What's really going on with the Zika virus?

The Zika virus and its possible health risks to pregnant women are very much in the public eye at the moment, in every newspaper and on every news channel. Dr Edward Wright explains more about the virus...

What is the projected spread of the Zika virus if left unchecked?

The scientists at the World Health Organization (WHO) predict there could be three to four million cases of Zika virus infection by December 2016.  However, as the virus is transmitted via a bite from a mosquito, local transmissions will be limited to areas where the mosquito is found (tropical and subtropical countries).

Can it only be transferred from mosquito bites?

Given the virus is present in areas where the Aedes aegypti mosquito is found suggests a strong link between the mosquito and the virus.  However, the reported sexual transmission case in Texas, USA, on 2 February 2016, coupled with a previous report in the literature of possible sexual transmission between a husband and wife following a trip to Senegal, means other modes of transmission cannot be ruled out.

Does the recent news that Zika can be transmitted sexually pose for those trying to battle the virus?

The reporting of a potential sexually transmitted case of Zika virus in Texas, USA, might at first come as a surprise but this is not the first documented case of possible sexual transmission. In 2008, an American scientist on a field trip to Senegal became infected with Zika virus and it is thought he transmitted it to his wife through sexual contact on this return home. Zika virus has also been found in semen from an individual who was infected during the 2013 outbreak in French Polynesia.  The Texas case further vindicates Public Health England’s guidance released at the weekend, namely that men who have recently returned from an area where Zika virus has been reported and experienced flu-like symptoms associated with the infection should use condoms.

At the moment the implications and additional risk associated with sexual transmission of Zika virus are unknown.  Given the information we have, potentially over a million cases of Zika caused by mosquito transmission versus two cases of sexual transmission, the additional risk appears small.  However, this is precisely the type of question that researchers are now seeking to answer with the additional funding and resources made available following the WHO’s statement on Tuesday declaring the potential link between Zika virus and microcephaly as a public health emergency of international concern.

Would the trials last year on GM male mosquitos be a viable option of reducing the mosquito population? What other methods are there?

Absolutely, the close association between the virus and mosquitos means that removing the mosquito will severely hamper, or hopefully completely inhibit, the ability of the virus to be transmitted from person to person. The trail of Oxitec’s genetically modified mosquito in Brazil that began in 2011 resulted in a 90% drop in the number of mosquitos over six months. The use of insecticides and removal or modification of mosquito breeding sites are other mechanisms by which mosquito populations can be controlled.

Would the use of Wolbachia bacterium be effective?

As the bacterium does not naturally infect the Aedes aegypti mosquito, they have to be infected in a laboratory and then released.  The Brazilian government initiated small trials in 2014 in an attempt to reduce mosquito populations and tackle the spread of dengue virus, but no results from these studies have been made available yet.

How long will it take for a vaccine to be made?

As there is no vaccine available, even one that has undergone basic laboratory testing, it is difficult to predict a timescale. However, consensus in the field is that it will take five to ten years before a vaccine is available for wide-spread use.  As DNA and live attenuated vaccines for the closely related West Nile virus and dengue virus are in development, similar approaches may be used for Zika. The best case scenario would be Phase I studies starting within the next 12 months.

If the virus was to reach the UK, would we be prepared for it as a country? 

If Zika virus is imported into the UK, there is no mechanism for the virus to be transmitted from person to person as the Aedes aegypti mosquito is not found in this country as it cannot survive in our cold temperatures. Therefore, the risk of an outbreak occurring in the UK is extremely low, even if someone was infected while travelling in a country where Zika virus is circulating and brought the virus back with them.

What is the importance of the WHO declaring Zika an international health emergency?

This means funding and resources will be made available to answer important questions - such as why the outbreak in Brazil is so large, whether there is a link between Zika and microcephaly, etc. - and to develop diagnostics, vaccines and antivirals to combat the infection.

Has a direct link been established between Zika and microcephaly? Many reports of Zika-caused microcephaly have been found to actually not be as a result of the virus.

No, there is no conclusive evidence available to prove, or dis-prove, a link between Zika virus and microcephaly.  However, there is enough evidence for the WHO to declare the possible link between Zika virus and microcephaly a public health emergency of international concern. Thereby, enabling extra funding and resources to be used to answer this important question.

Dr Edward Wright is a virologist and senior lecturer in Medical Microbiology at the University of Westminster.