France establish effective anti-mosquito measures to control Aedes albopictus and so prevent outbreaks of Zika, chikungunya and dengue. Although Aedes albopictus is currently not found in the UK, contingency plans should be established in case the mosquito extends its range further north in future years."

Related links:

• Media highlights: latest opinion from our experts in the news
• Previous expert comment on the Zika virus outbreak in the Americas