Expert comment on Zika virus outbreak in the Americas

What is it Zika virus, how does it spread and who is at risk?

The rapid spread of the Zika virus is an increasing concern for health authorities including the World Health Organization and Pan American Health Organization.

Although Zika only causes mild symptoms in most people, the virus has been linked to microcephaly in thousands of newborns. In primary microcephaly, newborns have small heads due to abnormal brain development. Some countries have advised women to consider postponing planned pregnancies.

The virus is native to Africa and was first found to be spreading in the Americas in Brazil in May 2015. There is no vaccine or known cure. Experts from the London School of Hygiene & Tropical Medicine have been providing comment and interviews for the world's media as the epidemic unfolds.

Laura Rodrigues, Professor of Infectious Disease Epidemiology at the School, said: "Zika is transmitted by the Aedes aegypti mosquito. It has previously been detected in Africa, Asia and the Pacific Islands.  In this outbreak 22 countries in the Caribbean and North and South America are affected. This includes Brazil which has the largest-known outbreak of the virus. Zika can be transmitted anywhere there is dengue fever as it is transmitted by the same species of mosquito. The infection is normally very mild with symptoms similar to mild dengue: malaise, rash, low fever, itching and red eyes. However, the concern is only with the risk during pregnancy in women who have visited, or who are visiting, the areas where the virus is present.

"Zika has caught the world by surprise as we know very little about it, but once a virus with a competent vector - in this case the mosquito - is introduced in a totally susceptible population there is always the chance of an epidemic. Potential factors for enhancing transmission are the high population density (large cities) with many breeding sites for the mosquito - the dengue vector mosquito is a domestic mosquito and is rarely found more than 100 metres from human habitations and can breed in any small deposit of water."

Dr Laith Yakob, Lecturer in Disease Vector Biology at the School, added: "Although there have been three reported cases of Zika in the UK there is no chance of there being an epidemic here. The virus does not pass between humans and can only be transmitted through mosquito bites. The Zika carrying mosquito does not occur naturally in the UK, our climate is too cold, so the only risk is for pregnant women travelling to areas in the world where there is Zika. Until we know more about Zika, pregnant women should seek advice about travelling to areas where the virus is present.

"There is no vaccine against the Zika virus. Efforts are underway to make one but it is a lengthy and costly process. However, Zika is related to dengue virus and the recent developments of a 'tetravalent' vaccine against the four distinct variations of dengue offers hope for the accelerated development of a vaccine for Zika, which only has one variation."

*Update - 28 January 2016*

The World Health Organization has predicted that three to four million people could be infected with Zika virus in the Americas this year. WHO Director-General, Margaret Chan, will convene an International Health Regulations Emergency Committee on Zika virus on 1 February.

Jimmy Whitworth, Professor of International Public Health at the School, said: "The WHO's decision to set up an emergency team for Zika virus infection is most welcome. This outbreak in south and central America is unprecedented and has caught the world unprepared once again, with no vaccine, no drugs and limited anti-mosquito measures. On Monday the WHO may well declare a 'public health emergency of international concern' as this epidemic has the potential to spread even more widely in tropical and sub-tropical regions. This action by WHO will stimulate international interest, funding and research to help tackle this outbreak on the ground and in laboratories around the world."

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